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Open Shortest Path First – OSPF Fundamentals – DR and BDR

Published

on February 18, 2009

in BDR, BSCI, BSCI Notes, Certification, Cisco Systems, Concepts and Constructs, DR, OSPF and VLAN

. 8 Comments

When routers are connected to the same broadcast segment (I.O.W. several routers are in the same VLAN, on the same switch you getting the idea). One router is assigned the duty to maintain adjacencies with all other routers on the segment. This is the designated router (DR) and the DR router is selected using information in the Hello messages. For redundancy purposes a backup designated router (BDR) is also elected (There is a reason for this, read on).

DRs are created on multi-access links because the number of adjacencies grows at a quadratic rate. For a network of n routers, the number of adjacencies required would be:

Two (2) routers require the following adjacencies:

Four (4) routers require the following adjacencies:

Ten (10) Routers require the following adjacencies:

Maintaining a OSPF segment consumes more bandwidth and requires more processing resources (CPU and memory) as more routers are added onto a OSPF network (Due to keeping the tables updated and probability of changes occuring more frequently etc).

The DR and maintaining relationships

The purpose of a DR is to be the “one router” (sounds like the matrix) to which all other routers are adjacent (the router that has all the routes on the network). Using a DR reduces the number of adjacencies that consume bandwidth and processing to n – 1 (Larger networks will however still require more processing even if you are using a DR). With a DR the adjacencies scale more effectively and efficiently with the network (as one can see in the below figure and table).

To show this in a graphic way one can see how this “adjacency” relationship works without a DR, with a DR, and with a DR and BDR with a small example network using 5 routers.

Taking this a step further and plotting out the exponential growth requirements of OSPF adjacencies the table below shows the number of adjacencies needed for 1 – 10 routers (imagine the CPU and Memory requirements, not to mention the bandwidth consumption). Plan accordingly when implementing OSPF (at this point you generally use OSPF because you have a non-homogenous network environment and need the open standard because of this fact, I dont really see a point otherwise cause its such a resource hog and mission to setup).

The job of the DR

The role of the DR is to receive updates and distribute these updates to each segment router, making sure that each router acknowledges receipt and has a synchronized copy of the Link-State Database (LSDB).

Routers advertise changes to the “AllDRs” multicast address of 224.0.0.6 where the DR then advertise the Link-State advertisements (LSAs) using the “AllSPF” multicast address 224.0.0.5 where each router then ack receipt.

The BDR listens passively to this exchange and maintains a relationship with all the routers.

If the DR stops producing hellos, the BDR promotes itself and assumes the role of DR.

NB. DRs and BDRs are only useful on multi-access links because they reduce adjacencies. The concept of a DR is not used nor usefull on point-to-point links because there can only be one adjacency.

DRs are still however elected on Point-to-Point Ethernet links (most common type of links in networking these days) which is a rather pointless and resource waste/hog (as a DR is not really needed) which is why you will find that many design guides recommend changing Ethernet links to Point-to-Point mode to stop this from happening.

If a DR fails, the BDR is pomoted. The BDR is elected on the basis of highest OSPF priority, ties in OSPF priority are broken in favour of the highest IP ADDRESS.

The default priority is 1 and a priority of 0 (zero) prevents a router from being elected to the DR or BDR role.

Priority can be set from 0-255 (manually) to change the priority from default from the interface,

Router(config-if)#ip ospf priority number

DRs are inherently seen as stable entities once elected into the position, even if a Router joins a network with a “greater” priority the DR will not change.

To give an example of this an OSPF Segment with 5 Routers ( A – E, with different priorities 0 – 3). Taking what has been discussed previously A would be the DR, B the BDR, and E would never be elected. However this neglects the following set of circumstances:

Imagine the following sequence of events in this small segment,

Router C starts first.
1. Router C sends out Hellos and waits the dead time for a response from other routers.
2. Receiving no Response, Router C conducts an Election and becomes the BDR.
3. As there is no DR on this network, Router C then promotes itself to DR.
Router E starts (priority= 0)
1. Router E will not become the BDR due to its priority setting
Router B starts and becomes the BDR.
Router A starts
Router D starts

In the above scenario the startup sequence of the routers caused the election of the DR and BDR (namely Router C is DR and Router B is BDR) which is not what would have been expected. This is because designated routers do not preempt, the elected DR/BDR serves in its role until reboot/failure (DR and BDR are stable entities on the network once elected).

In this network as it stands now If Router C restarts, Router B promotes itself to DR and Router A is elected BDR while C is down. If Router B goes down, Router A promotes itself and elects Router C or Router D (whichever has the highest IP Address). Finally when the BDR is rebooted, Router B wins the election for BDR.

NOTE: In addition to rebooting, clearing the OSPS process using the the command clear ip ospf process * on the DR will force the DR and BDR election.

Notes and Notices: This is a part of my personal BSCI notes and research to assist myself in learning and understanding the concepts and theory for the BSCI exam. I learn by making notes reading and writing things down and wish to file them where I canâ€™t lose them. These notes are not to be seen, judged or mistaken for replacements to Cisco recognized and authorized training which I personally support and attend and suggest you undertake if you are going for the BSCI Certification.

Update on Cisco Live! – World’s Leading Technologies Together in JHB

Published

Deon Botha

on October 10, 2008

in Asides, Cisco Systems and Vine

. 0 Comments

Cisco Live! is the Cisco annual ‘Networkers’ conference. For the first time ever the will be held in Sandton, Johannesburg on 1st – 4th December 2008. Cisco Live! will be the place for network engineers from all over Africa gather for technical training, education and networking. For the past eleven years, the conference has been at the forefront of educating delegates on new technologies.

The Cisco Live! conference will incorporate a new concept ‘Networkers at Cisco Live!’ with a mix of technical and business offerings. This format broadens traditional technical focused meet-ups to include executive tracks that examine the role of technology in driving business value in a challenging economic climate. The theme of this year’s conference is ‘The Power of Collaboration’ and delegates can look forward to thought-provoking keynotes from local and international Cisco executives and industry experts.

Networkers at Cisco Live! will be held at the Sandton Convention Centre and will attract more than 1,500 delegates, making it the largest Networkers conference in South Africa to date. The program will comprise various sessions, ranging from technical trainings to an invitation-only executive symposium. Delegates will also have the opportunity to view the World of Solutions demonstration area, which will showcase collaboration and communication tools and technology, such as TelePresence.

A Word from Steve Midgley the Managing Director of Cisco South Africa

“South Africa is the first country outside the United States to introduce the Cisco Live! brand. With Cisco Live!, we are taking the event to the next level to provide a platform where industry players can learn new technologies, discuss business trends, share ideas and network,” said Steve Midgley, Managing Director, Cisco Systems South Africa.“In recent years, specialization, globalization and new technologies have resulted in more collaborative environments made up of global, virtual networks and communities that improvise and find more productive, innovative and faster ways to do business. Cisco puts communications and collaboration capabilities within the context of a business process to allow workers increase their productivity, speed and agility,” added Midgley.

