Subject: Clarification in Tunnel

From: "Niveda Monyvannan" <[email-masked]>
Date: Tue, 20 Feb 2001 15:48:37 +0530

Hi all,
        Should configured tunnel always be a duplex one?

    A-------------B========C--------------------D

Let us say B is configured to encaptulate v6 packet to C. Should C have
a configured tunnel interface towards B to receive a encaptulated
packets from B?

take a look at the following scenario u still have reachability from D
to A. 
               A             D            F 
               |             |            |
               B======>======C======>=====E     

and THERE IS A CONFIGURED TUNNEL HALF-DUPLEX ONE, FROM E TO B. This way
packets from D can reach A right ?

Regards,
Niveda

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From: Dave Marquardt <[email-masked]>
Date: Wed, 21 Feb 2001 09:52:00 -0600

>         Should configured tunnel always be a duplex one?

Are you talking about tunneling IPv6 over IPv4?  I don't think you
need to have a duplex tunnel.  Try considering the tunnel "interface"
to be transmit only, i.e. half duplex.  The tunneling RFCs (2893 and
2473) treat tunneling as an encapsulation mechanism and decapsulation
is just "normal" protocol operation.  So I would say, no, you don't
need to have a full duplex tunnel.

> a configured tunnel interface towards B to receive a encaptulated

No, I don't think so.

> packets from D can reach A right ?

Okay, that's a good ROUTING setup.  Routing can always be assymmetric,
so this works fine.

One thing this made me wonder about, though.  Let's say we have your
ABCD scenario above:

C is a router.  All nodes have IPv6 addresses, call them A6, B6, C6,
and D6.  B and C have IPv4 addresses, B4 and C4.  Is it "legal" to
configure a tunnel from B to D by using B4 as the local IPv4 address
and C4 as the remote address, and configuring the local IPv6 address
as B6 and the remote IPv6 address as D6?  Packets to D would get
encapsulated at B in an IPv4 packet with B4 as source and C4 as
destination.  When the packet reached C, it would be decapsulated.
Since C is a router, it would forward the packet on to D.  Is this
allowed?  It's confusing, but I don't see why it wouldn't work.
-- 
Dave Marquardt
Sun Microsystems, Inc.
+1 512 401-1077
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From: Peter Bieringer <[email-masked]>
Date: Wed, 21 Feb 2001 21:22:42 +0100

> > a configured tunnel interface towards B to receive a encaptulated

Hmm, but C have to know about the IPv6 network between A and B and must 
route/tunnel such (response  from D) packets to IPv4-B back again.

>as B6 and the remote IPv6 address as D6?

Why would you setup D6 on C? What is the reason for that?

>   Packets to D would get

Perhaps it's better to clarify such szenarios using unnumbered tunnels 
first (for routing/tunneling issues this is enough IMHO).

On Linux using NBMA tunnels are the IMHO easiest method to setup tunneling. 
Only needed information for tunnel: IPv6 network of destination and IPv4 of 
tunnel endpoint, e.g.
         C must know about IPv6net(A-B) and IPv4(B)
         B must know about IPv6net(C-D) and IPv4(C)

That's all

Setup on Linux: route -A inet6 add $IPv6net(foreign) gw ::$IPv4(foreign 
tunnel) dev sit0
Perhaps on Solaris the same way can be done.

         Peter

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From: "Tony Hain" <[email-masked]>
Date: Tue, 27 Feb 2001 17:19:47 -0800

> allowed?  It's confusing, but I don't see why it wouldn't work.

The confusing part is asking about the tunnel as being from B to D. The
tunnel in your example would be from B to C, with the traffic flow between B
and D. This is legal, and is the basic premise for the 6to4 router as
defined in rfc3056. While 6to4 does this with implicit tunnels, there is no
operational difference between that and a configured tunnel between routers.