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Re: BGP TE attr last call by softwires WG
> Hello Don,
> Thanks for the response.
> >> 1. A CE is attached by parallel links to a single PE
> >> Suppose the links have the same switching types, but
> >> different bandwidths. Link-a has plenty of bandwidth
> >> available with an MTU size of x. Link-b has not much
> >> bandwidth available with an MTU size of y > x.
> > Interface MTU is part of the PSC TE attributes in the our spec. If the
> > MTUs are different they should not be aggregated.
> Right. Aggregation in this case is hard to make representative of reality.
> > Also In L1VPN (LSC and TDM) networks the Switching type
> > covers Switching granularity (which is like an MTU).
> Sure. But I wanted to keep in PSC, because that problem represents a single
> layer network.
> > I'm trying to understand if you are saying the following text would
> > fix the problem or you see a larger issue:
> > "Therefore, such routes and the corresponding TE information
> > SHALL NOT be aggregated unless they share identical Traffic
> > Engineering Attributes".
> The question I am asking is - is the solution to this problem to advertise
> two routes? (Clearly two is a special case of many.)
> I don't believe that in the general (non-TE case) we would consider the case
> of two parallel links between CE and PE as route aggregation. The PE would
> simply advertise reachability (through itself) to the CE.
Let's put the general (non-TE) case aside, and focus on the L1VPN
According to the bgp-auto-discovery and l1vpn-basic-mode drafts in
the context of L1VPN what is advertised in the BGP auto-discovery
information is the information about *ports*. Therefore, in the
context of L1VPN TE information advertisements are associated with
individual *ports*, not with a particular CE. Which means that if
a CE is connected to a PE by N ports, then the BGP auto-discovery
information has to advertise all these N ports, and associated with
each such advertisement may be the TE information.
> Hence my question below.
> >> Normally, we would expect the PE to advertise a single
> >> piece of reachability information for the CE leaving
> >> the actual choice of links to be made by the PE.
> >> What would the PE advertise in this case?
> >> - It cannot aggregate the TE information because that
> >> would imply that there was lots of bandwidth at the
> >> larger MTU size.
> >> - It could include duplicate Switching Capability
> >> Descriptors, but that would need some clarification as
> >> duplicate descriptors are intended for different
> >> switching caps in the IGP RFCs.
> >> - It could advertise two pieces of reachability
> >> information, but that would be a change to how the
> >> implementation currently works.
The answer to your question is that if the implementation follows
the spec, it would advertise information about *ports*. So, if a
CE has two ports that connect it to a PE, then the PE originates
two L1VPN advertisements, one per port, each with its own TE