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Tag Archive for 'Routing'

Open Shortest Path First – OSPF Fundamentals – Scenario

Published

on June 29, 2009

in BSCI, BSCI Questions, Certification, Cisco Systems, Concepts and Constructs, DR and OSPF

. 0 Comments

GIVEN: For a Given Network, all routers share a common multi-access segment. One router is elected the Designated Router (DR) and another is elected the Backup Designated Router (BDR).

1. Which Parameter determines the router that will be selected as the DR in an OSPF network?

The router with the Highest OSPF Priority on a particular network segment will become the designated router (more info). The DR default OSPF priority for a Cisco Router is 1 but can be manually changed. If there are multiple routers with default OSPF Priority then the Routers elect a Designated Router using the Router ID (more info) (RID) which is basically the highest IP Address with loopbacks being preferred (if configured)

2. Could a router with a priority value of zero assume the role of a DR or a BDR in the OSPF?

An OSPF Priority of 0 (zero) means that the Router is not eligible to be elected for either DR or BDR. The zero interface state is DROTHER.

3. How is the OSPF router ID determined on a Cisco Router?

The OSPF Router ID (RID) on a Cisco Router is determined by the highest IP address configured on an interface (if not manually configured), or IP Address on a loopback interface.

4. What is the role of the DR and BDR in the OSPF network?

The role of the DR and BDR in an OSPF Network is to handle and monitor adjacencies with other routers in the network. This is because in an OSPF network adjacencies grow at a quadratic rate. This means that instead of exchanging routing information with all other routers the routers exchange information with the DR and BDR. Then in turn the DR and BDR relay the information to other routers.

Resources:

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

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 cannot 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.

Open Shortest Path First – OSPF Fundamentals – Questions and Answers – Question 3

Published

Deon Botha

on June 17, 2009

in BSCI, BSCI Questions, Certification, Cisco Systems, Concepts and Constructs and OSPF

. 0 Comments

Working from the my last couple of OSPF posts I am going to try and crystallize some of the material found by working through questions found in Stewart, B,D., Gough, C (2008). CCNP BSCI Official Exam Certification Guide, Fourth Edition. Indianapolis: Cisco Press book.

3. Is it possible to have more than one OSPF process on a router. How would you do this?

Yes it is possible to have more than one OSPF process on a router.

You may want to do this to create two different OSPF domains / areas with separate routing policies.

To accomplish this simply specify two (or more) OSPF processes in the following way:

Router_2(config)#router ospf 1 Router_2(config-router)#network [ip address] [mask] area [number] Router_2(config-router)#exit Router_2(config)#router ospf 2 Router_2(config-router)#network [ip address] [mask] area [number]

Resources:

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

Open Shortest Path First – OSPF Fundamentals – Checking or Troubleshooting OSPF Troubleshooting

Published

Deon Botha

on June 12, 2009

in BSCI, BSCI Notes, Concepts and Constructs, Debug and Show

. 0 Comments

I’m using a Simulator and sometimes output differs from what it should be (which is happening more and more often). Make the best out of the explanations when things differ (I’ve used verbatim examples where the simulator just came up blank with output).

All the below is to test if OSPF is functioning properly and has been configured correctly.

Base the output (for examples that worked) on the show commands on the below OSPF Configuration.

Working from a functional configuration on a single router, Router_1 will be the DR on Fe1/0 unless another device on that segment has a priority greater than 100. The link attached to Fe1/0 has a cost of 1. The cost on Fe2/0 has been changed to 10.

The Config

Router_1(config)#router ospf 100 Router_1(config-router)#network 192.168.0.0 0.0.255.255 area 3 Router_1(config-router)#exit Router_1(config)#interface Ethernet 0/0 Router_1(config-if)#ip address 192.168.16.1 255.255.255.240 Router_1(config-if)#ip ospf priority 100 Router_1(config-if)#exit Router_1(config)#interface Ethernet 0/1 Router_1(config-if)#ip address 192.168.16.15 255.255.255.240 Router_1(config-if)#ip ospf priority 20 Router_1(config-if)#exit Router_1(config)#interface Ethernet 0/2 Router_1(config-if)#ip address 192.168.16.30 255.255.255.240 Router_1(config-if)#ip ospf priority 15 Router_1(config-if)#exit Router_1(config)#interface Ethernet 0/3 Router_1(config-if)#ip address 192.168.16.17 255.255.255.240 Router_1(config-if)#ip ospf cost 10

Checking the Configuration

As we’ve been through before in previous posts, the show commands are detailed and comprehensive views on the health and status of the network and hardware (there are a gazillion of them and the detail can be overwhelming same with debug commands). To understand the output from the show commands read-on.

The show-ip ospf Command

The show-ip ospf command shows how OSPF is running on a given router. Output includes the number of times that the SPF routing algorithm has run (indicates the stability of the network). From the previous posts the SPF routing Algorithm runs when there is “instability” on the network (the higher the number of “recalculations” the less stable the network).

Router_2#show ip ospf [process-id]

Output

Explanation

The show ip ospf Database Command

The show ip ospf database command when issued will display the contents of the routers topological database and the different Link State Advertisements (LSAs) that have populated the database (Internal Routers will only display router and network LSAs).

Router_2#show ip ospf database

Output

Explanation

Show ip ospf interface Command

The show ip ospf interface command shows how OSPF has been configured and how it is working on an interface. This level of detail is excellent to troubleshoot config errors.

Router_2#show ip ospf interface [type number]

The command shows information such as the Designated Router (DR) and Backup Designated Router (BDR), a list of neighbours, and the network type.

Output

Explanation

There are some things that don’t come up once again on my output. This would be because I am using a simulator when studying and not “real” kit. You can’t really expect the lab to do “Everything” you want but it does a good job of giving you the basic ideas. Use your imagination.

From here on in things are verbatim from the book. The deviations on the Simulator is so GREAT from what it should be (a.k.a a blank output) that I really can’t study from that).

Show ip ospf neighbour Command

The show ip ospf neighbour command shows OSPF neighbours (known neighbours can be viewed using this command).

Router_2#show ip ospf neighbor

Output

The command can be made more granular and the neighbours can be viewed in a per-interface method

The command can once again be expanded further to show a deep-dive per interface view in as much detail as possible. Use the command displayed below.

Router_2#show ip ospf neighbor {type number} {neighbour id} [detail]

Output

Explanation

Show ip protocols Command

The show ip protocols command shows the configuration of IP routing protocols configured on the router. The command brings up how protocols were configured and how they interact with one another (updates, interactions, etc). Great for troubleshooting configuration errors and understanding how the network is communicating about routes

Router_2#show ip protocols

Output

Explanation

Show ip route Command

The show ip route command shows the IP routing table on the router. This particular command shows how the network is known to the router and how the router discovered routes. Most of us know about this one and would have used it many times before. I know I have.

Router_2#show ip route

Debug Commands

A rather dangerous command is debug (this is because it can make a router totally freak out). This is due to the fact that the debug command has the highest process priority and can consume all resources on the router causing the router to freeze up and need a power cycle.

Good practice would be to turn on debug commands for a specific function and then turn off that debug command as soon as the needed information has been gathered.

To turn of all debug commands that could be active on the router:

Router_2#no debug all

The particular commands with relevance to OSPF:

Router_2#debug ip ospf events

This command displays information about OSPF-related events, such as adjacency, flooding information, designated router selection, and SPF calculation.

Router_2#debug ip packet

This command is IP debugging and includes packets received, generated, and forwarded. Fast-Switched packets do not generate messages.

