A machine with two IP addresses in the same subnet

[Enrico Venturi]

Hello colleagues,
I know that in HP-UX 11.11 it's forbidden to configure two lan cards on the same machine with thw IP addresses belonging to the same subnet.
My question is:
Was it possible do it in HP-UX 10.20?
Was it possible do it in HP-UX 11.0?

thanks a lot.
Enrico

[keith persons]

Enrico,

It is not the operating system that imposses this restriction but networking standards - and no, to best of my knowledge it is not allowed in any version.

Keith

[Ian Dennison_1]

Unless of course you purchase Port Aggregation Software that allows HP-UX to see the combined bandwidth of the network cards as one logical 'wire'. But this is at a different level to the basic addressing standards of IP.

Just in case you wanted to know 'how to'.

Share and Enjoy! Ian

[Enrico Venturi]

Thanks for the reply but it isn't correct :-)

On HP-UX 10.20 it was allowed ... I knew because an our customer (Telecom Italia) uses more times to assign the IP addresses in the same subnets even if the lan cards are in the same machine.
I agree with you that the standard forbids that, but in any case HP UX allowed it, at least in the past.

Bye

[Shannon Petry]

What happens when 2 LAN cards are configured in the same subnet is the real question here. Both Solaris and HPUX used to allow this configuration, but lots of people thought you would double the bandwidth and my guess is that this misconception made vendors put checks in that explicitly dis-allow it now.
When 2 LAN cards are on the same subnet, you can ping both IP's, and send data to both. The problem is that it would only be able to talk on the primary NIC.
Sometimes this does not work, but most of the time it does. But people could not double the bandwidth of their file servers this way as they would think (and so would I if not doing testing on this).

So anyway, while it used to be able to be done, it was really only done 1/2. This is networking standards though, and not a vendor problem.

Regards,
Shannon

[Jeff Schussele]

Hi Venturi,

As Shannon put it - You can do it, but it doesn't work.
Kinda sounds like government work, huh?

The problem is - You can route IN either NIC...BUT which NIC routes out?

You *could* setup tons of static routes IF you knew EXACTLY where trafic was coming from AND going to....BUT is all that work worth it?

IF you need more bandwidth than a single NIC can handle then you need an HP product called APA (Auto Port Aggregration) that consolidates a single IP into multiple NICs.

Rgds,
Jeff

[Tim D Fulford]

The lowest interface routes out

e.g. lan0 123.123.123.123
lan1 193.164.192.27
lan3 193.164.192.12

traffic will go out of lan1 on the 193.164.192.0/24 subnet

Tim