[pcp] draft-ietf-pcp-proxy and draft-cheshire-recursive-pcp

[Dan Wing <[e-mail]>]

I am trying to understand the difference between draft-ietf-pcp-proxy and draft-cheshire-recursive-pcp.   One of the significant differences seems to be if the proxy should function differently from an endpoint.  draft-ietf-pcp-proxy has a proxy operating differently from an endpoint with the sentence starting with "Nevertheless"

   6.  No NAT is Co-located with the PCP Proxy

   When no NAT is co-located with the PCP Proxy, the port numbers
   included in received PCP messages (from the PCP server or PCP
   client(s)) are not altered by the PCP Proxy.  Nevertheless, the PCP
   client IP Address MUST be changed to the address of the PCP Proxy and
   a THIRD_PARTY Option inserted to carry the IP address of the source
   PCP client.

The text is under-specified (as the PCP proxy can have have several addresses, even if it is a firewall), but I don't know why the PCP proxy needs to add the THIRD_PARTY option.  It could just send the packet as-is, with the original source IP address.  The proxy will see the response just as it will see the TCP SYNACK response to a TCP SYN.

WG thoughts?

-d