If I added some value to your Cisco Experience with this post please add some value to my studies and leave a comment, question, suggestion, note of thanks or encouragement for me to hurry up and complete my certifications. My reasoning for wanting some interaction is that the last Recruiter said I need CCNP, Juniper and a Specialization track. The LOOOOONG Road to Cisco Indeed. Thanks Deon

Open Shortest Path First – OSPF Fundamentals – Configuring OSPF in a Single Area

Published

Deon Botha

on April 9, 2009

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

. 5 Comments

The command requirements for configuring OSPF in a single area is relatively (compared to say other routing protocols) few in number and simple; the implications of the commands are somewhat complicated but need to be understood.

Required Commands for Configuring OSPF WITHIN a Single Area

We are going to configure an OSPF internal router. An Internal router being one with all interfaces that lie within a single area. The sole OSPF function on an internal router is to route within an area.

The Router needs to understand how to participate in the OSPF network:

OSPF Process – Declare an OSPF process.
Participating interfaces – Identify the interfaces to be used by OSPF.
Area – Definitions are done per interface. This discussion assumes that all active interfaces are in the same area.
Router ID – A unique 32-bit ID, usually drawn from an interface IP Address.

Enabling the OSPF Routing Protocol

Router(config)#router ospf process-number

In the above the process-number is not globally significant. It is possible to have more than one process running on a router (although that would be an unusual configuration, but not unheard of) and two OSPF processes could route for different parts of the network. The process number does not have to be the same on every router in the area.

The OSPF Network Command

Once OSPF is turned on (the above command), you must define the interfaces that are to participate in OSPF and the area that they reside in:

Router(config-router)#network network-number wilcard-mask area area-number

NB.Take note of the above command. Many errors occur in configuration with this command, normally due to misapplication of the wildcard-mask parameter, either including too many or too few interfaces in a particular OSPF area.

Similar to other routing protocols like RIP, the network command identifies the interface on which the OSPF process is to be active. Unlike RIP however this command has a wilcard mask that allows it to be very specific. All interfaces that match the network wildcard mask will be active within the given area.

One can apply the network command in different ways, each method will yield different yet similar results.

FE 0/0 : 192.168.0.1 / 24
FE 0/1 : 192.168.1.1 / 24
FE 0/2 : 192.168.2.1 / 24
FE 0/3 : 192.168.3.1 / 24
S o/1 : 10.10.1.1 / 30
s 1/1 : 10.10.2.1 / 30

We can enable OSPF area 0 (zero) on all interfaces with the following command:

Router(config-router)#network 0.0.0.0 255.255.255.255 area 0

When using this approach you may include interfaces inadvertently that you may not want to include (as this is a sweeping statement config line).

The second method would be to break the network into the 10 network and the 192 network, as follows:

Router(config-router)#network 10.0.0.0 0.255.255.255 area 0 Router(config-router)#network 192.168.0.0 0.0.3.255 area 0

This approach gives a little more control over the two different networks (192.x.x.x and 10.x.x.x) splitting them into two config lines.

Another method would be to separately enable OSPF on each interface;

Router(config-router)#network 192.168.0.1 0.0.0.0 area 0 Router(config-router)#network 192.168.1.1 0.0.0.0 area 0 Router(config-router)#network 192.168.2.1 0.0.0.0 area 0 Router(config-router)#network 192.168.3.1 0.0.0.0 area 0 Router(config-router)#network 10.10.1.1 0.0.0.0 area 0 Router(config-router)#network 10.10.2.1 0.0.0.0 area 0

This option is more time consuming to deploy but gives much more control over what interface specifically is included and not included in area 0 (zero) which will enable much more control over the routing process.

All the above achieve the same thing (six interfaces places in area 0 (zero) begin to process OSPF traffic).

The technique that is used should be functional, effective and efficient given the topology and application on the network while still maintaining the ability to be documented thoroughly (Keep It Simple Stupid KISS or as simple as possible, because you might not be the one to always maintain the network).

