Route Consolidation Issue

Unanswered Question
Dec 4th, 2008

Hi I have two internet links on my edge router. one of the ISP doesn't advertise about 4000 network in the Internet so either I have to share a BGP session with the ISP to exchange routes are I have do a route map which actually kills the router. My edge router is 2811 which I guess is sufficient for my two 3 Mbps links. Is there any other way to work around this issue. The fixed parameters are the ISP will never advertise those network and all the networks are non contiguous (which make more difficult)

also I dont mind keying in the 4000 static routes but i am not sure what would be the impact on the router. is there any limitation on the number of statics you can have on a router.

any help is highly appreciated, TIA

I have this problem too.
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Giuseppe Larosa Fri, 12/05/2008 - 02:59

Hello Satkis,

I'm not sure If I have understood:

you say:

>> one of the ISP doesn't advertise about 4000 network in the Internet so either I have to share a BGP session with the ISP to exchange routes

Are you receiving a full table from this ISP ?

A partial routing table ?

There is a second ISP I guess you only receive the default-route from it.

so for the 4000 routes missing you can use a default static route either injected from eBGP session either a locally configured static route.

you cannot configure 4,000 static routes in a router.

Hope to help

Giuseppe

sakthis_cantara Fri, 12/05/2008 - 15:29

Hi Giuseppe, thanks for your email. I will try to example more clearly.

ISP 1 -> my router has default static route. this ISP is fully functional

ISP 2 -> 4000 non Internet advertised routes. I have to have a BGP session which is not appropriate for a 2811.

given this scenario we cannot invest on 76xx routers for the internet connection.

TIA

sakthis_cantara Fri, 12/05/2008 - 15:17

hi thanks for your email. we are a small client and 76xx would be a overkill for out 3 meg Internet connectivity, the big problem is that ISP 1 which is full functional I have a default route to it. For the ISP 2, which is not advertising its 4000 routes in the Internet, in other words you have to become a BGP peer for them, which 2811 will not withstand ....

Joseph W. Doherty Fri, 12/05/2008 - 15:42

Actually, although a faster router would be nicer, I see it as possible to Internet peer with two ISPs using the 2811. You'll want more than the default 256 MB RAM, the maximum of 768 MB should do nicely for two peers.

I haven't done this with a 2811, but I have worked with 3660s that had two different provider Internet BGP full tables and had a T3 connection to their provider. As to performance, the 3660 and 2811 have about the same Kpps rating (about 120 Kpps) and you wouldn't be running a T3. With the foregoing noted, the two biggest issues might be the impact of the BGP scanner process, and BGP (I believe by default) will only use one link if the AS hops are the same.

[edit]

PS:

If it works for you, I think the OER/PfR would be even better than BGP peering (although it also works with BGP). Besides noticing unreachable networks using one provider, it can do other functions such as dynamically load balance your two links, move flows to the better performance path, etc.

sakthis_cantara Fri, 12/05/2008 - 15:46

2811 is having a default 128 / I will try to get a 512 and enable BGP peering. My case would be little easier just because of the fact I will use a default to one of my ISP.

Joseph W. Doherty Fri, 12/05/2008 - 15:54

I thought the 2801 comes with 128 MB and the 2811 with 256 MB? Perhaps that's only with the current models? However, I see the 2801 maxs at 384 MB vs. 768 MB for the 2811, the particular model would be important for the amount of RAM it can take (and the 2801's lessor 90 Kpps performance). I.e. you're sure it's a 2811?

As to the idea of only peering with one EBGP neighbor and using default for the other, you can configure this, but wouldn't specific routes take precedence over the default route? In other words, all traffic would flow to the provider with missing 4000 subnets except for those 4000 subnets?

sakthis_cantara Fri, 12/05/2008 - 15:56

but wouldn't specific routes take precedence over the default? In other words, all traffic would flow to the provider with missing 4000 subnets except for those 4000 subnets? ----> Yes thats how I want this to work.

sakthis_cantara Fri, 12/05/2008 - 15:54

2811 is having a default 128 / I will try to get a 512 and enable BGP peering. My case would be little easier just because of the fact I will use a default to one of my ISP.

Joseph W. Doherty Fri, 12/05/2008 - 05:12

If what you're describing is something like you currently use default routes to two different ISPs but one of those preclude you from reaching 4000 networks, what can you do beside BGP peering or maintaining 4000 static routes?

One possible solution, without BGP peering, might be to configure OER/PfR on your 2811. I think it can detect one of your two paths being unable to reach a destination and then dynamically insert a static route to force all traffic to that destination using the one provider.

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