Speakers

Rick Hutley, vice president of Global Innovations for Cisco Internet Business Solutions Group, will be a keynote speaker at the event. Hutley, responsible for engaging Cisco’s largest global customers, will discuss the role of collaborative technologies in addressing the key business challenges and opportunities faced by organisations today.

Also speaking at the conference will be World Wide Worx’s Arthur Goldstuck, who will present findings from the Cisco-sponsored Internet Access in South Africa 2008 research report. Goldstuck’s presentation will cover the latest trends in Internet access and will set the scene for a discussion around the future of connectivity in South Africa, which plays a crucial role in collaboration.

For more information on Networkers at Cisco Live! www.networkersafrica.co.za

Enhanced Interior Gateway Routing Protocol – Optional Configuration Commands for EIGRP – Tuning EIGRP

Published

Deon Botha

on September 2, 2008

in BSCI, BSCI Notes, Bandwidth, Certification, Cisco Systems and Hold Timer

. 0 Comments

Some South African/Anglo-African humour that is making me smile:

“Tune” to talk, especially to talk nonsense (“Are you tuning me?”)

But back to the topic at hand;

One can fine tune the EIGRP process in many ways. The most important of tuning methods would be the summarization of routes and load balancing. Other techniques however do exist and these include the frequency of the hello and hold timers and setting bandwidth.

The trade off to playing with timers would be that by decreasing hello traffic the network will take longer to notice failures, which in turn will delays convergence.

To go over some stuff from previous posts; EIGRP only sends updates when a new route is advertised or an existing route is withdrawn (changes state to down). A Link failure causes an interface to change state without delay (duh). But when a failed neighbour is not directly connected (on the other side of a Ethernet switch for example), the only way to notice failure would be that no hellos are received. The idea and concept of Neighbourship is important in EIGRP because it alerts the router to topology changes and because the router is responsible to the rest of the network to publicize the lost routes.

When fiddling with timers think about the wider ramifications. In most cases defaults are there for a reason. Instead of improving performance the opposite will most probably happen. (I.E. timers are changed per interface and changing timers on one side of a link and not the other side creates problems with neighbourship that forms and dissolves periodically).

Timer Values are based on the speed of the interface. Because the timers are assumed to be based on this speed, they will usually be the same (Timers are not communicated between neighbours and are not a requirement for neighbourship).

If Router A has a hello interval of 5 seconds and a hold time of 15 seconds (3x hello) and Router B has a hello interval of 30 seconds and a hold time of 90 seconds (3x hello), then the two routers will be neighbours for 15 seconds and then down for 15 seconds.

The Hello Timer

Tuning the Hello Timer directly affect the ability of the EIGRP Process to notice a change in the state of a neighbour. Only after a router’s interface is recognized as being down, or a router has failed to hear from a neighbour after a certain amount of time, does the router declare the neighbour dead and take action to update the Routing Table and neighbours.

For the above stated reasons, use of the

Router(config-if)#ip hello-interval eigrp autonomous-system-number seconds

command is typically used to decrease (AND NOT INCREASE) the amount of time between Hellos to ensure that the network converges QUICKER and not SLOWER (which would be done by INCREASING THE TIME). This however means MORE traffic devoted to EIGRP and more space used by EIGRP.

The defaults are as follows:

High Bandwidth links (every 5 seconds)
- Broadcast Media (Ethernet, Token Ring, FDDI)
- Point-to-Point Serial Links (PPP or HDLC Leased Circuits, Frame Relay Point-to-Point subinterfaces, and ATM)
- Point-to-point subinterfaces
- High Bandwidth (T1/E1 and greater) multipoint circuits (ISDN PRI and Frame Relay)
Lower Bandwidth Links (every 60 seconds)
- Multipoint Circuits (T1/E1 and slower, Frame Relay Multipoint interfaces, ATM multipoint interfaces, and ATM)
- Switched Virtual Circuits and ISDN BRIs

The Command to set how often hellos are sent to neighbours is applied to an interface and does not affect the ENTIRE EIGRP process:

Router(config)#interface serial 0/0 Router(config-if)#ip hello-interval eigrp autonomous-system-number seconds

To use this in an example we can change the hello timer of a WAN link, that is running on EIGRP AS 1. Doing so will not affect other interfaces running EIGRP AS 1 only this particular WAN link.

Router(config)#interface serial 0/0 Router(config-if)#ip hello-interval eigrp 1 10

The Hold Timer

The Hold Time as talked about here and is how long a router will wait for a hello before pronouncing the neighbour unavailable/dead. By Default the hold time is 3 times the hello time. TAKE NOTE that by changing the hello interval does not automatically change the hold time.

The hold timer for an interface must be changed manually using the following command:

Router(config-if)#ip hold-time eigrp autonomous-system-number seconds

Using this in the same example as above for the Hello time:

Router(config)#interface serial 0/0 Router(config-if)#ip hold-time eigrp 1 30

Authentication

EIGRP support two kinds of Authentication, simple passwords and MD5 hashes.

Simple passwords are sent as plain-text and matched to the key on the receiver. Simple passwords are not secure, because any listener can see this traffic and read the key value.
Hash keys, sent as MD5 values, are secure because the listener cannot use the value in one transmission to compute the key.

Using MD5 authentication, the router generates a had value for every EIGRP transmission and checks the hash of every received EIGRP packet.

To specify MD5 Authentication:

Router(config)#interface serial 0/0 Router(config-if)#ip authentication mode eigrp autonomous system md5

Once the MD5 authentication is set now comes the key:

Router(config-if)#ip authentication key-chain eigrp autonomous system chain-name

Then the key-chain is configured and the key is specified:

Router(config-if)#key chain chain-name Router(config-if)#key my-chain Router(config-keychain-if)#key-string key

An example using the WAN interface from above:

Router(config)#interface serial 0/0 Hello Interval Set Router(config-if)#ip hello-interval eigrp 1 10 Hold Interval Set Router(config-if)#ip hold-time eigrp 1 30 MD5 Authentication Set Router(config-if)#ip authentication mode eigrp 1 md5 MD5 Key Set Router(config-if)#ip authentication key-chain eigrp 1 My-Chain MD5 key-chain Set Router(config-if)#key chain My-Chain Router(config-if)#key 1 Router(config-keychain-if)#key-string cisco

Authentication results are not shown under show commands. A successful neighbourship means it works. You can however check command process using debug eigrp packets

Optional EIGRP Commands Over a WAN

EIGRP has some design and configuration issues when it comes to the WAN environment. In the WAN one must deal with limited capacity to a greater degree than at other points of the network (For example the LAN). EIGRP is limited in that it restricts its use of bandwidth to NO MORE than 1/2 the link capacity. This is superior to the considerations made by other protocols. Although EIGRP by default is usually sufficient, one might need to make small adjustments at times.

EIGRP Defaults in Bandwidth Utilization
Routers understand link capacity most of the time (MOST being important here). Serial interfaces are however problematic (and the exception to the rule) because they usually attach to a DSU. The router therefore assumes a default speed of 1544 kbps (which is in most cases on the WAN not true).

If the link is actually 56 kbps, then EIGRP would calculate incorrectly and -even limiting itself to 722 kbps -could saturate the link. This could result in dropped EIGRP and data packets because of congestion and dropped data.