NB.Be intimately familiar (CCNA) with wildcard masks and the network command to enable OSPF on router interfaces

The area parameter puts the designated interface into an area. A router can have different interfaces in different areas (as mentioned earlier thus making the router an Area Border Routers (ABR)). The area-number is a 32-bit field and format can either be a simple decimal (0, 1, 2, 3, 4) or dotted decimal( 0.0.0.1, 0.0.0.2, 0.0.03, 0.0.0.4). Some implementations of OSPF might only understand one of the formats (keep in mind that some vendors throw the dotted decimal around 0.0.0.1 will become 1.0.0.0), Cisco understands both formats.

After identifying the interfaces on the router that are participating in the OSPF domain, hellos are exchanged, LSAs are sent, and the router inserts itself into the network.

NB.If there are stub networks connected to a OSPF router, it is useful to issue the command redistribute connected subnets. This command includes the connected subnets in OSPF advertisements without actually running OSPF on these routers. A route-map is often used with this command to exclude interfaces that are explicitly configured with OSPF

Next up Internal Router Config in more detail….

Open Shortest Path First – OSPF Fundamentals – Multiple Areas

Published

Deon Botha

on March 3, 2009

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

. 0 Comments

An OSPF area is a logical grouping of routers that runs OSPF with identical topological databases. An area is a subdivision of the OSPF routing domain. Each area runs SPF separately and summaries are passed between each area.

Problems associated with OSPF in a Single Area

Consider a growing OSPF network with a single area. Several problems come out in relation to capacity capabilities:

The SPF algorithm runs more frequently the larger the network gets, the greater the probability of a network change and a recalculation of the entire area (iow the more resources OSPF chews up). Each of these recalculations in a large network takes longer and involves more “work” with each recalculation for a small area (the expenditure of scarce resources time, cpu, memory, etc).
The larger the OSPF area, the greater the size of the routing table (duh). The routing table is not sent out (like in Distance Vector Routing Protocols). In OSPF this means that the the greater the size of the table the longer the lookup becomes. The memory requirements on the router also increase as the size of the routing table increases.
In a large network, the routers topological database increases in size and eventually becomes unmanageable (the topological database is exchanged between adjacent routers at least every 30 minutes).

As the various databases (Routing Table, Topological Database, Neighbor Table) increase in size and the calculation increase in frequency the CPU utilization increases and memory availability decreases (inverse relationship). This can affect network latency or cause link congestion, resulting in various additional problems (convergence times, loss of connectivity, loss of packets, system hangs) which is bad for networks.

Area Structure

OSPF creates a two-level hierarchy of areas.

Area Zero (Naught) a.k.a the backbone are or transit area. This is always the central area; all the other areas (stub areas that move towards the edge) attach to Area Zero. Area Zero forms the top level in the hierarchy and remaining areas form the bottom level of the hierarchy. This hierarchical design supports summarization and minimizes routing table entries.

Routers within Area Zero are called backbone routers. Routers that link to Area Zero and another area are called Area Border Routers (ABR). OSPF routers that redistribute routing information from another protocol are called Autonomous System Boundary Routers (ASBR).

OSPF Type Packets

As OSPF link-state information is shared between areas, an intricate set of mechanisms is followed, relying on a number of different OSPF packet types. All OSPF traffic is transmitted inside IP Packets. Receivers recognize OSPF traffic because it is marked as IP Protocol (89).

OSPF includes five packet types:

Hello Packets – Establish communication with directly attached neighbors.
Database Descriptor (DBD) - Sends a list of router IDs from whom the router has an Link State Advertisements (LSA) and the current sequence number. This information is used to compare information about the network.
Link State Requests (LSR) – Follow the Database Descriptors (DBDs) to ask for any missing Link State Advertisements (LSAs)
Link State Update (LSU) – Replies to a link-state request with the requested data.
Link State acknowledgments (LSAck) - Confirm receipt of link-state information.

