Subject: Re: gre encap destination = point-to-point destination
To: None <firstname.lastname@example.org>
From: Gert Doering <email@example.com>
Date: 11/06/2006 23:12:02
In muc.lists.netbsd.tech.net Ignatios Souvatzis wrote:
>On Sun, Nov 05, 2006 at 02:23:11PM +0100, Gert Doering wrote:
>> [ possibly recursive tunnel routing in gre(4) and hackish workarounds ]
>I was about to recommend asking Gert Doering as he's the only gre
>user I know about; but if hi isn't, then I, too, am in favour of
>disallowing such configurations at some level.
*g* - thanks.
Actually I might be biased because I work too much with Cisco, and have
been hit on my head a number of times with the dreaded "tunnel disabled
due to recursive routing" error message.
While at it, the gre(4) man page needs serious rework - the configuration
example actually *suggests* that it might be a fairly normal thing to have
the same IP address for "tunnel inside destination" and "tunnel outside
-------- snip ---------
On host A (NetBSD):
# route add default B
# ifconfig greN create
# ifconfig greN A D netmask 0xffffffff linkX up
# ifconfig greN tunnel A D
# route add E D
-------- snip ---------
- just last week someone showed up on a Cisco mailing list with a
similarily broked gre(4) configuration [on FreeBSD]...
The second IPv4 example in the man page is much more useful.
Actually it might make lots of sense to be able to run gif(4) and gre(4)
tunnels "ip unnumbered" - don't attach a transit network to the "inside",
don't create any implicit routes, and enable setting of routes to
# route add -net 18.104.22.168 -netmask 255.255.255.0 dev gif0
I'm not sure whether this is possible today - the man page examples
all require a next-hop address, as in
# route add -inet6 0::0/0 2001:db8:ffff::2 -ifp greN
- which seems to imply that when I wrote that, just setting
# route add -inet6 0::0/0 -ifp greN
("I don't want to know or care what the other end's inside IP address
is - this is a point-to-point tunnel, just stuff the packet it, we don't
do any sort of layer2-next-hop resolution anyway")
didn't work. But that was quite a while ago.
PS: the gif(4) man page could use some IPv6 examples :)
firstname.lastname@example.org fax: +49-89-35655025 http://alpha.greenie.net/mgetty/
If the presence of electricity can be made visible in any part of a circuit, I
see no reason why intelligence may not be transmitted instantaneously by
electricity. -- Samuel F. B. Morse