[pcp] Comment on REQ-9A of LSN requirements (PCP)

["Reinaldo Penno (repenno)" <[e-mail]>]

"A.  It MUST NOT permit the lifetime of a mapping to be
               reduced beyond its current life or be set to zero
               (deleted)."

In the case of renumbering how a CPE that gets a new address can delete
stale mappings of the previous user of that IP address? Given some of the
requirements, it can not.

Before mapping 'nonce' CPE/host could just send a delete all and we would
rely on ingress filtering to make sure things are okay. But now with the
mapping nonce the new owner of an IP address has no way of deleting the
stale mappings because it does not know the nonce.

If renumbering happens frequently (as in some networks as short as 30
minutes) and there are many PCP MAP mappings from each CPE/host, then soon
depending on the Lifetime there will be no more resources on
CGN/AFTR/Firewall due to stale mappings

A possible solution would be for DHCP Server or other provisioning server
to send a PCP message with THIRD_PARTY to delete all MAP mappings. But
again, it does not know the nonce. Not to mention that coupling
provisioning and PCP becomes a barrier for adoption. Reducing the
'lifetime' defeats the purpose of having PCP.

Not sure of any solution given all requirements in place.

Thanks,

Reinaldo