All OSPF packets have a common format that contains the following nine fields:

Version – All packets are assumed to be Version 2 (at least for this part of Cisco stuff)
Type - There are five packet types, numbered 1 to 5
Packet Length - The length in bytes
Router ID – 32-bit identifier for the router
Area ID – 32-bit identifier for the area
Checksum - Standard 16-bit check sum
Authentication Type - OSPFv2 supports three authentication methods:
1. no authentication
2. plain text passwords
3. MD5 hashes
Authentication Data – 64-bit data, either empty, with a plain-text word, or with a “message digest” of a shared secret
Data – Values being communicated

And this took me almost 2 weeks. Shame on me.

Open Shortest Path First – OSPF Fundamentals – Neighbours and Adjacencies

Published

Deon Botha

on October 10, 2008

in BSCI, Certification, Cisco Systems, Concepts and Constructs and OSPF

. 0 Comments

OSPF develops neighbour relationships with routers on the same link by exchanging hello messages (a.k.a hellos).

At the initial exchange of hellos, the routers add each other to their respective Neighbour Tables (The Neighbour Table in this case acting as a list of connected OSFP enabled routers).

OSPF Enabled Routers send multicast hellos with a destination address 224.0.0.5 on all OSPF-enabled interfaces.

OSPF sends out hellos every 10 seconds on a broadcast link (a link with more than 2 nodes on the same segment like Ethernet) and 30 seconds on a non-broadcast (a link with only 2 nodes on the same segment; exceptions *shrug* exist for NBMA) link.

The Hello message contains:

After the initial hello exchange between two routers, an exchange of network information begins. After routers have synchronized their information they are adjacent.

Routers must go though various states from the initial relationship “hello” that transitions through a process before forming a “full” adjacency as shown above in the picture.

Once a full adjacency is achieved, tables between routers must be kept updated to prevent loops and routing errors. LSAs are re-sent when a change occurs, or every 30 minutes to keep routing information “fresh”.

Going through the different “states” a neighbour relationship can be in:

Down – This is the first OSPF neighbour state, this state means that no hellos (information) has been received from any neighbour(s).
Attempt - This state is only valid for manually configured neighbours in a Non-broadcast multi access (NBMA) environment. In Attempt state, the router sends unicast hellos every poll interval to the neighbour from which hellos have not been received within the dead interval.
Init - This state indicates that the router has received a hello packet from its neighbour, but the receiving router’s ID was not included in the hello.
2-way – This state indicates that the bi-directional communication has been established between two routers
Exstart – Once the Designated Router (DR) and Backup Designated Router (BDR) are elected, the actual process of exchanging link-state information can start between the routers and their DR and BDR.
Exchange – In this state, OSPF routers exchange database descriptor (DBD) packets.
Loading - In this state, the actual exchange of link-state information occurs.
Full - In this state, routers are fully adjacent with each other. All the routers and networks LSAs are exchanged and the router databases are fully synchronized.

Hellos between routers continue to be sent periodically and the adjacency is maintained as long as hellos are exchanged. Missing hello messages result in a router declaring the adjacency being declared dead.

As soon as OSPF identifies a problem, it modifies its LSAs accordingly and sends the updated LSAs to the remaining neighbours (with full adjacencies).

Being event-driven, this LSA process intrinsically improves convergence time and reduces the amount of information that needs to be sent across the network.

A key piece of information exchange in LSAs is the OSPF metric information. Many OSPF vendors assign each link a cost of 10, Cisco makes cost inversely proportional to a 100 Mbs

An Admin can override the default cost. This would be done for compatibility reasons (with other OSPF speakers or because the link is more than 100 Mbps).

Sometimes the meric is equivalent for multiple paths to a destination. In this case, OSPF will load balance over each of the equivalent interfaces. Cisco routers will automatically perform equal-cost load balancing for up to four paths, but this parameter can be increased by configuration to as many as sixteen paths.

The cost is applied to the outgoing interface. The routing process will select the lowest cumulative cost to a remote network.

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.

Open Shortest Path First – OSPF Fundamentals – Basics

Published

Deon Botha

on October 7, 2008

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

. 0 Comments

Open Shortest Path First (OSPF) is an open standard routing protocol, defined in detail in many Internet Engineering Task Force (IETF) Request For Comments (RFCs)Â including RFC 2328.

OSPF uses the Shortest Path First (SPF) Algorithm to calculate the best path to a given destination. OSPF builds loop-free paths that converge quickly, but often requires more processor power and memory than distance vector routing protocols (EIGRP).

OSPF can be more complicated because there are many topology and configuration options to consider versus EIGRP that has is has less of a learning curve.

OSPF is designed to offer flexibility in network design (OSPF is an open standard vs EIGRP that is Cisco Proprietary) which IOW allows OSPF to supports linking between different vendors Cisco, HP, etc.

OSPF Basics

OSPF as mentioned before is a Link-State routing protocol (basics) that is based on the Dijkstra Shortest Path First (SPF) Algorithm.

When one compares distance-vector routing to link-state routing;

link-state routing processes more information locally (on the router meaning more memory & CPU use) to reduce network bandwidth use.
Link-State routing protocols record all possible routes thus avoiding many of the techniques needed by distance-vector routing protocols to avoid loops.
Distance-vector routing protocols advertise routes to neighbours while link-state routing protocols advertise a list of connections.
In link-state routing, a neighbour is a directly connected router (or a router on the opposite side of a WAN link with the same network address).

OSPF is used within an Autonomous-System (AS). It has advantages over distance-vector routing protocols:

OSPF is classless + allows summarization
Converges quickly
OSPF is a standard, and fairly widely support can be found in a heterogeneous environment
Conserves bandwidth
uses multicast and not broadcast
sends incremental change-based updates
uses cost as the metric
KB is fairly widely available and less restricted than EIGRP

When a link goes up or down in a link-state routing protocol network, a link-state advertisement (LSA) is generated. LSAs are shared with neighbours and a topological database (a.k.a link-state database (LSDB) or Topology Table) is built.

LSAs are marked with sequence numbers so that older and/or newer versions of advertisements can be recognized (start 0×8000 0001 end 0xFFFF FFFF before rolling to the start again). The eventual goal is that all routers in the same AS has the same LSDB which is then processed using SPF from which the best routes are selected and a routing table created.

The Topology Database (LSDB) is the routers view of the network within the AS it operates. This includes every OSPF router within that area and all connected networks.

To view the current status of the link state database,
Router#show ip ospf database

The Topology Database is updated by LSAs and each router in a AS has exactly the same topology database. All routers must have the same view of the network otherwise routing loops or loss of connectivity will occur.

When a router realizes there has been a change to the network topology, the router is responsible for informing the rest of the routers in the area with a LSA. This happens mostly due to:

A router losing physical or data-link layer connectivity on a connected network
A router does not receive a predetermined number of consecutive OSPF hello messages
A router receives a LSA update from a adjacent neighbour, informing it of the change in the network topology

In any of the above cases, the router will generate an LSA and flood it to all neighbours with the following stipulations:

If the LSA is new, the route is added to the database, the route is flooded out other links so other routers are updated, SPF is rerun.
If the sequence number is the same as the current entry in the Topology Database, the router ignores the advertisement.
If the sequence number is older, the router sends the newer copy (in memory) back to the advertiser to make sure that all neighbours have the latest LSA.

All OSPF operations centre around populating and maintaining

Neighbour Table
Topology Table
Routing Table

Notes and Notices:

CCIE Command Memorizer

Published

Deon Botha

on September 12, 2008

in Asides, Off-Topic, Support and Vine

. 2 Comments

About a two weeks ago David Bombal from Configure Terminal contacted me about doing a write up for CCIE Command Memorizer. As a current CCNP student there is obviously some of the CCIE content that still goes over my head but most of the stuff I am fairly okay with. David didn’t seem to mind that I wasn’t a CCIE as yet and I sure didn’t mind giving CCIE Command Memorizer a spin so below are my thoughts and feelings.

