Re: default route on other subnet

[Jean-Yves Migeon <jeanyves.migeon%free.fr@localhost>]

On Mon, 27 Jun 2011 17:56:44 +0000 (UTC), Pierre-Philipp Braun wrote:
> I'm not sure using a fake mac address (fe:ff:ff:ff:ff:ff) for guests' 
> network
> interfaces is linux dom0 specific.  I would rather assume that 
> behavior come
> from xen tools' network scripts, and that NetBSD's version of xen 
> tools is
> modified to handle things in a better way.  Duh, well, I can't see 
> any
> modification for that in pkgsrc/sysutils/xentools41/patches/ either,
> so I guess
> that's linux specific in the end: linux and netbsd may handle xen 
> network
> scripts' differently.

Nope, it's the network backend that sets the MAC address for all xvif 
interfaces. It increments the third byte by one.

http://nxr.netbsd.org/xref/src/sys/arch/xen/xen/xennetback_xenbus.c#297

I hope that other dom0 will not go down that route. It's a real mess 
after a while, especially when you starting using IPv6 and link-local 
addresses.

> So is it that dom0 network behaviour that prevents the netbsd guests
> from using
> static routes?  If so what should I do?  Submit a bug, ask for a 
> feature
> request, or simply fix the network scripts myself? (setting up the 
> right mac
> addresses shouldn't be so hard)

The issue is clearly dom0 related; I am not familiar with Linux's 
network stack, so do not know if you can set the MAC address for backend 
interfaces by force.

> For the record, here's what I do,
>   ifconfig xennet0 <GUEST_IP> netmask 255.255.255.255 up
>   route add -host <DOM0_IP> -link xennet0 -iface
>   ping -c1 DOM0_IP
> (no response)
> note. I've also tryed -link xennet0:GW_MAC_ADDRESS as David Young 
> suggested
> and after a while (one minute or so) I start getting those lines 
> repeatedly:
>   fe:ff:ff:ff:ff:ff tried to overwrite permanent arp info for 
> <DOM0_IP>

What is DOM0_IP? The IP associated to a vif? tap? a physical NIC? ... 
bridge interface?

Under BSD, routing and arp tables share a lot in common. What's their 
content before and after you are trying to set your static route (arp 
-a/netstat -r)?

--
Jean-Yves Migeon
jeanyves.migeon%free.fr@localhost