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[M/MX/T] How to check MPLS MTU via sweep command (RSVP scenario)

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Article ID: KB28040 KB Last Updated: 25 Jan 2014Version: 1.0
Summary:
This article describes how to check the Multiprotocol Label Switching (MPLS) maximum transmission unit (MTU) via the sweep command for troubleshooting.
Solution:

The following example shows how to check the MPLS MTU using the sweep command.

Topology:

   1.1.1.1 lo0.0 R1 ----------------- <> R2 <> ------------------------- R3 lo0.0 3.3.3.3
                           

<-------------configuration-------------->

R1

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

R2

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

R3

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-------------->

Output

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
 

Use sweep command

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.

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