The MPLS WG Archive

[Philip Matthews <pmatthews@hyperchip.com>]

Title: RE: Node-id: Concerned about using one of the last RRO flag bits for this

Jean Philippe Vasseur wrote:
> if you define a new type code, you would need to add the new subobject in addition to the existing
> IPv4 subobject in order to be compliant with the FRR draft. Defining a new flag allows to use the
> same required IPv4 but just set the flag and use the router-id address instead of the outgoing
> interface.

I think I understand now:
a) You want each node to independently decide whether to push an interface address,
   a router id, or both.
b) I would like each node to always push an interface address, and optionally push a router id.

With option (a), there may be some advantage in using a flag, since routers out
there today that do not understand the flag will see just an IPv4/v6 Address subobject
and will hopefully do more-or-less the right thing. However, as Curtis points out,
there are routers out there that are known to have problems with new flags.

With option (b), there is no advantage to using a flag, assuming nodes can ignore
unknown sub-objects.

My concern with option (a) is that it removes my ability to parse the RRO and
tell which sub-objects belong to the same node. For example, if the RRO contains:

     (address-1, flag=0), (address-2, flag=1), (address-3, flag=0)

then I don't know whether this represents 2 nodes or 3 nodes. This makes it
impossible for a router to display the RRO to the operator in a nicely formatted
manner (that groups together the information for a single node).

Option (a) also gives the operator less information, because he/she will not always
see the egress interface of the LSP.

However, option (a) does have the advantage that RROs can be shorter.

So there seem to be three questions for the WG to decide:
1) Do we want to do for option (a) or option (b)?
2) Do we want to use a flag or a new sub-object?
3) Do we need to add capability advertisements to do any of this
   (as Curtis is suggesting)?

I personally have a medium preference for option (b), and a medium preference
for a new sub-object. I also hope that people will simply fix their routers
so we don't need to introduce capability advertisements.

- Philip