topic Re: "Multi-homed" host in Operating System - HP-UX

"Multi-homed" host

Don Bentz — Tue, 24 Jul 2001 19:31:37 GMT

We will be "merging" a K260 (11.00 32-bit)and a G50(11.00 32-bit) into a single server, an N4000 running HPUX 11.00 64-bit. I believe I can access the new (N4000) machine with 2 separate network cards utilizing the "old" IP addresses. I remember something from when I was on a Sun machine about having to modify a configuration file to prevent your system from thinking it's a "router". Does anybody right offhand know what Iif anything) I will need to do in this case?

Re: "Multi-homed" host

Don Bentz — Tue, 24 Jul 2001 19:40:20 GMT

I believe I've found it. In /etc/rc.config.d/nddconf, there is a reference to TRANSPORT_NAME[0]=ip
NDD_NAME[0]=ip_forwarding and an NDD_VALUE[0]=0. I suspect that this implies the host is not a router. On the Sun machine I set the IP_FORWARDING value to 0. If anybody has a different answer, please let me know... thanks.

Re: "Multi-homed" host

A. Clay Stephenson — Tue, 24 Jul 2001 19:53:06 GMT

Hi Don,

Yes, that's the puppy. I do have one concern, are these two NIC's on the same subnet?

Re: "Multi-homed" host

Don Bentz — Tue, 24 Jul 2001 20:05:49 GMT

Yes they are. The reason we're doing this has to do with the users' local "tnsnames" files and the IP addresses they're accessing the machines by. Also, the transition between the G50 and the N4000 will be done at a different time (sooner) than the K260. Initially we'll be using a "back to back" connection between each of the old servers and the N box to facilitate "no traffic" data transfer.

Re: "Multi-homed" host

John Poff — Tue, 24 Jul 2001 20:12:50 GMT

Hello,

So what would happen if he didn't change the setting and ran two interfaces?

JP

Re: "Multi-homed" host

A. Clay Stephenson — Tue, 24 Jul 2001 20:33:58 GMT

Uh-oh Don,

There's trouble right here in River City.

Note this (copied from 'Installing and Administering LAN/9000 Software):

Multiple LAN interfaces, intermittent failures: I have been having problems getting the two LAN interfaces on my system to operate at the same time. Occasionally the ethernet cards stop communicating with remote systems. When this happens, the remote system also cannot communicate with the local system.

Answer: Check that the two interfaces on your system do not have the same network number or, if you are subnetting, the same subnet address. If both LAN interfaces have the same value in the network (subnet) address portions of the IP address, the cards may not be enabled simultaneously (although they may both run separately.)

You may want to examine the document:

http://docs.hp.com/hpux/onlinedocs/B2355-90725/B2355-90725.html

The bad news is that this configuration almost works well but sometimes packets get interleaved between the two devices.

Clay

Re: "Multi-homed" host

Don Bentz — Tue, 24 Jul 2001 21:43:34 GMT

So if I understand what you're saying, if host A has an IP address of 198.10.2.33 and host B has an IP address of 198.10.4.1, and they have different NETMASK values (255.255.0.0 and 255.255.255.0, respectively), then, in theory, there isn't a problem. Right?

Re: "Multi-homed" host

Don Bentz — Wed, 25 Jul 2001 14:04:17 GMT

Well, Clay. After looking at the link you gave me I found that you can specify 2 IP addresses on the same subnet as long as you use the same card (eg. lan0:0 & lan0:1), but you cannot do so with 2 different cards and you cannot get away with specifying different subnet masks to solve the problem. Thanks for the very helpful caution. I will have to work out the issues and determine which of my 2 hosts's IP addresses/subnets is most precious....

Re: "Multi-homed" host

A. Clay Stephenson — Wed, 25 Jul 2001 14:13:48 GMT

Hi Don,

I'm glad you found the workaround; but here's another one. Why not make a CNAME entry in your DNS tables for the second server so that both hostnames resolve to the same IP address. If you are using NIS for hostname resolution then you would add an alias to the hosts map.

Please don't tell me that you are not using DNS or NIS; otherwise, you will need to change a herd of client host tables to add an alias.

Regards, Clay

Re: "Multi-homed" host

Don Bentz — Wed, 25 Jul 2001 16:26:44 GMT

Yes, we are using neither. The reason we are trying to retain the "old" IP address is that we have many "clients" who are accessing one of the machines by IP address and we don't want to have to go through having to have them all change their files they use to access it.

Re: "Multi-homed" host

rick jones — Wed, 25 Jul 2001 16:59:56 GMT

a cou;ple things. first, unless the K had an HSC 100BT interface, I suspect the performance sum of the NICs in the two old systems would be less than the perf limit of the 10/100 interface in the N replacing them.

that being the case, it would be simplest to simply use one NIC and have both IP addresses assigned to it.

if you really really want to run two nics, you can probably do it - but to get the behaviour you likely expect, you need to set ip_strong_es_model to a value of one. that will mean that source IP addresses will be used in route lookups, which tends to mean that replies will go back out the same interface on which the request was received. it also means that packets with the ip address of NIC A will _not_ be accepted on NIC B.

one other way to run two NICs would be to trunk them together with Auto Port Aggregation. This will look like one NIC to the transport, and you would assign both IP's to that virtual interface. If one NIC fails, traffic will continue to flow through the second NIC.

Re: "Multi-homed" host

weller — Thu, 26 Jul 2001 13:46:46 GMT

which MAC-addresses have both cards?

Re: "Multi-homed" host

Don Bentz — Tue, 31 Jul 2001 13:38:08 GMT

Thanks for the tips, Rick. Where is the ip_strong_es_model parameter set? And is there a link where I can read something about it and related items?

Re: "Multi-homed" host

Don Bentz — Tue, 31 Jul 2001 14:28:38 GMT

Never mind, Rick. I found it in the list of "supported" parameters for NDD. I suppose this means it is to be added to /etc/rc.config.d/nddconf?