The show interface command will allow you to check that the interface bandwidth is accurate. The output shows the configured bandwidth of the link.

The set bandwidth does not actually affect the speed of the link, but this value is used for routing protocol calculations and load calculations. Using the following command you can set the bandwidth:

Router(config)#interface serial 0/0 Router(config-if)#bandwidth speed-of-line

Configuring Bandwidth over an Non-Broadcast Multi-access (NBMA) Cloud

EIGRP plays well over WANs, including point-to-point and NBMA environments like Frame Relay and ATM. The NBMA topology can include either point-to-point subinterfaces or multipoint interfaces.

Cisco IDs three rules when configuring EIGRP over an NBMA cloud:

EIGRP traffic should not exceed the committed information rate (CIR) capacity of the virtual circuit (VC).
EIGRP aggregated traffic over all the VCs should not exceed the access line speed of the interface.
The bandwidth allocated to EIGRP on each VC must be the in the same directions.

Configuring Bandwidth over a Multipoint Network

In addition to being used in the EIGRP metric, the bandwidth command influences how EIGRP uses NBMA VCs. If a serial line has many VCs in a multipoint configuration, EIGRP will assume that each VC has an even share of the bandwidth. EIGRP will confine itself to using half that share for itself. This won’t work if a 56 kbps link has bandwidth set to 128 kbps because EIGRP will assume 64 kbps is for it’s own use.

The bandwidth command should reflect the access-link speed into the Frame Relay cloud. Your company might have five PVCs from your routers serial interface, each carrying 56 kbps. The access link will need a capacity of 5 * 56 kbps (280 kbps).

Configuring Bandwidth over a Hybrid Multipoint Network

If the multipoint network has different speeds allocated to the VCs, a more complex solution is needed.

Take the lowest CIR and multiply it by the total number of circuits. Apply the product (total) as the bandwidth of the physical interface. The problem with this configuration is that EIGRP will underutilize higher bandwidth links.
If possible, it is muse easier to configure and manage an environment that has used subinterfaces, where a VC is logically treated as a separate interface. The bandwidth command can be configured on each subinterface, which will allow different speeds on each VC. In this solution, subinterfaces are configured for each VC and the CIR is configured as the bandwidth. This is the preferred solution.

Configuring a Pure Point-to-Point Network

If there are many VCs, there might not be enough bandwidth at the access speed of the interface to support the aggregate EIGRP traffic. The subinterfaces should be configured with a bandwidth that is much lower than the real speed of the circuit. In this case, it is necessary to use the bandwidth-percent command that indicates to EIGRP that it can still function.

The ip bandwidth-percent eigrp command adjusts the percentage of capacity that EIGRP may use FROM THE default 50%. You would use the command because the bandwidth command does not reflect the TRUE speed of the link (The bandwidth command might have been altered to manipulate the routing metric and path selection of a routing protocol).

Router(config)#interface serial 0/0 Router(config-if)#ip bandwidth-percent eigrp autonomous-system-number percent

Software Study Resources:

The Command Memorizer was originally developed by a CCIE Candidate (David Bombal) for his own use and is now available to anyone who wants to use it.Command Memorizer helped him pass the CCIE Lab on the first attempt, and although I am not a CCIE candidate “officially” I have fiddling with it and finding it useful to test my command line retention and overall progress towards CCIE readiness as I do my current CCNP.The proof will be in the pudding as the Command Memorizer boasts 1000s of commands and hundreds of scenarios to test command line knowledge and retention. It has a section for EIGRP and I also like knowing where I am on my long road to Cisco.

Like most study aids / study tools this tool / aid has a specific focus. The Command Memorizer only works when used in conjunction with theoretical backing because you need to know what a command does and how it relates to the technology area. IOW You need to make the connection before you can start drilling actual commands repetitively to get them to start flowing and become second nature.

For a disclosure statement on my relationship with Configure Terminal.

Cisco Press Resources:

Stewart, B,D., Gough, C (2008). CCNP BSCI Official Exam Certification Guide, Fourth Edition. Indianapolis: Cisco Press.

Internetworking Technology Handbook – Intro to the Wan

Notes and Notices:

This is a part of my personal BSCI notes and research to assist myself in learning and understanding the concepts and theory for the BSCI exam. I learn by making notes reading and writing things down and wish to file them where I can’t lose them. These notes are not to be seen, judged or mistaken for replacements to Cisco recognized and authorized training which I personally support and attend and suggest you undertake if you are going for the BSCI Certification.

Linksys Brand to Disapear

Published

Deon Botha

on August 28, 2008

in Asides, Cisco Systems and Vine

. 1 Comment

Cisco acquired Linksys back in 2003 and the Linksys brand has been around in some way or form since then, kind of, I haven’t had problems with the product myself but have had logistics problems with the brand and this comes from up-channel from various distributors where they can’t promise due dates and shipping from Linksys.

This is a problem for the Linksys brand because although the brand as a whole has a great price point for Home, Home Office (SOHO) and Small, Medium Business (SMB) Market segments the availability sucks and not being able to promise delivery or give an indication of delivery makes using the brand as a plausible solution pointless. While an Enterprise customer might be willing to understand and “deal” that no stock is kept in a Emerging market of their class of products and that the lead time to delivery is longer that understanding is lacking with SMB customers where deals are lost on cents and the ability to start installation tomorrow.

There was talk about a year back from the channel and some of my networking buddies that the Linksys brand would be integrated into the Cisco “stable” for good, meaning that the Linksys brand would phase out totally and only one would emerge. There were obviously two views to this; while one said “Great Cisco all the way” and the other said “Linksys is a strong brand on its own, why kill it?”.

Be that as it may the first steps of the brand integration process has started. How this whole change management process will work is that soon the “Linksys a division of Cisco” will become “Linksys by Cisco” with Linksys and Cisco sharing as much product space and font size and finally only “Cisco” will be on the packaging and product. This process happens over years to get customers use to the idea and “new” packaging and branding and is the eventual process after the companies have assimilated into each other and adopted each others cultures and views.

Wasn’t around back in the day but I suppose the Catalyst Switching platform followed the same routine as this. I know that the IBM and Lexmark Printing and Imaging System did this back in the day.

Enhanced Interior Gateway Routing Protocol – Tables

Published

Deon Botha

on August 8, 2008

in BSCI, BSCI Notes, Certification, Cisco Systems, Concepts and Constructs and EIGRP

. 2 Comments

EIGRP builds and maintains three tables,

A Neighbour table – used to make sure all ACKs are received.
A Topology Table – used to understand paths through the network.
An IP Routing Table – the best paths from the Topology table.

Creating the Neighbour Table

As previously stated, the neighbour table is maintained through Hello packets (These are multicast announcements that the router is alive).

Hello packets place the router into an adjacent routers’ neighbour tables.
- Reciprocal Hellos build the local Neighbour Table.
- Once the Neighbour Table is built, Hellos continue periodically to maintain neighbourship.

Each Layer-3 Protocol supported by EIGRP (IPv4, IPv6, IPX and AppleTalk) has its own separate Neighbour Table. Information about neighbours, routes, or costs are not shared between protocols.

