topic Re: Two interfaces on the same subnet? in Operating System - HP-UX

Two interfaces on the same subnet?

Roger Baptiste — Sat, 16 Feb 2002 01:09:23 GMT

hi,

Can we have more than one network interface on a system pointing to the same subnet? I thought no. But, i came across this on one of the systems few days back and something seemed wrong with it.
**
#netstat -in

Name Mtu Network Address Ipkts Opkts
lan3 1500 10.59.2.0 10.59.2.116 3533460 3814801
lo0 4136 127.0.0.0 127.0.0.1 5190510 5190519
lan4* 1500 10.59.2.0 10.59.2.115 5587668 46868
**

The lan4* entry was later removed . My question is, can the system allow/configure two ports on the same subnet? if so, what are the results?

What does the "*" (star) signify here?
(i have seen that in cluster systems, it denotes a card not being used (standby)).

thanks
-raj

Re: Two interfaces on the same subnet?

Sanjay_6 — Sat, 16 Feb 2002 02:41:26 GMT

Hi Rajman,

You cannot have two interface from the same system on the same subnet.

http://docs.hp.com/cgi-bin/fsearch/framedisplay?top=/hpux/onlinedocs/B2355-90725/B2355-90725_top.html&con=/hpux/onlinedocs/B2355-90725/00/00/41-con.html&toc=/hpux/onlinedocs/B2355-90725/00/00/41-toc.html&searchterms=interface%7csame%7csubnet%7cmultiple&queryid=20020215-184556

http://us-support2.external.hp.com/cki/bin/doc.pl/sid=dd94ec2d15ff02af9d/screen=ckiDisplayDocument?docId=200000007950529

Hope this helps.

Regds

Re: Two interfaces on the same subnet?

Sanjay_6 — Sat, 16 Feb 2002 02:48:38 GMT

Hi Rajman,

Even novell does not allow multiple interfaces on the same system to bind to the same subnet,

http://us-support2.external.hp.com/cki/bin/doc.pl/sid=dd94ec2d15ff02af9d/screen=ckiDisplayDocument?docId=200000030704577

Hope this helps.

Regds

Re: Two interfaces on the same subnet?

Ron Kinner — Sat, 16 Feb 2002 03:15:27 GMT

I think Microsoft allows this but the second interface is a backup to the first and is not active at the same time.

Ron

Re: Two interfaces on the same subnet?

Sanjay_6 — Sat, 16 Feb 2002 03:25:05 GMT

Hi,

Service Guard has something like that. If you have a standby card on the system connected to the netowrk and configured in SG, in case of a network card failure, the ip will get transferred to the standby card,

http://us-support2.external.hp.com/cki/bin/doc.pl/sid=fae88c100b67aec3ae/screen=ckiDisplayDocument?docId=500000000092632

Hope this doc will make it clearer.

Hope this helps.

Regds

Re: Two interfaces on the same subnet?

Helen French — Sat, 16 Feb 2002 04:11:09 GMT

Hi Rajman,

This will describe the answer:

http://us-support2.external.hp.com/cki/bin/doc.pl/sid=6aa57e860890b36f79/screen=ckiDisplayDocument?docId=200000048086687

HTH,
Shiju

Re: Two interfaces on the same subnet?

Helen French — Sat, 16 Feb 2002 04:16:42 GMT

Hi,

Again, see this thread. This says about two interfaces configured on the system in the same subnet. It is working ! But you can see the difference when system routing the information (incoming/outgoing):

http://us-support2.external.hp.com/cki/bin/doc.pl/sid=6aa57e860890b36f79/screen=ckiDisplayDocument?docId=500000000092418

HTH,
Shiju

Re: Two interfaces on the same subnet?

Duncan Edmonstone — Sun, 17 Feb 2002 21:06:52 GMT

This has been discussed a lot on the old newsgroup... comp.sys.hp.hpux, but also on the forum quite a bit - you can set a TCP tuneable parameter called ip_strong_es_model which ensures packets are sent back out the interface they are received on when you have two interfaces on the same subnet... do a seaRch on the forum on ip_strong_es_model, and it will turn up plenty of info on this - there are a lot of gotchas!

HTH

Duncan

Re: Two interfaces on the same subnet?

harry d brown jr — Mon, 18 Feb 2002 02:33:08 GMT

It is possible, but only with 11, as Duncan says you need to set ip_strong_es_model.

follow these threads:

look for Rick's and Duncan's answers.

http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0x775f46ff9277d511abcd0090277a778c,00.html

http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0xc57337f45ef7d4118fef0090279cd0f9,00.html

http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0xd6a379bffde7d4118fef0090279cd0f9,00.html

live free or die
harry

Re: Two interfaces on the same subnet?

Roger Baptiste — Mon, 18 Feb 2002 05:13:14 GMT

Thanks for the responses. For the folks who answered saying two interfaces can't have the same subnet -- My question had the netstat output showing the interfaces having the same subnet!.

Shiju's link seemed to be the most likely explanation and the point about ip_strong_es_model was intresting. (though i don't remember the system having that set).

thanks
-raj