BGP, Internet router, route table from provider

wilson_1234_2 · ‎07-06-2009

We have our Internet provider advertising network 0.0.0.0 via BGP.

#sh ip bgp nei 1.2.3.1 routes

BGP table version is 7, local router ID is 255.255.255.255

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf Weight Path

*> 0.0.0.0 1.2.3.2 0 0 123 i

Total number of prefixes 1

This is the only route we are getting from them, and everything from us goes to the next hop PE router.

We distribute the default route into our local core network via OSPF.

If we loose the dynamic default route, the Internet traffic gets routed through our DR site.

I recently had a network guy tell me that when he was getting BGP routes from his provider, he had them distribute a full route table to his CE router to speed up internet traffic, and he suggested we do the same.

I do not understand this thinking.

It seems to me that if everything from my network is going to go to the only the next hop, which is the PE router, it makes no sense for me to get a full Internet route table in my edge router.

This, if anything would slow things down because my route table would be much larger, utilizing resources on my CE router.

Any thoughts on this?

Jon Marshall · ‎07-06-2009

Richard

I have to agree with you on this. If you only have one exit point from your network then a default-route is fine. Receiving a full Internet routing table would as you say utilise far more resources with no apparent benefit.

Perhaps you could ask him to explain his reasoning.

Jon

wilson_1234_2 · ‎07-06-2009

Thanks Jon,

Is there a situation where a full route table would be beneficial?

I can understand a Provider's WAN router needing a full table, but would there ever be a situation where an end user needs to have a full route table from the provider?

Jon Marshall · ‎07-06-2009

Richard

If you had multiple exit points to your network you might find it useful to have the full routing table eg.

you have 2 exit points, 1 in USA, 1 in Asia. You want to route traffic from your internal network to the exit point that is nearest the destination. So your 2 routers in USA and Asia would receive full routing tables from your ISP(s).

Jon

wilson_1234_2 · ‎07-06-2009

Thanks Jon.

Joseph W. Doherty · ‎07-06-2009

"Is there a situation where a full route table would be beneficial? "

(Regarding just single Internet WAN path.)

If you have a full route table, and a packet's source or destination isn't within it, you can drop the packet. (However, benefit of this, usually, is slight.)

Giuseppe Larosa · ‎07-06-2009

Hello Richard,

>> Is there a situation where a full route table would be beneficial?

There is a possible advantage in the security field:

a full BGP table combined with Netflow allows to identify the destinations of flows towards the internet and of sources of traffic coming from the internet.

It is also possible with Netflow and a BGP full table to classify traffic according to BGP AS numbers that can be useful to understand traffic patterns over the Internet.

Hope to help

Giuseppe

huangedmc · ‎07-07-2009

If you anticipate rapid growth, and foresee a need for a redundant circuit, having full routes will get you ready for the redundant setup.

This means you won't have to call ISP to request full routes.

Just need to make sure your router can handle it.