When is ARP cache entry is changed from reachable to stale exactly???

sivareddy_jntu · 06-10-2009, 03:52 AM

hai all,
I want to know when ARP cache entry become STALE from reachable state.

In my system am using eth0 adapter and this interface settings are as follows.

base_reachabe_time=30
gc_stale_time=60
gc_first_probe_time=5
ucast_solicit=3
mcast_solicit=3

By having above settings i have observed the following.

Entry in ARP cache table becomes stale from reachable differently from time to time.
once it becomes for 60 sec,some other time it is 64 sec,some other time 50 sec and so on.

Why is it happening??

Any help would be appriciated highly.

Regards,
siva

grepmasterd · 06-11-2009, 03:12 PM

from 'man 7 arp':

Code:

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.

sivareddy_jntu · 06-13-2009, 12:23 AM

hai,
First of all thanks for your replay.

As per man page the time taken by entry to change from reachable

to stale will be between 15 and 45 secs.But sometimes it takes more

than 60 secs. Moreover it is changing from time to time.

What is the reason for this behaviour??

Any help would be appreciated greatly.

Regards,
siva.