"sprite-mtu" identifies conditions under which the ITR must fragment outer packets which the ETR must reassemble. (And, from the list discussions, we seem to be reaching consensus that any reassembly at the ETR must be limited to 1500 byte or smaller original packets.) But, sprite-mtu further defines a "dance" that needs to be orchestrated between the ITR and ETR when IPv4 fragmentation and reassembly are occurring, which may be too onerous for some deployments.
The reason for the dance is that the 16-bit ip_id needs to be carefully monitored when IPv4 fragmentation is occurring such that any reassembly misassociations are detected. But, if we disable IPv4 fragmentation and instead define a LISP-specific fragmentation and reassembly at the LISP shim layer immediately above UDP, then we can have the shim layer insert a 32-bit id which would avoid the RFC4963 issues and eliminate the need for close coordination with the ETR. I have already specified such a mechanism for DHCP: http://www.ietf.org/internet-drafts/draft-templin-dhcpmtu-00.txt and a similar specification for LISP would be nearly identical. The penalty is extra LISP encapsulation overhead, but the benefit of avoiding the need for synchronization between the ITR and ETR is substantial. (In fact, it may be essential to the successful deployment of LISP.) Also, when the path MTU is large enough to accommodate all 1500 byte and smaller packets without fragmentation, the extra encapsulation overhead can be eliminated. So, I am inclined to write this up as a draft but probably won't be able to get to it until after the 1st of the year. It could either go as part of the sprite-mtu draft, or as an independent draft like the DHCP one. But better yet would probably be to just put it directly into the LISP specification itself. What does anyone think? Thanks - Fred [EMAIL PROTECTED] -- to unsubscribe send a message to [EMAIL PROTECTED] with the word 'unsubscribe' in a single line as the message text body. archive: <http://psg.com/lists/rrg/> & ftp://psg.com/pub/lists/rrg
