[c-nsp] EoMPLS VC on Cisco 7609 is up, but with very small MTU (42 bytes)

[Eric Xu]

I have two directly connected Cisco 7609 routers running MPLS with OSPF
being IGP,  and a EoMPLS VC has been created.

On router 1:

interface Vlan100
ip address 192.168.168.2 255.255.255.0
xconnect 10.200.0.158 100 encapsulation mpls

On router 2:

interface Vlan100
ip address 192.168.168.3 255.255.255.0
xconnect 10.200.0.157 100 encapsulation mpls

*VC is up on both routers with MTU 1500:*

*router1#sh mpls l2transport vc 100 detail*
*Local interface: Vl100 up, line protocol up, Eth VLAN 100 up*
*Interworking type is Ethernet*
*Destination address: 10.200.0.158, VC ID: 100, VC status: up*
*Output interface: Te1/0/0.18000064, imposed label stack {16}*
*Preferred path: not configured*
*Default path: active*
*Next hop: 10.200.0.38*
*Create time: 00:12:14, last status change time: 00:12:14*
*Last label FSM state change time: 00:12:14*
*Signaling protocol: LDP, peer 10.200.0.158:0 <http://10.200.0.158:0> up*
*Targeted Hello: 10.200.0.157(LDP Id) -> 10.200.0.158, LDP is UP*
*Status TLV support (local/remote) : enabled/supported*
*LDP route watch : enabled*
*Label/status state machine : established, LruRru*
*Last local dataplane status rcvd: No fault*
*Last BFD dataplane status rcvd: Not sent*
*Last BFD peer monitor status rcvd: No fault*
*Last local AC circuit status rcvd: No fault*
*Last local AC circuit status sent: No fault*
*Last local PW i/f circ status rcvd: No fault*
*Last local LDP TLV status sent: No fault*
*Last remote LDP TLV status rcvd: No fault*
*Last remote LDP ADJ status rcvd: No fault*
*MPLS VC labels: local 214, remote 16*
*Group ID: local 0, remote 0*
*MTU: local 1500, remote 1500*
*Remote interface description:*
*Sequencing: receive disabled, send disabled*
*Control Word: On (configured: autosense)*

*router2#sh mpls l2transport vc 100 detail*
*Local interface: Vl100 up, line protocol up, Eth VLAN 100 up*
*Interworking type is Ethernet*
*Destination address: 10.200.0.157, VC ID: 100, VC status: up*
*Output interface: Te2/11.18000064, imposed label stack {214}*
*Preferred path: not configured*
*Default path: active*
*Next hop: 10.200.0.37*
*Create time: 00:13:06, last status change time: 00:12:53*
*Last label FSM state change time: 00:12:53*
*Signaling protocol: LDP, peer 10.200.0.157:0 <http://10.200.0.157:0> up*
*Targeted Hello: 10.200.0.158(LDP Id) -> 10.200.0.157, LDP is UP*
*Status TLV support (local/remote) : enabled/supported*
*LDP route watch : enabled*
*Label/status state machine : established, LruRru*
*Last local dataplane status rcvd: No fault*
*Last BFD dataplane status rcvd: Not sent*
*Last BFD peer monitor status rcvd: No fault*
*Last local AC circuit status rcvd: No fault*
*Last local AC circuit status sent: No fault*
*Last local PW i/f circ status rcvd: No fault*
*Last local LDP TLV status sent: No fault*
*Last remote LDP TLV status rcvd: No fault*
*Last remote LDP ADJ status rcvd: No fault*
*MPLS VC labels: local 16, remote 214*
*Group ID: local 0, remote 0*
*MTU: local 1500, remote 1500*
*Remote interface description:*
*Sequencing: receive disabled, send disabled*
*Control Word: On (configured: autosense)*
*SSO Descriptor: 10.200.0.157/100 <http://10.200.0.157/100>, local label:
16*
*Dataplane:*
*SSM segment/switch IDs: 4144/4142 (used), PWID: 9*
*VC statistics:*
*transit packet totals: receive 32, send 15*
*transit byte totals: receive 2318, send 1020*
*transit packet drops: receive 0, seq error 0, send 0*

*MTU between the routers are more than 9000:*

*router1#ping 10.200.0.158 size 9000 df-bit source l0*
*Type escape sequence to abort.*
*Sending 5, 9000-byte ICMP Echos to 10.200.0.158, timeout is 2 seconds:*
*Packet sent with a source address of 10.200.0.157*
*Packet sent with the DF bit set*
*!!!!!*
*Success rate is 100 percent (5/5), round-trip min/avg/max = 12/13/16 ms*

*router2#ping 10.200.0.157 size 9000 df-bit source l0*
*Type escape sequence to abort.*
*Sending 5, 9000-byte ICMP Echos to 10.200.0.157, timeout is 2 seconds:*
*Packet sent with a source address of 10.200.0.158*
*Packet sent with the DF bit set*
*!!!!!*
*Success rate is 100 percent (5/5), round-trip min/avg/max = 12/20/44 ms*

*However, MTU on the VC is only 42 bytes, which makes it unusable:*

*router1#ping 192.168.168.3 size 42 df-bit source vlan 100*
*Type escape sequence to abort.*
*Sending 5, 42-byte ICMP Echos to 192.168.168.3, timeout is 2 seconds:*
*Packet sent with a source address of 192.168.168.2*
*Packet sent with the DF bit set*
*!!!!!*
*Success rate is 100 percent (5/5), round-trip min/avg/max = 8/9/12 ms*

*router1#ping 192.168.168.3 size 43 df-bit source vlan 100*
*Type escape sequence to abort.*
*Sending 5, 43-byte ICMP Echos to 192.168.168.3, timeout is 2 seconds:*
*Packet sent with a source address of 192.168.168.2*
*Packet sent with the DF bit set*
*....!*
*Success rate is 20 percent (1/5), round-trip min/avg/max = 8/8/8 ms*

*router1#ping 192.168.168.3 size 44 df-bit source vlan 100*
*Type escape sequence to abort.*
*Sending 5, 44-byte ICMP Echos to 192.168.168.3, timeout is 2 seconds:*
*Packet sent with a source address of 192.168.168.2*
*Packet sent with the DF bit set*
*.....*
*Success rate is 0 percent (0/5)*


ESM20G 7600-ES20-10G3C card on router 1 and 7600 ES+ 76-ES+XC-20G3C card on
router 2.


Any ideas why?

Thank you.