Network performance with 2nd lan card on same network

[Peter Brook_1]

Hi,

I just need to have my suspicions confirmed on this one.

Someone is recommending the addition of a 2nd 100BT card in an N-Class (HP-UX 11.00) which will be on the same lan as the first. This is to relieve any potential network congestion on the first lan card.

As far as I remember, the packets may well be received on the 2nd lan card (if directed to do so), but will always be sent back on the first lan card (or whichever interface is listed first in the routing table entry for the local lan). Is this true?

Thanks in advance.

[Stefan Farrelly]

Yes, thats true, unless you purchase and install Auto port aggregation sofwtare which will then balance the load (in+out) over the 2 lancards (team the 2 lancards in Wintel speak).

[Colin Topliss]

..and these LAN connections also have to go through a switch that supports this, else aggregation will not work.

Take a look at:
http://www.hp.com/products1/unixserverconnectivity/adapters/apa_overview.html

APA isn't free either.

Col.

[Johan Lorimier]

Hi,

just an update to say that HP does not support two lan on the same network unless you use APA.

Nothing will warn you when you configure 2 lan on a same network but this can produce some weird situation with your applications.

Johan

[Peter Brook_1]

Thanks for all your replies - looks like APA is the answer - probably not an option for this exercise.

Just a quick thought - as we will be only talking to a single remote host via the additional lan card, is it possible to add a host route to the remote host to go via the 2nd interface?

thanks again

[Duncan Edmonstone]

If, as you state, both the network cards were on the same IP subnet as the first, *and* the remote host is on a seperate IP subnet then no.

Remember with static routes you can only specify the next hop. If the host you were talking to was on the same subnet then you could do this:

example

nclass has IP addresses 10.1.1.1/255.255.255.0 and 10.1.1.2/255.255.255.0

remote has IP address 10.1.1.3/255.255.255.0

you want traffic for remote to always go out of 10.1.1.2. You can set up a static route as follows:

route add 10.1.1.3 10.1.1.2 0

However if remote was on a different subnet you could not do this, as the first hop has to at least point to a router, and you then can't control what interface is used for getting at the router.

HTH

duncan

[rick jones]

Your recollection about the routing of packets when two physical interfaces are configured into the same IP subnet is correct.

As for "support/notsupport" without APA, I thought there was a clarification that said it would be "supported" but it might not do what one wanted.

Anyhow.... you could indeed set a specific host route pointing at the IP of the desired egress interface. Or, depending on whether this system initiates the connection and/or if the applications can be convinced to call bind() before calling connect(), you could consider setting ip_strong_es_model - this causes source IP to be considered in the route lookups. It also means that packets will only be accepted on the interface with the corresponding IP address.

Finally, I'm not sure what HP are charging for a PCI 100BT NIC these days, but you might compare that with whatever we are charging for the latest GbE NIC(s) - it might be just as effective to upgrade to GbE. And to continue the shameless plug, there are some not-too-badly-priced GbE ProCurve switches these days :)

[Sanjay_6]

Hi,

in HP-UX env, it is not recommended to use multiple lan cards on the same system in the same subnet. So you should not have multiple lan cards in the same subnet on the same system.

To answer to your quesation about traffic, traffic can come through different ports, but it goes out through the default gateway. However you can specify an additional route for a specific subnet.

Hope this helps.

Regds