[wplug] Talk, IP masquerading, and port forwarding

Hagbard Celine goldandappel at softhome.net
Tue Dec 19 16:36:39 EST 2000


Hi people,

I am trying to use talk with IP masquerading and port forwarding, and am running
into a situation.  Maybe some of you have some ideas?

Here's the story:  I lave a private LAN masqueraded to the internet.  There is
also a dynamic hostname for the router (fnordnet.dnsalias.net).  Masquerading
rules are as follows:

ipchains -P forward DENY
ipchains -A forward -s 192.168.0.0/24 -j MASQ

As concerns masquerading, everything works well, and has for over a year.

Recently, I had the idea to run talk on one of the private machines, for the
purpose of communicating with folks Out There who are using talk, ntalk, or
ytalk.  Knowing that I was going to have to forward packets from router to
internal box, I installed these forwarding rules:

ipmasqadm portfw -f
ipmasqadm portfw -a -P udp -L x.y.z.w 517 -R 192.168.0.11 517
ipmasqadm portfw -a -P udp -L x.y.z.w 518 -R 192.168.0.11 518

where x.y.z.w was the IP bound to ppp0 at the time, and 192.168.0.11 is the
private box in question (the one I'm sitting at at the moment).

A friend and I undertook to test this setup.  We were /msg-ing back and forth
on IRC at the time, so I did a /whois to get her hostname.  She ran

ytalk fnord at fnordnet.dnsalias.net

to try to get to me (I was logged into fnord on a second VT), and I did receive
a talk request.  Funny thing is, though, that her entire host name was not
specified in the request.  Given that she was uuuu at xxxxxx.yyyyy.zzz, I saw

Talk request received from uuuu at yyyyy.zzz

I tried to run

talk uuuu at yyyyy.zzz

and also

talk uuuu at xxxxxx.yyyyy.zzz

but could not reach her with either invocation.

Does anyone have an idea of what might he happening here?  Her request reaches
me, so it appears that port forwarding is working.  Do I have to do
something besides what I am already doing else to get my packets out to her?
Port forwarding is a unidirectional thing, of course, but I was hoping I could
get talk packets out with my system as-is...

Any assistance would be greatly appreciated,
Hagbard




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