two interfaces one subnet
Matlock, Kenneth L
MatlockK at exempla.org
Mon May 11 16:50:42 CDT 2009
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.
matlockk at exempla.org
From: Chris Meidinger [mailto:cmeidinger at sendmail.com]
Sent: Monday, May 11, 2009 3:39 PM
To: Dan White
Cc: nanog at nanog.org
Subject: Re: two interfaces one subnet
On 11.05.2009, at 23:31, Dan White wrote:
> Chris Meidinger wrote:
>> This is a pretty moronic question, but I've been searching RFC's on-
>> and-off for a couple of weeks and can't find an answer. So I'm
>> hoping someone here will know it offhand.
>> I've been looking through RFC's trying to find a clear statement
>> that having two interfaces in the same subnet does not work, but
>> can't find it that statement anywhere.
>> The OS in this case is Linux. I know it can be done with clever
>> routing and prioritization and such, but this has to do with
>> vanilla config, just setting up two interfaces in one network.
>> I would be grateful for a pointer to such an RFC statement,
>> assuming it exists.
> If your goal is to achieve redundancy or to increase bandwidth, you
> can bond the interfaces together - assuming that you have a switch /
> switch stack that supports 802.3ad.
> Then you could assign multiple IPs to the bonded interface without
> any layer 3 messyness.
I should have been clearer. The case in point is having two physical
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
bonding going on. The customers usually have the idea of running one
interface for administration and another for production (which is a
_good_ idea) but they want to do it in the same subnet (not such a
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