nagios server networking glitch..?

Patrick Friedel pfriedel at copweb.com
Fri May 27 21:23:56 CEST 2005


I know this isn't really Nagios related, but since it causes Nagios to 
freak out when it happens, I hoped the list might have an idea of where 
to check.  Occasionally, not more than once per day, my Nagios box gets 
a route for an IP address that sends the traffic away from the intranet 
WAN out to the internet, causing the packet to die and Nagios begins to 
page me.  Caught it happening today and logged some information:

Remote IP: 204.75.219.254
Nagios server: 199.242.227.113
Intranet WAN gateway: 199.242.227.253
Internet WAN gateway: 199.242.227.254

When it's failing, it goes to:
pjf at jord:~$ ip route get to 204.75.219.254
204.75.219.254 via 199.242.227.254 dev eth0  src 199.242.227.113
    cache <redirected>  mtu 1500 advmss 1460 hoplimit 64

The correct route is:
pjf at jord:~$ ip route get to 204.75.219.254
204.75.219.254 via 199.242.227.253 dev eth0  src 199.242.227.113
    cache  mtu 1500 advmss 1460 hoplimit 64

  Standard Sarge Debian distro, not running any funny routing daemons.  
netstat is, IIRC, completely ignorant of the new route. The default 
route sticks at .253, like it should, and no other entries in the 
netstat routing table.  None of the other hosts are affected, so it's 
not a global issue, it's usually highly specific to a single IP address. 
(the problem host, however, seems to rotate, it's not a single IP 
problem _that_ way.) 98% of my traffic goes through the intranet, only a 
small percentage goes out the internet link.  I _suspect_ it's something 
weird on the nagios monitor box, as my usual first reaction is to ping 
the dead host from my workstation, where it works fine, then have pings 
fail from the nagios box.  The only thing I can think of is that the 
monitor box gets an ICMP REDIRECTED packet from the intranet router for 
one of the internet monitored hosts and it sticks somehow.

  Ideas?



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