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route recursive-lookup tunnel is Needed to force Huawei CX600 Router to route packets using MPLS tunnel

Publication Date:  2012-07-27 Views:  53 Downloads:  0
Issue Description
Topology: CE-1 --- PE-1 --- P --- PE-2 --- CE-2

Huawei CX600 PE routers are running OSPF as IGP and BGP for Internet routes and MPLS in the Core network.
P router only running OSPF as IGP and MPLS.

PE-1 and PE-2 can learn CE-1 and CE-2 network via BGP and the routes are in the routing table. However, CE-1 and CE-2 are not reachable to each other.


Alarm Information
Null

Handling Process
Configure "route recursive-lookup tunnel" at both PE-1 and PE-2 routers to force the routers to route packet using MPLS tunnel. Without this command, PE router will just route packets using normal IP routing to P router, which results P router dropping the packets since P router does not has the route to CE networks.

After configure with this command, PE router route should has a value for Tunnel ID,

Routing Table : Public
Summary Count : 1

Destination: 121.123.132.48/30
Protocol: OSPF Process ID: 100
Preference: 10 Cost: 230
NextHop: 58.71.233.2 Neighbour: 0.0.0.0
State: Active Adv Age: 12h44m57s
Tag: 0 Priority: low
Label: NULL QoSInfo: 0x0
IndirectID: 0x0
RelayNextHop: 0.0.0.0 Interface: GigabitEthernet3/0/0
TunnelID: 0xc21e43 Flags: D

Root Cause
Perform traceroute from CE-1 and CE-2 and the hop between PE and P router can be seen as below:

4 202.151.254.14 7 ms !N * 9 ms !N

When check the routing of CE-2 destination,

Routing Table : Public
Summary Count : 1

Destination: 121.123.132.48/30
Protocol: OSPF Process ID: 100
Preference: 10 Cost: 230
NextHop: 58.71.233.2 Neighbour: 0.0.0.0
State: Active Adv Age: 12h44m57s
Tag: 0 Priority: low
Label: NULL QoSInfo: 0x0
IndirectID: 0x0
RelayNextHop: 0.0.0.0 Interface: GigabitEthernet3/0/0
TunnelID: 0x0 Flags: D

The Tunnel ID is 0x0 which is incorrect as there should be a value in the Tunnel ID so that the packet is switched to P router using MPLS tunnel.

Suggestions
Always remember to configure "route recursive-tunnel lookup" at PE router if P router only runs MPLS.

END