Contents of the Neighbour Table (Resource 1, 2)

The Layer-3 Address of the neighbour (IP Address)
The interface through which the neighbours Hello was heard (fe0/1)
The holdtime (how long the neighbour table waits without hearing a Hello from a neighbour before declaring the neighbour unavailable and purging the database). Holdtime is three times (x3) the value of the Hello timer by default.
The uptime (period since the router first heard from the neighbour).
The sequence number. The neighbour table tracks all the packets sent between neighbours (both the last sequence number sent to the neighbour and the last sequence number received from the neighbour).
Retransmission timeout (RTO), the time a router will wait on a connection-orientated protocol without ACK before retransmitting the packet.
Smooth Round Trip Time (SRTT), calculates the RTO. The SRTT is the time (milliseconds) that it takes a packet to be sent to a neighbour and a reply to be received.
The number of packets in a queue, which is a means by which administrators can monitor congestion on the network.

Becoming a Neighbour

All EIGRP routers periodically announce themselves with the Hello packet using multicast (224.0.0.10). On hearing a Hello (receiving) routers add an entry in the Neighbour Table (the continued receipt of Hello packets maintain the neighbour table).

If a Hello packet is not received from a neighbour within the holdtime (3x the Hello timer) the neighbour is removed from the Neighbour Table.

LAN = Hello timer 5 seconds, Holdtimer 15 seconds.
DS1 (1.5Mbps) or slower WAN links = Hello timer 60 second, Holdtimer 180 seconds.

To become a neighbour, the following conditions must be met:

The router muse hear a Hello packet from a neighbour,
The EIGRP Autonomous System (AS) number in the Hello packet must be the same as the receiving router,
the K-values used to calculate the metric must be the same.

Creating the Topology Table

After a router knows who neighbours are, it can create a Topology Table, assign Successors and Feasible Successors for each route (The Topology Table has a record of all routes not only Successors and Feasible Successors). The other routes are referred to as possibilities.

The topology table includes the following information:

Whether the route is passive or active.
Whether an update has been sent to the neighbour.
Whether a query packet has been sent to a neighbour
- if positive at least 1 route will be market active.
Whether a query packet has been sent
- if positive another field will track whether any replies have been received from neighbours.
That a reply packet has been sent in response to a query packet from a neighbour.
Prefixes, masks, interface, next-hop, and Feasible and Advertised Distance from remote networks.

The Topology Table is built from Update Packets that are exchanged by neighbours and by Replies to Queries sent by the router.

Queries and Responses used by EIGRP are sent reliably as multicast using RTP. If a router does not hear an ACK within the allotted time, it retransmits the packet as a unicast (16 times) after which the router marks the neighbour as dead.

Each time the router sends a packet, RTP increments the sequence number by one. The router must hear an ACK from EVERY router before it can send the next packet.

When all this is done the router has an understanding of the topology, it then runs DUAL to determine the BEST PATHS to the remote network. The result is entered into the Network Table.

Maintaining the Topology Table

The Topology Table may be recalculated because

A new network is added,
Successors change,
A network is lost.

Adding a Network to the Topology Table

As soon as Router A becomes aware of the new network (right),
1. It starts sending Hello packets out the new interface.
  1. No one answers (there is no router out the interface).
    - There will be no entries in the Neighbour Table because no neighbours responded to the Hello.
    - There is however a new entry in the Topology Table because it is attached to a new network.
EIGRP, sensing a change, must send an update to all neighbours on it’s old interface, informing neighbours of the change. These updates are tracked in the Topology Table and the Neighbour Table because updates are connection-orientated and ACKs from neighbours must be received within a timeframe.
Router A has completed its work.
1. Neighbours on the old network will update their sequence numbers in their Neighbour Tables and add the new network to the Topology Table.
  1. They will calculate FD and the Successor to place in the Routing Table.

Deleting a Path or Router from the Topology Table

If a network connected to Router A is disconnected (right),
1. Router A updates its Topology Table and Routing Table and sends an update to its neighbours.
When a neighbour receives the update ,
1. it updates the neighbour table and the topology table.
The neighbour searches for an alternate route to the network. It examines the Topology table for alternatives (none will be found there is only one path).
The neighbour then sends out a query to its neighbours requesting that they look in their tables for paths to the remote network.
1. This marks the route active in the Topology Table.
The query is tracked and when all replies are in the Topology Table and Neighbour Table is updated.
DUAL (which starts as soon as network change registers) runs to determine the best path, which is placed in the routing table.
Before routers respond, routers query their own neighbours (the search for alternative paths extends or diffuses throughout the entire organization).
If no alternative is found, the neighbours reply to the query stating that they have no path.
When no router can supply a path to the network, all the routers remove the network from their Routing Table and Topology Table.

Finding an alternate path to Remote Network

The router marks the routes that were reached by sending the traffic to that neighbour.
The router looks in the topology table to determine if there is an alternate route (Feasible Successor).
If a successor is found, the router adds the feasible successor to it’s routing table. If the router did not have a feasible successor, it would have placed the route into an active state while sending queries to neighbours for an alternate path.
After interrogating the topology table, if a feasible route is found, the neighbour replies with the alternative path. This path is placed in the Topology Table.
If no answer is heard, the messages are propagated through the network.

Creating the Routing Table

The Routing Table in EIGRP is built from the Topology Table using DUAL. The Topology Table holds all routing information known to the router and from this information successors and feasible successors are selected. Successors are passed to the Routing Table and used for routing decisions.

EIGRP Path Selection

Go here for more information on the metric.

Updating the Routing Table in Passive Mode with DUAL

When a path is lost, DUAL first looks in the Topology Table for a FD; If none the router stays in passive mode (as opposed to active mode where the router actively queries for alternative paths).

The FD from Router A to Router G is 10 ( A – D – G)
The AD from Router A to Router G is 5 (advertised from Neighbour D)
- Because 10 > 5 (FD > AD). The FD meets the feasibility condition allowing it to become FD.
- If the link between Router D and Router G goes down. Router A looks in its Topology Table.
- The Alternative Routes through Routers A to D to E to G (A-D-E-G) have an AD of 19
  - Because 10 < 19 (original FD), it does not qualify as a feasible successor.
- The Path through Router D to H to F to G (D-H-F-G) has an AD of 20
  - Because 10 < 20 (original FD), it does not qualify as a feasible successor.
- The Path through Router A to E to G has an AD of 7
  - Because 10 > 7 (original FD), it does qualify as a feasible successor.
- After the link between Router D and G dies, the Routing Table would be updated from the Topology Table while the router remains in Passive Mode.

Updating the Routing Table in Active Mode with DUAL

When no alternative route is found in the Routing Table, the following actions occur. The Topology Table of Router A starts with a path (successor) of A to D to G to X. The FD is 20, and the AD from Router D is 15. When Router D dies, Router A must find an alternate path to X.