During my initial research on the CCIE Command Memorizer I found that CCIE Command Memorizer was geared towards the CCIE Routing and Switching (R&S) Lab. When I received the application Monday two weeks ago my initial impression was that it covers without many frills and spills in an effective and efficient manner the commands in a Do-It-Yourself fill in the blanks task to objective orientated format. There is no round-about, search for things “what now” moments; everything is straight and to the point. Another bonus is that the download isn’t enormous either.

The CCIE Command Memorizer application itself is written in an e-book format, which works for the content and in that format. If like myself you like using the keyboard when you get going on command line (IOW dislike moving between the mouse+keyboard) some of the shortcuts might feel “off” and take a bit to get use to. Take heart that once you get going it all starts flowing like second nature.

My feelings on how the CCIE Command Memorizer would fit into my studies it that as a study tool / study aid as it helps you practice commands anywhere at any time as long as you have your notebook handy (face it as a CCNP I realize I am a Geeks and my notebook goes on holiday with me so this pretty much means anywhere). My current situation with a LAB is that I am busy getting racks, cabling, and other kit together to put a LAB up, the actual LAB is non-existent. In my situation the CCIE Command Memorizer is my stop-gap for actual “command” time practice as I don’t really have kit and at times no block time to zero in on a specific Technology Area and do some quick revision work with a specific focus only on that technology. This is different from the LAB where you need to setup and configure peripheral services and technologies to get to the meat close to the bone, CCIE Command Memorizer lets you focus ONLY on those parts to give you practice on those parts.

In my opinion students that would find the CCIE Command Memorizer useful would be individuals who have problems with instant recall of information when under stress or duress (people with classic test condition issues that forget as they walk through the door when in normal day-to-day they are Uber networkers) and students who need to drill things to remember (repetition, repetition, repetition) information to get it to pass from short term into long term memory (this one would be me). Most other students may also find it handy to bridge the book theory and lab practical (where you just went through the theory to quickly go over the practical again to cement the knowledge just a bit more).

From my perspective as a CCNP student the CCIE Command Memorizer shares most (if not all) of the content material with the CCNP that I cared to check up on. In the two weeks I have been working through EIGRP and OSPF (notes to follow shortly) for the BSCI. Everything I covered in theory the CCIE Command Memorizer covered + some more.

To close off for those who want a one-size-fits-all study solution don’t mistake the CCIE Command Memorizer for something it wasn’t built to be. The CCIE Command Memorizer is a STUDY TOOL / STUDY AID and not a “Complete Blended Solution” or All-In-One (aio) Product like the guys from IP Expert offer. This will mean that you will probably either attend classes from a Cisco Learning Partner and/or do labs at home or through a Rack Rental Company and/or also have Cisco Press books that will ADD TO THE VALUE the CCIE Command Memorizer.

In summation I suggest taking a serious look at the CCIE Command Memorizer and how to integrate it into your study plans. Taking all things into consideration I would seriously recommend the CCIE Command Memorizer even to current CCNP level students. The value add is easy to find and it helps to have something that you can take along as you travel that does command line study effectively without the need to spend hours on “setting up other things” before you get to play with advanced topics.

Enhanced Interior Gateway Routing Protocol – Scalable EIGRP – Scenario Two

Published

Deon Botha

on September 10, 2008

in BSCI, BSCI Questions, Certification and Cisco Systems

. 0 Comments

Working from the my last couple of EIGRP consists I am going to try and crystallize some of the material found by working through questions found in Stewart, B,D., Gough, C (2008). CCNP BSCI Official Exam Certification Guide, Fourth Edition. Indianapolis: Cisco Press.

The 256 kbps access line to the hub has 56 kbps access lines to each of ten spoke sites. Each link has a Frame Relay Committed Information Rate (COR) of 56 kbps. The access line to each router reflects the CIR. The access line to the hub router, Router A, is 256 kbps, but the CIR of the hub is the same as its access line.

