Note that all of this is a routing issue, and assumes that SLIP or PPP are already working. If you can ping the other end of the link, then you are ready for the next level. Thank you for playing routing roulette!
Site W contains the WAN router (named
wan-router.domain) and the SLIP server host,
server.domain. Site S contains several hosts
on the same IP network as site W, one of which is the SLIP
client, client.domain. The other machines in site
S are S1.domain and S2.domain that
need to route through the host client.domain. Additionally, the
hosts at site S need to talk to several hosts at site
W: W1.domain, W2.domain, and
W3.domain. Additional hosts on each side can be accomodated by
just adding them to the appropriate host.
See the section on troubleshooting below
for things that can go wrong when using Proxy ARP.
Again, add additional If you also start slip or ppp from
/etc/init.d/network.local on the client (dialing side), it
should be started before you run the arp and route
commands, you probably will need a sleep after starting
ppp and before the arp commands. Experience shows
that at least 20 seconds (sleep 20) is needed for ppp
to initialize the interface.
Also, running a routing daemon like routed or gated will screw up the
routing we are doing by hand, so disable them:
This creates a default route pointing at client.domain. Putting
it in
If incorrect routes have been advertised (via routed, etc), then
it usually requires waiting the 3 minute route timeout after
correcting it before things could start working again.
The best solution would be to set up a quiet
Last modified: Fri Mar 12 13:49:25 1999
General Configuration Rule
Each end of the SLIP or PPP link needs to advertise both proxy-ARP and host
routes to the hosts on the other end of the link. This is
in addition to the normal default routes needed at site S
in order to communicate to the rest of
your network.
Quicky Proxy ARP Primer
ARP (Address Resolution Protocol) is how one host converts an IP (logical)
address into a MAC (physical: ethernet, etc) address. Proxy ARP is when a
host answers the request for for a MAC address for an IP address other than
it's own (in this case, for the hosts on the other end of the SLIP or PPP
link).
Configuration
The configuration on the two ends of the SLIP or PPP link is similar, but
there are enough differences that I will describe each one separately.
Configuration of server.domain
On host server.domain, create an
/etc/init.d/network.local script (with a symlink in
/etc/rc2.d to run after S30network) that contains
the following commands:
arp -s client.domain `netstat -ian | grep :` pub
arp -s S1.domain `netstat -ian | grep :` pub
arp -s S2.domain `netstat -ian | grep :` pub
route add host S1.domain client.domain 1
route add host S2.domain client.domain 1
Additional arp and route commands would need to
be added for each additional host at site S.
Configuration of client.domain
On host client.domain, create an
/etc/init.d/network.local script (with a symlink in
/etc/rc2.d to run after S30network) that contains
the following commands:
arp -s wan-router.domain `netstat -ian | grep :` pub
arp -s server.domain `netstat -ian | grep :` pub
arp -s W1.domain `netstat -ian | grep :` pub
arp -s W2.domain `netstat -ian | grep :` pub
arp -s W3.domain `netstat -ian | grep :` pub
route add host wan-router.domain server.domain 1
route add host W1.domain server.domain 1
route add host W2.domain server.domain 1
route add host W3.domain server.domain 1
arp and route commands for
each additional host that needs to be accessed accross the SLIP or PPP
link. If you are running IRIX-4.x, then you will need to add a default
route, as well (slip and ppp in IRIX-5.1 and pater
can do this automatically, see the respective man pages or my docs).
chkconfig routed off
chkconfig gated off
Configuration of Other Hosts at S
On each host at site S (S1.domain,
S2.domain, etc), create a file
/etc/init.d/network.local with a symlink in
/etc/rc2.d such that it will start after the
S30network script, and include the following commands:
route add net default client.domain 1
/etc/gateways (and run routed) should work
as an alternative to creating an /etc/init.d/network.local
script (though I haven't tested it in this case). Troubleshooting Problems
Cisco router is 4 hours, which is absurdly long.
Reducing it to 20 minutes (the default in Irix) or to
10 minutes helps a lot when fixing problems.
/etc/init.d/network.local
scripts ran fine, but the routes were trying to use ec0
interfaces instead of sl0. This was because the
SLIP interface was not up when the route
add commands were done. Part of the problem was that some
enterprising engineers manually added some of their own routes so
debugging was not straight-forward.
SLIP
link on IRIX 5.2, but this was not an option here. We
brought the SLIP link back up, and manually removed the
routes and re-added them to get them routed through the appropriate
interfaces. In addition, to prevent this happening again, or
actually, to make it much easier to recover, the route
add were removed from /etc/init.d/network.local
and a separate, manually run script was created to run from the
client at site S that does a killall
slip, then removes all the routes that used to be added in
/etc/init.d/network.local, kicks off SLIP,
re-adds the routes that used to be added in
/etc/init.d/network.local, then removes and re-adds
routes on the SLIP server with rsh server.domain. This
makes sure that all the routes are clean, and allows the end
initiating the SLIP connection to straighten the link
AND routes out with one command.
Scott Henry
<scotth@sgi.com>