The router rejects neighbours Router B, Router C, Router E and Router F as Feasible Successors.
- Router B 20 < 27
- Router C 20 < 27
- Router E 20 = 20
- Router F 20 < 21
  - Because all neighbours have a AD greater than or equal to the successors FD. They do not meet Feasibility requirements.
Router A goes into Active Mode and sends out queries.
Both Router E and F reply
- Router E 20 > 5
- Router F 21 > 5
  - The network returns to Passive Mode. The FD is acceptable, the Topology Table and Routing Table will be updated.
  - Router E is selected as the best route based on a lower FD
The result is placed in the Routing Table as the valid neighbouring router.
Router F will be the feasible successor.

EIGRP Network Design

EIGRP is designed to work in very large networks.
EIGRP is very design Sensitive.
Scaling a network properly is a major concern.
New demands are constantly driving the networks to use applications that require more bandwidth with less delay; while networks are becoming larger and more complex.

Factors that can affect of EIGRP include:

Amount of information sent between neighbours.
Number of routers that receive updates.
distance between neighbouring routers.
number of alternative paths to remote networks

Poorly scaled EIGRP networks result in:

A stuck-in-Active route
Network Congestion
Lost routing information
Flapping routes
Retransmission
Low Router memory
Over utilized Router CPU

Other factors (poor design) cause some of these symptoms because resources are overwhelmed with assigned tasks.

EIGRP Design Issues

Major concern in scaling an organizations network is controlling advertisements and limiting query range (NB over slow WAN links). Sending less information about the network there is more bandwidth available to clients and servers. This relieves the network and speeds convergence, it provides less information for alternate paths though.

EIGRP automatically summarizes at classful network boundaries because summarization is generally helpful and EIGRP is built to recognize opportunities such as this to optimize the network (Most Admins disable auto summarization because it does not match their needs, instead manually configure it at interface level).

Certain topologies pose problems for EIGRP networks. Like the hub-and-spoke design often used between remote sites and regional offices. Popular dual-hub configuration provides redundancy and allows for potential for routers to reflect queries back to one another. Summarization and filters make network design work well while also allowing queries to be managed effectively.

Guideline to Scaling Issues

Assign addresses and organize links so that natural points for summarization exist. A hierarhical network design IOW.
Provide sufficient hardware resources (mem and CPU) on network devices.
Use sufficient bandwidth on the WAN links.
Use filters to limit advertisements.
Monitor the network.

I’m very strange. Every time I type Hello, I have a voice in my head going “Hello Kitty”. So share my pain “Hello Kitty”!

Hello Kitty
I’m going to kick myself later when I read over this post again cause this is going to get stuck in my head again.

Resources:

Stewart, B,D., Gough, C (2008). CCNP BSCI Official Exam Certification Guide, Fourth Edition. Indianapolis: Cisco Press.

Notes and Notices:

Enhanced Interior Gateway Routing Protocol – Introduction

Published

Deon Botha

on August 5, 2008

in BSCI, BSCI Notes, Certification, Cisco Systems, Concepts and Constructs and EIGRP

. 2 Comments

This is the Introduction to Enhanced Interior Gateway Routing Protocol (EIGRP) most of this paragraph you will find here; moving swiftly along EIGRP is a Cisco Proprietary distance vector routing protocol that uses the same sophisticated metric that Interior Gateway Routing Protocol (IGRP) uses plus the Diffusing Update Algorithm (DUAL) convergences algorithm for loop-free routing. EIGRP is able to converge quickly and uses little bandwidth (like OSPF) because it separates keepalives, routing information and uses reliable updates. EIGRP is sometimes referred to as a hybrid routing protocol.

EIGRP was created (maybe read modified/updated) to solve scaling limitations that IGRP faced while still keeping the advantages of distance vector routing protocols (simplicity, economy of memory usage, and economy of processor resources). EIGRP is scalable in terms of hardware resources and network capacity. EIGRP is also very quick.

I use British English there will be a few small differences in spelling versus American English (the English Cisco Uses). Example: Neighbour vs Neighbor

Neighbourship and Reliable Incremental Updates

EIGRP supports several routed protocols independently (IP, IPX, Appletalk and IPv6) This means that each routed protocol has a best path that is not shared between other routed protocols.

EIGRP produces reliable (receiver ACKs the transmission was received and understood) updates by identifying its updates using IP protocol 88.

EIGRP uses five (5) types of packets to communicate:

Hello - Identifies neighbours; Hellos sent via multicast periodically and ACK.
Update – Advertises routes. Updates sent as multicast only when there is a change.
ACK – ACK receipt of an update.
Query – Used to ask about routes for which previous best path has been lost.
- If an update indicates that a path down, multicast queries used to ask other neighbours if they still have path.
- If querying router does not receive reply from each of its neighbours, it repeats query as a unicast to each unresponsive neighbour until it either gets a reply or gives up after sixteen (16) attempts.
Reply – Used to answer query. Each neighbour responds to the query with a unicast reply indicating an alternative path or that it does not have a path.

Neighbour Discovery and Recovery

EIGRP uses a reliable update procedure; this creates two problems,

The router needs to know how many other routers exist so that it knows how many ACK to expect.
The router needs to know whether a missing advertisement should be interpreted as “no new information” or “neighbour disconnected”.

EIGRP uses neighbourship to address these problems (periodic hellos).

The first hellos build a list of neighbours (Neighbour Table).
following hellos indicate that the neighbours are still alive.

If hellos are missed (for the period of the hold time) then the neighbour is removed from the EIGRP table and routing reconverges.

The discovery process begins with multicast advertisements being sent out and individual routers replying with unicast ACK. The neighbour table tracks replies to make sure that each neighbour responds. If a neighbour does not respond with an ACK a follow-up unicast message is sent, after 16 times attempts the neighbour is removed from the neighbour table and EIGRP continues with its next task.

Sophisticated Metric

EIGRP uses a sophisticated metric that takes into account bandwidth, load, reliability, and delay. The metric equation is:

EIGRP selects paths based on the fastest path (lowest value). To do that it uses K-values (K1 to K5 in the equation). The K-values are constants(don’t change) that are used to adjust the relative contribution of the various parameters to the total metric. The EIGRP K variables are set as follows:

Bandwidth – 107 kbps divided by the slowest link along the path. Because routing protocols select the lowest metric, inverting bandwidth makes faster paths have lower costs.
Load and reliability – 8-bit calculated values based on the performance of the link. Both are multiplied by a zero K-value (neither used).
Delay – a constant value on every interface type, and is stored in terms of microseconds (serial has a delay of 20,000 microseconds and Ethernet has a delay of 1000 microseconds). EIGRP uses a sum of all delays along the path, in microseconds.

By default:

K1 = K3 = 1 and
K2 = K4 = K5 = 0 (if you followed the maths if K5=0 then the metric equals 0).

Because the metric basically = 0 which will not be useful EIGRP ignores everything outside the parentheses.

Using the default K-values the equation then becomes:

Substituting the earlier description of variables, the equation becomes 10,000,000 divided by the chokepoint (worst/slowest link along the path) bandwidth plus the sum of delays:

Exercise to crystallize

This entire section is so that I understand how EIGRP selects the route using the below diagram (from Brent D, Stewarts CCNP book) lets plug in some values and see it work.

If we want to send traffic from Router A to Router D, which path would be used?

