Re: BGP load balancing! - Page 2

kawin · ‎03-11-2002

Okay BGP gurus, here's one for you:

Currently, we have 4 T-1's going into our 7206VXR Router. We just turned 2 of the 4 up this past week.

The new 2 T-1's go to one ISP, while the 2 others go to 2 separate ISP's. We run BGP between all three ISP's. The new ISP is providing us with full routing tables for the 2 T-1's. (We have 512MB of memory, plenty for this scenario). Another ISP is announcing just their routes to us, while the last ISP (which we have problems constantly with) is announcing just their routes as well. I believe we'll eventually want the other 2 ISP's to announce to us full routing tables as well, which would be ideal.

Here's the problem:

The configuration of BGP is exactly the same for the two T-1's from the new ISP, so apparently most/all traffic is going to one T-1 since they're distinguished only by IP address. The ISP provided us with a configuration to help load balance/load share the two T-1's, but they do so by spliting up our IP blocks equally. This assumes that half the traffic will go to the fist half of the block, and so on.

The other option is to mess with the attributes for BGP, which I'm quite taken aback with, since many documents says tweaking the BGP attributes is very risky.

The larger problem is load balancing among all four T-1's.

Any help would be greatly appreciated!!!

Thanks,

Kawin

Gilles Dufour · ‎03-13-2002

if the best path is learned via the ISP to which you have 2 T1, then 2 routes will be inserted in your routing table (if you configure the max-path 2 command).

If the best path is through another ISP, only 1 route will be installed.

for CEF. You're wrong.

CEF is not a protocol. This is the name given to the internal function that does the packet forwarding on the router.

In other words, this is something local to your router. It does not matter whether or not your ISP uses CEF.

kawin · ‎03-13-2002

Hi,

For CEF, I guess my ISP was lying to me then? :)

For my setup, would you advise turning on CEF?

Thanks,

Kawin

Gilles Dufour · ‎03-13-2002

YES. CEF is definitely recommended.

However, make sure you run one of the latest version to get rid of potential know CEF bugs.

kawin · ‎03-13-2002

Thank you very much,

I will research more on CEF implementation.

Just for reference, I run Cisco IOS Version 12.1(6)E

Thanks,

Kawin

james.feger · ‎03-13-2002

Does the BGP session with two T1's go to the same ISP on the same remote router? Or is this a setup where you have a T1 going to ISP-A-Router1 and another going to ISP-A-Router2? If it is two t1's between the same two routers, peer with loopbacks, that will load balance for you. If you have ISP-A-Router 1 and Router 2 scenerio, maybe MEDS is something you want to look at.

kawin · ‎03-13-2002

Hi,

The setup is my one router where there are 4 T-1's. 2 each go to a separate ISP, While the 2 other

T-1's terminate to two separate routers to the same ISP:

|----------| T-1 #1 _______________

| |---------------------|ISP#1 router |

| | ---------------

| | T-1 #2 _______________

| |---------------------|ISP#2 router |

| MY | ---------------

| Router | T-1 #3 ________________

| |---------------------|ISP#3 router#1|

| | ----------------

| | T-1 #4 ________________

| |---------------------|ISP#3 router#2|

|----------| ----------------

qshaw · ‎03-13-2002

What the new ISP suggested isn't wrong and it really works to load balance your incoming traffic between 2 T1 line if your IP network addressed well. Meanwhile, you can announce the whole IP block to them via each T1, that provides you redundancy. Where are your IP block getting from? Each ISP?

kawin · ‎03-14-2002

Hi,

Thanks for the response. We are advertising 3 net blocks, each from our 3 providers, we are advertising them to all ISP's.

qshaw · ‎03-14-2002

okey, tell me more about your network:

1. Are you using the private AS number?

2. Does each ISP announce your 3 net blocks to their peers? this question related to your contract with them.

3. Between incoming and outgoing traffic, which one is bottleneck since you only own T1 line for upstreaming.

Gilles Dufour · ‎03-14-2002

Ok. So now you're trying to loadbalance incoming traffic.

Since you have 3 blocks, and 3 ISPs, I would suggest to advertise the 3 block to each isp the following way.

ISPA

NetA

NetB + as prepend

NetC + as prepend

ISPB

NetA + as prepend

NetB

NetC + as prepend

ISPC

NetA + as prepend

NetB + as prepend

NetC

Like this, the prefer route to reach NetA is via ISPA, NetB via ISPB and NetC via ISPC.

This off course won't give you true loadbalancing but at least all your T1 will be used.

To prepend a route, use the following commands:

route-map ToISPA permit 10

match ip address 101

set as-path prepend

!

route-map ToISPA permit 20

match ip address 199

!

acc 101 permit ip

acc 199 permit ip any any