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New Member

BGP Help

We have a 2600 router connected to the internet and have a T1 interface to an ISP who is providing our IP address block. We are now adding a 2nd TI connection from another ISP provider for redundancy and possibly some load sharing but are not getting another IP address block from them. Since our router is small, I was only going to request default routes from each ISP. On our 2600, would I set up:

router bgp ASxxxxx (our AS number)

neighbor X.X.X.X remote-as XXXXX

neighor Y.Y.Y.Y remote-as XXXXX

Then set up default routes to both of them:

ip route X.X.X.X 250

ip route Y.Y.Y.Y 250

I realize everything would go out neighbor X.X.X.X (who provides our IP address) but could possibly come back through either link. Some posts say this is bad, others say not to worry. Are there other configuration items I should set up? Would this configuration provide the redundancy we are seeking and possibly provide some load sharing?

Thanks for any input and sorry for my lack of knowlege of BGP.


Re: BGP Help

If you will be receiving default routes from each ISP, you dont have to add static defaults. These defaults will be propagated to you by your ISPs themselves and appear/disappear as your ISP link/routes appear/disappear. Also for two different ISPs the about XXXXX should not be same.

INCOMING LOAD-BALANCING: If your block is a sub of /24 that belongs to ISP_Old, most probabaly your incoming traffic will start coming to you from you ISP_New. However, if your block is unique from both the ISPs' ranges or atleast /24, you can achieve incoming load-balancing.

OUT-GOING LOAD-BALANCING: If you receive same attribute defaults from both ISPs, outgoing load-balancing should work.

You can use some Looking Glass to verify your prefixes on the internet. Also, you can limit what you get and send via BGP.


New Member

Re: BGP Help

Can I clarify. When you referred to aboutXXXX, did you mean my remote as reference? I know they should be the appropriate as number but evidently my fingers don't! Our block from our carrier1 is x.x.x.x/24. We are not getting another block from carrier2; just having them advertise our block from carrier1. Will this then achieve some load-balancing if both ISP's advertise it? Can this all be achieved with just the three statements, ie. router bpg OUR ASN #

neighbor x.x.x.x remote-as xxxxx

neighbor y.y.y.y remote-as yyyyy


Re: BGP Help

This should work. However, your ISP_Old should not advertise your space as an aggregate but as /24 to achieve incoming load-balancing. You will also need network statements to advertise your space to ISPs.