ARP: Error Message in if_ether.c "arprequest: cannot find matching address"

[Juan Mojica]

Hey David,

  That's not quite the scenario we're dealing with, but it is disconcerting
to here that it looks like this path can be triggered from an incoming
frame.  We had been seen it frequently when quickly
unconfiguring/configuring interfaces from a host.  An application would
receive the configure message, start trying to send out traffic, but not
get the unconfigure in time.  That was the working theory.  We've not hit
it recently - could just be a dormant race condition.

I have attach my proposed solution, which takes what Gleb provided, adds a
KASSERT, and wraps it all up with a sysctl so that it can be turned off.

Thanks,
Juan

On Mon, Apr 22, 2013 at 3:21 PM, David DeSimone <fox at verio.net> wrote:

> Juan Mojica <jmojica at gmail.com> wrote:
> >
> > We manage to hit the following message with some regularity.
> >
> > arprequest: cannot find matching address
> >
> > The code shows a printf:
> >
> > printf("%s: cannot find matching address\n", __func__);
> >
> >
> > Any reason this is a printf and not a
> >
> > log(LOG_ERR,
> >
> > The only things I can come up with are:
> >
> > a) it is a really severe and should be printed out, which if that is the
> > case why isn't there an assert there?
> > b) whoops, that should probably be a log(LOG_ERR,
> >
> > On our end we need to figure out exactly why we're intermittently hitting
> > this patch of code.
>
>
> We see this regularly on our network, because we have multiple overlaid
> subnets on the same VLAN.  The server sees an ARP request come in, but
> it does not match any of its confgired subnets, so it generates this
> error when trying to formulate an ARP reply.
>
> For example, the server might be configured to use 192.168.1.10/24 on an
> interface, but if it receives an ARP request for 172.31.250.249 on that
> interface, it won't know how to reply, and will generate this error.
>
>
> You might see this error if someone is inserting hosts with wrong IP's
> on your network, and they start trying to ARP for one another.
>
> --
> David DeSimone == Network Admin == fox at verio.net
>   "I don't like spinach, and I'm glad I don't, because if I
>    liked it I'd eat it, and I just hate it." -- Clarence Darrow
>
>
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-- 
Juan Mojica
Email: jmojica at gmail.com
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