# Troubleshooting MTU Problems in Point-to-Point LSPs

In an MPLS-enabled network with point-to-point LSPs, you can use the data-size keyword with the ping mpls command to detect MTU failures in different types of MPLS applications and network topologies. You can use the data-size keyword to troubleshoot MTU problems in point-to-point MPLS LSPs to determine whether MPLS packets with a particular size can be forwarded over an MPLS point-to-point LSP, when the size of the packets exceeds the MTU size at any of the LSRs that are nodes of the LSP. If you specify the packet size for MPLS echo requests, you can determine the exact LSR where the MTU size is exceeded and the MPLS packets are discarded.

Tasks to verify and troubleshoot MTU problems in point-to-point LSPs are:

- Troubleshooting MTU Problems in a Point-to-Point MPLS LSP Associated with an IP or IPv6 Address
- Troubleshooting MTU Problems in a Point-to-Point MPLS LSP Associated with an L3VPN IP or IPv6 Prefix
- Troubleshooting MTU Problems in a Point-to-Point MPLS LSP Associated with a Martini Circuit
- Troubleshooting MTU Problems in a Point-to-Point MPLS LSP Associated with an RSVP-TE Tunnel
- Troubleshooting MTU Problems in a Point-to-Point MPLS LSP Associated with a VPLS Instance

## Troubleshooting MTU Problems in a Point-to-Point MPLS LSP Associated with an IP or IPv6 Address

To discover the LSR in a point-to-point MPLS LSP, associated with an IP or IPv6 prefix, that causes MPLS packets to be discarded owing to the size of the packet exceeding the MTU size:

- Issue the trace mpls ip command with the data-size keyword.
  host1:pe1#trace mpls ip 192.168.25.1/32 data-size 60

## Troubleshooting MTU Problems in a Point-to-Point MPLS LSP Associated with an L3VPN IP or IPv6 Prefix

To discover the LSR in a point-to-point MPLS LSP, associated with an L3VPN IP or IPv6 prefix, that causes MPLS packets to be discarded owing to the size of the packet exceeding the MTU size:

- Issue the trace mpls l3vpn command with the data-size keyword.
  host1:pe1#trace mpls l3vpn vrf pe11 10.2.3.21/32 data-size 60

## Troubleshooting MTU Problems in a Point-to-Point MPLS LSP Associated with a Martini Circuit

To discover the LSR in a point-to-point MPLS LSP, associated with a Martini circuit, that causes MPLS packets to be discarded owing to the size of the packet exceeding the MTU size:

- Issue the trace mpls l2transport command with the data-size keyword.
  host1:pe1#trace mpls l2transport FastEthernet1/0.1 data-size 60

## Troubleshooting MTU Problems in a Point-to-Point MPLS LSP Associated with an RSVP-TE Tunnel

To discover the LSR in a point-to-point MPLS LSP, associated with an RSVP-TE tunnel, that causes MPLS packets to be discarded owing to the size of the packet exceeding the MTU size:

- Issue the trace mpls rsvp tunnel command with the data-size keyword.
  host1:pe1#trace mpls rsvp tunnel west1 data-size 60

## Troubleshooting MTU Problems in a Point-to-Point MPLS LSP Associated with a VPLS Instance

To discover the LSR in a point-to-point MPLS LSP, associated with a VPLS instance, that causes MPLS packets to be discarded owing to the size of the packet exceeding the MTU size:

- Issue the trace mpls vpls command with the data-size keyword.
  host1:pe1#trace mpls vpls vplsA sender-site-id 1 remote-site-id 2 data-size 60

#### Related Documentation

- ping mpls ip
- ping mpls l2transport
- ping mpls l3vpn
- ping mpls rsvp tunnel
- ping mpls vpls
- trace mpls ip
- trace mpls l2transport
- trace mpls l3vpn
- trace mpls rsvp tunnel
- trace mpls vpls