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BGP routing

Running BGP through two ISP's and am trying to use one ISP as more for critical departments and the other for the rest.  Any suggestions on doing this?
3 Solutions
use route-maps. Define critical department traffic with an access-list and force it out a specified next-hop gateway. Only problem is that you lose some resiliency that you have from dual ISP's. If the next-hop gateway is down, then you don't have automatic failover to the other ISP. You have to get very creative with combination of route-maps and SLA monitoring.
Some information Below. You need combination of basic route-map to define your traffic to go which direction, then you need another route-map to make sure the SLA traffic goes out the correct interface...

BGP is a very robust routing protocol, it can be very simple or highly complex. The point is , there is an enormous amount of built in traffic engineering capabilities with BGP that makes using rout-maps less than optimal.  You could use the route-maps but then why use BGP at all.

The problem as I see it is that you would like to use one link for critical dept traffic and all other dept's use the remaining link. Inbound traffic may come from anywhere and will be hard to perfrom traffic engineering as you perscribe. Outbound traffic is another story.  Again, you can use route maps to do as you perscribe, but why would you?

You have 2 BGP feeds from diverse ISPs, if one route becomes unavailble BGP will route you out the other,  this is what BGP is supposed to do, provide you high availability while dual homing. The route-maps will circumvent your BGP policy. Is one ISP less dependable than the other?

if you want to use both links then you can perfrom traffic enginneing and distribute your outbound traffic by using weight or local preference to mark routes preferring one link over the other.  Here you can use route-maps to match on destination prefixes or AS numbers. This route map is different than the one above because this route-map only modifies one of the BGP attributes that all routes are tagged with by BGP. As far as performing traffic engineering on incoming traffic you cam use MEDs to influnece ingress traffic however this BGP attribute is far down on the BGP descision making process and often is ignored. The other way is to manipulate you prefix advertisements to your ISPS or working with your ISPs to tag routes using communities. Also, you could jsut have them influence your inbound traffic via a config change on their side.

In summary, BGP can be complex. I would advise against using the route-maps, this could make this situation very confusing,

harbor235 ;}

kenkup90Author Commented:
Currently looking at these two possibilities

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