On Sun, Nov 08, 2009 at 09:42:00AM -0500, lanas wrote:
>   Is it possible to connect two eth interfaces from different umls
> together w/o using a switch ?  I've tried by having them two go
> through different host tap devices, as in:
> 
> tunctl -u user -t tap0
> ip a a 192.168.2.100/24 dev tap0
> ip l s dev tap0 up
> 
> tunctl -u user -t tap1
> ip a a 192.168.2.101/24 dev tap1
> ip l s dev tap1 up

No, don't assign IP addresses to the tap interfaces. Set them "up",
then add them to a server-side bridge, which can even be bridged to
real Ethernet if you like. See brctl(8), and probably numerous
examples in UML documentation.

> These two umls cannot ping each other.  In fact, tap0 and tap1
> tcpdumps on the host side show no ICMP traffic.  I'm doing
> something squarely wrong, but what is it ?

This could be a matter of running your UML as "user". ICMP is a
privileged operation, note that your ping(1) binary is SUID.

On further thought, I doubt that is the issue, yours is just a
lack of routing, and tap should avoid the ICMP privilege problem.
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