%Technology% Archives %%page%%

Tag Archive for 'Technology'

CCIE Command Memorizer

Published

on September 12, 2008

. 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 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.

Enhanced Interior Gateway Routing Protocol – Optional Configuration Commands for EIGRP – Verifying EIGRP Operation

Published

Deon Botha

on September 2, 2008

in BSCI, BSCI Notes, Certification, Cisco Systems and Troubleshooting

. 0 Comments

The EIGRP show commands are highly detailed and give a comprehensive understanding of the state of the network. Troubleshooting EIGRP should start with the generic routing commands (show ip route and show ip protocols) before jumping into EIGRP-specific troubleshooting.

The show ip eigrp neighbors Command

The show ip eigrp neigbors command shows the Neighbours Table.

The table below explains the command output above

The show ip eigrp topology Command

The show ip eigrp topology command shows the topology table. This command shows the effect of DUAL. It shows whether the successor or the route is in an active or passive state and if there is a Feasible Successor.

The table below explains the command output above

The Show ip eigrp traffic Command

The show ip eigrp traffic command shows the EIGRP traffic received and generated by the router.

The table below explains the command output above

Troubleshooting EIGRP

There are many mehtods and tools that help one to troubleshoot a network. One of the most benificial tools would be the endless Cisco Documentation available for free at Cisco.com this would be because you can progress and easily eliminate the obvious in a checklist manner.

One of the most frequent troubleshooting techniques would be the use of debug commands, which provide the ability to see traffic and router processes in real time.

That being said debug is a resource hog. If you want to crash a router try debug all. For this reason use only specific feature options and for finite periods of time. When you are done, no debug all or undebug all which will disable debugging

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.

Notes and Notices:

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:

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:

Enhanced Interior Gateway Routing Protocol – Optional Configuration Commands for EIGRP – Load Balancing in EIGRP

Published

Deon Botha

on September 1, 2008

in BSCI, BSCI Notes, Certification, Cisco Systems and Load Balancing

. 1 Comment

EIGRP automatically load balances across equal-cost path links. You can also configure load balancing proportionally across unequal-cost paths using the variance command.

When variance anything other than 1, the EIGRP process multiplies the metric of the best path is multiplied by the variance. All paths to the same destination that have metrics less than this products are now included in load balancing. The amount of traffic sent over each link is proportional to the metric for the path. Alternatively paths with a feasible distance (FD) lower than that of the product (total) are used for load balancing.

The command is as follows:

Router(config)#router eigrp autonomous-system-number
Router(config-router)#network network-number
Router(config-router)#variance multiplier

The multiplier is a whole number between 1-128. The default is 1 which is equal cost path load balancing.

Take note:
-A Variance of two or three will do in most cases. Using higher values could cause EIGRP to start activating old 28.8 modems to load-balance with DS1s.
-Variance should be used with caution with delay-sensitive traffic. A DS1 link takes 8ms to transmit a 1500 B packet while a 256-kbps link takes 47ms. VoIP traffic, if shared over two links would see the difference as 39ms jitter.

To show this in an example for the EIGRP Process in the network from Router A to Router D

What you are looking at has been used before in my notes and comes from the CCNP Book referenced at the bottom of the post. The metric for the top half (Router A-B-C-D) is 4,869,120 and the bottom half (Router A-E-D) is 6,024,000. If one configured unequal-cost path load balancing on Route B

Router(config)#router eigrp 1
Router(config-router)#network network-number
Router(config-router)#variance 2

The end result is as that because the clockwise metric is about 5 bar (5,000,000), a variance of 2 will balance with paths less than 10 bar (10,000,000). So the resulting unequal cost path load balancing will be that for every 6 packets sent Router A-B-C-D (clockwise), 5 packets will be sent Router A-E-D (anticlockwise).

Only paths that are in the topology table as FDs are eligible to be included in the variance command.

Software Study Resources:

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.

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.

Notes and Notices:

Enhanced Interior Gateway Routing Protocol – Optional Configuration Commands for EIGRP – Stub Routers

Published

Deon Botha

on September 1, 2008

in BSCI, BSCI Notes, Certification, Cisco Systems and Stub Router

. 0 Comments

From Cisco IOS Release 12.0 is it possible to configure remote routers as an EIGRP Stub Router. A Stub Router in EIGRP networks use EIGRP to send limited information between the STUB and the CORE routers. A Stub router is typically used on routers to minimize processor and CPU utilization (this makes it good for slower / maybe older routers)

A Stub router only has one neighbour, a Distribution layer router. The remote router only needs a default route pointing to the distribution router (everywhere else can be reached via the default route).

Configuring Stub Routers can also assist the rest of the network. Queries are responded to much quicker and convergence occurs much faster. Sometimes queries can cause delays that result in SIA. If Stub configuration is applied, the router responds to queries as inaccessible, thus limiting the scope of the query range and preventing SIA from occurring.

The command for Stub is as follows:

Router(config)#router eigrp autonomous-system-number
Router(config-router)#network network-number
Router(config-router)#eigrp stub

With the table below explaining the options available with the use of the command

To use the above an example found in the CCNP Book, the below diagram shows a network with 5 stub routers because they have no other networks connected to them and they are each connected to a Distribution layer router.

Looking at the situation between Router A and Router B.

Router A is the Distribution Layer device for Router B (10.1.100.8);
Router B only has one network connected to it (10.1.1.0).

What one would want is that Router B only knows about what is relevant to it (Stub Router) and that the routing table only consists of networks 0.0.0.0 (default gateway), 10.1.100.8 (Distribution Layer Device) and the connected network (10.1.1.0).

