If you are going to connect machines with different kind of network
cards, you need an router. Maybe it's simplest to add an mtu 1500 card
to one of the machines and use that one as a router between the two
networks. Stay clear of NAT, it seems to me NAT is just f*** up the
whole network.

Cincerely,
Sigmund

Tue, 29,.08.2006 kl. 18.16 +0200, skrev Tobias Nygren:
> I have a gigabit ethernet network with mostly mtu 9000 equipment.
> I need one of my mtu 9000 machines (ip .33) to talk one that does only
> mtu 1500 (.33). This can be done by manipulating the routing table.
> 
> ti0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 9000
>         capabilities=3f00<...>
>         enabled=0
>         address: 00:60:6d:21:1d:9f
>         media: Ethernet autoselect (1000baseSX full-duplex)
>         status: active
>         inet 172.18.1.33 netmask 0xffffffe0 broadcast 172.18.1.63
>         inet6 fe80::260:6dff:fe21:1d9f%ti0 prefixlen 64 scopeid 0x1
> 
> Ping from 172.18.1.33 to 172.18.1.35 with packets smaller than 1500 works.
> I tried "route add -host 172.18.1.35 -mtu 1500 -interface 172.18.1.33",
> which gives this netstat -rn output:
> 
> 172.18.1.32/27     link#1             UC          -   ti0
> 172.18.1.34        00:60:08:f6:08:bc  UHLc        -   ti0
> 172.18.1.35        172.18.1.33        UHS      1500   ti0
> 
> But now no ping packets leave the box. Maybe I misunderstood the
> intended use of the -interface flag?
> 
> So instead I added a static arp entry for .35:
> 
> arp -s 172.18.1.35 00:50:56:00:00:01
> route change -host 172.18.1.35 -mtu 1500
> 
> Which gives this netstat -rn output:
> 
> 172.18.1.35        00:50:56:00:00:01  UHLS     1500   ti0
> 
> This works as expected. Packets larger than 1500 get fragmented
> on their way out.
> 
> Is is possible to fragment packets to 172.18.1.35 without a static
> arp entry?
> 
> Thanks,
> -Tobias