The MPLS WG Archive

[Leonardo Balliache <lbb@opalsoft.net>]

At 01:55 p.m. 10/09/03 -0400, you wrote:

>Title           : Encapsulating MPLS in IP or Generic Routing 
>Encapsulation (GRE)
>Author(s)     : Y. Rekhter, E. Rosen
>Filename        : draft-ietf-mpls-in-ip-or-gre-03.txt
>Pages           : 9
>Date            : 2003-9-10
>

    With these encapsulations, it is possible for two LSRs that are
    adjacent on an LSP to be separated by an IP network, even if that IP
    network does not provide MPLS.

           IP Header
                 This field contains an IPv4 or an IPv6 datagram header
                 as defined in [RFC791] and [RFC2460] respectively. The
                 source and destination addresses are set to addresses
                 of the encapsulating and decapsulating LSRs respectively.

Ok.

I draw a little scheme:

                          head                  tail
    A             M         X      IP tunnel     Y          N                 B
---o------o------o---------o....................o----------o--------o--------o
   LSR    LSR    LSR   encapsulator        decapsulator    LSR      LSR 
  LSR

My doubts:

Q1: Your specification calls for:

Both, X & Y must be MPLS capable?     or,

X, but not necessarely Y, must be MPLS capable?     or,

Y, but not necessarely X, must be MPLS capable?     or,

Neither of them have to be necessarely MPLS capable?

Which router pop the last top label? M or X?

Which router push again a label? Y or N?

Q2: This paragraph:

    In some cases, the tunnel head receives, for encapsulation, an IP
    packet, which it first encapsulates in MPLS and then encapsulates in
    MPLS-in-IP or MPLS-in-GRE.  If the source of the IP packet is
    reachable from the tunnel head, and if the result of encapsulating
    the packet in MPLS would be a packet whose size exceeds the Tunnel
    MTU, then the value which the tunnel head SHOULD use for the purposes
    of fragmentation and PMTU discovery outside the tunnel is the Tunnel
    MTU value minus the size of the MPLS sencapsulation.

Could be explained a little better?

Best regards,

Leonardo Balliache

Pd: Perhaps, the scheme is not too bad to include it in the draft.

Practical QoS
http://opalsoft.net/qos