topic Re: Two NICS on Same Subnet???? in Operating System - HP-UX

Two NICS on Same Subnet????

joe_91 — Thu, 19 Sep 2002 20:02:44 GMT

Team:

We have MC/SG environment. Lan1 and Lan3 are the primary NIC cards and here are the addresses..
lan1: 135.51.27.23
subnetmask: 255.255.255.192

lan3: 135.51.103.90
subnetmask: 255.255.255.224

I was told that they are in the same subnet. Is that so? Please tell me how network gurus? Also please tell me whether i can carry on w/o changing the ip OR subnetmask?

Thanks
Joe.

Re: Two NICS on Same Subnet????

John Poff — Thu, 19 Sep 2002 20:22:12 GMT

Hi Joe,

I'm definitely not a network guru, but I'll give it a shot. Your subnet mask specifies the hostid portion of your IP address. The first subnet mask specifies 6 bits for the hostid, and the second subnet mask specifies 5 bits for the hostid. Looking at it that way, I don't see how the first IP address could possibly consider the second one to be on its subnet. If they were both 135.51.27 or both 135.51.103, it might work.

Is this setup in an existing MC/SG cluster, or is this a new cluster you are trying to configure? When you run 'cmcheckconf', it will complain loudly if the lan cards aren't configured on the same subnet.

Like I said, I'm not a network guru, so I could be wrong.

JP

Re: Two NICS on Same Subnet????

Ray Brewer — Thu, 19 Sep 2002 20:37:02 GMT

The two IP's you have given are not in the same subnet. If they were they would have the same subnet mask. If you want to use these two IP's then I think you would have to change the subnetmask on both to 255.255.0.0. Also your network people would have to define a 135.51.0.0 network that could route to whichever networks you need to communicate with.

Ray

Re: Two NICS on Same Subnet????

Sridhar Bhaskarla — Thu, 19 Sep 2002 21:25:00 GMT

Nop. They are different subnets. You shouldn't have any problem setting up that way.

-Sri

Re: Two NICS on Same Subnet????

Sridhar Bhaskarla — Thu, 19 Sep 2002 21:48:52 GMT

Got little more time before call it a day today. Though you have a class B address, you are treating it like a Class C address.

I am sure who designed the subnetmasks might have already told you. The IP Address range in the first case (lan1) is 135.51.27.1 - 62 with the broadcast being .63. 192 will give you four subnets (two are traditionally valid but all four are practically usable).

In the second case, the range you will get in the subnet you configured is 135.51.103.65-94 with the broadcast .95. 224 will spawn 8 subnets.

I just wanted to make sure you know the ranges. For ex., if you configure another system in the same LAN with the IP 135.51.103.100 with the mask 255.255.255.224, these two won't talk unless you have a router in between.

-Sri

Re: Two NICS on Same Subnet????

Anil C. Sedha — Thu, 19 Sep 2002 21:54:52 GMT

They are not on the same subnet buddy.

Ideally you should have had the subnet masks 255.255.0.0

You may continue without changing anything

Regards,
Anil

Re: Two NICS on Same Subnet????

joe_91 — Fri, 20 Sep 2002 14:09:49 GMT

Team:

You are all right. Thanks. But my problem is we made some SG changes to have the messageque to route thru lan3, but what i see (netstat -i) is
the packets go out thru lan3 but comes in via lan1. How could that happen? Also sometimes it never uses lan3 (I have set up SG with lan1 and lan3 as primary with lan failover to lan4 and lan5).
Can someone help here?

Thanks
Joe.

Re: Two NICS on Same Subnet????

Sridhar Bhaskarla — Fri, 20 Sep 2002 14:19:05 GMT

Hi Joe,

It depends on how you configured your clients and your routes on the server. As stated before, these two are seperate networks and it depends on the default route you setup on the server to send the packets out.

If your client is on a different subnet than what you have and is configured to connect to lan1's IP address, you will get the traffic through that interface. Since the client is on a seperate subnet, your system will send the packets back through the default router that is reachable through lan3.

-Sri

Re: Two NICS on Same Subnet????

joe_91 — Fri, 20 Sep 2002 14:24:06 GMT

Hi Sri:

Thanks. Is there a way i can confirm this???

Thanks
Joe.

Re: Two NICS on Same Subnet????

Sridhar Bhaskarla — Fri, 20 Sep 2002 14:30:48 GMT

Hi (again) Joe,

1. Get the IP address (IPc) of the client that your system is using to connect to. Run the following command on the server.

ping -o IPc -n 2

Observe the path that you get at the end.

2. Get the IP address (IPs) that the client is using to connect to your server.

On the client, run

ping -o IPs -n 2

If it doesn't support -o, try traceroute or any other command that can give you the trace.

-Sri