Policy based routing or something else?

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Oct 21st, 2008
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Good afternoon, I have a small question about PBR or an alternative. Right now our edge router has 2 links to seperate ISPs. The first is a T1 to Verison and the second is a DSL link to Verizon. I also have a cable connection ready to go in the building that will replace the DSL and we are getting a fiber to replace the T1. We want to direct web traffic out the cable and the more critical services over the fiber. What is the best way to do this? Is Policy Based Routing the way to go or is there something else? Thank you all.

Tom Waterman, CCNA

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Collin Clark Tue, 10/21/2008 - 13:05
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If the critical services have manageable, static IP's, you could just use static routing. PBR would work OK too.

Jon Marshall Tue, 10/21/2008 - 13:11
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PBR is the way to go if you want to direct all http traffic over one link and other services over the other link.

If you NAT source IP's to one of the public IP's assigned by corresponding ISP then return traffic will be sorted as well.


tcordier Tue, 10/21/2008 - 13:18
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I would say PBR is the best solution if you want to achieve a strict traffic separation (www on one link, and the rest of the traffic on the other link). However, it is neither an elegant nor scalable solution, and can lead for instance to the effect that one link is empty while the other is overutilized.

You also have to find a solution for making sure the inbound traffic (back to your client hosts) is also respecting this traffic separation. One way of doing this would need PBR together with NAT where all www traffic would be policy-routed out one link, and NAT-ed on the router. The outside address of the NAT translation could be advertized as a host address and www traffic from this address would also return via this link due to the more specific advertizement. Another option is using a proxy server.

Bottom-line: PBR gets quickly complex, and you may want to consider using a Quality of Service (QoS) configuration where you give higher priority to non-www traffic, and load-balance across both links. This is a more scalable and elegant solution, and would achieve the same goal. Using QoS you can guaruantee bandwidth for non-www applications, or even give them strict priority. This is also more useful in the event of a failure of the T1 or fiber link where PBR has no way of protecting the non-www traffic, while QoS would protect it also.

BTW: I like you provider selection policy ;-)

HTH, Thomas

thomas.waterman Wed, 10/22/2008 - 04:38
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Thank you all for your help. I believe that I am going to research the Cisco documentation on setting up QoS on our network. It looks like the best way to go. My current PBR solution showed a critical flaw yesterday when we lost our DSL connection for an hour to maintenence. We also lost all internet. If I had a QoS design it would not have made a difference.

thomas.waterman Wed, 10/22/2008 - 06:03
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ok, I am having a little difficulty finding a good article that explains configuring both QoS and load balancing at the same time. Does anyone have any articles they could share?

tcordier Wed, 10/22/2008 - 06:10
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You do not need to tie QoS and Load Balancing together, both can be configured separatedly and independently. LB is only a particular to configure your routing. What is your current routing setup, and how do you exchange routing with your ISPs?

Regards, Thomas


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