[177108] in North American Network Operators' Group
Re: Charter ARP Leak
daemon@ATHENA.MIT.EDU (Brett Frankenberger)
Mon Dec 29 12:35:50 2014
X-Original-To: nanog@nanog.org
Date: Mon, 29 Dec 2014 11:35:42 -0600
From: Brett Frankenberger <rbf@rbfnet.com>
To: Jay Ashworth <jra@baylink.com>
In-Reply-To: <28388313.750.1419874023962.JavaMail.root@benjamin.baylink.com>
Cc: NANOG <nanog@nanog.org>
Errors-To: nanog-bounces@nanog.org
On Mon, Dec 29, 2014 at 12:27:04PM -0500, Jay Ashworth wrote:
> >
> > Valdis, you are correct. What your seeing is caused by multiple IP
> > blocks being assigned to the same CMTS interface.
>
> Am I incorrect, though, in believing that ARP packets should only be visible
> within a broadcast domain,
broadcast domain != subnet
> and that because of that, they should not be
> being passed through a cablemodem attached to such a CMTS interface unless
> they're within the IP network in which that interface lives (which is
> probably not 0/0)?
>
> This sounds like a firmware bug in either the CMTS or the cablemodem.
int ethernet 0/0
ip address 10.0.0.1 255.255.0.0
ip address 11.0.0.1 255.255.0.0 secondary
ip address 12.0.0.1 255.255.0.0 secondary
The broadcast domain will have ARP broadcasts for all three subnets.
Doing it over a CMTS doesn't change that.
-- Brett
