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Troubleshooting Tag Switching Connections

Troubleshooting Tag Switching Connections

This chapter provides troubleshooting information for connectivity and performance problems in tag switching environments. For an overview of tag switching on an ATM switch. See the chapter "Configuring Tag Switching" in the LightStream 1010 ATM Switch Software Configuration Guide.

Before you begin, make sure that all physical port connections are working correctly. (See the chapter "Troubleshooting ATM Switch Interface Connections.")

This chapter contains the following sections:

Tag Switching Overview

Tag switching is a high-performance packet-forwarding technology that assigns tags to multiprotocol frames for transport across packet-based or cell-based networks.

In conventional Layer 3 forwarding, as a packet traverses the network, each router extracts forwarding information from the Layer 3 header. Header analysis is repeated at each router (hop) through which the packet passes.

In a tag switching network, the Layer 3 header is analyzed just once. It is then mapped into a short, fixed-length tag. At each hop, the forwarding decision is made by looking at the value of the tag only; there is no need to reanalyze the Layer 3 header. Because the tag is a fixed length, an unstructured value, looking it up is fast and simple.

A tag switching network consists of tag edge routers and tag switches, as shown in Figure 7-1. Tag edge routers are located at the edge of a tag switching network. They use standard routing protocols---such as Open Shortest Path First (OSPF)---to create routing tables, that identify routes through the network. Based on the routing tables, tag edge routers use the Tag Distribution Protocol (TDP) to apply and distribute tags to other tag edge routers or tag switches. Tag switches are located at the core of a tag switching network. They receive TDP information from the tag edge routers and build their own forwarding database. Tag switches then switch the packets based on the tags only (without looking at the Layer  3 header).

How Tag Switching Works

When a tag edge router at the entry point of a tag switching network receives a packet for forwarding:

    1. The router analyzes the network layer header and performs any applicable network layer services such as security, accounting, or quality of service (QoS) classification.

    2. The router chooses a route for the packet based on the information in its routing table, applies a tag, and forwards the packet to the next-hop tag switch.

    3. The tag switch receives the tagged packet and switches the packet from switch to switch based on the tag only. The switches do not reanalyze the network layer header; they look only at the short, fixed-length tag.

    4. The packet reaches the tag edge router at the exit point of the tag switched network, where the tag is removed and the packet is delivered.

Example of Troubleshooting Tag Switching

In the example network (see Figure 7-1) the primary campus network backbone is made up of two LightStream 1010 switches connected to two Cisco routers:


Figure 7-1: Tag Switching Example Network


This network example is used to describe the troubleshooting examples in the rest of this chapter.

For detailed configuration information about tag switching refer to the chapter "Configuring Tag Switching" in the LightStream 1010 ATM Switch Software Configuration Guide.

Initial Troubleshooting of Tag Switching

This section describes initial troubleshooting steps that you should perform when beginning to troubleshoot a tag switching connection.

At the LightStream 1010 ATM switch use the following commands to check the tag switching configuration:
Command Task

show tag tdp discovery

Confirm the TDP identifier for the tag switching ATM switches or routers that might to be malfunctioning.

ping tdp_id_of_neighbor

Confirm that each tag switching ATM switch or router can connect to the TDP identifier of its neighbor.

show running-config

Confirm that tag switching is enabled on the switch.

show tag-switching interfaces

Confirm the tag switching configuration on the ATM interface.

show tag interface detail

Confirm the tag switching VPI1 range on an interface.

show interface loopback 0

Confirm the loopback interface 0 configuration.

show ip ospf

Confirm the OSPF configuration.

1VPI = virtual path identifier

Follow these steps to confirm the TDP identifier for the tag switching ATM switches or routers that might be malfunctioning:

Step 1 Use the show tag tdp discovery command to determine the tag discovery protocol identifier of the tag switching ATM switch.

Step 2 Check the Local TDP Identifier field. This field indicates the TDP identifier for the local tag switching ATM switch or router for this session.

Step 3 Check the Interfaces field. This field displays the interfaces engaging in TDP discovery activity:

If either xmit or recv do not appear, refer to the chapter "Configuring Tag Switching," of the LightStream 1010 ATM Switch Software Configuration Guide.

Follow these steps to Ping each tag switching ATM switch or router. This process confirms that each can connect to the TDP identifier of the neighbor:

Step 1 Use the ping command to confirm the connection to the TDP of the neighbor.

Step 2 Check the Success rate field. This field should indicate 100 percent. If not, continue with the following troubleshooting steps.

Follow these steps to confirm that tag switching is configured on the ATM switch and its interfaces:

Step 1 Use the show running-config command to confirm that tag switching is enabled on the switch.

Step 2 Check the tag switching ATM switch interface to confirm that tag switching is enabled on the connections.

For detailed interface configuration information about tag switching, refer to the section "Enabling Tag Switching on the ATM Interface," in the chapter "Configuring Tag Switching," in the LightStream 1010 ATM Switch Software Configuration Guide.

