This article describes how to check the Multiprotocol Label Switching (MPLS) maximum transmission unit (MTU) via the sweep command for troubleshooting.
sweep
The following example shows how to check the MPLS MTU using the sweep command.
1.1.1.1 lo0.0 R1 ----------------- <> R2 <> ------------------------- R3 lo0.0 3.3.3.3 <-------------configuration-------------->
set interfaces fe-0/0/0 unit 0 family inet address 10.1.1.1/30 set interfaces fe-0/0/0 unit 0 family mpls set interfaces fxp0 unit 0 family inet address 10.141.227.38/24 set interfaces lo0 unit 0 family inet address 1.1.1.1/32 set routing-options static route 0.0.0.0/0 next-hop 10.141.227.100 set routing-options autonomous-system 100 set protocols rsvp interface all set protocols rsvp interface fxp0.0 disable set protocols mpls path-mtu allow-fragmentation set protocols mpls path-mtu rsvp mtu-signaling set protocols mpls label-switched-path test from 1.1.1.1 set protocols mpls label-switched-path test to 3.3.3.3 set protocols mpls label-switched-path test no-cspf set protocols mpls interface all set protocols mpls interface fxp0.0 disable set protocols bgp group INT type internal set protocols bgp group INT local-address 1.1.1.1 set protocols bgp group INT neighbor 3.3.3.3 set protocols bgp group INT neighbor 2.2.2.2 set protocols ospf area 0.0.0.0 interface fe-0/0/0.0 set protocols ospf area 0.0.0.0 interface lo0.0
set interfaces fe-0/0/0 unit 0 family inet address 10.1.1.2/30 set interfaces fe-0/0/0 unit 0 family mpls set interfaces ge-0/2/0 unit 0 family inet address 20.1.1.1/30 set interfaces ge-0/2/0 unit 0 family mpls set interfaces fxp0 unit 0 family inet address 10.141.227.13/24 set interfaces lo0 unit 0 family inet address 2.2.2.2/32 set routing-options static route 0.0.0.0/0 next-hop 10.141.227.100 set routing-options autonomous-system 100 set protocols rsvp interface all set protocols rsvp interface fxp0.0 disable set protocols mpls path-mtu allow-fragmentation set protocols mpls path-mtu rsvp mtu-signaling set protocols mpls interface all set protocols mpls interface fxp0.0 disable set protocols bgp group INT type internal set protocols bgp group INT local-address 2.2.2.2 set protocols bgp group INT neighbor 1.1.1.1 set protocols bgp group INT neighbor 3.3.3.3 set protocols ospf area 0.0.0.0 interface fe-0/0/0.0 set protocols ospf area 0.0.0.0 interface ge-0/2/0.0 set protocols ospf area 0.0.0.0 interface lo0.0
set interfaces ge-1/2/0 unit 0 family inet address 20.1.1.2/30 set interfaces ge-1/2/0 unit 0 family mpls set interfaces fxp0 unit 0 family inet address 10.141.227.60/24 set interfaces lo0 unit 0 family inet address 3.3.3.3/32 set routing-options static route 0.0.0.0/0 next-hop 10.141.227.100 set routing-options autonomous-system 100 set protocols rsvp interface all set protocols rsvp interface fxp0.0 disable set protocols mpls path-mtu allow-fragmentation set protocols mpls path-mtu rsvp mtu-signaling set protocols mpls label-switched-path test1 from 3.3.3.3 set protocols mpls label-switched-path test1 to 1.1.1.1 set protocols mpls label-switched-path test1 no-cspf set protocols mpls interface all set protocols mpls interface fxp0.0 disable set protocols bgp group INT type internal set protocols bgp group INT local-address 3.3.3.3 set protocols bgp group INT neighbor 1.1.1.1 set protocols bgp group INT neighbor 2.2.2.2 set protocols ospf area 0.0.0.0 interface ge-1/2/0.0 set protocols ospf area 0.0.0.0 interface lo0.0 <-------------configuration-------------->
On R1 lsp name test from 1.1.1.1 to 3.3.3.3:
lab@R1> show mpls lsp name test extensive Ingress LSP: 1 sessions 3.3.3.3 From: 1.1.1.1, State: Up, ActiveRoute: 0, LSPname: test ActivePath: (primary) LSPtype: Static Configured LoadBalance: Random Encoding type: Packet, Switching type: Packet, GPID: IPv4 *Primary State: Up Priorities: 7 0 SmartOptimizeTimer: 180 Received RRO (ProtectionFlag 1=Available 2=InUse 4=B/W 8=Node 10=SoftPreempt 20=Node-ID): 10.1.1.2 20.1.1.2 11 May 14 05:38:06.795 Selected as active path 10 May 14 05:38:06.795 Record Route: 10.1.1.2 20.1.1.2 9 May 14 05:38:06.794 Up 8 May 14 05:37:55.408 No Route toward dest[4 times] 7 May 14 05:37:01.450 Deselected as active 6 May 14 05:37:01.450 No Route toward dest[2 times] 5 May 14 05:37:01.437 Down 4 May 14 05:34:01.417 Selected as active path 3 May 14 05:34:01.416 Record Route: 10.1.1.2 20.1.1.2 2 May 14 05:34:01.415 Up 1 May 14 05:34:01.399 Originate Call Created: Tue May 14 05:34:01 2013 Total 1 displayed, Up 1, Down 0 Egress LSP: 1 sessions Total 0 displayed, Up 0, Down 0 Transit LSP: 0 sessions Total 0 displayed, Up 0, Down 0 lab> show interfaces ge-1/2/0 extensive |match mtu Link-level type: Ethernet, MTU: 1514, Speed: 1000mbps, BPDU Error: None, MAC-REWRITE Error: None, Loopback: Disabled, Source filtering: Disabled, Flow control: Enabled, Carrier transitions: 1, Errors: 0, Drops: 0, Collisions: 0, Aged packets: 0, FIFO errors: 0, HS link CRC errors: 0, MTU errors: 0, Resource errors: 0 Protocol inet, MTU: 1500, Generation: 176, Route table: 0 Protocol mpls, MTU: 1488, Generation: 177, Route table: 0 <<< see protocol mpls MTU is 1488 Protocol multiservice, MTU: Unlimited, Generation: 178, Route table: 0 lab> lab> ping mpls rsvp test1 size 1488 <<< Protocol MTU under interface extensive is 1488 !!!!! --- lsping statistics --- 5 packets transmitted, 5 packets received, 0% packet loss lab> lab> ping mpls rsvp test1 size 1489 <<<< exceeding MTU 1489 lsping can't send Message too long lsping can't send Message too long lsping can't send Message too long
MX> ping mpls rsvp <lsp-name> sweep
To find the MTU, use the following command:
lab> ping mpls rsvp test1 sweep 100! 5052. 2576. 1340! 2580. 1960. 1652. 1496. 1420! 1500. 1460! 1480! 1492. 1488! 1496. 1492. --- lsp ping sweep result--- Maximum Transmission Unit (MTU) is 1488 bytes
The max MTU on physical interface on Juniper Routers is 9192.