ARP's frustrating behavior

ARP's frustrating behavior

[Stuart Duncan]

Hi,

I'm noticing on a machine with dual NICs that they they all seem to answer 
ARP queries, even if the request is not directed to their IP.  Here's an 
example:

---8<---
10:52:03.177863 eth1 B arp who-has eddy tell soliton
10:52:03.177895 eth1 > arp reply eddy (0:3:47:8:1a:64) is-at 0:3:47:8:1a:64 
(0:90:27:41:c9:f4)
10:52:03.177875 eth0 B arp who-has eddy tell soliton
10:52:03.177908 eth0 > arp reply eddy (0:b0:d0:78:bc:92) is-at 
0:b0:d0:78:bc:92 (0:90:27:41:c9:f4)
--8<--

This is a problem for me because eth1 is 1000Mb fibre while eth0 is 100Mb, 
and almost all of the clients are caching the response from eth0 in 
preference to the response from eth1.

I know this appeared on the list once before (20/08/1999, Chris 
Leech.  "ARP (mis)behavior") however there was no definite answer.  My 
questions are:  Is this ARP behavior intentional?  (I can't recreate the 
fault in other UNIX's) and if it is, is there a way to turn it off?

Thank you,
Stuart Duncan


----
Stuart Duncan
Systems Administrator
WNI Weathernews
31 Bishop Street
JOLIMONT WA 6014

Re: ARP's frustrating behavior

[Ben Greear]

Stuart Duncan wrote:
> 
> Hi,
> 
> I'm noticing on a machine with dual NICs that they they all seem to answer
> ARP queries, even if the request is not directed to their IP.  Here's an
> example:
> 

Evidently, this is considered a feature.  However, to turn it off:
echo 1 > /proc/sys/net/ipv4/conf/all/arp_filter

Ben

-- 
Ben Greear <greearb@candelatech.com>          <Ben_Greear@excite.com>
President of Candela Technologies Inc      http://www.candelatech.com
ScryMUD:  http://scry.wanfear.com     http://scry.wanfear.com/~greear

Re: ARP's frustrating behavior

[Stuart Duncan]

>Evidently, this is considered a feature.  However, to turn it off:
>echo 1 > /proc/sys/net/ipv4/conf/all/arp_filter

I've tried this and it doesn't work.  I understand that arp_filter uses 
routing tables to determine which interfaces should respond to ARP 
queries.  In my case, both interfaces are on the same network.

There isn't a lot of documentation available for the use of arp_filter.

Thanks,
Stuart Duncan


----
Stuart Duncan
Systems Administrator
WNI Weathernews
31 Bishop Street
JOLIMONT WA 6014

Re: ARP's frustrating behavior

[Ben Greear]

Stuart Duncan wrote:
> 
> >Evidently, this is considered a feature.  However, to turn it off:
> >echo 1 > /proc/sys/net/ipv4/conf/all/arp_filter
> 
> I've tried this and it doesn't work.  I understand that arp_filter uses
> routing tables to determine which interfaces should respond to ARP
> queries.  In my case, both interfaces are on the same network.
> 
> There isn't a lot of documentation available for the use of arp_filter.
> 

I put interfaces on the same network too, and it works for me.  I do
use source-based routing (using the 'ip' command) though, which
may be why it works for me...

Ben

-- 
Ben Greear <greearb@candelatech.com>          <Ben_Greear@excite.com>
President of Candela Technologies Inc      http://www.candelatech.com
ScryMUD:  http://scry.wanfear.com     http://scry.wanfear.com/~greear

Re: ARP's frustrating behavior

[Roland Kuhn]

Hi!

On Tue, 7 Aug 2001, Ben Greear wrote:

> Stuart Duncan wrote:
> >
> > Hi,
> >
> > I'm noticing on a machine with dual NICs that they they all seem to answer
> > ARP queries, even if the request is not directed to their IP.  Here's an
> > example:
> >
>
> Evidently, this is considered a feature.  However, to turn it off:
> echo 1 > /proc/sys/net/ipv4/conf/all/arp_filter

This doesn't work for me, which is quite annoying: the machine answers arp
for 192.168.1.254 (its IP on the private net on eth1) when arping'ed on
the official side (eth0). Networks are physically separated, the official
side is inside a big network which routes 192.168 internally, so this is
really bad. If anyone could fix it I would be pleased...

Ciao,
					Roland

Re: ARP's frustrating behavior

[Chris Friesen]

Stuart Duncan wrote:
> 
> >Evidently, this is considered a feature.  However, to turn it off:
> >echo 1 > /proc/sys/net/ipv4/conf/all/arp_filter
> 
> I've tried this and it doesn't work.  I understand that arp_filter uses
> routing tables to determine which interfaces should respond to ARP
> queries.  In my case, both interfaces are on the same network.

Interesting.  This works fine on 2.2.17.  It actually uses the ip address to
network device mapping, so that a NIC won't respond to arp requests for
addresses that are not assigned to that NIC.


-- 
Chris Friesen                    | MailStop: 043/33/F10  
Nortel Networks                  | work: (613) 765-0557
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