Two interfaces on the same subnet?

[Roger Baptiste]

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

[Sanjay_6]

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

[Sanjay_6]

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

[Ron Kinner]

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

Ron

[Sanjay_6]

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

[Helen French]

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

[Helen French]

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

[Duncan Edmonstone]

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

[harry d brown jr]

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

[Roger Baptiste]

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