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Beginner

2911 with partial eBGP routes

Hello folks,

  a customer of us asked if C2911 (to be bought) is ok for partial BGP routes.

This is the situation:

2 cisco 2911, each peering with 3 other AS (AS1, AS2, AS3), and maybe, in the future, at a small IXP (AS4, AS5, AS6, AS7).

They will accept defaults plus partial routes from upstream AS1, AS2, AS3.

When deployed at the IXP they also will accept partial routes from AS4-7.

My idea is to use this filter for partial routes:

ip as-path access-list 17 permit _3$

ip as-path access-list 17 permit _3_[0-9]+$

So, is 2911 ok for that configuration?

the default route is included in the first row of as-path, isn't it?

PS: I have no experience with partial routes, only with full (for our datacenter) and default only (for other customers).

thanks

bye

Everyone's tags (5)
5 REPLIES 5
Beginner

Re: 2911 with partial eBGP routes

maybe this as-path access-list is better...

ip as-path access-list 17 permit ^(130_)+$

ip as-path access-list 17 permit ^(130_)+_[0-9]+$

--

Stefano Sasso - Triskel s.r.l.

http://www.triskel.it/">http://www.triskel.it/

Advocate

Re: 2911 with partial eBGP routes

Hi,

what's your goal exactly?

ip as-path access-list 17 permit _3$ - permits any prefix originated from AS 3 (coming through any other ASes)

ip as-path access-list 17 permit _3_[0-9]+$ - permits any prefix by the AS 3's direct neighbors (coming through 3), fails though if the originting AS prepends anything

ip as-path access-list 17 permit ^(130_)+$ - permits prefixes containing AS 130s only in the AS-PATH (at least once)

ip as-path access-list 17 permit ^(130_)+_[0-9]+$ - the same as above  but the prefix has to be originated by 130's direct neighbor (again fails in a case of prepending).

Maybe the file attached might help you.

It's my compilation from several BGP books/articles I used for my BGP study.

HTH,

Milan

Beginner

Re: 2911 with partial eBGP routes

Hi, I'm not in trouble with as-path regex

I successfuly use them with route-map in full bgp table routers.

My only trouble is if the 2911s can "support" partial routes from 3 upstreams and N simple peers.

The partial routes will be filtered with the "accept peer routes and peer's customer routes" philosophy.

I'll repeat, I'm not in trouble with as-path acl

thanks anyway

bye,

stefano

--

Stefano Sasso - Triskel s.r.l.

http://www.triskel.it/
Advocate

Re: 2911 with partial eBGP routes

Hi,

I'm sorry, I missed your question originally.

And missing it still.

What do you mean by "... if the 2911s can "support" partial routes from 3 upstreams and N simple peers."?

Do you mean "how many BGP prefixes can a 2911 handle?"?

Do you have any idea how many prefixes will be received from the neighbors?

Then you could calculate the size of memory necessary on your router.

HTH,

Milan

Beginner

Re: 2911 with partial eBGP routes

Hello Milan,

  thanks for your answer.

with 1 or 2 GB of ram I can handle almost everything

I think the customer will buy 2Gb to support future ipv6 prefixes (I can't actually know the exact number of ipv6 prefixes the peers will announce )

My only doubt is about CPU consumption by bgp processes in case they have to process lots of updates...

bye,

stefano

--

Stefano Sasso - Triskel s.r.l.

http://www.triskel.it/
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