Re: Getting slip(4) to work beyond two machines

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Tue, Mar 10, 2020 at 08:45:17PM +0000, Björn Johannesson wrote:
> Hello.
> 
> I'm trying to connect two machines via slip(4) and then get communication going outside those two.
> One of the machines have a NIC and I wan't to get the machine behind that one to reach outside.
> I have done this once long ago and I had jotted down these notes: https://pastebin.com/UK43aV5x
> I'm trying to get this working on again now. IP's have changed ofc.
> 
> On the machine w/o NIC I do:
> ifconfig sl0 create
> slattach -s 115200 /dev/tty00
> ifconfig sl0 inet 192.168.0.51 192.168.0.50
> route add default 192.168.0.50
> 
> On the machine with NIC:
> ifconfig sl0 create
> slattach -s 115200 /dev/tty00
> ifconfig sl0 inet 192.168.0.50 192.168.0.51
> arp -s 192.168.0.51 6c:3b:e5:1f:98:d8 pub proxy
> sysctl -w net.inet.ip.forwarding=1
> (The real NIC on this machine has ip 192.168.0.114 netmask ffffff00)

6c:3b:e5:1f:98:d8 is the mac address of your real nic, right ?

> 
> The two machines communicate fine with each other - however the forwarding part does not.
> 192.168.0.51 cannot communicate past .0.50 and cannot be reached from outside .0.50.
> There is also a _significant_ delay when communicating from .51 to .50 after adding the "route" command.
> If I ping .50 from .51 it takes many seconds (>10) before it starts sending packets.

Probably a DNS-related timeout.

You could try running tcpdump on the real NIC and watch for traffic from/to
192.168.0.51. Also watch for ARP traffic.

I've used a very similar setup with netbsd-8, it works.
I'm not use I tried with -9 yet.

Also in my notes I see that I set the sl0 MTU to 1500, maybe because by
default the MTU is too low.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--