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Strange problem with sibling squids in accelerator mode

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Hi,

I encountered a strange problem in using sibling squids as accelerators.
I have two accelerator squids, A and B (on two different boxes). They
are set up as sibling cache peers which both point to the same parent
cache_peer origin content server. I used the following commands to run
my test:

1. Load an object into A:

	%squidclient -h host.name.of.A URL

2. Purge the object from B:

	%squidclient -h host.name.of.B -m PURGE URL

3. Double check to make sure A has the object and B does not:

	%squidclient -h host.name.of.A -m HEAD -H "Cache-Control:
only-if-cached\n" URL
	Resulted in TCP_MEM_HIT

	%squidclient -h host.name.of.B -m HEAD -H "Cache-Control:
only-if-cached\n" URL
	Resulted in TCP_MISS

4. Request the object from B:

	%squidclient -h host.name.of.B URL

Now the strange problem comes in. If I run the last step on the box A,
the ICP communication occurs, and in A's log I see UDP_HIT and
TCP_MEM_HIT, and in B's log I see TCP_MISS and SIBLING_HIT. However, if
I run the last step in B, then there is no ICP communication, squid B
simply goes to the parent origin server to get the object (in B's log
FIRST_UP_PARENT and nothing in A's log). When I run the same test with
squidclient on a third machine, the result is negative too. So it seems
that only if I run the squidclient utility on the same box where the
cached object is, then its sibling cache will retrieve the object from
this box.

The configuration for Squid A is:

#=======================================================================
====================
# ACL changes
#=======================================================================
====================
# acl for purge method
acl acl_purge method purge

# acl for origin app server
acl acl_gpl_app_servers dstdomain vmprodcagpcna04.firstamdata.net

# acl for cache peer squid server
acl acl_gpl_cache_sibling src host.name.of.A

#=======================================================================
====================
# http_access changes
#=======================================================================
====================
# allow purge method from localhost or sibling
http_access allow acl_purge localhost
http_access allow acl_purge acl_gpl_cache_sibling
http_access deny acl_purge

# allow http access to app servers and from cache sibling
http_access allow acl_gpl_app_servers
http_access allow acl_gpl_cache_sibling

#=======================================================================
====================
# icp_access changes
#=======================================================================
====================
# allow icp queries from cache sibling
icp_access allow acl_gpl_cache_sibling

#=======================================================================
====================
# cache_peer changes
#=======================================================================
====================
cache_peer vmprodcagpcna04.firstamdata.net parent 7533 0 no-query
originserver name=cp_gpl_app_servers
cache_peer host.name.of.A sibling 3128 3130 name=cp_gpl_cache_sibling
proxy-only

#=======================================================================
====================
# cache_peer_access changes
#=======================================================================
====================
# Allow peer connection to the origin app server and sibling cache peer
cache_peer_access cp_gpl_app_servers allow acl_gpl_app_servers
cache_peer_access cp_gpl_cache_sibling allow acl_gpl_cache_sibling


Configuration for B is almost identical except the host.name.of.A in the
acl and cache_peer tags is switched with B's. 

Can someone point out what might be the problem here?

Thanks.
Roy
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