Anatoly Oreshkin wrote:
Hello,
We have squid server version squid-3.0.STABLE11-20090112 running on
Scientific Linux 4.4.
I noticed that sometimes, usually in working hours input traffic sharply
increases. I saw this increase in GANGLIA graph for proxy server I
looked into squid log files but did not found that proxy clients
increased their activity during these input traffic peaks.
Then I continued to investigate the case with tcpdump:
tcpdump -A -i eth0
and discovered many tcp connections to external sites on port 80.
But I did not find the names of these sites in squid logs
although if clients access these sites then site names should be
present in squid logs.
Here is extract from tcpdump output:
11:28:15.232848 IP 194.187.97.85.webazilla.com.http >
proxyter.pnpi.spb.ru.55605: . 1:1449(1448) ack 349 win 33304
<nop,nop,timestamp 2902195045 1662548939>
11:28:15.232871 IP proxyter.pnpi.spb.ru.55605 >
194.187.97.85.webazilla.com.http: . ack 1449 win 2184
<nop,nop,timestamp 1662549003 2902195045>
11:28:15.232878 IP 194.187.97.85.webazilla.com.http >
proxyter.pnpi.spb.ru.55605: . 1449:2897(1448) ack 349 win 33304
<nop,nop,timestamp 2902195045 1662548939>
11:28:15.232889 IP proxyter.pnpi.spb.ru.55605 >
194.187.97.85.webazilla.com.http: . ack 2897 win 2908
<nop,nop,timestamp 1662549003 2902195045>
11:28:15.232896 IP 194.187.97.85.webazilla.com.http >
proxyter.pnpi.spb.ru.55605: P 2897:4097(1200) ack 349 win 33304
<nop,nop,timestamp 2902195045 1662548939>
11:28:15.232906 IP proxyter.pnpi.spb.ru.55605 >
194.187.97.85.webazilla.com.http: . ack 4097 win 3632
<nop,nop,timestamp 1662549003 2902195045>
proxyter.pnpi.spb.ru is our proxy server name. It is trying to access
194.187.97.85.webazilla.com on port 80. However there is no references
to 194.187.97.85.webazilla.com in squid log files.
But there might be a reference to another name that maps to the same
IP... http://en.wikipedia.org/wiki/Reverse_DNS_lookup
When you see odd traffic like this, run...
squidclient cache_object://localhost/active_requests|grep ^uri
...to get a list of the hosts which are involved in active connections.
Find the IP address each of these hosts maps to, and then perform a
reverse DNS lookup on each of those IPs.
For what it's worth, webazilla.com appears to be a hosting company, so
it's likely that one of your customers was surfing to a site hosted with
webazilla.com's service.
It is very strange. When I stop squid then these tcp connection
disappear.
The names of these sites are different, for example just IP
address,88.208.22.108 or 80-239-152-58.customer.teliacarrier.com.
Probably the same story, different hosts.
We have such squid logs enabled: access.log, referer.log, store.log,
useragent.log.
Here is extract from squid.conf:
---------------------------------
acl manager proto cache_object
acl localhost src 127.0.0.1/32
acl to_localhost dst 127.0.0.0/8
...
acl allowed_hosts src <intranet client hosts>
...
acl SSL_ports port 443
acl Safe_ports port 80 # http
acl Safe_ports port 21 # ftp
acl Safe_ports port 443 # https
acl Safe_ports port 70 # gopher
acl Safe_ports port 210 # wais
acl Safe_ports port 1025-65535 # unregistered ports
acl Safe_ports port 280 # http-mgmt
acl Safe_ports port 488 # gss-http
acl Safe_ports port 591 # filemaker
acl Safe_ports port 777 # multiling http
acl CONNECT method CONNECT
...
http_access allow manager localhost
http_access deny manager
http_access deny !Safe_ports
http_access deny CONNECT !SSL_ports
http_access deny to_localhost
http_access deny denied_hosts
http_access allow allowed_hosts
http_access deny all
http_port 3128
icp_port 0
That looks fine.
-----------------------------------------
What might be the cause of this strange situation ?
How could I figure out why this happens ?
Any hints, any thoughts.
Thanks.
Chris
