Understanding the Problem:

The ports between the access switches and the distribution switch are shutting down when the L2PT configuration is applied. This typically happens due to a mismatch in port configurations or protocol incompatibilities.

Examining the Configurations:

L2PT (Layer 2 Protocol Tunneling) allows tunneling of Layer 2 traffic, which includes protocols like STP (Spanning Tree Protocol), CDP (Cisco Discovery Protocol), VTP (VLAN Trunking Protocol), etc. over a Layer 2 network.

If the L2PT is applied on access ports, it may lead to conflicts or shut down the ports as access ports are typically not configured to handle Layer 2 protocol traffic beyond their designated VLAN.

Solution: Configure Trunk Ports:

By configuring the links between the access switches and the distribution switch as trunk ports, you allow multiple VLANs to be carried over a single physical link. Trunk ports can carry tagged traffic for multiple VLANs, which includes the tunneled Layer 2 protocols.

This setup prevents the ports from shutting down and enables the correct tunneling of Layer 2 protocols.

References:

Juniper Documentation on L2PT Configuration

Troubleshooting Layer 2 Protocol Tunneling Issues