[v4tov6transition] Comment on draft-despres-softwire-6a44-01.txt

[Dong Zhang <[e-mail]>]

Hi Remi,

The IPv6 host address is directly obtained by an indication message from the 6a44 server. Here is the format of the IPv6 address.
     +-------+-------+-------+-------+-------+-------+-------+-------+
     |  ISP 6a44 prefix (D)       | Customer IPv4 |NAT ext|   Host IPv4      |
     |                                  |   address (N)   |port(Z) |  address (A)    |
     +-------+-------+-------+-------+-------+-------+-------+-------+

According to the draft, N:Z is the address and port used on the CPE NAT44's external side. 
                         _                        .-------.
            Host      /   \       CPE         /          \     6a44 Relay
        +------+  . IP  .    +-----+     .   IPv4    .     +-------+    IPv6
        |6a44-C|--| no |--|NAT44|---| Provider  |--O 6a44-S|-- network
        +------+  . NAT .  +-----+     .  network  .   +-------+
             ^   ^   \ _ /        ^           \          /      |    ^
              |   A                  |            '---.---'       |    |
              |               A:W <-> N:Z                     |    |
              |   |                                                 |    |
              |   |                                                 |    |
              |    <- - - - - IPv6/UDP/IPv4 - - - - - -<      |
              |                                                           |
              |                                                           |
              < D.N.Z.A (/128) - - - - -  - - -IPv6 - - - - < D (/48)

Is the A:W<->N:Z mapping created staticly? Or dynimicly?When the host reqests the IPv6 address to the 6a44 server, the server gives the host IPv6 address and liftime directly.  If  the mapping on the CPE is allocated dynamically, how does the lifetime of the allocated host IPv6 address will be set? I mean this lifetime should longer than the expire time of the mapping on the CPE. It is because if the mapping is deleted first and the host still uses the IPv6 address embeded N:Z. It will arise problem. For instance, the CPE may allocate another port, A:W<->N:Y.

Therefore, there may be two ways to solve this.
a) set the lifetime of the allocated host IPv6 address shorter than the expire time of CPE NAT44. Thus, the host is able to re-request its IPv6 address within the NAT mapping expire time.
b) require the CPE comply with endpoint-independent mapping in RFC4787,RFC5382. But for this behavior, the premise is the host re-send the address request message must use the same source address and port, A:W. Thus, the NAT can provide the same N:Z.

I suppose this should be clarified in 6a44 draft, if I am correct and not missing someting.


Thanks.




2010-10-15 



Dong Zhang