Robert
RFC 5283 provides LDP extension for inter area for LPM summary FEC however
in this specification the component prefixes are probated via LDP which is
how the LDP inter-area extension is able to support summarization.
The problem here is you make IGP scalable with this LDP inter-area
extension but then you pass the buck to MPLS which now is not scalable as
all the flooded prefixes are summarized in the IGP but now the LFIB has to
suffer from the domain wide flooding.
This issue with domain wide flooding gets much worse with seamless MPLS
with E2E LSP requirements from core to aggregation layer so now all the
area and levels within the entire domain had all host routes. This can be
pretty tremendous for large operator networks and a huge scalability issue
that needs a solution.
See section 7.2
The solution documented in this document reduces the link state
database size in the control plane and the number of FIB
entries in the forwarding plane. As such, it solves the scaling of
pure IP routers sharing the IGP with MPLS routers. However, it does
not decrease the number of LFIB entries so is not sufficient to solve
the scaling of MPLS routers. For this, an additional mechanism is
required (e.g., introducing some MPLS hierarchy in LDP). This is out
of scope for this document.
Bottom of section 7.2
For protocols and applications which need to track egress LER
availability, several solutions can be used, for example:
- Rely on the LDP ordered label distribution control mode -- as
defined in [LDP
<https://datatracker.ietf.org/doc/html/rfc5283#ref-LDP>] -- to know
the av.ailability of the LSP toward the
egress LER. The egress to ingress propagation time of that
unreachability information is expected to be comparable to the IGP
(but this may be implementation dependent).
- Advertise LER reachability in the IGP for the purpose of the
control plane in a way that does not create IP FIB entries in the
forwarding plane.
Gyan> So for this to work for egress convergence availability tracking
you either are back to flooding the routes in the IGP or use LDP
ordered label distribution.
Even if you used LDP ordered label distribution is still does not
solve the problem of robbing Peter to pay Paul now dumping the
flooding of host routes on MPLS LFIB making it not scalable.
Most vendors by default use LDP ordered label distribution defined in RFC 3036.
However, net-net the problem is not solved.
Kind Regards
Gyan
On Fri, Nov 19, 2021 at 3:25 PM Robert Raszuk <rob...@raszuk.net> wrote:
> Peter,
>
>
>> yes, but it's not specific to flat areas. Even in multi-area deployments
>> the host routing is mandated by MPLS.
>
>
> In the early days of MPLS yes that was the case.
>
> But that "mandate" was fixed by Ina, Bruno and Jean-Louis in 2008 :)
>
> https://datatracker.ietf.org/doc/html/rfc5283
>
> In these multi-area deployments
>> the host routes are sent everywhere, updates are triggered regardless of
>> the failure type. IGPs are effectively providing liveness service
>> between PEs in any MPLS network.
>>
>
> That is true too - as folks just do not know how to configure BGP properly
> (if BGP is used for services).
>
> That leaves us the space what to do where there is no BGP carrying
> services. Or BGP implementation is broken and can not do the right thing.
>
> For the pulse proposal - no one answered the question posted what is a
> definition of mass failure. But maybe that will be the secret sauce of a
> vendor :) ?
>
> The fact that we are all in agreement that some network events will not
> work that well with the proposed solution seems to be a sufficient reason
> for me to consider different solution(s).
>
> Thx,
> R.
>
--
<http://www.verizon.com/>
*Gyan Mishra*
*Network Solutions A**rchitect *
*Email gyan.s.mis...@verizon.com <gyan.s.mis...@verizon.com>*
*M 301 502-1347*
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