Re: how to tweak ARP timer on kernel 2.6.9

Le mardi 09 mars 2010 à 12:32 -0700, Tom Ammon a écrit :

Hi,

I've been trying to figure out how to adjust the ARP timeout on kernel 
2.6.9 and I found the following in /proc/sys/net/ipv4/neigh/ib0 (its an 
IB interface I am interested in changing) with the following values. 
This is on kernel 2.6.9-89ELsmp (RHEL4) :

When I test this, along with per-flow ECMP (using the iproute2 utils), I 
see that the ARP cache is timing out about every 10 minutes (I observe 
this by load balancing an iperf flow between two different gateway 
machines and then graphing the interface traffic)

10 minutes seems out of specs.

On a newer kernel, 2.6.18-164.11.1.el5 (RHEL5), I see mostly the same 
parms available, but a few new ones have been added. However, all of the 
parms that are the same name between the two kernels are the same values:

Yet when I observe the same traffic flow with this machine, the ARP 
cache times out about once per minute.

This seems normal, old kernels were a bit lazy about arp.

Is there another set of parameters somewhere that govern how often the 
kernel times out the ARP cache? If so, where might I find that? Is there 
any kernel documentation that talks about changing ARP timers on the 
linux kernel?

I would suggest :

man 7 arp

http://linux.die.net/man/7/arp



base_reachable_time
        Once a neighbour has been found, the entry is considered to be
        valid for at least a random value between base_reachable_time/2
        and 3*base_reachable_time/2. An entry's validity will be
        extended if it receives positive feedback from higher level
        protocols. Defaults to 30 seconds.

gc_interval
        How frequently the garbage collector for neighbour entries
        should attempt to run. Defaults to 30 seconds.

gc_stale_time
        Determines how often to check for stale neighbour entries. When
        a neighbour entry is considered stale it is resolved again
        before sending data to it. Defaults to 60 seconds.
        


and "ip -s neigh"