Routing with SLIP & Ethernet

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From: kmedcalf@io.org (Keith Medcalf)
Newsgroups: comp.os.os2.networking.tcp-ip
Subject: Re: Routing with SLIP & Ethernet
Date: 11 Oct 1994 13:17:50 GMT
Organization: Keith Medcalf and Associates
Lines: 86
Distribution: world
Message-ID: <37e39u$4hh@ionews.io.org>
References: <36ioic$t4u@geraldo.cc.utexas.edu> <2e965dde.45585452454d45@extreme.mayn.sub.de>
Reply-To: kmedcalf@io.org (Keith Medcalf)
NNTP-Posting-Host: zealot.net2.io.org
X-Newsreader: IBM NewsReader/2 v1.02

In <2e965dde.45585452454d45@extreme.mayn.sub.de>, pilgrim@extreme.mayn.sub.de (Bjoern "Pilgrim" Karlowsky) writes:
>Hi Kevin!
>: *************************               *************************
>: *    128.97.97.10 (lan0)*===============*    128.97.97.30 (lan0)*
>: *                       *   ethernet    *                       *
>: *    128.23.35.20 (sl0) *               *                       *
>: *************************               *************************
>:         ||
>:         ||
>:         ||  SLIP
>:         ||
>:         ||
>: *************************
>: *    128.23.35.250      *
>: *                       *
>: *                       *
>: *************************
>
>: The current routing table for PC #1 is
>: 128.97.97.0     128.97.97.10            lan0
>: default         128.83.35.250           sl0
>
>: The current routing table for PC #2 is
>: 128.97.97.0     128.97.97.30            lan0
>
>
>: Any help or information is appreciated.
>
>: Thanks,
>: Kevin
>
>
>Kevin Tapperson (kevintap@mail.utexas.edu) wrote:
>
>: The ethernet network works fine, and the SLIP connection works fine, however PC 
>: #2 cannot communicate with computers on the other side of the SLIP connection. 
>: (ie. packets are not being transfered between the ethernet (lan0) and SLIP (sl0)
>: interfaces)
>
>: Is the problem with the routing, if so, how should this be routed.
>
>You have to publish an ARP entry onto the lan for the SLIP machine with the
>hardware adress of the lan0 interface from PC#1.
>You get the adress with netstat -n there. And do:
>arp -s <hostname_slip_far> <hardwareadress_lan0_pc1> pub
>

You have violated rule uno of using SLIP -- you forgot to use a
separate network or subnetwork for your SLIP network.  It works
exactly as it should work.  You must not mix topology types within
the same subnet.  TCP/IP was not designed for such foolish setups.

Alternatively, you can merely run dynamic routing on all the machines
in the network, that is, detach routed -g -s on EVERY MACHINE ON THE
NETWORK including making sure that RIP routing is active on all the
routers in the network.

Then, make sure that the GATEWAYS file on the node that connects to the
badly formed SLIP node is correct, and that the GATEWAYS file on the
SLIP node with the defective address is correct.  And that the GATEWAYS
file on the default router for your network accurately reflects the
remote routers that access the slip nodes. Then all will work as you
expect.

Isn't Dynamic Routing wonderful?  This is precicesely why it was
invented.  Isn't it cool that computers on a network can talk to
each other and tell them how to route packets from one place to
another?

You can also make the defective SLIP node arpable by proxy, however then
you will have to contend with the difficulties created by having
inaccurate hop counts to the outside world.  It may truncate the extents
of the world a little, but that should not be too much of a problem,
depending on how far you are from the rest of the internet.

Your proper course of action is to allocate a non-arpable network number
to use as you slip network.  Then run routed on both sides of all slip
connections.

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| Keith Medcalf              | Internet:  kmedcalf@io.org            |
| Software Engineer          | SnailMail: 275 Broadview Ave #152     |
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