On Mon, 2009-10-05 at 12:01 -0400, Sales wrote: > We have two bgp sessions with different providers using the same > interface. One provider is metered the other is flat rate. However we > seem to send 80% of traffic to the metered provider. Is there a way to > tell a mt router using bgp which path you prefer it to use ? I would > like to make our flat rate primary choice with the metered secondary.
While I can't give you a full tutorial here, I will try to clarify some things. If you want to create a preference in your router for how it handles OUTBOUND traffic (from you to the internet), then you will create an IN-FILTER (associate it with the peer statement) with one or more of the following attributes: BGP-WEIGHT - More weight = more likely to be used This attribute is NOT propagated outside this router. BGP-Local-Preference - Similar to weight with a couple of exceptions. First, it will be propagated in your iBGP network. If you have only one router speaking BGP out to the internet, then weight is the most likely way to create this preference. There are other attributes that you can use, but these are the most popular. If you are wanting to alter INBOUND traffic, then the best bet is to use community strings. This would be configured with an OUT-FILTER for a peer. You can add the community strings in the filter. Contact your BGP peers to see which community strings are available that will allow you to best engineer your inbound traffic. Many providers will automatically prioritize traffic to your AS to use their direct circuit to you. In most cases, this is not a problem, however, if they are a very well connected provider (like AT&T for example) AND you wish to have another circuit to be "primary", then you will have to cause AT&T to NOT prefer your circuit. This is done using a community string in your outbound BGP session with AT&T. Once you do that, often, just a few prepends will cause traffic to start flowing the other way. Prepends are not the BEST way, but it does still work for relatively simple traffic shaping. I have seen some posts in response to your question that make this seem much harder than it really is. Once you understand the basics (briefly explained above), traffic engineering is not too bad. (Until you want to actually balance traffic. LOL) -- ******************************************************************** * Butch Evans * Professional Network Consultation* * http://www.butchevans.com/ * Network Engineering * * http://www.wispa.org/ * Wired or Wireless Networks * * http://blog.butchevans.com/ * ImageStream, Mikrotik and MORE! * ******************************************************************** -------------------------------------------------------------------------------- WISPA Wants You! Join today! http://signup.wispa.org/ -------------------------------------------------------------------------------- WISPA Wireless List: [email protected] Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/
