[squid-users] 502 Bad Gateway - ISP problems 2.2 Stable 4

hi,

for an industry customer I'm managing some dozen Netscape Proxy servers
on NT who are routed through

the ISP's Squid 2.2 Stable 4.
The ISP uses a round robin for 3 Squids on different IP addresses.

If one squid isn't up (or if there are any network problems) the
Netscape Proxy writes to the error log
"can't connect to ..."
This happens quite often and was a problem in the past when the duration
of "can't connect" was a bit too long (some minutes). Then the Netscape
proxy needed a service restart since it could take a while until he sees
the connection
re-established. This problem I've solved for the main proxy with more
than 1500 users per day building a proxy and parent array. Advantage:
the proxies are routing through the best connection internally. Means:
if there is really no connection to the internet, then it's very
probably the fault of the ISP.
That happened Thursday between 8 and 10; at 8 intranet was running and
no connection to the internet; I've phoned the customers responsible
persons to blame the ISP. Finally it turned out after 10 (!) they had to
change a nic (what apparently needed 2 hours :< ?)
My real problem in this little conflict is that the error log of the
Netscape proxies contains
"502 Bad Gateway"
for this accident what was apparently produced by squid2.2.
Of course, this message appears quite often too within the error log for
individual connections. I do not want to fight with the ISP, I could
offer them to update their squid plus the configuration, what they
probably are not willing for. I need arguments what a 502 all may
be.This is very general (rfc 2068):
"The proxy server received an invalid response from an upstream server"
Reasons may be:
- interface defect (as it was here)
- upstream server and the gateway/proxy do not agree on the protocol for
exchanging data (misconfiguration)
- poor IP communication between back-end computers, chain broken

any other ideas, suggestions?
thanks

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