IP aliases One Interface, Two Subnets ?????

IP aliases One Interface, Two Subnets ?????

Post by Syste » Thu, 11 Jun 1998 04:00:00



I have one ethernet interface running on an Origin 200 Irix 6.4

Primary IP address is 192.9.100.10        /24
The alias on the interface is 192.168.100.2    /24

I need to set this machine up as a gateway between the two sub-nets. At the
moment whenever packets are sent from this machine, it sends out the primary
address as the source IP address. This is not helpfull.

Is there any one who has successfully setup an alias on a different sub-net
and correctly got the routing right.

I need a way of routing between the interfaces, setting the machine up as a
gateway. I cannot seem to do this ???

Suggestions please

Thank you in advance

Rob

 
 
 

IP aliases One Interface, Two Subnets ?????

Post by Walter Robers » Thu, 11 Jun 1998 04:00:00




:I have one ethernet interface running on an Origin 200 Irix 6.4
:Primary IP address is 192.9.100.10        /24
:The alias on the interface is 192.168.100.2    /24
:I need to set this machine up as a gateway between the two sub-nets. At the
:moment whenever packets are sent from this machine, it sends out the primary
:address as the source IP address. This is not helpfull.

At least up through IRIX 6.4, all packets sent out will have the primary
address as the source IP address, and you cannot change that.

On the other hand, for most purposes you should not care what the
source IP address is. The destination machines are going to be listening
for their IP addresses as the destination, not listening according to
which machine is the source. If you set the destination machines up
to gateway through the O200 (which is something you would arrange
on the destination machines, not on the O200) then the only remaining
thing to worry about [usually] is ensuring that broadcast and multicast
packets get properly bridged (or not, according to your needs.)

 
 
 

IP aliases One Interface, Two Subnets ?????

Post by Alexis Cousei » Sat, 13 Jun 1998 04:00:00



> I have one ethernet interface running on an Origin 200 Irix 6.4

> Primary IP address is 192.9.100.10        /24
> The alias on the interface is 192.168.100.2    /24

> I need to set this machine up as a gateway between the two sub-nets. At the
> moment whenever packets are sent from this machine, it sends out the primary
> address as the source IP address. This is not helpfull.

Depends on patches. FWIW, we're routinely using this here, and it works --
though most destination machines would not care whether the source IP
address was on their subnet or not.

--
Alexis Cousein                          Added to confuse the enemy:



 
 
 

IP aliases One Interface, Two Subnets ?????

Post by Alexis Cousei » Thu, 25 Jun 1998 04:00:00




> > I have one ethernet interface running on an Origin 200 Irix 6.4

> > Primary IP address is 192.9.100.10        /24
> > The alias on the interface is 192.168.100.2    /24

> > I need to set this machine up as a gateway between the two sub-nets. At
> > the moment whenever packets are sent from this machine, it sends out the
> > primary address as the source IP address. This is not helpfull.

> Depends on patches.

I'll have to explicit my response a bit, as many people have misunderstood
me.

Whether routing between two subnets attached to the same interface works
using aliases depends on patches, but the original requesters of alias
functionality specifically *wanted* outgoing packets to use the primary IP
as source address.

This usually does not break the routing, as TCP/IP stacks of machines on the
`alias' network are usually prepared to accept non-RIP encapsulated packets
originating from any source, as long as the destination address is OK. We're
using it (both in the Brussels office and SGI at large), and many of our
customers use it.

But the source IP address is *always* the primary IP of the interface, and
in this respect aliases do *not* behave as `virtual interfaces'. We'll have
two conflicting sets of requests from customers, as some want the IP source
to be the primary interface address, and others apparently want the IP
source to be the alias, though I'm sure you could file an RFE requesting
that both behaviours be supported, of course ;).

This is even true in 6.5.

--
Alexis Cousein                          Added to confuse the enemy: