Re: dual-homed ping
On Sunday 15 July 2007 05:58, koffiejunkie wrote:
> Daniel D Jones wrote:
> > On a dual-homed ping, is it possible to ping one IP address from the
> > other address and force the packet to go out the interface and travel
> > through the network? Using -I to source the packet does not work, and
> > turning off ip_forward does not seem to make a difference.
>
> http://lartc.org/lartc.html#LARTC.RPDB.MULTIPLE-LINKS
Thanks for the link but it isn't clear to me how this is relevant to what I'm
attempting to do. I have two interfaces: eth1 172.16.100.101 and eth2
172.16.200.101. Even with explicit routing rules in place to route
172.16.100.0 via eth2 src 172.16.200.101, the kernel seemingly will not
ignore the fact that 172.16.100.101 is directly connected and send the ping
out the designated interface. This is true, so far as I can tell, whether
I'm routing using a single table or setting up multiple routing tables as the
article indicates. If I'm missing something from the link you posted,
please elaborate on the approach to take.
For background info, I'm setting up a CCNP lab. The labs require that I have
hosts connected to various points in the network, and that I configure the
routers and switches so that the various hosts can ping one another. It
seems a waste of resource and money to go buy four or so computers so I can
set them up and do nothing but ping from them. I'm trying to accomplish the
same thing with a single host and multiple interfaces. In order for this to
work, I need to be able to ping one interface from another interface and have
the packet traverse the network. If the network is broken, I need the ping
to fail.
Another option I've considered is to use Xen and set up virtual machines, each
with their own interface and IP. (Each has to use a different physical
interface, since the interfaces need to be connected to different switches in
the network.) I'm not sure, however, how networking is handled within Xen.
There's obviously a method to share the resources, since you can have
multiple VMs using a single network interface. I'm not sure if the Xen
network sharing code will recognize that I'm pinging from one VM to another,
and "helpfully" route the packet internally rather than simply send it out
the interface. Anyone know the answer to this before I go to the trouble of
configuring and installing multiple VMs?
Any advice or suggestions greatly appreciated.
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