Re: [gentoo-user] Multiple Routes to the same Subnet

[kashani]

Dan Farrell wrote:
> Thanks for your responses, all.
>
>
> On Wed, 07 Nov 2007 10:30:22 -0800
> kashani <kashani-list@××××××××.net> wrote:
>
>> First off don't assign separate IPs to each port on your four port
>> card, bond them into a single interface. That will simplify your
>> config and perform better.
>
> Perhaps I will; that's not a bad idea.  However, I will still have
> another interface that is to handle non-NFS traffic.  (The reason I
> split it this way, by the way, is that NFS is the only network service
> that might potentially be limited by bandwith.
>
>> Second, what sort of routing are you doing? If all the clients are on
>> the same subnet as the four port card you should not need routing.
>> Additionally if they are on the same subnet you should not be limited
>> by the speed of your gateway which may or may not be able to route at
>> 4 Gb/s whereas your switch may actually have that sort of
>> performaance. Are the clients on a separate subnet and if so can you
>> put them on the same subnet?
>
> No, they're all on the same subnet.  Each of the 5 interfaces adds a
> route to that subnet (no gateway, as you said, it's the same broadcast
> domain) but the routes all have different metrics.  The first such
> route chosen is the one that gets all the traffic.   The NFS server is
> used primarily for Read access, so this routing problem does a pretty
> good job mitigating any benefit of having so many interfaces.
>
> Oh, by the way, this is 100-T, not Gigabit.  Do I sound rich to
> you : ) ?

Buying a single GigE card would appear to be simpler and cheaper unless 
you don't have a GigE switch. :-)

> So, let's say I bond the 4 together.  Now I have 2 interfaces, a bond
> and eth0.  I still need to route through one or the other, so I still
> have the problem.
>
> I am reading about policy routing, which should be able to solve the
> problem by allowing routing based on the source rather than the
> destination.  I will keep the lists informed...

You should not need to do any routing and I'd be surprised if Linux is 
actually doing any routing in this case. However depending on how you 
are testing you might see some issues.

Let's assume you've got this network.

server eth0 10.11.12.21/24
server eth1 10.11.12.22/24

client1 eth0 10.11.12.101/24
client2 eth0 10.11.12.102/24

The server will have all sorts of nonsense about 10.11.12.21 
255.255.255.255 routes and you can ignore all that. Additionally when 
you initiate a connection from your server it will always originate from 
eth0 because 0 comes before 1 IIRC. Just one of those things. However 
when you initiate a connection from a client to eth1 the server should 
respond out the same interface. I'd play around with tcpdump on a client 
and see if this is happening like it should be.

	You might also try forcing portmap to bind to one IP in 
/etc/conf.d/portmap.

	If for some reason I'm completely off base and Linux is defaulting out 
eth0 for connections coming into eth1 you can always do the lo tech 
solution. Assuming the above network we then assign a separate subnet to 
eth1 and an alias to each client.

server eth0 10.11.12.21/24
server eth1 10.11.88.21/24

client1 eth0 10.11.12.101/24
client1 eth0:0 10.11.88.101/24
client2 eth0 10.11.12.102/24
client2 eth0:0 10.11.88.102/24

	The machines connect on 10.11.88.0/24 and you avoid any interface 
confusion.

kashani
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