WAAS via asymetric routing in a triangle mash

[joepena2012]

Hi all,

due a misconfiguration i had an asymetric routing scenario in my network environment between three different locations.

The effect was:

traffic from A to C ran directly.

traffic from C to A ran via B.

So far so good.

for sure i know that this scenario is not recommended. However from my experiences i would expect that everything runs cause

WAE in Lokation B would not touch anything as long as WAE in A and WAE in C are closet to client and Server.

Now to my question:

Would WAAS work in an asymetric scenario like this?

In each of these locations i have a WAE connected implemented via WCCP redirection on my outgoing interfaces.

[Bhavin Yadav · Accepted solution]

Hi Dieter,

The basic condition for WAAS to optimize the traffic is that the WAAS appliance needs to see SYN, SYN-ACK thru the same WAE unit for any TCP session. If it does not, WAAS will not optimize the traffic.

Now looking at your case scenario,

Traffic from A to C runs directly but C to A runs via B.

If you have WAAS at all three sites, it will optimize traffic between A to C, B to A and C to B and vice versa.

Now, for the traffic between A and C, when the traffic passes thru B while returning from C, (second scenario), it will automatically find out that server or client A is not in its local side so it will let it put in pass thru as Pass-through intermidiate (On WAAS B) and sent it to other site (A/C).

But if A or C WAAS does not recieve Syn,SYN/ACK for the tcp session, it will be asymmetric and will not be optimized. Further, it might adversely affect the performance.

On the other side, if you have WAAS at all three sites, Asymmetry exists only for site B and not for A or C. This is not a "TRUE" network asymmetry. Network Asymmetry happens when the device misses any of the initial tcp handshake packets.

Hope this helps.

Regards.

PS: Please mark this as Answered, if it answers your question.

[joepena2012]

Hi Bhavin,

thanks for your detailed explanaiton.

This is exactlly how i assumed that it should work.

And meanwhile i found the cause for the interuptions in my scenario.

It was not because of this "triangle routing" It was because WAE was not able to reach GRE endpoint of backup router in location C.

After i put a static route on WAE for GRE endpoint on backup router everything is fine.

So thanks for your help, and have a good weekend.

Dieter