Re: [Int-area] IP-in-IP, TTL decrementing when forwarding and BITW

On 6/2/06, Joe Touch <touch@isi.edu> wrote:
> Do you recall what was the case that motivates the condition ("IF")
> regarding how TTLs interact with forwarding on the head and tail of tunnels?

I was only peripherally involved, but my recollection is that the
intent was to make a host<->host tunnel look the same as a physical
point-to-point interface.  The TTL decrement that it refers to is
simply the TTL  decrement that you would perform during IP forwarding,
and you're not doing IP forwarding if you originated the packet on the
tunnel interface.

(Talking about this is a little tough without shared terminology for
some of these concepts.  Steve Deering drew me a picture long, long
ago which I always wanted to turn into ASCII art for an I-D but never
did.)

Given that, the BITW implementation should decrement the TTL if it
thinks it's a router, or not if it is pretending to be part of the
host.

  Bill

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