How WAAS optimize Internet traffic for branch sites?

Unanswered Question
Sep 16th, 2009

Assuming a company has central site A and multiple branch sites B, C, D, etc., connected through WAN circutis. Central site A has Internet connectivity and also provides Internet access for Branch site B and C. Branch D has its own Internet access, not going through the company WAN.

Now all sites have WAE installed, peering with each other. Here are my questions:

Site A or D's WAE will not optimize its users' Internet traffic, because the WAE does not have a peer for the connections going out to Internet. Is this correct?

Site B and C's users' Internet traffic will be optimized because the Internet access goes through the central site,and there's a pair of WAE's between B and A, or C and A. Is this correct?

Thanks for any help

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Zach Seils Wed, 09/16/2009 - 12:03


Based on your description of the topology, you are correct.



gwhuang5398 Wed, 09/16/2009 - 19:18

Hi Zach:

Thanks for the help. I was not too clear about the scenario where a remote site gets Internet access through a central site, and both sites have a WAE in place. I seem to have the impression that a pair of WAE form a peering for a particular connection if the source and destination of the connection fall into the local subnet of the respective WAE. If that's true, becasue a Internet connection would not have source and destination in the subnets of branch and central WAE, the connection would not be optimized.

However it also seems to everybody that the connection should be optimized by WAAS, because that's what people think WAAS should do.

PLease let me know what you think.

Thanks again


Zach Seils Thu, 09/17/2009 - 04:46


By default WAAS does not place any IP restrictions on what traffic will be optimized (it only cares that it is TCP traffic). So as long as the Internet traffic traverses 2 WAEs, it has the potential to be optimized.



gwhuang5398 Thu, 09/17/2009 - 07:05


If there's 3 WAE along a TCP connection, how does the middle one identify it's in the middle of the connection and should not apply any optimization again?

Maybe be using WCCP redirect-list to filter out any transit networks? how about if the middle WAE is inline?




You don't need to do anything special. It is all part of the auto-discovery process.

When the middle WAE receive the SYN from the client it will already have TCP option 21 set so the WAE will know it is not the closest to the client.

When the middle WAE receives the SYN ACK from the server it will already hat the TCP option 21 set so the WAE will know it is not the closest to the server.

Now it know it is the middle WAE and will simply pass the traffic back to the router.


gwhuang5398 Thu, 09/17/2009 - 13:32

Thanks much Paul. I once read about the mechanism somewhere, but couldn't find the reference again. Thanks for the explanations.



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