Re: IP aliasing and ARP

From: Casey Carter (ccarter@cs.uiuc.edu)
Date: Mon Mar 03 2003 - 23:59:03 EST


This is a route-cache-flushing issue. After changes to the route table
(including the local route for an interface IP address) there is a
configurable delay before the route cache is flushed. By default, that
delay is 2 seconds. Since ARP decides to respond be looking for a local
route, it is still seeing the cached entry up to 2 seconds after
removing the address. If this really bothers you, either change the
delay value in /proc/sys/net/ipv4/route/max_delay, or echo 1 >
/proc/sys/net/ipv4/route/flush to flush the route cache after
deconfiguring the address.

Martin A. Brown wrote:

>For the record, I configured IP A on host A, and used ping and arping
>to hit IP A from from host B.
>
>Host A continued to respond to the ping and arping requests for
>predictably 2-3 seconds after the "ip addr del IP/A dev eth0" command was
>executed. The lag between the removal of the IP and the kernel
>ceasing to respond to ARP requests and echo requests appeared to be
>exactly the same.
>
>-Martin
>
> : I couldn't reproduce same thing here ie., no late ARP replies,...
> : (-- maybe supply more details?)
> :
> : btw.,
> : net/core/neighbour.c:
> : #define NEIGH_DEBUG 2
> : ;; (and NEIGH_PRINTK2("neigh %p is suspecteded.\n", neigh);
> : ;; => NEIGH_PRINTK2("neigh %p is suspected.\n", neigh);)
> : seem to help a bit around here.
> :
> : > Does
> : > behavior of a process using that address affect this?
> :
> : this part - I don't know (still suspecting it's not the case).
> :
> : regards,
> : kenji
> : -
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> :
>
>
>

-- 
Casey Carter
Casey@Carter.net
ccarter@uiuc.edu
AIM: cartec69

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