The top path ABCD has a chokepoint bandwidth of 768 Kbps and would go along 3 serial lines and look like this in the equation:

The bottom path AED has a chokepoint bandwidth of 512 Kbps and would go across 2 serial lines and look like this in the equation:

The result is that EIGRP chooses ABCD (top path) based on bandwidth.

Diffusing Update Algorithm (DUAL)

EIGRP uses the Diffusing update Algorithm (DUAL) which is a modification to the way distance-vector routing typically works. DUAL allows routers to identify loop-free failover paths. Using the same graphic as above lets do an exercise and figure out how DUAL works.

How DUAL works is that neighbouring routers advertise costs (using the below diagram. Lets say router A wants to send a packets to Router D). The two costs advertised by neighbours are as follows:

To send a packet from A to D the Advertised Distance (AD) is either via BCD or ED and excludes the first hop.
The other advertised metric is the Feasible Distance (FD) which is to send a packet the total distance ABCD or AED.

The idea that a path through a neighbour is loop free if the neighbour is closer is called the feasibility requirement and can be restated as “using a path where the neighbour’s advertised distance is less than our feasible distance will not result in a loop”.

The neighbour with the best path will be referred to as the successor. Neighbours that meet the feasibility requirements are called feasible successors. In emergencies, EIGRP knows that using feasible successors will not cause routing loops and instantly switches to the backup path.

Using the above diagram again I am going to be trying to reach Router D. What I did was plug in values using the same equation from the above exercise, just using each individual router (A, B, C, E) to get to D.

Queries

Having a Feasible Successor provides the best convergence. A feasible successor is a backup path and can be substituted should the active path go down at any point (without the need to change state and ask neighbours for a path). Should an active path go down and no Feasible Successor exist, a router will send out queries to remaining neighbours. If a neighbour does not know of a an alternative path, it will recursively ask neighbours.

Recursive queries can loop, forcing the router to time-out the query. This is known as stuck in active (SIA). EIGRP uses split horizon (a router should not advertise a network down a link from which it learned about the network – CCNA).

Queries will continue until an answer is found or until no one is left to query. When queries are produced the router changes to an Active State (actively querying for an alternative path) and sets a timer (3 minutes default). If the timer expires before an answer is returned the router is considered SIA. SIA typically occurs because queries are not properly limited to an area.

The primary way to limit how far queries travel (called query scoping) is to summarize (also allows quick convergence).

Incremental Updates

EIGRP periodically sends hellos to maintain neighbourship, but only sends updates when a change occurs. When a route is changed or withdrawn, an incremental update is sent including only those changes.

Multicast Addressing for Updates

EIGRP sends some packets using a reliable transport protocol (RTP). An example would be EIGRP sending a single multicast hello packet with an indicator that says it need not be ACK. Other types of packets like updates indicate that packet ACK is required.

EIGRP uses both multicast and unicast addressing.

Some packets are sent using Real-Time protocol (RTP), a Cisco Proprietary (?? Can’t find a source for this ??) protocol that oversees the communication of EIGRP packets. These packets are sent with sequence numbers to make the transmission of data reliable. Hellos and ACKs do not require acknowledgement.

Incremental Updates cannot be anticipated; update, query, and reply packets must be ACK by the receiving neighbour.

Updates are sent using reliable multicast (Reserved Class D address, 224.0.0.10). When a neighbour receives a multicast, it ACKs the receipt with an unreliable unicast.

Unequal-Cost load sharing

All IP routing protocols on Cisco routers support equal-cost load sharing. EIGRP is unique in its support for unequal-cost load sharing.

Unequal-cost load balancing takes the best FD and multiplies it by variance. Any other path with an FD less than this product (the product of multiplication read answer) is used for load sharing. EIGRP also does proportional unequal-cost load sharing.

EIGRP will pass a relative portion of the traffic to each interface (60/40) allowing links to a destination to be used to carry data without saturating the slower links or limiting the faster links.

Resources:

Stewart, Brent, D. 2008, CCNP BSCI Official Exam Certification Guide, 4th Ed. Indianapolis: Cisco Press.

Have a look at EIGRP Aragoen Celtdra notes on the same section of work

Introduction to EIGRP

Internetworking Technology Handbook – EIGRP

EIGRP Technology Whitepaper

The Dual Algorithm

Notes and Notices:

BSCI IP Foundation – IP Addressing

Published

Deon Botha

on July 29, 2008

in Addressing, BSCI, BSCI Notes, CIDR, Certification, Cisco Systems and Concepts and Constructs

. 0 Comments

IPv4 uses 32-bit numbers that combine a network and a host address. IP addresses are written in four dotted decimal fields. Each number represents a byte (meaning 192 would be a byte cause in decimal its actually made up of 8 bits). The far left bits are the network address because all hosts on this network have addresses that start with that pattern, the right bits are host addresses and each host has a different value.

Resources for IP address Internetworking Technology Handbook: Internet Protocol

Binary Review

IP Addresses are composed of four bytes (8 bits) and in networking binary works one bit at a time from 0000 0000 to 1111 1111 (0 to 2555) IRL networking that’s what you need to know (test are different cause they ask more than just 255). This is a CCNA topic and I filled note pads with examples just to be able to get it as natural as quick as possible, after a while you start remembering 1010 1100 (172) and 1100 0000 (192). The old CCNA Prep Centre (now Cisco Learning Network) had a Java based game to get this into your head where you had to convert Binary to Decimal against the clock. Helped me because its repetition, repetition, repetition.

Classfull Network Ranges

The above network address (192.168.16.2) at the top of the post starts with 192.xxx.xxx.xxx if you didnt have this table to the right here are the steps to find out which network it belongs to.

Step 1: Converting the first byte to binary 1100 0000 (192).

Step 2: You take the first 4 bits and compare them to what you know:

Class A starts with 0,
Class B starts with 10, and
Class C starts with 110.

This means that the address is a Class C address.

This is something that you must just know, get to know the first column and associate that column with the Class on the table above and then the you can figure out the range easily enough (if you are good with memorizing tables just memorize the bits, range and class).

Network Range by Subnet Masks

Subnetting is when you take the assigned network and break it into smaller pieces this can be useful to conserve IP address space (or when I was doing the CCNA I did this to practice on my office network). The book I am using (Brent D. Stewart, CCNP BSCI Official Exam Certification Guide; Fourth Ed.) uses a Truth Table for AND that is really easy to use and master.

Another method would be to use a table, its also not rocket science but means that you don’t actually know how to do this on the fly.

Moving along lets use the AND method and an example. What network does PC 3 belong to with the IP 192.168.5.100 and the subnet mask 255.255.255.224 and what are the usable addresses on this network.

STEP 1: If the mask is given in decimal notation, convert it to CIDR notation (maybe a long way but you going to need the binary in a second anyway).

STEP 2: To determine the network address of the IP address, copy the network bits from the address as shown by the CIDR notation. Fill in the remaining bits with zeros.

STEP 3: The last Address in the range is the broadcast address. To find this out do the following:

STEP 4: The usable network addresses fall between STEP 2 and STEP 3.

