two interfaces one subnet

Chris Meidinger cmeidinger at sendmail.com
Mon May 11 16:38:30 CDT 2009


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- 
>> 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  
good idea...)

Chris




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