Multi homed host address clash

Multi homed host address clash

Post by Hans Wurste » Sat, 11 Dec 2010 17:45:18



Hi

Unfortunately I cannot test this myself due to lacking equipment:
Assume I have a multi homed Linux server. I have two hosts A and B
with the same IP address I, one on each interface (I know this is a
situation to avoid). I receive a packet from A and try to reply to it.
Where will the packet be sent to? THanks

hw

 
 
 

Multi homed host address clash

Post by David Schwart » Sat, 11 Dec 2010 19:08:11



Quote:> Unfortunately I cannot test this myself due to lacking equipment:
> Assume I have a multi homed Linux server. I have two hosts A and B
> with the same IP address I, one on each interface (I know this is a
> situation to avoid). I receive a packet from A and try to reply to it.
> Where will the packet be sent to? THanks

The routing table will decide. Where does the route to that IP address
go?

DS

 
 
 

Multi homed host address clash

Post by Pascal Hambour » Sun, 12 Dec 2010 08:08:37


Hello,

David Schwartz a crit :


>> Unfortunately I cannot test this myself due to lacking equipment:
>> Assume I have a multi homed Linux server. I have two hosts A and B
>> with the same IP address I, one on each interface (I know this is a
>> situation to avoid).

It is more than just a situation to avoid : it is a *wrong* setup.

Quote:>> I receive a packet from A and try to reply to it.
>> Where will the packet be sent to? THanks

> The routing table will decide.

Actually the routing decision is based on more than a routing table. It
involves several routing tables and routing rules, which can use
criteria such as source address, input interface or netfilter mark to
select which routing table to use.
 
 
 

Multi homed host address clash

Post by Rick Jone » Sun, 12 Dec 2010 07:37:19


I would think that if systems A and B were on the same LAN (Ethernet)
it would be whichever had their MAC address in the ARP cache on the
last-hop system/router.

--
a wide gulf separates "what if" from "if only"
these opinions are mine, all mine; HP might not want them anyway... :)
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

 
 
 

Multi homed host address clash

Post by Pascal Hambour » Sun, 12 Dec 2010 19:20:07


Rick Jones a crit :

Quote:> I would think that if systems A and B were on the same LAN (Ethernet)
> it would be whichever had their MAC address in the ARP cache on the
> last-hop system/router.

According to the original post, A and B are on separate LANs.
 
 
 

Multi homed host address clash

Post by David Schwart » Tue, 14 Dec 2010 22:51:23




Quote:> > The routing table will decide.
> Actually the routing decision is based on more than a routing table. It
> involves several routing tables and routing rules, which can use
> criteria such as source address, input interface or netfilter mark to
> select which routing table to use.

Collectively, these tables and rules are referred to as "the routing
table". Common usage is that the term "routing table" refers to all
information the guides the packet forwarding decision, including
information that is not currently used for that purpose but would be
if circumstances changed. (Such as routes with worse metrics than
other routes. Or routes whose next hop is unreachable currently.)

For example, the Wikipedia article on 'Routing table' says: The
remainder of this article will ... refer to the entire routing/
forwarding information subsystem as the "routing table".

DS

 
 
 

Multi homed host address clash

Post by Lawrence D'Oliveir » Sun, 19 Dec 2010 10:38:35


In message


> Assume I have a multi homed Linux server. I have two hosts A and B
> with the same IP address I, one on each interface (I know this is a
> situation to avoid). I receive a packet from A and try to reply to it.
> Where will the packet be sent to?

I think the ARP cache can have only one entry per IP address. So the reply
will go to whatever MAC address is in that cache.

Thats for a directly-reachable machine. For one thats only reachable
through a router, the above would apply to whatever node provides the last
hop.

 
 
 

1. ? multi home + multi cgi, multi email, multi log, multi support

Is there any httpd package that could do not only multi web-home
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Does Netscape do that, OpenMarket do that, Or otehrs?

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