Bjoern A. Zeeb bzeeb-lists at
Fri Sep 15 02:25:13 PDT 2006


[just replying to a random mail of one of the various NAT-T threads
  at this point]

I had started to review the code (to find some problems people had
with the patch) and came up with the following so far. This work
was done based on the old freebsd6-natt.diff which is no longer
available:( but should equally apply to the new one.

Here is what the patch[1] changes:

- do not request more data to be collapsed into one contiguous data
   area of a mbuf than needed. sizeof(struct udphdr) is already
   included in off.

- remove unused variable 'family'

- the original patch did a m_dup() to get another writable copy (not
   only a reference) of the mbuf chain but did this after touching/changing
   data of the original mbuf. As it shouldn't matter in either case do
   it the right way and create the copy before moving data around so the
   original mbuf stays untouched.

- After removing the UDP part  correctly set the new ip_len. The value
   already is in hbo so arithmetics were wrong. The new value should not
   be needed by functions called (though they may change it too) but if
   we adjust it do it correctly.

- NICs like bge(4) do support IP/TCP/UDP checksum offloading. That
   means once a natt packet hits udp_input a csum for the IP and UDP
   payload was already validated.
   UDP checksumming is generally optional so nobody really cares in
   case it's a) not requested and b) the NIC doesn't do it already.
   But in case the NIC does, the flags are set on the mbuf that the
   csum was/is correct.
   While this mbuf (or a 1:1 copy) is passed on to ESP handling and
   later for example TCP handlig the valid csum flags are still there
   but our paket has changed and of course the original checksum for
   the UDP natt part is no longer the same and valid for the TCP
   payload and thus the packet gets dropped.
   So clear the csum flags if set before handing the packet off to
   ESP processing.

Now that it looks that finally all the bits and pieces are there for
NAT-T support I'll continue the review as time permits.




Bjoern A. Zeeb				bzeeb at Zabbadoz dot NeT

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