IP Aliasing: Route Statement Necessary?

I have a dns server that I'm getting ready to move to a different
public network. (I already contacted the Registrar.) In order to
allow customers who are not ready to convert IPs to continue to reach
this server, I aliased its eth0 interface and plan to connect the two
Ethernet switches together this weekend. Does anyone see any problem
with this so far?

Some say to add a route statement when setting up aliasing. On a
machine with only one interface and a default route out it, is there
any reason to add another route?

Finally, a question about terminology: is IP aliasing the same thing
as multinetting?

--
Bob Simon
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"Bob Simon" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> I have a dns server that I'm getting ready to move to a different
> public network. (I already contacted the Registrar.) In order to
> allow customers who are not ready to convert IPs to continue to reach
> this server, I aliased its eth0 interface and plan to connect the two
> Ethernet switches together this weekend. Does anyone see any problem
> with this so far?

I did something similar when migrating DNS ranges of an internal
network from 192.168.0 to 10. allowing more hosts. Key servers
just aliases eth0:1 to their old address and those clients with static
addresses continued to work once DHCP was pumping out addys
in the new range.

> Some say to add a route statement when setting up aliasing. On a
> machine with only one interface and a default route out it, is there
> any reason to add another route?

AFAIR an ifconfig eth0:1 192.168.0.X did it all for us. If there was
a routing table line it was put in automatically.

Cheers,

Dave.

On Thu, 12 Feb 2004 15:53:31 -0600, Bob Simon <(E-Mail Removed)> wrote:
> I have a dns server that I'm getting ready to move to a different
> public network. (I already contacted the Registrar.) In order to
> allow customers who are not ready to convert IPs to continue to reach
> this server, I aliased its eth0 interface and plan to connect the two
> Ethernet switches together this weekend. Does anyone see any problem
> with this so far?

Not sure exactly what you are doing, but if connecting to 2 ISPs at the
same time, replies to traffic coming in from non-default route may go out
the other default route, and the question is whether that ISP would accept
traffic that to them appears to have a spoofed source IP (not on their
network).

> Some say to add a route statement when setting up aliasing. On a
> machine with only one interface and a default route out it, is there
> any reason to add another route?

In the 2 ISP scenario, you may need more advanced routing so replies go
out the route they came in (per Adv-Routing HOWTO).

> Finally, a question about terminology: is IP aliasing the same thing
> as multinetting?

Not necessarily, aliasing could be used for more than 1 subnet on the same
wire, but can also be used for multiple IPs on same subnet.

--
David Efflandt - All spam ignored http://www.de-srv.com/

On Fri, 13 Feb 2004 02:25:38 +0000 (UTC), (E-Mail Removed) (David
Efflandt) wrote:

>On Thu, 12 Feb 2004 15:53:31 -0600, Bob Simon <(E-Mail Removed)> wrote:
>> I have a dns server that I'm getting ready to move to a different
>> public network. (I already contacted the Registrar.) In order to
>> allow customers who are not ready to convert IPs to continue to reach
>> this server, I aliased its eth0 interface and plan to connect the two
>> Ethernet switches together this weekend. Does anyone see any problem
>> with this so far?
>
>Not sure exactly what you are doing, but if connecting to 2 ISPs at the
>same time, replies to traffic coming in from non-default route may go out
>the other default route, and the question is whether that ISP would accept
>traffic that to them appears to have a spoofed source IP (not on their
>network).

Actually, my ISP gave me a new /23 block of addresses over a new ATM
PVC and they want back the original /23 from Sprint that they assigned
us three years ago. Apparently, the Sprint DS3 is just too expensive
for them to justify keeping.

>> Some say to add a route statement when setting up aliasing. On a
>> machine with only one interface and a default route out it, is there
>> any reason to add another route?
>
>In the 2 ISP scenario, you may need more advanced routing so replies go
>out the route they came in (per Adv-Routing HOWTO).

This sounds interesting. I'll check this out.

--
Bob Simon
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