Re: IP aliasing and ARP

[Casey Carter <ccarter@cs.uiuc.edu>]

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
> : -
> : : send the line "unsubscribe linux-net" in
> : the body of a message to majordomo@vger.kernel.org
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> :
>
>  

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



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