Cisco Systems A9014CFD manual Troubleshooting Tips, 13-9

Chapter 13 Configuring MST on EVC Bridge Domain

Contents

Troubleshooting Tips

Table 13-1	Troubleshooting Scenarios
Problem		Solution
Multiple Spanning Tree Protocol (MSTP) incorrectly or		To avoid BPDU loss, re-configure these on the following
inconsistently formed due to misconfiguration and BPDU		nodes:
loss		•	Configuration name
		•	Bridge revision
		• Provider-bridge mode
		• Instance to VLAN mapping
		Determine if node A is sending BPDUs to node B. Use the
		show spanning-tree mst interface gi1/1 service instance
		command for each interface connecting the nodes. Only
		designated ports relay periodic BPDUs.
MSTP correctly formed, but traffic flooding occurs		Intermittent BPDU loss occurs when the spanning tree appears
		incorrectly in the show commands, but relays topology change
		notifications. These notifications cause a MAC flush, forcing
		traffic to flood until the MAC addresses are re-learned. Use the
		debug spanning-tree mst packet full {received sent}
		command to debug topology change notifications.
		Use the debug spanning-tree mst packet brief {received
		sent} command on both nodes to check for missing BPDUs.
		Monitor the timestamps. A time gap greater than or equal to
		six seconds causes topology change.
MSTP shows incorrect port state		When the spanning tree protocol (STP) attempts to change the
		port state, it uses L2VPN. Check the value of the sent update.
		If the value is Yes, then STP is awaiting an update from
		L2VPN.
Packet forwarding does not match the MSTP state		Complete the following steps to verify and troubleshoot:
		1. Shut down redundant links, remove MSTP configuration,
			and ensure that basic bridging works.
		2. Check the state of each port as calculated by MSTP, and
			compare it with the packet counts transmitted and
			received on ports and EFPs controlled by MSTP. Normal
			data packets should be sent/received only on ports in the
			forwarding (FWD) state. BPDUs should be sent/received
			on all ports controlled by MSTP.
		3. Ensure that BPDUs are flowing and that root bridge
			selection is correct and check the related scenarios.
		4. Use the show l2vpn bridge-domain detail command to
			confirm the status of the members of the bridge domain.
			Ensure that the relevant bridge domain members are
			active.
		5. Check the forwarding state as programmed in hardware.

	Cisco ASR 901 Series Aggregation Services Router Software Configuration Guide
OL-23826-09		13-9