[c-nsp] mpls ip -> lost packets

[Jeff Bacon]

Forgive what is 

I'm setting up MPLS on a framework of cat6500s (sup32s and 720-3Bs). 

Scenario: line between a device that is going to be a P-router (a sup32,
device A), and on a PE (sup720, device B).

Line is a "metro-e" fiber (essentially two dark fibers with a juniper in
the middle which is doing passthru). Line is configured as a dot1q trunk
with two VLANs on it, mtu 9216. Confirmed with vendor that it will pass
full gig jumbo frames. Line has run fine for many months, rock solid.

Switches are running SXH6.
Device A has another gig port connecting us to a vendor. Said interfaces
will not run MPLS, and are in the global scope. We inside-NAT to the
vendor.
Device B is a boundary device for the main datacenter, has all the
clients behind it, several WAN lines in, etc etc.

Goal was to pass MPLS across one of the VLANs on the line (VLAN 300).
VLAN300 is the main transport between the two switches, and all sorts of
TCP and multicast traffic run across it, load in the 100-150M range,
plus microbursts.

All I did was set "mpls ip" and "mpls mtu 1500" on the relevant SVI
interfaces. 

Shortly thereafter, TCP connections from clients off device B to vendor
off device A running via VLAN 300 started dropping packets. Not
consistently, but in bursts every few seconds. 

Disable the "mpls ip" statements on the VLAN 300 SVI on device B,
problem goes away. 

Before I start really digging, am I doing something completely idiotic
and obviously wrong? Or do sup32s suck at MPLS? 


Intf to vendor:
interface GigabitEthernet1/8
 ip address 10.132.61.10 255.255.255.0
 ip nat outside
 ip pim sparse-dense-mode
 ip multicast boundary blah
 ip igmp static-group 224.0.62.2
 load-interval 60
 hold-queue 2000 in
 hold-queue 80 out

intf on dev B:
interface Vlan300
 mtu 1546
 ip address 10.201.192.145 255.255.255.252
 ip nat inside
 ip pim sparse-dense-mode
 load-interval 60
 delay 25
 hold-queue 2000 in
 hold-queue 80 out

intf on dev A:
interface Vlan300
mtu 1546
 ip address 10.201.192.146 255.255.255.252
 ip pim sparse-dense-mode
 load-interval 60
 delay 25
 mpls ip
 hold-queue 2000 in