[114446] in North American Network Operators' Group
RE: two interfaces one subnet
daemon@ATHENA.MIT.EDU (Matlock, Kenneth L)
Mon May 11 18:02:49 2009
Date: Mon, 11 May 2009 15:50:42 -0600
In-Reply-To: <5AF650D0-1378-494D-B4A6-09B099E64B84@sendmail.com>
From: "Matlock, Kenneth L" <MatlockK@exempla.org>
To: "Chris Meidinger" <cmeidinger@sendmail.com>, "Dan White" <dwhite@olp.net>
Cc: nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
If it were me and had the requirement of having both NICs in the same L2
segment, but unique IP addresses, I'd assign a secondary IP address to
the Layer3 SVI on the upstream device, and give the 2nd NIC on the
server an IP on that secondary IP block.=20
Ken Matlock
Network Analyst
Exempla Healthcare
(303) 467-4671
matlockk@exempla.org
-----Original Message-----
From: Chris Meidinger [mailto:cmeidinger@sendmail.com]=20
Sent: Monday, May 11, 2009 3:39 PM
To: Dan White
Cc: nanog@nanog.org
Subject: Re: two interfaces one subnet
On 11.05.2009, at 23:31, Dan White wrote:
> Chris Meidinger wrote:
>> Hi,
>>
>> This is a pretty moronic question, but I've been searching RFC's on-=20
>> and-off for a couple of weeks and can't find an answer. So I'm =20
>> hoping someone here will know it offhand.
>> I've been looking through RFC's trying to find a clear statement =20
>> that having two interfaces in the same subnet does not work, but =20
>> can't find it that statement anywhere.
>> The OS in this case is Linux. I know it can be done with clever =20
>> routing and prioritization and such, but this has to do with =20
>> vanilla config, just setting up two interfaces in one network.
>> I would be grateful for a pointer to such an RFC statement, =20
>> assuming it exists.
>
> If your goal is to achieve redundancy or to increase bandwidth, you =20
> can bond the interfaces together - assuming that you have a switch / =20
> switch stack that supports 802.3ad.
>
> Then you could assign multiple IPs to the bonded interface without =20
> any layer 3 messyness.
I should have been clearer. The case in point is having two physical =20
interfaces, each with a unique IP, in the same subnet.
For example, eth0 is 10.0.0.1/24 and eth1 is 10.0.0.2/24, nothing like =20
bonding going on. The customers usually have the idea of running one =20
interface for administration and another for production (which is a =20
_good_ idea) but they want to do it in the same subnet (not such a =20
good idea...)
Chris
