Detect and rewrite a prefix embedded in an ICMPv6 original packet that was
rewritten by a corresponding DNPT/SNPT rule so it will be recognised by
the host that sent the original packet.
Example
Rules in effect on the 1:2:3:4::/64 + 5:6:7:8::/64 side router:
* SNPT src-pfx 1:2:3:4::/64 dst-pfx 5:6:7:8::/64
* DNPT src-pfx 5:6:7:8::/64 dst-pfx 1:2:3:4::/64
No rules on the 9🅰️b:c::/64 side.
1. 1:2:3:4::1 sends UDP packet to 9🅰️b:c::1
2. Router applies SNPT changing src to 5:6:7:8::ffef::1
3. 9🅰️b:c::1 receives packet with (src 5:6:7:8::ffef::1 dst 9🅰️b:c::1)
and replies with ICMPv6 port unreachable to 5:6:7:8::ffef::1,
including original packet (src 5:6:7:8::ffef::1 dst 9🅰️b:c::1)
4. Router forwards ICMPv6 packet with (src 9🅰️b:c::1 dst 5:6:7:8::ffef::1)
including original packet (src 5:6:7:8::ffef::1 dst 9🅰️b:c::1)
and applies DNPT changing dst to 1:2:3:4::1
5. 1:2:3:4::1 receives ICMPv6 packet with (src 9🅰️b:c::1 dst 1:2:3:4::1)
including original packet (src 5:6:7:8::ffef::1 dst 9🅰️b:c::1).
It doesn't recognise the original packet as the src doesn't
match anything it originally sent
With this change, at step 4, DNPT will also rewrite the original packet
src to 1:2:3:4::1, so at step 5, 1:2:3:4::1 will recognise the ICMPv6
error and provide feedback to the application properly.
Conversely, SNPT will help when ICMPv6 errors are sent from the
translated network.
1. 9🅰️b:c::1 sends UDP packet to 5:6:7:8::ffef::1
2. Router applies DNPT changing dst to 1:2:3:4::1
3. 1:2:3:4::1 receives packet with (src 9🅰️b:c::1 dst 1:2:3:4::1)
and replies with ICMPv6 port unreachable to 9🅰️b:c::1
including original packet (src 9🅰️b:c::1 dst 1:2:3:4::1)
4. Router forwards ICMPv6 packet with (src 1:2:3:4::1 dst 9🅰️b:c::1)
including original packet (src 9🅰️b:c::1 dst 1:2:3:4::1)
and applies SNPT changing src to 5:6:7:8::ffef::1
5. 9🅰️b:c::1 receives ICMPv6 packet with
(src 5:6:7:8::ffef::1 dst 9🅰️b:c::1) including
original packet (src 9🅰️b:c::1 dst 1:2:3:4::1).
It doesn't recognise the original packet as the dst doesn't
match anything it already sent
The change to SNPT means the ICMPv6 original packet dst will be
rewritten to 5:6:7:8::ffef::1 in step 4, allowing the error to be
properly recognised in step 5.
Signed-off-by: Michael Zhou <mzhou@cse.unsw.edu.au>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
d5608a0578