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Re: draft-wbeebee-ipv6-cpe-router-03
On Wed, 19 Nov 2008, Brian E Carpenter wrote:
How about auto-enabling 6to4 assuming it can actually reach a
192.88.99l.1 gateway?
That doesn't guarantee connectivity; you actually need to see an
IPv6 reply before you know that 6to4 is working. So you really
need to enable 6to4, run a reachability test, and disable it if
no response.
Well, while this is one possible approach, and it may be the simplest
test from a human perspective, an implementation could do a test
without enabling 6to4.
You just need to craft a packet using a raw socket that resembles that
kind of 6to4 packet, and watch for replies. As an example of how
Microsoft has done it, the implementation sends a proto-41 packet with
IPv6 TTL=1 to an IPv6 address corresponding relay's v4 address, so the
relay will return _something_ if connectivity at least up to the relay
is working, the relay has v6 enabled, etc.
Live example from a relay:
08:31:01.202671 IP (tos 0x0, ttl 119, id 174, offset 0, flags [none], proto IPv6 (41), length 68) 93.106.184.x > 192.88.99.1: IP6 (hlim 1, next-header ICMPv6 (58) payload length: 8) 2002:5d6a:b8xx::5d6a:b8xx > 2002:c058:6301::c058:6301: [icmp6 sum ok] ICMP6, echo request, length 8, seq 2
08:31:01.202752 IP (tos 0x0, ttl 40, id 32297, offset 0, flags [none], proto IPv6 (41), length 116) 192.88.99.1 > 93.106.184.x: IP6 (hlim 64, next-header ICMPv6 (58) payload length: 56) 2002:c058:6301::1741 > 2002:5d6a:b8xx::5d6a:b8xx: [icmp6 sum ok] ICMP6, time exceeded in-transit, length 56 for 2002:c058:6301::c058:6301
--
Pekka Savola "You each name yourselves king, yet the
Netcore Oy kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings