22 Nov
2019
22 Nov
'19
9:38 a.m.
Scott,
I did a little digging but my C is rusty and I’m not a kernel hacker either. It was Linux
4.19.0.6 amd64 as provided by Debian 10.
I ended up solving the problem by doing 4in6 (IPIP6) and then 6in4 as an inner layer to
get tunneling of both v4 and v6 in from the gateway. For IPv4 outer endpoints is 4in4
(IPIP) and then 6in4 inside that. Works well and the packet header overhead isn’t
problematic so far.
Jason
From: Scott Nicholas <scott.nicholas(a)scottn.us>
Sent: Friday, November 22, 2019 7:58 AM
To: AMPRNet working group <44net(a)mailman.ampr.org>
Cc: Jason McCormick <jason(a)mfamily.org>
Subject: Re: [44net] Linux GRE Tunnels
I'm no gre expert. I have only used it over v4. But I am willing to look at code.
What kernel version are you using?
On Sat, Nov 16, 2019, 9:01 PM Jason McCormick via 44Net
<44net@mailman.ampr.org<mailto:44net@mailman.ampr.org>> wrote:
I'm running into an interesting problem I thought maybe someone in this community
would have run into before.
We're working on a project to redesign and re-IP our entire radio network. Part of the
goal is to stop using OpenVPN and IPSec tunnels (long story) and move exclusively to
GRE-based tunnels. The plan is to have two Linux VPS hosts running at a provider with our
44Net allocation and an IPv6 allocation advertised and then routed into the radio network
over GRE tunnels to 3 different locations that are all backhauled together. One of the
primary goals is to do dual-stack throughout the network.
I have one site setup working perfectly - "gre0". It's passing IPv4 and
IPv6 traffic over the GRE tunnel. One *key* point to this is that the GRE connection
endpoints are iPv6. IPv4 isn't doable for this connection (again, long story but not
an option). When setting up the second GRE tunnel "gre2", nothing would work
even though the configuration was the same EXCEPT for the fact that the second GRE tunnel
was using IPv4 addresses for the GRE tunnel endpoints. Linux keeps spitting out a very odd
error when I try to ping across the tunnel I cannot find reasonably documented anywhere:
ip6_tunnel: gre2 xmit: Local address not yet configured!
The key was the "ip6_tunnel" part that took me awhile to figure out. After
experimenting, I've found that if I have one GRE tunnel using IPv6 endpoints (ip -6
tunnel add gre0 mod ip6gre) and one using IPv4 endpoints (ip tunnel add gre2 mode gre),
only the gre0 tunnel will work and the gre2 tunnel seems to believe it's missing an
IPv6 address. If I delete the gre0 tunnel, the gre2 tunnel immediately beings working with
both IPv4 and IPv6 traversing the GRE. I cannot find any documentation that describes this
behavior or why it would be the case.
I can't switch to IPIP tunnels because I haven't found a way to do a dual-stack
tunnel between the endpoints - seems like you can only do one IPIP tunnel between two
endpoint IPs regardless of type (ipip, ipip6, ip6ip6, sit)
Anyone have any deep wisdom on GRE tunnels?
Jason
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