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Old 01-20-2011, 12:12 PM   #1
trist007
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Registered: May 2008
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A weird networking issue...


I have a Slackware 13.0 server that is not replying to icmp pings. However, I have double checked that /proc/sys/net/ipv4/icmp_echo_ignore_all is set to 0.

The weird thing is I can run nc -v slackware 22 from any computer on my lan and the banner comes up just fine. The nic is on the same netmask and broadcast as all the other computers on my lan. I can log into it as well, it just doesn't respond to pings. I can even ping other computers and get replies just fine when pinging from inside the Slackware server.

I have even added an iptables INPUT rule for -p icmp -j ACCEPT. Although I've never had to do this.

I ran tcpdump -vv icmp and I can see ping requests coming into the computer, however slackware simply doesn't respond.

What could be causing this? A corrupt arp cache? It's been happening for more than a few hours so I wouldn't think so.

How can I view the arp cache table? How do I clear it?

What other troubleshooting tests can I run?

Last edited by trist007; 01-20-2011 at 12:23 PM.
 
Old 01-20-2011, 12:25 PM   #2
trist007
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Oh man, nevermind. I flushed iptables and it worked. I just needed to insert the iptables icmp rule. I had added it, which came after the drop all packets rule. Sorry for the trouble. In either case I'd still like to know how to display arp table and flush it and modify refresh time values.

Last edited by trist007; 01-20-2011 at 12:29 PM.
 
Old 01-20-2011, 12:28 PM   #3
corp769
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You can use arp -d for each client to remove the cache, and try to ping again and see if it works.

---------- Post added 01-20-11 at 06:29 PM ----------

Oops, nevermind, looks like you got it.
 
Old 01-20-2011, 01:20 PM   #4
szboardstretcher
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If not in production, Disable IPtables for a moment and see if you can ping. Then you will know whether or not it is a firewall issue.
 
Old 01-20-2011, 01:31 PM   #5
trist007
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Thanks.
 
Old 01-20-2011, 01:33 PM   #6
szboardstretcher
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Quote:
Originally Posted by trist007 View Post
Thanks.
Welcome. Mark [Solved] ?
 
  


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