1 HP-Server - Several NICs - On the same subnet ???

[Rolf Schmidt]

Hello there,

I just was facing a network diagram showing a HP-server with several NICs each connected to the same subnet. Comming from a LINUX point of view, this scenario looks *unusual* -not to say impossible- to me.

My question:

"Does HP-UX11 support several network adapters in the same machine to be configured using the same subnet?"

Thank you.

Rolf

[Herve BRANGIER]

Hi

You can do that with Linux also, but consequences
are really strange, you have duplicate packets
in entry (test with ping command...) and I think
you need to configure routing with differents
priorities. It may be useful to secure your
system (NIC faults), but I don't know exactly
if it's really use and without other problems ?

Regards,

Herv?

[Volker Borowski]

Hi Rolf,

this depends on the drivers,
even on Linux you can do this,
question is, are they on the net
with a diffrent IP-Address.

We have INTEL-dual-port Cards active
in linux-netservers, to have speed increase
and fault tolerance.

Guess this works with the apropriate drivers for HPUX as well.

Volker

[John Bolene]

Well it sorta works, but is not a good situation to have.

Better to have extra IP's on the subnet point to one NIC (if that is what is needed, DNS will not be very happy with this unless you use alias's), and the other Nic on another subnet connected to another router.

Please explain why this is done this way.

[Ian Cameron]

To my understanding the cards should be on seperate subnets or you are going to have issues. Each card them has unique ip addresses and a unique name but you can set up one main hostname in dns to see both addresses (do an nslookup on ibm.com and you will see what I mean).

The actual loading on each card goes beyond what I understand of networking but the shortest distance will prevail unless you have some software on the server to balance the activity. So if you are on xxx.xxx.33 and xxx.xxx.34 the data from each of those subnets should stay on their own 'sides' of the network.

Good luck,
Ian

[Jim Turner]

Rolf,

The installation you describe appears to lend itself well to port aggregation. HP calls it "Auto Port Aggretation" and Cisco calls it "Fast EtherChannel (FEC)".

FEC allows you to have multiple NICs using the same IP address. It works quite nicely.

Here's a good link:
http://www.hp.com/products1/unixserverconnectivity/infolib/cisco.html

Cheers,
Jim

[Bill Thorsteinson]

If you need multiple addresses on a subnet, it is
standard practice to alias a single card.

I got stuck with two cards 10mb and 100mb on the same
subnet.

I know of three situations that warrant multiple cards on the same subnetwork.

1 - Unused ports on a machine generate errors during
startup. I ran into this situation with a 10mbs card.
Connecting it to the subnet caused it to handle all
traffic for the subnet. Solution is to add software or
readdress the card to a private subnet. Don't expect
traffic on the card.

2 - Extremely heavily loaded server. Modern cards can handle receiving and sending traffic at maximum rate.
If your traffic exceeds the capacity of the card, then you
could agregate traffic. (10.20 will send all outgoing traffic to the subnet over one card unless you add the appropriate aggregation software. Your switch must
also support the aggrecation.

3 - Hot failover of the network card (use seperate cards).
(HP-UX 10.20 has optional software to do the failover.)
I believe this can be done with either the same or different addresses on the card. Different addresses make DNS set up and failover recovery more difficult.

[Rolf Schmidt]

Thank you all.

The reason why we want to do this is: We want to create failover for our switches, which connect the webservers to the HP-UX application servers. What we don't want to do: loadbalancing, aliasing.

To go more in depth, here our Scenario:
We need to connect a bulk of webservers (equipped with single-port-NICs) to less Application servers. To create failover, we want to connect each Application server physically twice to different switches. Connect the half of the webservers to switch1, the other half to switch2. Connect switch1 <-> switch2. In case of failure, there would be still enough webservers and all ASs available. So far the theoretical part.

We are dicussing wether we could have a failover at a lower level, most likely at MAC level. The idea of having several ip-adresses rises problems, as some of you already have remarked. There could be furthermore a problem of binding our application to more than one IP-address.

Thank you, Jim, for delivering a useful link. We will dicuss this. How much does it cost? Any more experiences would be welcome.

Best regards

Rolf