The MPLS-OPS Archive

[Eric Gray <eric.gray@sandburst.com>]

Saroj,

    The operative portion of this quote is the statement: "We will see below..."

    Subsequent to the text you quote is the following:

   "It is worth pointing out a few consequences of these rules:

      -  A packet may be sent on the LSP whose Address Prefix FEC
         element is the address of the packet's egress router ONLY if
         there is no LSP matching the packet's destination address.

      -  A packet may match two LSPs, one with a Host Address FEC
         element and one with an Address Prefix FEC element.  In this
         case, the packet is always assigned to the former.

      -  A packet which does not match a particular Host Address FEC
         element may not be sent on the corresponding LSP, even if the
         Host Address FEC element identifies the packet's egress router."

The second and third bullets are the more important ones.  The key
distinction in selecting an LSP is spelled out by the second bullet.  I
believe the key distinction in handling labeled packets at the egress
is high-lighted by the third bullet - the intention is that the Host
Address FEC is used to route packets to a host _or_host_function_
at_a_router_ while the Address Prefix FEC is used to direct packets
to a router's forwarding function.  For some routers, this may not be
a critical distinction - but, for others, this is a useful optimization.


You wrote:

> All,
>
> In the section 2.1 FEC's of the RFC 3036, I have a query in
> the section below ::
> Following are the currently defined types of FEC elements.  New
> element types may be added as needed:
>
> 1. Address Prefix.  This element is an address prefix of any
>    length from 0 to a full address, inclusive.
>
> 2. Host Address.  This element is a full host address.
>
> (We will see below that an Address Prefix FEC element which is a full
>  address has a different effect than a Host Address FEC element which
>  has the same address.)
>
> The above statement that "Address Prefix FEC element which is a full
>  address has a different effect than a Host Address FEC element"
>
> I want to know what kind of difference will that be, as my understanding
> is that the "Address Prefix FEC element which is a full address"
>  is same as "Host Address FEC element". Can some one let me know.
>
> Regards,
> Saroj.
>
>
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--
Eric Gray (mailto:eric.gray@sandburst.com)
http://www.mindspring.com/~ewgray



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