[Softwires] The port mapping issue

[Tom Taylor <[e-mail]>]

The meeting minutes record a disagreement over what port mapping 
algorithm to use. This affects both MAP-E and LW 4over6. As I understand it:

- either of these two technologies will work with either contiguous 
ports or ports scattered according to the GMA algorithm

- the real objection to GMA comes from Alain Durand, who wants to set up 
simple min-port, max-port filters on his network equipment.


We all agree that port scattering offers negligible security advantage.

The reason that I heard given for preferring GMA for MAP-E is that it 
eliminates a restriction on the End-User Ipv6 address because the PSID 
is free to range from 0 upwards rather than from some higher number 
upwards. I don't follow this argument for two reasons:

- you now have a restriction that the offset field A must range from 1 
upwards

- the PSID field has an upper limit 2^k-1 imposed by the sharing ratio, 
imposing a further restriction on the End-User IPv6 address value.

Could someone spell out more clearly why the GMA was seen as necessary 
for MAP-E?