[lug] forcing certain services to use eth1 instead of eth0

[John Hernandez]

There's really no "right" way.  What you're trying to accomplish isn't
really possible with traditional destination-based (ie simple) routing.
 To do what you originally requested (enforce path symmetry) you
probably need to use policy-based routing, as described earlier in the
thread.  For the case of servers, using a default gateway, it's really
not too complicated.

It might also be helpful to re-evaluate WHY you want to do this.  Did
you diagnose a specific performance bottleneck?  Is it because you are
periodically saturating a 100Mbps interface?  Are you running full
duplex on a switched network?  Maybe Gig-E is the answer?  Or maybe
802.3ad link aggregation?  Or a faster server?

Michael Belanger wrote:
> On Wednesday 04 January 2006 01:23, Sean Reifschneider wrote:
> 
> 
>>I agree with Kevin that setting up a different network range on the net
>>interface is probably going to be the most robust in the long term and
>>easiest to deal with.  In theory you can do what you want using MARK and
>>iproute2, but in my experience this setup can be difficult to manage and
>>understand, aided partly by extremely poor iproute2 documentation, and
>>therefore can be fragile and hard to debug.
> 
> 
> I re-configured eth1 to be on a separate subnet and this seemed to do the 
> trick, however, it appears that eth1's gateway is now the default.
> 
> (Fedora Core 2): If no GATEWAY is defined in the /etc/sysconfig/network, but 
> IS defined in network-scripts/ifcfg-eth0 and 1, it seems to use eth1's 
> setting as the default gateway.   I manually altered the default gateway to 
> be on eth0 and eth0's gateway, but this seems to have caused traffic routing 
> to eth1 to be responding with eth0 for sending mail with SMTP.
> 
> I infer from this behavior that though we ask sendmail to send from eth1, 
> sendmail just uses the default.  
> 
> So, even though I did it this way (which is the right way), I still may have 
> to add some routes with MARKs to make this work as expected.  I don't think I 
> want eth1 to be the default route as it has far less accessibility on our 
> network and may break our backups and other services.
> 
> Does this sound correct?
> 
> Thanks again for all the help.
> 
> 
> 
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