News Group Posts

Using ipal and arp

IP aliases on SCO could be confusing. As explained at this other other ipal related post, you can also do:

/usr/internet/etc/ipal -n ipaddress

to just get a list of the commands that you'd need to run to get the ip alias you want.

From: evanh@sco.COM (Evan Hunt)
Newsgroups: comp.unix.sco.misc
Subject: Re: <> IP on same NIC , possible ?
Date: 9 Apr 1999 22:30:53 GMT
Message-ID: <7elv2t$t37$1@hobbes.sco.com> 


Don't blame me, I voted for spcecdt@deeptht.armory.com. (John DuBois).
>>> man ifconfig. look for 'alias'.
>
>>Yes ifconfig is the tool, you will need to also run an arp statement as
>>well so that two mac addresses can co-exist on the server at the same
>>time. Otherwise you will keep getting Arp table overwritten errors.
>
>Hmmm?  He wants two IP addresses on the *same* NIC.  That's one mac address.

That's true; the reason given for running arp was incorrect... but
actually, it may still be necessary to run arp.

Suppose you're on a class C network, 1.2.3.xxx.  Your system is named
1.2.3.4, and you want it to respond to another IP address as well.

If the new IP address is *also* going to be on the 1.2.3 subnet--
say 1.2.3.5--then you need to run arp to publish another IP address
for your existing mac address.  However, if the new IP address is a
whole different set of numbers (say, 4.3.2.1), then you don't
need to run arp (but your router does need to know how to route
to that address, of course).

I don't know if that made any sense at all.

Fortunately, on 5.0.4 and 5.0.5, there's a handy-dandy little tool
that can save you from having to understand any of this.  It's called
ipal, and all you have to do is type "/usr/internet/etc/ipal <ip address>"
and it will run ifconfig and (if necessary) arp *for* you.  Later,
if you want to delete the alias, run "ipal -d <ip address>".

The -f flag tells it to handle a list of IP addresses taken from
standard input, one to a line.  The -n flag tells it to print out the
commands it would normally have executed, without actually executing
them.

-- 
                  Evan Hunt   -   evanh at sco dot com

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