[Click] NAT changes

[Eddie Kohler]

Hi all,

Currently IPRewriter will not reuse a source port until the connection using 
that source port goes away.  This is harsher than necessary; in particular, 
IPRewriter could reuse the same source port for different destination 
addresses and/or ports, which would really raise the best-case number of 
concurrent connections supported.

IPRewriter also allocates source ports sequentially.  It would be better to 
allocate them randomly to reduce the risk of blind TCP attacks.

I'd like to address both of these issues.  But it may make IPRewriter a bit 
slower.  (Currently IPRewriter can tell immediately whether or not "the 
current" source port is used, although it may take 2^16 tries to find an 
unused source port.  In the new design, it will require a hash lookup to tell 
whether or not a source port is used, and it may still take 2^16 tries to find 
an unused source port.  But the new design will use a bit less memory.)  Any 
comments?

Eddie