The MPLS WG Archive

[Eric Rosen <erosen@cisco.com>]

Kireeti> One could use the 'check first  nibble' hack :-( It would be neater
Kireeti> to use the L3PID. 

Eric> Well, I wouldn't want  to have to set up a separate  TE tunnel just to
Eric> handle the  IPv6 traffic,  so I'd recommend  the "check  first nibble"
Eric> hack.  

Actually, there is a real  interoperability issue lurking here which we need
to get clear on. 

In  conjunction with  php, "check  first nibble"  could mean  either  of the
following: 

1. The penultimate  node pops the last  label off the stack,  creates a data
   link layer frame with IPv4 as the protocol type, and transmits the frame.
   The receiver  of the  frame checks the  first nibble  to see what  the IP
   version is  and treats  the packet as  IPv4 or  IPv6 depending on  the IP
   version.

2. The penultimate node pops the stack,  checks the first nibble to see what
   the IP version  is, and creates a data link layer  frame with either IPv4
   or IPv6  as the protocol type, depending  on the value of  the IP version
   field. 

What I meant was 1; I'm not sure which Kireeti meant.