[Serusers] UDP fragmentation

[Thilo Salmon]

Happy near year everybody,

this year started with a surprise: UACs I had behind a NAT would not
take calls. Further research revealed, that my INVITE messages would be
to large to fit my MTU of 1500 of traversing three proxies.
Unfortunately, the fragmented UDP packets would NAT traverse my NATs.

Now, looking at the INVITE messages, my first idea was to strip some
header fields which are not strictly required to set up a call at the
last proxy - such as 'User-Agent'. Would that be a way to go? If so, is
there a way of doing this with ser? Or would I need tunnel those
messages through a B2BUA (if so, which one would you use)?

Naturally my favourite option would be to find a univeral solution to
force UDP fragments through a NAT. However, my understanding as of now
is, that UDP fragments do not carry port information so they will not
make it through a NAT which does not keep state, suahc as my D-Link
residential router.

Thilo