BGP

[onlinecorp]

Can someone clarify this? I have 2 T1s with one carrier and 1t1 with another. After implimenting BGP I now have all my traffic routing through one carrier and none on the other. I am being told that with BGP this is way it is supposed to work. That the other carrier is just a fail over. I thought that I could config during regular operations that I can use all my T1 bandwidth and only during a failure does it switch to the other carrier?
Does anyone know for sure how this is supposed to work???
Can I use all my bandwidth and only BGP on failure???

 

[jneiberger]

1. How big is your assigned address space (prefix length, e.g. /24 or /19, etc.)?

2. Did you get your addresses from one of your providers or did you get them directly from an organization like ARIN?

3. Is the bulk of the traffic using the carrier with which you have two T1s or the other single T1 carrier?

 

[onlinecorp]

1. How big is your assigned address space (prefix length, e.g. /24 or /19, etc.)?

I have 5 Class C all are /24 and 1 is /23


2. Did you get your addresses from one of your providers or did you get them directly from an organization like ARIN?

All of the addresses are from my provders. I have my own AS# from ARIN

3. Is the bulk of the traffic using the carrier with which you have two T1s or the other single T1 carrier?

As of now, since I installed BGP 100% of my traffic is going to the carrier with 2 ts. and 0% to the other carrier. I have 2 t1 from PDT and 1 t1 from AT&T.

What I want and need if possible, is all of the traffic going to all of my t1s UNLESS there is a failure then route to the good lines.
Is this possible? I was told that it was possible prior to installing, and now I am told that it is not possible? I dont know what to do or believe any more.
Thanks for your help and interest.

 

[jneiberger]

Sorry, I forgot a couple of important questions:

1. Is the problem that traffic leaving your network only uses one provider or is it that traffic coming back to you uses only one provider?

2. Do all of these circuits terminate on the same router? If not, are you running iBGP between your routers?

3. Which carrier did you get your addresses from, or at least the addresses that you use the most often?

4. What sort of routes are you accepting from your providers (full routes, partial routes, default route only)?

 

[onlinecorp]

Sorry, I forgot a couple of important questions:

1. Is the problem that traffic leaving your network only uses one provider or is it that traffic coming back to you uses only one provider?
Right now ALL traffic in and out is going through only PDT and not hitting AT&T at all.

2. Do all of these circuits terminate on the same router? If not, are you running iBGP between your routers?
Not sure, I will check.

3. Which carrier did you get your addresses from, or at least the addresses that you use the most often?
I get all the address from the both companies.

4. What sort of routes are you accepting from your providers (full routes, partial routes, default route only)?
Dont know but I will check

 

[jneiberger]

Regarding #3 above, you can't get all of your addresses from both companies. You must have received some addresses from one ISP and other addresses from the other. We need to determine which addresses you got from which provider.

 

[onlinecorp]

Sorry I mis-understood.

We get 4 class C from PDT and 2 from AT&T

 

[jneiberger]

Okay, excellent. Are you using all of these addresses or do you just use some of them at the moment? (I am actually going somewhere with this so be patient <g>)

 

[onlinecorp]

I use all the ips on the PDT side and so far only half the ip on the /23 AT&T side.

 

[jneiberger]

Are these used mostly for internal devices to reach the Internet, for external devices/customers to reach internal servers, or a mixture of both?

 

[onlinecorp]

We host web sites. They are all for web servers

 

[jneiberger]

Okay, then. I had two different problems in mind and that makes me lean toward one in particular, with just a pinch of the other thrown in.

Now we need to know more about your connectivity, which you're already checking into. We need to know how many routers are involved and if you're running iBGP between them.

 

[onlinecorp]

2 3640 routers and I think we have ibgp between them

 

[jneiberger]

Alright. The only remaining thing that we really need to troubleshoot this is to know what routes you accept from your providers. Sanitized configs would be pretty handy, as well, but we might be able to resolve this without them.

Let us know when you find out what routes you accept from your ISPs. I have a feeling that that information might lead us to the answer to your problem.

 

[onlinecorp]

We accept default routes

 

[jneiberger]

Great! The most likely cause of the problem is that your routers have selected a single default route as the most preferred route. If you want to get better load sharing, you'd want to accept either partial routes or full routes. You could also try modifying the weight attribute on your "secondary" router so that it prefers the default learned from the second ISP.

If it were me, I'd start out with partial routes to see if that has the desired effect. From there you can move up to full routes if you'd like. Make sure you have plenty of CPU and memory on those routers, though.

What models are these routers? How much DRAM do they have?

 

[sbonete]

I agree with jneiberger in that point. The best solution is learning partial or full routes from Internet, but as he points, to achieve that you should have large memory at those routers.

Also, another thing, is quite strange that you are only reciving traffic from one of the ISP and not from both., even more when you have your public AS Number.

Could you provide the following info:

sh ver
sh run
sh ip bgp
sh ip route

Regards.

Samuel Bonete.

 

[jneiberger]

Samuel,

It's not that strange, actually. My guess at this point is that it is some sort of aggregation issue.

For example, let's say he has a /24 assigned to him by AT&T. He is advertising this prefix to AT&T and PDT. However, when advertising that route to rest of the world, AT&T might aggregate it into a larger supernet route.

So, on some far distant router you might see a /24 route that came through PDT and a /19 supernet that came from AT&T. The router will select the longest-match prefix for traffic to that /24 so it will always select the route learned via PDT.

I have a feeling that something similar to that situation is at least partially at play here. It's not the whole picture, of course, but it might be part of it.

 

[sbonete]

I agree with your comment, but AT&T should not being agregating routes from the address space of other provider, isn't it?

Therefore, the C classes provided by AT&T will be agregated at AT&T and the C classes provided by PDT will be agregated at PDT.

Please, correct me if I am wrong in that point.

Ummm... is Sam Halabi behind that jneiberger nick? ;-)

Regards all.

 

[onlinecorp]

We have 3640 routers with 128 / 32 I was told that may be the problem. I am looking at getting 2800 anyone know of a good place to get them from?