Thanks to the people who responded especially:
Jason Yanowitz <yanowitz_at_eternity.cs.umass.edu>
Patrick O'Brien <pobrien_at_draco.harvard.edu>
David Warren <warren_at_atmos.washington.edu>
"Peter Hunt, NaC (Australia)" <hunt_at_ozy.dec.com>
who gave good hints. The problem was a very simple one (obviously not for 
me but for the DECpeople who solved it):
reboot of locr (see below) because only then it reads the /etc/rc.config 
and especially the ROUTER='yes' flag to enable IP forwarding.
I didn't try this because the machine has important server functions.
My original message follows:
On Sun, 7 Jan 1996, Rudolf Gabler wrote:
>   Hello managers,
> 
>   I have the following net configuration:
> 
> 
>      --------    ethernet      --------
>      | remh |------------------| remr |  remote.net (in the 192.168 .. range)
>      --------                  --------
>                                  |
>                                  v
> 
>                                 ISDN ppp link
>                
>                                  ^
>                                  |
>     ---------     ---------    --------    ethernet       -
>     | loch1 |-----| loch2 |----| locr |------------------ | local.net class B
>     ---------     ---------    --------                   -
> 
>   remr and locr work as router for the two nets and have both two interfaces
>   (remr: pppremr and ethremr and locr: ppplocr and ethlocr).
>   locr is a AXP 3000/300LX with isdn interface and the x25 distribution which 
>   includes isdnppp. The interface is automatically created during isdnstart.
> 
>   Here my problem:
>   
>      On locr there exist static route for the remote.net over the ppp link.
>      I can ping/telnet to remh remr from locr and everything works as 
>      expected. 
> 
>      On loch2 (or any host on local.net) there exist a route to ppplocr and I
>      can ping/telnet to this. Also on this hosts exist a route for remote.net
>      over this ppplocr interface 
>   
>        b u t
> 
>      I can't ping or telnet any machine on the remote.net from other hosts
>      but locr on the local.net.
> 
>  What did I missed?
> 
> 
> I would be greatful for any advice.
> 
> Rudi Gabler
> 
>  +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  !Rudolf Gabler                                                  !
>  !Uni.-Sternwarte Muenchen     Internet:  RUG_at_USM.Uni-Muenchen.DE!
>  !Scheinerstr. 1               Voice:     +49-89-98290305        !
>  !81679 Muenchen  FRG          FAX:       +49-89-92209427        !
>  +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Received on Thu Jan 11 1996 - 08:49:51 NZDT