[j-nsp] EX4200 MPLS Label Stacks

[Alexandre Snarskii]

On Tue, Jun 08, 2010 at 07:25:47AM +0100, Matthew Walster wrote:
> I'm aware that the Juniper EX4200 can do MPLS - indeed, I've used it
> with RSVP signalled LSPs using CCC encapsulation. It's been made clear
> to me that the EX series can only operate on 1 label, which completely
> rules out most MPLS scenarios such as Fast Reroute, Martini/Kompella
> L2VPNs, VPLS etc, leaving it just with the CCC capabilities, with
> extreme loose possibilities of LDP support in the distant future.
> 
> What I'm interested in is if the EX4200 can be used as a P router,
> just for RSVP LSPs, regardless of how many labels there are. That is,
> if an MPLS encapsulated packet comes in with two labels, providing the
> operation RSVP calls for is only a swap on the outer label, will that
> work? Presumably as the inner labels are not touched/inspected except
> for the L2 checksum, so it *should* work?

Theoretically, yes, it should. But last time I checked it (9.5R1
or some, first version with MPLS support), label swap operation 
was completely broken: when packet with two labels arrives to switch 
and top label should be swapped leaving other labels untouched, 
switch swapped all the label stack to the single label instead: 

ingress packet: 

16:45:51.826995 00:23:9c:7d:fa:03 > 00:23:9c:03:57:c2, ethertype MPLS unicast
(0x8847), length 124: MPLS (label 299808, exp 0, ttl 255)
        (label 114576, exp 0, [S], ttl 255)

operation: 

snar at SW0001> show route table mpls.0 label 299808 extensive
[...]
                Next hop: XX.XXX.XXX.XXX via ge-0/0/1.0 weight 0x1, selected
                Label-switched-path NNNNN-NNN
                Label operation: Swap 102080

egress packet: 

16:45:51.827002 00:23:9c:03:57:c1 > 00:19:e2:45:e3:82, ethertype MPLS unicast
 (0x8847), length 120: MPLS (label 102080, exp 0, [S], ttl 64)

Juniper confirmed that it is hardware limitation.

> The scenario I'm envisioning is that the two XFP slots can act as a
> "pass-through" and the 48 ports act as an MPLS CCC injector at a POP,
> saving the necessity to use large amounts of rack space and cash on
> MX80/240s when the EX4200 should cope.

I was interested in the same scenario.