Subject: (ngtrans) conversion problems in nat-pt!

From: [email-masked]
Date: Fri, 30 Mar 2001 21:00:17 +0300

hello all,

I have found some problems regarding converting icmpv6 to icmpv4 error
messages using nat-pt. For example consider sending a packet from v4 host to
a v6 host...the packet will have saddr = v4 host's addr and daddr = a v4
addr assigned to the v6 end node by nat-pt box...the nat-pt box will
translate it to ipv6 packet with daddr = ipv6 addr and saddr = PREFIX::v4
addr ... and now suppose a router on the ipv6 side finds some problem with
this packet and sends back an icmp error message...the icmp message has the
saddr as the ipv6 router's address and dest addr as PREFIX:v4 address...

v4 host ------------> nat-pt -------------->router------>v6 host

my question is: when the nat-pt box translates this error message from ipv6
back to ipv4 packet what address should it use as the saddr in the
translated packet?? Since the router can be any host in the ipv6 subnet and
most probably might not have any ipv4 address assigned to it by the nat-pt
box. 

I haven't thought what happens in the case of SIIT..

regards
imran

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From: Erik Nordmark <[email-masked]>
Date: Fri, 30 Mar 2001 11:35:43 -0800 (PST)

> I haven't thought what happens in the case of SIIT..

FWIW RFC 2765 says to use the unspecied address (0.0.0.0) when translating
such packets from IPv6 to IPv4.

This means that traceroute from an IPv4 node through SIIT to an IPv6 endpoint
will atleast report something - you just can't tell the identity of
those IPv6 routers.

I don't see why NAT-PT wouldn't do the same.

  Erik