STEP 5:To check this subtract the CIDR notation from 32 that’s 32 – 27 (not the other way around cause you going to get a negative number). To determine the “amount” of addresses then plug it into this formula 2n-2 (n = number of host bits).

Resources for Subnet Mask and Classes: Internetworking Technology Handbook IP Address Classes

Summarization

Summarization (route summarization) is a technique used to group IP networks together to minimize IP advertisements. Doing this allows one to hide unimportant details (flapping links) and to simplify the routing process (make better use of router CPU and memory than to process and store routing information). One of the keys to scalable routing is to take large complicated sets of advertisements and reduce them as much as possible (think internet).

Step 1: Write each network in binary

Step 2: Determine the number of bits that match. This gives a single summary that includes all the routes, but may include a range of addresses that is too large (over-summarization)

Step 3: If step 2 unacceptably over-summarizes, start from the first address and add bits to the prefix until a portion of the range is summarizes. Take the remaining addresses and start this process again.

Step 4: Write each network in binary

Step 5: Determine the number of bits that match.

Step 6: Because step 2 did not over-summarize, the process is complete. Answer is 192.168.0.0/21 and 192.168.0.0/23

Address Planning

Summarization is not possible if network numbers are randomly assigned within an organization. When designing a network it is important to keep in mind the requirements for summarization.

Notes and Notices:

BSCI Design Foundation – Routing Protocols

Published

Deon Botha

on July 25, 2008

in BGP, BSCI, BSCI Notes, CIDR, Certification, Cisco Systems, Concepts and Constructs, EIGRP, IGRP, IS-IS, OSPF, RIP, RIPv2 and VLSM

. 2 Comments

Routing protocols employ one of two basic strategies to communicate/propagate routing information:

Distance vector routing protocols work by passing copies of their routing tables to their neighbours (a.k.a routing by rumour).
Link State routing protocols work by advertising a list of neighbours and the network attachment state to their neighbours until all routers have a copy of all the lists, routers then run the Shortest Path First Algorithm to analyse all paths and determine the best paths available.

Distance vector routing are less processor and memory intensive than link state routing, but can have loops because routing decisions are made on incomplete information.

Link state routing is loop-proof because routers know all possible routes, but link state routing requires more CPU time and memory.

Classless and Classful Routing

An important characteristic of routing protocols is how they advertise their routes. Older routing protocols (RIP and IGRP) assumed the subnet mask the same as the one the receiving on the interface or that it is the default one (Class A is /8, Class B is /16 and Class C is /24). This is called classful because the assumption is based on the Class of the IP address.

Modern routing protocols (OSPF, IS-IS, and EIGRP) explicitly advertise the mask. There is no assumption made with regard to the mask, it is clearly indicated. This is called classless because no assumption is made and an address alone is not a good indicator subnet mask.

Variable Length Subnet Masks (VLSM) refers to the property of a network that allows different subnet masks to be mixed throughout the network.

Classless Interdomain Routing (CIDR) is a property of a network that allows classful networks to be aggregated.

Classless routing protocols support both VLSM and CIDR.

Interior and Exterior Gateway Protocols

Most protocols are “Interior Gateway”, meaning that they are designed to be run inside a network (inside the trusted boundaries of the company).

BGP on the other hand is an exterior gateway protocol (EGP) and is used for routing between autonomous systems (AS) on the Internet (outside the trusted boundaries of the company). As BGP is the only EGP you will have to consider using it if you connect your network to the Internet.

Convergence Times

A distinguishing characteristic of routing protocols is the speed of convergence times. To explain convergence, when a routing protocol is forwarding data, it is converged. In this state the routing protocol has shared routing table information and each router in the topology knows the best paths available. If there was a change (a router going down, another router being added, etc) this would require all routers to share information again because there are routes they do not have information on. The time between network change and forwarding would be “convergence”. This is generally classed as either slow or fast.

Fast convergence would mean that the routing protocol is able to recognize a problem on the network and fix that problem faster than a user can call to report a given problem.

Slow protocols, such as RIP and IGRP, can take up to minutes to converge when a problem occurs.

Fast protocols (OSPF, IS-IS, EIGRP) generally take less than 10 seconds to converge.

Proprietary and Open Standard Protocols

The important aspects to look for in routing protocols is speed of convergence and whether the protocol is classless (OSPF, IS-IS, and EIGRP). While OSPF and IS-IS are open standards (plays well with other vendors kit), EIGRP is Cisco proprietary (Cisco Only). Of the three protocols EIGRP is the easiest to configure and maintain but requires a pure Cisco environment to run.

Routing Protocol and the ECNM

The ECNM mentioned in previous posts can assist in showing where a particular routing protocol will run in the enterprise. Using information discussed above and using the ECNM the above diagram shows what the advanced routing protocols (EIGRP, OSPF, IS-IS) are best suited for when considering size of network, speed of convergence, VLSM, open or proprietary, and support staff knowledge needs.

The object (ideal) is to have a single routing protocol running throughout the enterprise (reality however is another story) where the enterprise edge will require BGP as the only EGP and at least one if not more of the IGPs within the enterprise boundaries depending on needs/requirements of end-points or design specifications.

In Summation

Older routing protocols (RIP, RIPv2 and IGRP) are slow because they send a full copy of their information periodically, these periodic transmissions act as both routing advertisement and keepalive message. In addition to being slow they consume a lot of bandwidth relative to their function (RIP every 30 seconds).

More modern routing protocols are faster because they separate the routing advertisements and the keepalive messages. Updates are only sent out when new networks need to be advertised or old networks need to be withdrawn; otherwise routers just need to verify that neighbours are still alive (EIGRP every 5 seconds).

RIP and IGRP

These are older distance vector routing protocols that are slow and classful. Some legacy systems (UNIX) expect to learn their default gateway by eavesdropping on RIP advertisements. If you deploy RIP use RIPv2 which is classless.

EIGRP

A modern distance vector routing protocol. It is classless and fast as well as being easy to configure and maintain. Some organizations refuse to implement proprietary standards though (EIGRP provides equivalent performance to OSPF but is easier to implement and maintain).

OSPF

OSPF is a modern classless and fast link-state routing protocol. OSPF has a steep learning curve and uses more processor time and memory than EIGRP. This is the open standard if an organization supports a heterogeneous mixture of routers or has a philosophical problem with proprietary standards.

IS-IS

This routing protocol was developed to compete with OSPF and the two are more similar than they are dissimilar. It is moderately difficult to find anyone who has experience working with IS-IS even if it is open, fast, and classless. There is still however some interest in IS-IS because it can be adapted to support MPLS and IPv6.

BGP

BGP is a routing protocol used between AS on the Internet and you will have to use it to connect your network to the Internet.