Similarly Router A must know about all connected stub routers.

The configuration on Router B would be:

Router(config)#router eigrp 1
Router(config-router)#network 10.0.0.0 255.0.0.0
Router(config-router)#eigrp stub

Software Study Resources:

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.

Notes and Notices:

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

Published

Deon Botha

on September 1, 2008

in BSCI, BSCI Notes, Certification, Cisco Systems, Concepts and Constructs, auto-summary and summary-address

. 1 Comment

Scalability in EIGRP comes from Summarization. In EIGRP Summarization limits advertisements, minimizes the size and optimizes the speed of the routing table, limits route recalculation, and keeps to a minimum the amount of memory and processor resources consumed.

Summarization also solves a unique problem in EIGRP known as query scoping. This is when queries do not stop until they reach a dead-end; because of this, queries can loop. Routing convergence cannot proceed until all queries sent out have a reply. Summarization limits queries by stating “only these routes are found past this point” in effect making dead-ends. Summarization at logical points of the network is important to prevent SIA.

As of IOS 12.2(8) auto summarization happens at the classful network boundaries. This is EIGRP being helpful, however most networks use the private address classes 10.0.0.0/8 or 192.168.x.0/24. But some networks combine the two network-numbers and in that case automatic summarization will need to be disabled.

To disable auto summarization do the following:

Router(config)#router eigrp autonomous-system-number
Router(config-router)#network network-number
Router(config-router)#no auto-summary

Used in an example:

Router(config)#router eigrp 1
Router(config-router)#network 10.0.0.0
Router(config-router)#no auto-summary

From here Summarization may be applied at any point in the network. You can configure manual summarization on any router interface. Summarization for upstream should receive consolidated routes and downstream should receive the default route.

Router(config)#router eigrp autonomous-system-number
Router(config-router)#network network-number
Router(config-router)#no auto-summary
Router(config-router)#exit
Router(config)#interface fastethernet 0/1
Router(config-if)#ip summary-address eigrp autonomous-system-number address mask

Used in an Example:

Router(config)#router eigrp 1
Router(config-router)#network 10.0.0.0
Router(config-router)#no auto-summary
Router(config-router)#exit
!Downstream
Router(config)#interface fastethernet 0/1
Router(config-if)#ip summary-address eigrp 1 0.0.0.0 0.0.0.0
Router(config-if)#exit
!Upstream
Router(config)#interface fastethernet 0/2
Router(config-if)#ip summary-address eigrp 1 10.0.0.0 255.255.255.0
Router(config-if)#exit

Summarizing a default route is useful but where there are multiple default paths, this will reduce routing options and prevent failover when the primary route fails.

Software Study Resources:

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.

Notes and Notices:

Cisco’s winner for an Extreme Business Makeover

Published

Deon Botha

on August 14, 2008

in Cisco Systems and Vine

. 0 Comments

Pimping

Last night in Johannesburg (13th August 2008) Cisco announced the winner of the Extreme Business Makeover Competition.

This competition might just be the thing a growing SMB needs to get more competitive, agile and ready for business in the fast paced economy of today so that the SMB can communicate at the speed of business unlike Extreme Makeover: Home Edition that’s the show where the people go and demolish the families house, build a totally new house and pimp it out with stuff the family couldn’t afford in the first place in a month of Sundays.

Where this prize from Cisco will be different from the Extreme Makeover: Home Edition is that

Cisco products are reliable in that they generally don’t just break down,
Cisco products and solutions are well integrated and
If one compares apples with apples Cisco products are cost effective (I’m not going to go get technical here but comparing other SMB products and what you get between vendors I feel Cisco is very well priced with lots of Enterprise Class Technology).

For SMB companies that are struggling with managing vast amounts of data in a secure, reliable and cost effective manner there really is only one technology partner that offers you complete peace of mind in one neat package. All this while offering employees, customers, partners, and vendors access information anywhere and any time without breaking the bank.

On the topic of breaking the bank generally SMB business have cash-flow issues because operational activities take precedence over large capital expenditure projects and Cisco knows this and run amazing leasing deals and rentals offers (recently prime less 4%) for those of us not lucky enough to get this kit for free.

But now back to the competition; The competition was launched in March 2008 and invited local businesses to compete for the first price of a total network transformation featuring all the pimped out Cisco products and solution worth R 300,000 ( $ 37,500 USD). In Cisco products and solutions that should do some heavy pimping!

The winner of the first prize was a company by the name of redpeg a SETA accredited education and training services provider that offers training programs and workplace interventions. The company broadly operates within the workplace HIV/Aids arena and consults to businesses of all sizes to enable them to build capacity to implement manageable and sustainable HIV/Aids workplace programmes.

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:

Network Ninja

Tag Archive for 'Technology'

CCIE Command Memorizer

Enhanced Interior Gateway Routing Protocol – Scalable EIGRP – Scenario One

Enhanced Interior Gateway Routing Protocol – Optional Configuration Commands for EIGRP – Verifying EIGRP Operation

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

Enhanced Interior Gateway Routing Protocol – Optional Configuration Commands for EIGRP – Load Balancing in EIGRP

Enhanced Interior Gateway Routing Protocol – Optional Configuration Commands for EIGRP – Stub Routers

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

Cisco’s winner for an Extreme Business Makeover

Enhanced Interior Gateway Routing Protocol – Tables

Enhanced Interior Gateway Routing Protocol – Introduction

Search

About

Latest

Archives

Categories