[c-nsp] MPLS Recirculation

[James Bensley]

Hi All,

I have a long running and complex issue with some 7600 PEs, the crux
of the matter may be down to the command "mls mpls recir-agg" and
aggregate labels, my problem is that Cisco are not clearly explaining
to me (nor is it clearly documented) how/when/why this is command is
needed.

Does anyone clearly understand the command "mls mpls recir-agg"?

I see that the command “mls mpls tunnel-recirc” is required if two
operations are required relating to tunnelling activities, such as
using MPLS over GRE tunnels. In that example when a packet which
requires an MPLS push/swap that is then encapsulated into a GRE tunnel
it must be recirculated to allow for both operations to occur.

So for the command "mls mpls recir-agg" if I have understood it
correctly the intention is that ingressing MPLS labelled packets would
be recirculated when they match an aggregate label in the LFIB;

- the incoming label would be popped
- RP requests a IPv4 lookup within the VRF to the PFC/DFC
- request made over the DBUS
- response over the RBUS is the egress interface ID and adjacency
details based on the FIB TCAM lookup within the PFC/DFC

We already have aggregate labels present within our network and on our
7600 PEs so I’m not sure why this command is needed, how is aggregate
labelled traffic working already if recirculation needs to be maually
activated via that command?

abr1#show run all | i mls mpls
mls mpls qos input uniform-mode

The command is not present by default.

I have seen in the list archives that it has helped some people with
issues relating to packet loss with aggregate labelled traffic (which
is kind of what we have):

https://groups.google.com/forum/#!msg/cisco-nsp-/HrEbiY-APs8/lIhBcFLAisgJ
and
https://puck.nether.net/pipermail/cisco-nsp/2014-March/095390.html

On the first post the OP says: "The CLI help says that this command
only impact new aggregated labels but it worked immediately".

And on the second post the OP says "Problem solved. no mpls mls
tunnel-recir and then applied command back. Once I did this it
worked."

So seems like maybe this command is possibly on by default but not
working until you "no" it and then re-add it, and not showing in the
"show run all" until then? It also seems to have an immediate affect
when it says it won't?

How are we even processing aggregate labelled traffic without this command?

Its all very unclear.

Any input is apprecicated,
James.