Resources:

Internetworking Technology Handbook Routing Basics

Internetworking Technology Handbook RIP

Internetworking Technology Handbook IGRP

Internetworking Technology Handbook OSPF

Internetworking Technology Handbook EIGRP

Notes and Notices:

BSCI Design Foundation – Network Models

Published

Deon Botha

on July 25, 2008

in BSCI, BSCI Notes, Certification, Cisco Systems, Concepts and Constructs, ECNM, Enterprise Architecture, IIN and SONA

. 0 Comments

Design – Hierarchical

Where networks once were non-hierarchical (layer-1 design, layer-2 design, layer-3 design) they are generally now three-layer hierarchical in design (above). Cisco has been using this model for years and it gave a high-level overview of how a reliable network could be conceived but was largely conceptual because it did not provide specific guidance on “how-to” implement certain things, like:

Implementing redundancy,
Adding Internet Access,
Accounting for remote users,
Locating workgroup and enterprise services

Design – Enterprise Composite Network Model (ECNM)

Revisions to the hierarchical design showed redundant distribution and core devices and connections to make the hierarchical model more fault tolerant. The switch block design (above) explained how redundancy fit into a network, but still did not really adequately specify other parts of the network design. This lead to the Enterprise Composite Network Model (ECNM) development to address the failures of both the hierarchical model and switch block model.

This ECNM is broken into three large pieces:

Enterprise Campus,
Enterprise Edge,
Service Provider Edge.

Enterprise Composite Network Model

ECNM – Campus

The enterprise campus looks very much like the above switch block design with some added details:

Campus Backbone (like the core layer of the hierarchical model),
Building Distribution,
Building Access,
Management,
Server Farm (Enterprise Services).

The ECNM Campus builds onto the Switch block design but gives specific guidance as to where to place servers and management equipment. Take note that the servers look like a switch block and are redundantly attached (dual-homed) to the switches (not really shown nicely in the diagram).

ECNM – Enterprise Edge

The Enterprise edge shows the connections that the enterprise has with the wide area (other networks) and include:

E-Commerce,
Remote Access,
Internet Connectivity,
WAN (Internal links to other branches).

ECNM – Service Provider Edge

The service provider edge includes the public networks that facilitate wide area (other networks) connectivity:

Internet Service Provider (ISP),
Public Switched Telephone Network (PSTN) for dialup,
Frame Relay, ATM, and PPP for private connections.

Multiplexing

Historically voice traffic used one set of circuits and data traffic another. Also if you wanted more than one “number” the telecommunications company installed another physical line to your premises. If you wanted access to a data network they installed a data line for that purpose.

With line technologies like the T-carrier system (USA, Japan, Korea) 24 pulse-code modulated (I don’t know need to ask one the engineers about this), time-division multiplexed speech signals are carried over 2 copper pairs. This type of technology saved the telecommunications companies a lot of money in building out subscriber lines. The problem with T1 as a technology is that it cannot adjust as the customer usage requirements changes (see E-carrier system for Europe and other countries).

As technology changes so does the requirements from that technology; Modern networks are designed to carry voice, video, enterprise applications, normal LAN traffic and management traffic all on the same single secure infrastructure (convergence). The traffic is forced (statistically multiplexed) to share access to the network.

Service-Orientated Network Architecture (SONA) and Intelligent Information Network (IIN)

As covered above “Multiplexing” described the idea of a converged network as a system that integrates what was previously disparate systems (voice, video, data). The traffic types usually found on a converged network would include, but may not be limited to:

voice signalling and bearer traffic,
Core application traffic (ERP and CRM),
Transactional traffic related to database interactions (SQL),
Network management traffic for monitoring and maintaining the network structure (including routing protocol traffic),
Multicast multimedia,
Other traffic (web, e-mail, file transfer).

Each of the above traffic types has its own requirements and expectations that govern its successful execution. These requirements include security, QoS, transmission capacity, and delay.

To support this kind of multiplexed traffic, Cisco routers are able to implement filtering, compression, prioritization, and policing (dedicating network capacity). Except for the filtering process these processes are collectively known as QoS.

As an alternative to QoS, Cisco has an ideal called the Intelligent Information Network (IIN). This vision describes a network that integrates network and application functionality cooperatively allowing the network to be “smart” about how it handles traffic to minimize the footprint of applications. The IIN evolution is described in three phases:

Phase 1: Integrated Transport, deals with a converged network, built along a similar fashion of the ECNM and based on open standards (cross-compatibility)
Phase 2: Integrated Services, posits virtualization of resources such as servers, storage and network access; to move to an “on-demand” model. Don’t think marketing/advertising “virtualization” think practical virtualization the ISR routers (routing, switching, voice, network management, security and wireless) designed as an aio (all-in-one) appliance and Vitalizing Servers (if you have proper designed for the job servers) you can’t be trying this on SMB servers or try recycling 10 year old technology and thinking “bargain let’s load 5 operating systems on this”.
Phase 3: Integrated Applications, using application orientated networking (AON) to make the network “aware” allowing the network to actively monitor and participate in service delivery.

Service-Orientated Network Architecture (SONA) is the practical application or “how-to” of IIN in enterprise networks. SONA breaks down IIN into three layers;

SONA Infrastructure Layer is basically the same as IIN Phase 1,
SONA interactive Services Layer maps to IIN Phase 2,
SONA Application Layer has the same concepts as IIN Phase 3.

Resources:

Aragoen Celtdra on BSCI: Network Architecture and Design

Notes and Notices:

Cisco South Africa Partner Career Day

Published

Deon Botha

on July 15, 2008

in Cisco Systems and Vine

. 0 Comments

So I attended the Cisco South Africa Career Day 2008 and it was well worth going. The event was hosted by Cisco in conjunction with the Cisco Networking Academy and the University of Pretoria.

A way that I have used to gauge the importance of an event has been to look at the “headline” act. In todays case the introduction was done my General Manager of Cisco Systems, Mr Steve Midgley and the key note address was given by Deputy Minister of Education Mr Enver Surty.

The drill-down of the presentations was that there is a skills shortage and there are initiatives already happening and in the pipelines to help address this global problem.

The event took place at the the University of Pretoria in the Entertainment Hall and Lecture Room 100 and centred around the development and availability of skill in the Information and Communication Technology (ICT) Sector mainly locally but also touched on it globally (China and India).

The event was held at the University of Pretoria to provide Cisco Networking Academy graduates the opportunity to get some “face time” with Cisco channel partners. The event provided the Cisco partners an opportunity to meet the future talent and interview graduates face-to-face. This exposed Cisco Networking Academy graduates to openings within Partner organisations, while allowing Partners to asses prospective employees.

From Cisco systems there was a clear message that they were going to be actively involved in developing and building the skills needed to assist partners and in turn the local economy through various initiatives. They drove this message home by making this the “public” launch of the Cisco Talent Partner Portal that I posted about here 2 weeks ago.

I stole a few business cards myself and talked to some of the bigger partners, one never knows when that might come in handy.

Kudos again to JP for organizing the invite.

Network Ninja

Tag Archive for 'networking'

Open Shortest Path First – OSPF Fundamentals – DR and BDR

Update on Cisco Live! – World’s Leading Technologies Together in JHB

Enhanced Interior Gateway Routing Protocol – Optional Configuration Commands for EIGRP – Tuning EIGRP

Linksys Brand to Disapear

Enhanced Interior Gateway Routing Protocol – Tables

Enhanced Interior Gateway Routing Protocol – Introduction

BSCI IP Foundation – IP Addressing

BSCI Design Foundation – Routing Protocols

BSCI Design Foundation – Network Models

Cisco South Africa Partner Career Day

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