Packets go back and forth from CSS to CE to CSS - Why?

Unanswered Question
Feb 22nd, 2008
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I am trying to read this dynamic bypass behaviour of Cache Engine (WAE 612) running ACNS 5.5.1 S/W and CSS11503 to try and understand a behaviour I am noticing:


http://www.cisco.com/en/US/docs/app_ntwk_services/waas/acns/v55/configuration/local/guide/adtsprt.html#wp1056963


I have a CSS load balancing between 2 x Cache Enginers (WAE612).


I have a problem where a CSS sends a SYN packet to the CE pointing to the Origin Web Server's IP address and the CE sends the same SYN packet back to the CSS. All that changes is that the source MAC address in the packet from CSS to CE is the CSS MAC address and the packet from the CE to CSS is CE's MAC address. But everything from layer 3 and above including source and destination IP addresses of the packets from CSS to CE and the return packet of CE to CSS are identical.

Then the CSS tries again and send the SYN packet to the CE and the CE sends the packet back to the CSS. After 3 attempts the CSS sends a TCP RST.


Everything works fine for about 20 minutes and then the above behaviour starts. The clients web browser just hangs after loading say about 20 Kbytes or so.


If the service on the CSS to the Cache Engine is suspended then everything works fine for ever and do not have this problem after 20 mins.


Full Data Path:


For Cache Hits in Cache Engine:

================================

Hand-held Portable device to CSS to WAP Gateway (WAP Packets). Then WAP Gateway back to same CSS (HTTP Packets) then to CE. If cache hit then CE to CSS to WAP Gateway (HTTP Packets). Then WAP Gateway to CSS to Hand-held Portable device (WAP Packets).


For Cache-misses:

=================


Hand-held Portable device to CSS to WAP Gateway (WAP Packets). WAP GAteway to same CSS (HTTP Packets). Then CSS to CE (HTTP Packets). If cache miss then CE to CSS and then to Internet (HTTP Packets). Internet to CE via CSS (HTTP Packets). Then CE to CSS to WAP Gateway (HTTP Packets). Then WAP Gateway to CSS to Hand-held portable devices (WAP Packets).


Very convoluted.




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