The neighbor information branch can have information about all TDP neighbors or can be limited to the neighbor with a specific IP address or, TDP identifier, or to TDP neighbors known to be accessible over a specific interface. Follow these steps to display the status of TDP sessions:

Step 1 Use the show tag-switching tdp neighbor command to display the status of TDP sessions.

Step 2 Check the Peer TDP Ident field. This field indicates the TDP identifier of the neighbor (peer device) for this session.

Step 3 Check the Local TDP Ident field. This field indicates the TDP identifier for the local tag switching ATM switch or router for this session.

Step 4 Check the TCP connection field. This field indicates the TCP connection used to support the TDP session. The format for displaying the TCP connection is peer IP address.peer port local IP address.

Step 5 Check the PIEs sent/rcvd (Protocol Information Element sent or received) field. This field indicates the number of TDPPIEs sent to and received from the session peer device. The count includes the transmission and receipt of periodic keepalive PIEs, which are required for maintenance of the TDP session.

Step 6 Check the Up time field. This field indicates the length of time the TDP session has existed.

Follow these steps to confirm the tag switching interface configuration on the ATM switch:

Step 1 Use the show tag-switching interface command to confirm the configuration and connection of the tag switching interfaces.

Step 2 Check the IP field. This field indicates whether the interface is configured to tag IP packets.

Step 3 Check the Operational field. This field shows whether the packets are being tagged.

Step 4 Use the show tag interface detail command to confirm the tag switching VPI range on an interface.




Step 5	 Check the IP tagging enabled field. This field indicates whether tag switching is enabled on this interface.



Step 6	 Check the ATM tagging field. This field indicates the VPI range of the interface.


 For detailed interface configuration information about tag switching, refer to the section "Enabling Tag Switching on the ATM Interface," in the chapter "Configuring Tag Switching," in the LightStream 1010 ATM Switch Software Configuration Guide.


 Follow these steps to confirm the loopback interface 0 configuration on the ATM switch:



Step 1	 Use the show interface loopback 0 command to confirm the loopback interface 0 configuration on the switch.






Step 2	 Check the Loopback 0 status field. It should be up.



Step 3	 Check the line protocol field. It should be up.



Step 4	 Check the Internet address field. It should display the IP address of the loopback interface on this ATM switch.


 For detailed interface configuration information about loopback, refer to the section "Configuring a Loopback Interface," in the chapter "Configuring Tag Switching," in the LightStream 1010 ATM Switch Software Configuration Guide.


 Follow these steps to confirm the OSPF configuration on the ATM switch:



Step 1	 Use the show ip ospf command to confirm the OSPF configuration of the ATM switch.






Step 2	 Check the Routing Process field. The ospf field and ID fields should match the numbers configured.


 If not, refer to the OSPF configuration information, refer to the section "Configuring OSPF," in the chapter "Configuring Tag Switching," in the LightStream 1010 ATM Switch Software Configuration Guide.


 Troubleshooting TDP Neighbors

 
 This section describes how to troubleshoot TDP control channel VPI and virtual channel identifier (VCI).


 Although not necessary for most configurations, you can change the default VPI and VCI of the TDP control channel if you want to use a nondefault value. 



Note The default TDP control channel is on VPI 0 and VCI 32. TDP control channels exchange TDP Hellos and PIEs to establish two-way TDP sessions. Tag virtual channels (TVCs) are created by the exchange of PIEs through TDP control channels.



 Use the following commands to check the tag switching TPD neighbor connections: 




Commands
Task



 show tag-switching tdp neighbor


 Confirm the tag switching TDP neighbor connection.











 


 Follow these steps to check the tag switching TPD neighbor connections:



Step 1	 Use the show tag-switching tdp neighbor command to confirm the tag switching TDP neighbor connections:



Step 2	 Check the Peer TDP Identifier field. This field indicates the TDP identifier of the neighbor (peer device) for this session. 



Step 3	 Check the Local TDP Identifier field. This field indicates the TDP identifier for the local tag switching ATM switch or router for this session. 



Step 4	 Check the TCP connection field. This field indicates the TCP connection used to support the TDP session. The format for displaying the TCP connection is peer IP address.peer port local IP address.



Step 5	 Check the PIEs sent/rcvd (sent or received) field. This field indicates the number of TDP PIEs sent to and received from the session peer device. The count includes the transmission and receipt of periodic keepalive PIEs, which are required for maintenance of the TDP session. 



Step 6	 Check the Up time field. This field indicates the length of time the TDP session has existed. 


 Follow these steps to confirm the VPI and VCI configuration of the tag switching interface on the ATM switch interface:



Step 1	 Use the show tag interface atm card/subcard/port detail command to confirm the configuration and connection of the tag switching interface VPI and VCI.






Step 2	 Check the IP tagging field. This field shows whether the interface is configured to tag IP packets.



Step 3	 Check the Tagging operational field. This field shows whether the packets are being tagged.



