Re: problem with router---NAT and caching?

From: Phillip Helbig---remove CLOTHES to reply (helbig_at_astro.multiCLOTHESvax.de)
Date: 04/03/05 

Date: Sat, 2 Apr 2005 22:43:56 +0000 (UTC)

In article <1112477771.30a44d6f285e33f4fba0a98847877464@teranews>, JF
Mezei <jfmezei.spamnot@vaxination.ca> writes:

> How do you change the IP address of your VMS box ? Do you use the
> TCPIP$CONFIG menus, or the TCPIP> Utility ?

The latter.

> Do you destroy the old
> interface with SET NOINTERFACE ?

No.

> Have you used ifcongig -a which displays kernel (live) data to ensure
> that the TCPIP commands actually took effect on the running system ?
>
> (you can also use ifconfig to set the ip address of an interface)

I guess this is as good a time as any to learn ifconfig. (With 5.4,
which I will move to soon, this is necessary for some things, even for
some things which in 5.3 are possible over the TCPIP> interface.)
 
> > That's what I expected, and why I am surprised that it didn't work.
> > Even if it is an arp problem, why does it affect only port 6000?
>
> Are you sure about that ? If you change the IP address of your VMS
> systems, then you have to update your router's NAT table to tell it to
> forward the required ports to the new IP address.

Yes, of course.

> If your VMS box is
> still responding to the old IP address and your router is still
> ofrwarding other ports to the old IP address, tben those ports would
> still work.

Yes, but that's not the case here.

After changing the address on the VMS box and the router, I can then
come in from outside via telnet, ftp etc and everything works fine.
Only port 6000 doesn't work. I can tell the router to forward packets
to another box on the LAN. This takes place immediately. It's only a
problem with port 6000, and only if I use a new IP address on the same
machine which previously was the recipient of forwarded packets from the
router with a different IP address.

> > to another machine on the same network. The entire TCPIP configuration
> > looks fine on both machines (VAX and ALPHA). However, on the VAX I
> > cannot see the ALPHA at all: it says it doesn't respond.
>
> Have you tried to traceroute to it ? Does it go to the router first ?

Yes and no.

> Does your VAX have a default route pointing to the right ip address (the
> router) ?

Yes.

> Are you sure that both VAX and ALPHAs think that they are in the same
> subnet (hence no need to go via router).

Yes.

I restarted TCPIP on the ALPHA, and now connectivity is OK.

Note that this is V5.0A - ECO 1 on the ALPHA and 4.2 on the VAX. These
are just some machines I need to get up and running so I can do some
tests etc. I will then upgrade/fresh install to the newest stuff.
Thus, small bugs won't surprise me, but really basic stuff which causes
problems does.

> Aoso, at the TCPIP prompt, SHOW ARP seems to be more "VMS" than "arp -a"
> which simply spawns a subprocess to execute the foreign arp command.
> Also gives you number of seconds since last interaction.

Thanks; I prefer VMS-style stuff if available!