BGP Multihoming with a Single ISP

Steve · **Posted:** Wed Jul 21, 2010 10:54 am

Comments for BGP Multihoming with a Single ISP.

Chinese Buffet · **Joined:** Fri May 02, 2008 11:06 pm **Posts:** 102

Another way of doing local pref is you can send a community outbound and have the ISP set the local pref on your prefixes inbound according to the community value. This allows the customer to have some control as to which link they want to be primary and secondary. ISP prefer this method as well because it cuts down on the administrative work at their end.

CB

wirerat · **Posted:** Wed Jul 21, 2010 1:12 pm

Chinese Buffet wrote:

Another way of doing local pref is you can send a community outbound and have the ISP set the local pref on your prefixes inbound according to the community value. This allows the customer to have some control as to which link they want to be primary and secondary. ISP prefer this method as well because it cuts down on the administrative work at their end.

CB

I have seen this talked about on mailing lists a few times. I can see why the service provider would love this method. Set it up one time and no more hassles. Just give the customer the community values to use and you are done.

errtime · **Posted:** Mon Jul 26, 2010 12:40 pm

With weight and local_pref you are affecting only outbound direction not inbound, so the traffic could flow towards internet through your primary link but it could flow back to you through your backup link, etc. So you should use some other attributes to achieve the goal completely (MED, as_path prepending, origin, etc.).

wirerat · **Posted:** Mon Jul 26, 2010 1:02 pm

errtime wrote:

With weight and local_pref you are affecting only outbound direction not inbound, so the traffic could flow towards internet through your primary link but it could flow back to you through your backup link, etc. So you should use some other attributes to achieve the goal completely (MED, as_path prepending, origin, etc.).

Quote:

Q) What you have shown helps with Company XYZs outbound traffic but not inbound. Traffic could come back asymmetrically. What can be done about inbound traffic?
A) You cannot tell another AS how to handle their traffic to you. You can mildly suggest to them how you would like them to handle your traffic. This can be handled with MED.

errtime · **Posted:** Mon Jul 26, 2010 1:39 pm

indeed, my bad. didn't read the FAQ :oops:

BGP Multihoming with a Single ISP

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