Archive for the ‘BGP’ Category

Router gets pissed off

I tried creating an aggregate summary route just for kicks and this is what I got from the router. Man IOS is getting very bossy these days! RSRack1R1(config-router)#aggregate-address 0.0.0.0 0.0.0.0 summary-only % Aggregating to create default makes no sense, use a network statement instead.

September 20th, 2008 | BGP | Read More

BGP Finished! Still need to work on REGEXP

After spending a week on BGP, I think I have a good understanding of the basic concepts of BGP. There have been a few gotchas and ohsnaps but over all I am satisfied by the way Narbik's workbook has carried me through. I am still looking at IE Vol 1 but I think I am going to get done with these workbooks...

July 25th, 2008 | BGP | Read More

Cisco Regular Expression Characters

I found this great list of all the characters that we can use. I think this might be helpful for everyone and it's right from Cisco's website. Regular Expression Character Function Examples . Matches any single character. 0.0 matches 0x0 and 020 t..t matches strings such as test, text,...

July 25th, 2008 | BGP | Read More

BGP Attributes

AS-Path We can use AS-Path attribute to influence choice of paths in another AS. Since routers chose the path with the shortest AS-Path, using set as-path prepend command can be used to add additional values of originating AS so the receiving router will choose the router with the least AS-path value. We...

July 25th, 2008 | BGP | Read More

BGP Communities

The community attribute is a numerical value that can be assigned to a given prefix using a route-map/access-list combination and then can be advertised to a neighbor. By default community attributes are NOT sent to the neighbors and you must use the "send-community" option with the neighbor statement...

July 24th, 2008 | BGP | Read More

BGP Route Aggregation

We can use route aggregation in BGP to decrease the size of the BGP routing tables. This helps in speeding up the convergence time and improves network performance. Just keep in mind that aggregate route gets forwarded ONLY if there is atleast ONE specific route in the routing table. This is why it is...

July 23rd, 2008 | BGP | Read More

BGP Route Dampening

Route dampening is a BGP feature designed to minimize the propagation of flapping routes across an internetwork. A route is considered to be flapping when its availability alternates repeatedly. Since BGP routing tables are huge, you don't want that many routing updates to be traveling all over the place...

July 23rd, 2008 | BGP | Read More

BGP Backdoor Routes and Conditional Advertisement

We often run into situations where we have two different routes to a network and we know one is faster than the other. However, a router will only keep one route in the routing table and that will be the one with the shortest administrative distance. Now if two routers (R1 and R2) in an AS are directly...

July 23rd, 2008 | BGP | Read More

BGP Route Reflectors

One of the requirements of BGP is that all IBGP peers MUST be fully meshed. This is not a big deal when you are dealing with 4-5 routers, but in larger networks, this can be an administrator's nightmare. Route-reflectors take care of this problem. The only requirement is that each IBGP speaker MUST establish...

July 22nd, 2008 | BGP | Read More

BGP Peer Groups & Peer Templates

BGP Peer-Groups are used to optimize BGP Networks. If you have a number of BGP peers, Peer-Groups can simplify configuration and updates can be more efficient. Key is that all those peers share the same update policies such as outbound route-maps, distribute-lists etc. Some of the benefits of BGP Peer-groups: Peer-groups...

July 22nd, 2008 | BGP | Read More