Scenario - Tower 5 connecting to new Tower 6 - MPLS back to the core, all working under RoS6 fine.

I'm looking to use an RB5009 (7.2.3) in place of an RB4011 passing MPLS and LDP in an RoS6 (6.48.6) environment on Tower 6 talking back to Tower 5 (and beyond) and connecting the AP's of Tower 6.

T5-R1 (Ros6) ----wireless bridge ----T6-R1 (RoS7)------T6-AP2 (RoS6)

NB - OSPF works wonderfully and all routes appear as expected and we have full reachability with MPLS disabled. Originally T6 had its upstream link in the backbone and all downstream's in a seperate OSPF Area - I subsequently temporarily changed this to simplify by putting all of T6 in the backbone for testing - no apparent difference.

Currently when I set this up the T6-R1 MPLS forwarding table only has the immediately adjacent links shown and in the local and remote mapping all the labels (except adjacent routers) show DI or DIG (Dynamic Invalid or Dynamic Invalid Gateway - what makes them Invalid ?

[admin@xxxxxxxxxx] /mpls/forwarding-table> pr
Flags: L, V - VPLS
Columns: LABEL, VRF, PREFIX, NEXTHOPS
# LA VRF PREFIX NEXTHOPS
0 L 64 main 10.255.200.120 { label=impl-null; nh=172.31.0.73; interface=vlan-1001 } - Tower 5 R1
1 L 16 main 10.255.200.143 { label=impl-null; nh=172.31.14.14; interface=vlan-1003 } - Tower 6 AP2

Tower 6 Router RoS 7.2.3
/mpls interface
add disabled=no input=yes interface=all mpls-mtu=1550
/mpls ldp
add afi=ip disabled=no lsr-id=10.255.200.140 transport-addresses=10.255.200.140
/mpls ldp accept-filter
add accept=yes disabled=no prefix=10.255.0.0/16
add accept=no disabled=no prefix=::/0
/mpls ldp advertise-filter
add advertise=yes disabled=no prefix=10.255.0.0/16
add advertise=no disabled=no prefix=::/0
/mpls ldp interface
add accept-dynamic-neighbors=yes afi=ip disabled=no interface=vlan-1004 transport-addresses=""
add accept-dynamic-neighbors=yes afi=ip disabled=no interface=vlan-1002 transport-addresses=""
add accept-dynamic-neighbors=yes afi=ip disabled=no interface=vlan-1001 transport-addresses=""
add accept-dynamic-neighbors=yes afi=ip disabled=no interface=vlan-1003 transport-addresses=""

** Have tried adding the transport address to the individual interfaces with no success so ;leaving LDP to get that from LDP global settings.

Yet the downstream router (T6 AP) running RoS6 seems to be getting all the labels in its forwarding table but cannot reach beyong T5 R1 with MPLS enabled:

[admin@MN-xxxxxxxx-AP2] /mpls forwarding-table> pr
Flags: H - hw-offload, L - ldp, V - vpls, T - traffic-eng
# IN-LABEL OUT-LABELS DESTINATION IN NEXTHOP
0 expl-null
1 L 274 49 10.255.200.76/32 et 172.31.14.13
2 L 275 22 10.255.200.13/32 et 172.31.14.13
3 L 276 20 10.255.200.8/32 et 172.31.14.13
4 L 277 34 10.255.200.38/32 et 172.31.14.13
5 L 278 46 10.255.200.70/32 et 172.31.14.13
6 L 279 56 10.255.200.87/32 et 172.31.14.13
7 L 280 29 10.255.200.30/32 et 172.31.14.13
8 L 281 36 10.255.200.49/32 et 172.31.14.13
9 L 282 24 10.255.200.16/32 et 172.31.14.13
10 L 283 18 10.255.200.5/32 et 172.31.14.13
11 L 284 26 10.255.200.19/32 et 172.31.14.13
12 L 285 57 10.255.200.90/32 et 172.31.14.13

/mpls interface
set [ find default=yes ] mpls-mtu=1550
/mpls ldp
set enabled=yes lsr-id=10.255.200.143 transport-address=10.255.200.143
/mpls ldp accept-filter
add prefix=10.255.200.0/24
add accept=no
/mpls ldp advertise-filter
add prefix=10.255.200.0/24
add advertise=no
/mpls ldp interface
add interface=ether1

Interesting on the RoS7 router under LDP Neighbours it shows the upstream as Dynamic Operational and the dowstream as Dynamic Operational Passive.

The downstream router (AP) can tracerout to the upstream router and show MPLS labels in the result but will not traverse the upstream router to go back to the core of the network. Disable MPLS on the T6-AP and I can happily Traceroute back to the core.

Is this an interop issue or am I missing something in my v7 MPLS config ??

** SOLVED **

I've found the issue - LDP Loop Detect - this had been enabled on some upstream routers and worked (despite not all routers having it set) on a pure RoS6 network. NB - All LSR's should have it enabled or none according to the Wiki and not to use it on TTL networks, only ATM.

As soon as an RoS7 router was introduced the Loop Detect stopped labels correctly reaching the RoS7 router from its immediate upstream which was on of the routers with Loop detect enabled.

Disable LDP Loop Detect on all RoS v6 MPLS routers and all working.

This was a bug its fixed in the latest ROS7.4rc2!

So now even networks with loop detection turned on in LDP on ROS6 works!