From a Frame relay perspective, a circuit is considered oversubscribed when the sub of the CIRs of the remote circuits is higher than the CIR of the hub location. With ten links, each with a CIR of 56 kbps, this circuit is oversubscribed (56 kbps * 10 = 560 kbps).

How much bandwidth has each circuit been allocated? why was this value chosen by the administrator?
The maximum allowed bandwidth is controlled by the hub (256 kbps) in this hub-and-spoke network, because the maximum total spoke bandwidth is more than the hubs CIR (560 kbps), one cannot allow any individual Permanent Virtual Circuit (PVC) to utilize more than (256 kpbs / 10) 25 kbps at one time.
What bandwidth utilization is available to EIGRP? why was this value chosen by the administrator?
Because not much user data traffic is expected and the data rate is low one can allow EIGRP to use as much as 90% of the bandwidth.
If Router A fails, what would the effect be on the network?
If Router A fails there would be no communication between spoke sites as Router A is the hub. Each individual site would function but WAN connectivity would be lost. Each spoke router will stop receiving Hellos for the Hold time duration (3x Hello) and then and assume that the neighbours are dead. There not being any neighbours to ask for a route,the Topology Table will be updated and the router will send updates out about this change.
Is summarization possible on the routers entering the WAN cloud, or is it possible on the network not shown in the figure that are on the other side of the routers? Give a reason for your answer.
EIGRP allows summarization at the interface level (barring that the addressing scheme is such that it will allow this to happen). This is an advantage of EIGRP over OSPF (OSPF allows summarization only at Area Border Router (ABR))

Resources:

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

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.

Enhanced Interior Gateway Routing Protocol – Scalable EIGRP – Scenario One

Published

Deon Botha

on September 10, 2008

in BSCI, BSCI Questions, Certification and Cisco Systems

. 0 Comments

Working from the my last couple of EIGRP posts I am going to try and crystallize some of the material found by working through questions found in Stewart, B,D., Gough, C (2008). CCNP BSCI Official Exam Certification Guide, Fourth Edition. Indianapolis: Cisco Press. The Scenario works from the EIGRP Technology White Paper Sections on Cisco.com

The above network is experiencing timeouts and network crashes. In addition, EIGRP appears to be losing routes from its routing tables, which is adding to the problem.

What changes to addressing or EIGRP could affect the route drops and network problems? State the configuration commands necessary to activate this solution on Router A.
Summarization is the keystone to scalable EIGRP operation. Summarization will limit the query range preventing query scoping. This will also prevent the routes in the Topology Table from being SIA, which affects performance.
Enter Router Mode to Define Routing Protocol RouterA(config)#router eigrp 1 Define EIGRP Network for Routing Protocol RouterA(config-router)#network 10.0.0.0 Disable Auto Summarization RouterA(config-router)#no auto-summary This is me being strange and clean exiting from the routing protocol sub-section RouterA(config-router)#exit Enter the Serial Interface where to start defining your Hub on the Hub-and-Spoke Network RouterA(config)#interface serial 0/0 Define summary for this interface RouterA(config-if)#ip summary-address eigrp 1 10.1.0.0 255.255.0.0 RouterA(config-if)#exit
The WAN is a Frame Relay cloud, and Router A is the hub in the hub-and-spoke configuration. Each Virtual Circuit (VC) is 56-kbps. Give commands to configure Router A for EIGRP over this Non-Broadcast Multi-Access (NBMA) Cloud.
This Cisco.com Configuration Note should explain why the below is done.
RouterA(config)#interface serial 0/0 RouterA(config-if)#frame-relay encapsulation RouterA(config-if)#bandwidth 168 RouterA(config-if)#exit
Give the commands to configure Router B for EIGRP over this NBMA cloud.
RouterA(config)#interface serial 0/0 RouterA(config-if)#frame-relay encapsulation RouterA(config-if)#bandwidth 56 RouterA(config-if)#exit

Resources:

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

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.

Network Ninja

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