Multiple NIC question.

[Earl Mott]

I am running a rp4440 under HPUX 11.11. This server has 4 NICs configured, each with a different IP address. I have configured lan0, lan1, lan3 and lan5. Regardless of which interface you log in on, all the out bound packets go out through lan5. How do I configure the NICs so that the interace you log in on is the interface that packets will go out on?

[paolo barila]

try

# netstat -r

It seems that lan5 is your default gateway.

You have to configure "static routes" to reach other destination

# route add ...

[Geoff Wild]

lan5 must be on same subnet as the default gateway...

http://docs.hp.com/en/B2355-90777/index.html

So you have 4 lan cards - are they all on different subnets?

If not, then you will always go out lan5...

Rgds...Geoff

[Steven E. Protter]

Shalom Earl,

You must have a recent release of HP-UX, because in the early 11i v1 days this situation of multiple NIC cards on the same network would lead to an immediate and sudden failure of network services.

Its still not recommeneded to have such a setup unless you have APA, Auto Port Aggregation, a pay for add in program.

The statement about the packets going out a particular interface above is true. There is an option in the OS setup to pick a primary LAN, this option will probably be the lan that the packets go out.

For system stability,I recommend you make immediate changes to your network setup.

To review, lets say the following is the configuration:

192.168.0.10 netmask 255.255.255.0

The network is 192.168.0
The host is 10

You should be configured to have no other hosts on this machine on network 192.168.0

SEP

[Bill Thorsteinson]

If you have multiple addresses on the
same network segment then they should all
be on the same NIC. lan1, lan1:1, ...

If you have multiple nics on different
networks, you still get routed back to
you by the shortest path. It doesn't matter
which NIC you arrived on the shortest path
back is always the same.

You can segemnt the load over multiple nics
on the same subnet, by routing using a mask
which gives you a smaller subnet over
different NICS. This only works for traffic
local to the segement unless you have
multiple gateway addresses.

[rick jones · Accepted solution]

In broad handwaving terms it is indeed "best" to use APA if you want multiple "physical" (from the standpoint of the transport, not necessarily "true physical" - eg, an APA link-aggregate is considered a "physical" NIC by the transport) NICs in the same IP subnet.

If you configure multiple physical NICs in the same IP subnet, HP-UX will receive traffic on all of them, but only one of them will be used for outbound traffic. It may be the first one ifconfiged, it may be the last, but regardless, only one will be used, and you must not depend on it being one or the other.

Now, if you set ip_strong_es_model to a value of 1, outbound route selection will include the source (local) IP address. In practice for a server this means traffic starts going-out the interface on which it arrived.

It has the side effect that traffic to a given IP will only be accepted on the interface with that IP assigned.

The early (perhaps even contemproary) writeups on HP-UX 11i networking probably say the rather drastic things about networking ceasing to work because if all the pyshical NICs configured into the same IP subnet do not have equal connectivity to the rest of the world, the one selected for outbound traffic (without ip_strong_es_model set) may not reach everyone and so it appears as though the system has one off net

[Earl Mott]

Thanks for the feedback.

All IP addresses are on the same subnet.

A follow up question. Is there more to using ip_strong_es_model than setting it to 1 in /etc/rc.config.d/nddconf?