Choosing one ISP for SMTP traffic

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I need your help. I have two ISP's going from my network to my other location. I want simply to route my SMTP traffic through ISP1 and all other traffic through ISP2. I don't want to use PBR on 6509 switch since that will include all ports on that vlan( unnecessary traffic inspection). IS there any way I can accomplish this. I a m using eigrp over GRE tunnel and also HSRP between these two routers.

I have this problem too.
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lee.reade Wed, 07/30/2008 - 00:03


Probably the best way to do this would be to have your internal servers use the mail relay server of your preferred ISP, then on your BGP peer points, simply prefer the route to that host via the preferred ISP, using either WEIGHT or LOCAL PREF.



tdrais Wed, 07/30/2008 - 04:25

It is confusing since you say you use EIGRP and gre tunnels but you also say isp which implies internet. The above post suggests the best path if this is internet since you must use BGP.

First option if you have 2 tunnels and run eigrp over both is to inject /32 for the servers that run smtp and use the eigrp metrics to force the correct path. I am making the assumption here that these servers do not run much other than SMTP. If they do more then this does not solve your requirement.

Your other option is to send all the traffic to the sp2 router and have it policy route the smtp traffic over to sp1. Now this only works if your gre tunnels are on your routers if you have the tunnel on the 6509 and the tunnel itself moves back and forth between the isp it is much harder. You could mark the packets and then policy route the gre tunneled traffic based on the packet markings but not the best thing to be doing.


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