Re: WHy do LDP dont assign labels for BGP learned route ?

Not sure why you call it a constraint, but it is an implementation fact.
In fact, it seems to be against RFC3031, section 4.1.2.2, that says that
a router MUST bind labels to all the prefixes in its routing table.

I was puzzled by this too, and got someone to enlighten me, quoted w/o
permission:

Eric Rosen @ 01/06/2011 16:38 -0300 dixit:
>> The issue is that routers do not generate labels for BGP learnt
>> prefixes.
>
> If one is using MPLS to send an IP packet from one BGP router (ASBR)
> to another, across an ISIS or OSPF network, then within the ISIS/OSPF
> network all one needs are labels for the IGP-learned prefixes.
>
> The early implementors of MPLS realized this, and decided to
> implement it this way. You are correct that this is not precisely
> what the spec says. I think this implementation practice is correct,
> and I should have modified the spec to reflect it. I don't really
> remember why I didn't, maybe the implementors didn't bother to tell
> me about it until it was too late
>
> Since the number of ASBRs in a network is much less than the number of
> BGP-learned prefixes, this practice saves a lot of state in the
> forwarding table, and saves a lot of control messages.

-Carlos

CCIE KID @ 19/04/2012 06:23 -0300 dixit:
> Hi all
>
> I know that LDP wont assign label for BGP learned route. I just want to
> know the logic behind this idea. Is it a design constraint or else it is
> the implementation constraint ?
>
>
>

-- 
Carlos G Mendioroz  <tron_at_huapi.ba.ar>  LW7 EQI  Argentina
Blogs and organic groups at http://www.ccie.net