[CentOS] Neighbour table overflow

Robert Moskowitz rgm at htt-consult.com
Fri Nov 28 17:19:59 UTC 2008

tdukes at sc.rr.com wrote:
> ---- Robert Moskowitz <rgm at htt-consult.com> wrote: 
>> Thomas Dukes wrote:
>>> *From:* centos-bounces at centos.org [mailto:centos-bounces at centos.org] 
>>> *On Behalf Of *chloe K
>>> *Sent:* Thursday, November 27, 2008 9:10 PM
>>> *To:* CentOS mailing list
>>> *Subject:* Re: [CentOS] Neighbour table overflow
>>> what is your netmask?  
>>> eth0 =
>> Why do you have such a large subnet?  There are a number of potential 
>> performance problems with such a setup.  I typically only see this in 
>> large, bridged wireless campuses.  Little justification for it in a 
>> wired network.  (I do have lots of networking experience and knowledge, 
>> having consulted with a number of large deployments).
>> Even with a large subnet, you should not be arping everywhere.  Either 
>> two things are happening:
>> Your system is recording every ARP request it sees ('Who has IP 
>> x.x.x.x') to avoid arping later.  Bad behaviour (IMNSHO), given your 
>> network.
>> Your system is ARPing for every IP address in the subnet to learn all of 
>> its neighbors.  WHy would it do that?  Unless you have some snooping 
>> software running on your system.
> Hi Robert,
> I did not set this value.  Something did but not me.
> I am on a roadrunner connection with a dynamic ip.  What do you suggest I change it to?
You might not have much control over it if you are using DHCP.

route -n

will supply you with your router address. Once you now that and your 
assigned IP address (and lease) you can use ifconfig to change your 
netmask so that your router and you are in the same subnet.

What is the address also of your nameserver (/etc/resolv.conf) and mail 
server? If these are also within that hugh subnet, your netmask has to 
keep them 'local'.

Roadrunner.... hmm.

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