[nsp] Cisco Content Engine Problem

[Craig Spiers]

Hi All,
 
I've got a cisco content engine box, doing http caching on my network.
Having a couple of problems with tcp recieve window sizes on the network
with it enabled - this is affecting performance of http traffic.
 
Here's a tcpdump with the content engine enabled - browsing to google..
 
[root at neptune root]# tcpdump -v src www.google.co.nz
tcpdump: listening on eth0
16:44:24.907863 216.239.53.99.http > neptune.concept.net.nz.2732: S [tcp sum
ok] 957199238:957199238(0) ack 3579382432 win 5840 <mss 1432,nop,nop,sackOK>
(ttl 63, id 59570, len 48)
16:44:24.909980 216.239.53.99.http > neptune.concept.net.nz.2732: . [tcp sum
ok] ack 689 win 6880 (ttl 63, id 59571, len 40)
16:44:25.544010 216.239.53.99.http > neptune.concept.net.nz.2732: P
1:1049(1048) ack 689 win 6880 [tos 0x4]  (ttl 63, id 59572, len 1088)
16:44:25.544012 216.239.53.99.http > neptune.concept.net.nz.2732: P [tcp sum
ok] 1049:1073(24) ack 689 win 6880 [tos 0x4]  (ttl 63, id 59573, len 64)
16:44:26.403998 216.239.53.99.http > neptune.concept.net.nz.2732: .
1073:2503(1430) ack 689 win 6880 [tos 0x4]  (ttl 63, id 59574, len 1470)
16:44:26.543628 216.239.53.99.http > neptune.concept.net.nz.2732: P
2503:2867(364) ack 689 win 6880 [tos 0x4]  (ttl 63, id 59575, len 404)
16:44:27.623790 216.239.53.99.http > neptune.concept.net.nz.2732: F [tcp sum
ok] 2867:2867(0) ack 690 win 6880 [tos 0x4]  (ttl 63, id 59576, len 40)
 
Note the recieve window size of 6880 bytes..
 
Here's the same tcpdump of the same browsing session, but with the content
engine disabled..
 
16:46:27.162504 216.239.53.99.http > neptune.concept.net.nz.2735: S [tcp sum
ok] 1167226350:1167226350(0) ack 3696859296 win 8190 <mss 1460> (ttl 243, id
25739, len 44)
16:46:27.312105 216.239.53.99.http > neptune.concept.net.nz.2735: .
1:1431(1430) ack 689 win 31460 [tos 0x10]  (ttl 52, id 61247, len 1470)
16:46:28.215162 216.239.53.99.http > neptune.concept.net.nz.2735: P
1431:2097(666) ack 689 win 31460 [tos 0x10]  (ttl 52, id 63152, len 706)
16:46:28.356372 216.239.53.99.http > neptune.concept.net.nz.2735: P
2097:2843(746) ack 689 win 31460 [tos 0x10]  (ttl 52, id 63372, len 786)
 
Note the window size of 31460 bytes this time..
 
The content engine has the following options in the config..
 
tcp server-send-buffer 128
tcp client-send-buffer 128
tcp server-receive-buffer 128
tcp client-receive-buffer 128
 
Should this not be telling the box to use something larger, and more
efficent than 6880 b ?
 
if anyone can shed some light on the subject, it would be much appreciated!
 
Thanks