Step 4	 Check the ATM tagging field. This field indicates the VPI range of the interface.


 For detailed tag switching VPI and VCI configuration information, refer to the section "Configuring a VPI Range," in the chapter "Configuring Tag Switching," in the LightStream 1010 ATM Switch Software Configuration Guide, 


 Troubleshooting Tag Switching on VP Tunnels

 
 This section describes how to troubleshoot a tag switching connection configured on a VP tunnel.


 For detailed information about VP tunnel tag switching configuration refer to the section "Configuring Tag Switching on VP Tunnels," in the chapter "Configuring Tag Switching" in the LightStream 1010 ATM Switch Software Configuration Guide. 


 To confirm VP tunnel configuration of tag switching, perform the following task in EXEC mode: 




Command
Task



 show atm vp


 Confirm the VP tunnel configuration on an interface.




 show tag-switching tsp-tunnels {ip_address | all | head | middle | tail | remote} [tunnel-interface-num] [brief]


 Confirm the TSP1 tunnel status and configuration.








1TSP = tag switching path






 Follow these steps to confirm the VP tunnel configuration of tag switching:



Step 1	 Use the show atm vp command to confirm VP tunnel configuration.






Step 2	 Check the Status field. The PVP status should be up. If not, check the VP tunnel configuration. Refer to the section "Configuring Tag Switching on VP Tunnels" in the chapter "Configuring Tag Switching," in the LightStream 1010 ATM Switch Software Configuration Guide.


 Follow these steps to confirm the tag switching VP tunnel configuration:



Step 1	 Use the show tag-switching tsp-tunnels command to confirm VP tunnel configuration on each router or ATM switch in the network. The following example starts at the headend:






Step 2	 Use the show tag-switching tsp-tunnels command to confirm VP tunnel configuration at the middle ATM switches or routers:






Step 3	 Use the show tag-switching tsp-tunnels command to confirm VP tunnel configuration at the tailend ATM switch or router:






Step 4	 Verify that the TSP Tunnels Process is running. If not, enter the tag-switching tsp-tunnels command to enable the process globally on the ATM switch or router.



Step 5	 Verify that the RSVP Process is running. If not, enter the tag-switching tsp-tunnels command on the interfaces used by the tunnel to enable the process on the interface.



Step 6	 If this is a router connection, verify that Forwarding is enabled on the router. If not, enter the ip cef distributed switch or ip cef switch commands to enable IP Cisco Express Forwarding (CEF) globally on the router.



Step 7	 Use the show tag-switching interface command to check the VP tunnel interface configuration at each ATM switch or router in the tunnel. The following example starts at the headend:






Step 8	 Use the show tag-switching interface command to check the VP tunnel interface configuration at the middle ATM switches or routers:






Step 9	 Use the show tag-switching tsp-tunnels command to confirm VP tunnel configuration at the tailend ATM switch or router:






Step 10	 Verify that the interfaces used by the tunnel have "Yes" in the Tunnel column. 


 If not, use the tag-switching tsp-tunnels command on the interfaces used by the tunnel to enable TSP tunnels.


 Refer to the section "Configuring Tag Switching on VP Tunnels," in the chapter "Configuring Tag Switching," in the LightStream 1010 ATM Switch Software Configuration Guide.



Step 11	 Verify that the interfaces used by the tunnel are operational. The interfaces should have "Yes" under the Operational column. 


 If not, check the interface configuration and refer to the section "Configuring Tag Switching on VP Tunnels," in the chapter "Configuring Tag Switching," in the LightStream 1010 ATM Switch Software Configuration Guide.


 Troubleshooting Tag Switching Using debug Commands

 
 This section describes debug commands that you can use to troubleshoot tag switching connections on an ATM switch.


 Use the following commands to debug tag switching connections on an ATM switch: 




Command
Task



 debug tag-switching adjacency


 Debug tag switching adjacency database events.




 debug tag-switching atm-tdp {api | routes | states}


 Debug tag switching ATM Tag Distribution Protocol (TDP) events.




 debug tag-switching packets {atm card/subcard/port | atm-p card/subcard/port | cbr card/subcard/port | ethernet card/subcard/port | loopback 0 | null}


 Debug tag switching packets.




 debug tag-switching tdp {advertisements | bindings | directed-neighbors | pies [received | sent] | session [io | state] | transport [connections | events | timers]}


 Debug TDP switching events.




 debug tag-switching tfib {cef | enc | state | struct | tsp}


 Debug tag switching TFIB1.




 debug tag-switching traffic-eng {events | interfaces | metrics | routing-table}


 Debug tag switching traffic engineering.




 debug tag-switching tsp-tunnels {events | signalling | tagging}


 Debug tag switching TSP tunnels.








1TFIB = Tag Forwarding Information Base



 


 For detailed interface configuration information, refer to the section "Enabling Tag Switching on the ATM Interface," in chapter "Configuring Tag Switching," in the LightStream 1010 ATM Switch Software Configuration Guide.







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