[bess] draft-rosen-idr-rfc3107bis-00

Eric C Rosen <erosen@juniper.net> Wed, 13 January 2016 18:11 UTC

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From: Eric C Rosen <erosen@juniper.net>
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Subject: [bess] draft-rosen-idr-rfc3107bis-00
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Folks,

Pardon the cross-post, but I think this may be of interest to all three 
of the IDR, MPLS, and BESS WGs.

I've posted draft-rosen-idr-rfc3107bis-00 ("Using BGP to Bind MPLS 
Labels to Address Prefixes"), which is intended of course to obsolete 
RFC 3107 ("Carrying Label Information in BGP").  (While I put "idr" in 
the name of the draft, it's not completely obvious which WG should own 
this draft (assuming it progresses)).

The purpose of this draft is the following:

- It fixes a number of errors in RFC3107.  It attempts to do so in a way 
that is compatible with existing implementations.

- It removes the material about "Advertising Multiple Routes to a 
Destination".  This is a feature that was never implemented as 
specified, and the text about it just causes confusion.  The 
functionality that this feature was intended to provide can now be 
better provided by using add-paths; this is discussed in the draft.

- It is explicit about its applicability to SAFI 128 as well as to SAFI 4.

- It clarifies the procedures for withdrawing and replacing label bindings.

- It discusses the relationship between SAFI-1 routes and SAFI-4 routes, 
which is very unclear in RFC3107.  Different implementations have 
treated the SAFI-1/SAFI-4 interactions differently, and the draft 
discusses these differences.  However, as the draft is not intended to 
favor any one implementation over another, it can't do much more than 
point out some of the differences among implementations.

- RFC 3107 provides an encoding that allows BGP to assign multiple 
labels (i.e., a label stack) to a given prefix.  However, it provides no 
semantics for this, and this feature has been only rarely implemented.  
In fact, it is believed that some implementations will not parse the 
Updates correctly if they encode multiple labels in the NLRI.  Therefore 
the draft only allows a label stack to be assigned to a given prefix if 
a new Capability has been exchanged.  It also discusses the semantics of 
assigning a label stack, and gives some examples of how this might be used.

I hope that those of you who are interested in this topic will provide 
your comments.  I've tried to make the draft compatible with existing 
implementations and deployments, so if anyone sees anything that 
negatively impacts an existing implementation, please comment on that.

I also removed most of the text that explains why it is a good idea to 
use BGP to distribute label bindings.  That text was important in the 
'90s, but now seems rather out of date.  However, I would welcome 
comments on whether an updated "motivation/positioning" section should 
be added.

Thanks,

Eric