The MPLS WG Archive

[Curtis Villamizar <curtis@workhorse.fictitious.org>]

In message <FFFC48AEAA5F7447929F4F0D93FCC12D02B927EB@zcard031.ca.nortel.com>, "
David Allan" writes:
> 
> Rahul:
> 
> You are missing the point, if we do not know how ECMP is implemented, we
> cannot critique the solutions or participate in the design. IMHO properly
> characterizing the dataplane is a pre-requisite to being able to design
> maintenance procedures. For example VCCV proposes using the router alert
> label as an alternative to the PW-CW **because** after much teasing out, the
> proposing vendor's ECMP implementation only hashes bottom label and payload
> and the RA label would be above the bottom label. Is that true of other
> vendors???? Is this solution acceptable only because everyone else would
> have to use the CW...(so there is an escape clause)?
> 
> IMHO the variations in ECMP that would be encountered by OAM are of
> practical interest to both protocol design and independent of generating a
> framework document. It is not an issue with the architecture, it is a
> pre-requisite to working on it.
> 
> cheers
> Dave


Dave,

We've described all the ECMP methods in use either explicitly in this
email thread or through reference to RFC2991 and RFC2992.  At least
one implementation will split based on the bandwidth configured for an
RSVP/TE LSP rather than an equal split.  Otherwise very few details
have not been discussed.

Some implementations use only labels.  Some implementations look for
an IP header *if configured to do so* and hash the IP src/dst, falling
back to labels if the header is not IP.  Most implementations
(probably all) limit label stack depth before using hashed labels.
Whether the bottom label of the whole stack is hashed will varry.

You are not going to get the actual hash function itself and the
method of seeding it.  You also won't get a list of companies and
which feature is released in what version and which line cards support
what (that would be a competitive analysis that is not needed for this
sort of technical discussion).

What *relevant* detail are you missing?

Curtis