- Index
- Preface
- Product Overview
- Command-Line Interfaces
- Initial Switch Configuration
- Supervisor Engine 720 Configuration
- Supervisor Engine 32 Configuration
- Supervisor Engine 2 and Switch Fabric Module Configuration
- NSF with SSO Supervisor Engine Redundancy
- RPR and RPR+ Supervisor Engine Redundancy
- Interface Configuration
- Layer 2 Ethernet Interface Configuration
- Flex Links
- Layer 3 and Layer 2 EtherChannel
- VLAN Trunking Protocol (VTP)
- VLANs
- Private VLANs (PVLANs)
- Cisco IP Phone Support
- IEEE 802.1Q Tunneling
- Layer 2 Protocol Tunneling (L2PT)
- Standard-Compliant IEEE MST
- STP and IEEE 802.1s MST
- STP Features
- Layer 3 Interface Configuration
- UDE and UDLR
- Multiprotocol Label Switching (MPLS)
- IPv4 Multicast VPN Support
- IP Unicast Layer 3 Switching
- IPv6 Multicast Layer 3 Switching
- IPv4 Multicast Layer 3 Switching
- IGMP Snooping
- PIM Snooping
- MLDv2 Snooping
- Router-Port Group Management Protocol (RGMP)
- Network Security
- Understanding Cisco IOS ACL Support
- VLAN ACLs (VACLs)
- Denial of Service (DoS) Protection
- DHCP Snooping
- Dynamic ARP Inspection (DAI)
- Traffic-Storm Control
- Unknown Unicast and Multicast Flood Blocking
- PFC QoS
- MPLS QoS
- PFC QoS Statistics Data Export
- Cisco IOS Firewall Feature Set
- Network Admission Control (NAC)
- IEEE 802.1X Port-Based Authentication
- Port Security
- Cisco Discovery Protocol (CDP)
- UniDirectional Link Detection (UDLD)
- NetFlow Table Configuration
- NetFlow Data Export (NDE)
- Local SPAN, Remote SPAN (RSPAN), and Encapsulated RSPAN
- SNMP IfIndex Persistence
- Power Management and Environmental Monitoring
- Online Diagnostic Configuration
- Top N Utility Reports
- Using the Layer 2 Traceroute Utility
- Online Diagnostic Tests
- Acronyms
Using the Layer 2 Traceroute Utility
This chapter describes how to use the Layer 2 traceroute utility. Release 12.2(18)SXE and later releases support the Layer 2 traceroute utility.
Note For complete syntax and usage information for the commands used in this chapter, refer to the Cisco IOS Master Command List, Release 12.2SX at this URL:
http://www.cisco.com/en/US/docs/ios/mcl/allreleasemcl/all_book.html
This chapter contains these sections:
•Understanding the Layer 2 Traceroute Utility
•Using the Layer 2 Traceroute Utility
Tip For additional information about Cisco Catalyst 6500 Series Switches (including configuration examples and troubleshooting information), see the documents listed on this page:
http://www.cisco.com/en/US/products/hw/switches/ps708/tsd_products_support_series_home.html
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Understanding the Layer 2 Traceroute Utility
The Layer 2 traceroute utility identifies the Layer 2 path that a packet takes from a source device to a destination device. Layer 2 traceroute supports only unicast source and destination MAC addresses. The utility determines the path by using the MAC address tables of the switches in the path. When the Layer 2 traceroute utility detects a device in the path that does not support Layer 2 traceroute, it continues to send Layer 2 trace queries and allows them to time out.
The Layer 2 traceroute utility can only identify the path from the source device to the destination device. The utility cannot identify the path that a packet takes from the source host to the source device or from the destination device to the destination host.
Usage Guidelines
When using the Layer 2 traceroute utility, follow these guidelines:
•Cisco Discovery Protocol (CDP) must be enabled on all the devices in the network. For the Layer 2 traceroute utility to function properly, do not disable CDP. If any devices in the Layer 2 path are transparent to CDP, the Layer 2 traceroute utility cannot identify these devices on the path.
Note For more information about CDP, see Chapter 48 "Configuring CDP."
•A switch is defined as reachable from another switch when you can test connectivity by using the ping privileged EXEC command. All devices in the Layer 2 path must be mutually reachable.
•The maximum number of hops identified in the path is ten.
•You can enter the traceroute mac or the traceroute mac ip privileged EXEC command on a switch that is not in the Layer 2 path from the source device to the destination device. All devices in the path must be reachable from this switch.
•The traceroute mac command output shows the Layer 2 path only when the specified source and destination MAC addresses belong to the same VLAN. If you specify source and destination MAC addresses that belong to different VLANs, the Layer 2 path is not identified, and an error message appears.
•If you specify a multicast source or destination MAC address, the path is not identified, and an error message appears.
•If the source or destination MAC address belongs to multiple VLANs, you must specify the VLAN to which both the source and destination MAC addresses belong. If the VLAN is not specified, the path is not identified, and an error message appears.
• The traceroute mac ip command output shows the Layer 2 path when the specified source and destination IP addresses belong to the same subnet. When you specify the IP addresses, the Layer 2 traceroute utility uses the Address Resolution Protocol (ARP) to associate the IP addresses with the corresponding MAC addresses and the VLAN IDs.
–If an ARP entry exists for the specified IP address, the Layer 2 traceroute utility uses the associated MAC address and identifies the Layer 2 path.
–If an ARP entry does not exist, the Layer 2 traceroute utility sends an ARP query and tries to resolve the IP address. If the IP address is not resolved, the path is not identified, and an error message appears.
•When multiple devices are attached to one port through hubs (for example, multiple CDP neighbors are detected on a port), the Layer 2 traceroute utility terminates at that hop and displays an error message.
•The Layer 2 traceroute utility is not supported in Token Ring VLANs.
Using the Layer 2 Traceroute Utility
To display the Layer 2 path that a packet takes from a source device to a destination device, perform one of these tasks in privileged EXEC mode:
These examples show how to use the traceroute mac and traceroute mac ip commands to display the physical path a packet takes through the network to reach its destination:
Router# traceroute mac 0000.0201.0601 0000.0201.0201
Source 0000.0201.0601 found on con6[WS-C2950G-24-EI] (2.2.6.6)
con6 (2.2.6.6) :Fa0/1 => Fa0/3
con5 (2.2.5.5 ) : Fa0/3 => Gi0/1
con1 (2.2.1.1 ) : Gi0/1 => Gi0/2
con2 (2.2.2.2 ) : Gi0/2 => Fa0/1
Destination 0000.0201.0201 found on con2[WS-C3550-24] (2.2.2.2)
Layer 2 trace completed
Router#
Router# traceroute mac 0001.0000.0204 0001.0000.0304 detail
Source 0001.0000.0204 found on VAYU[WS-C6509] (2.1.1.10)
1 VAYU / WS-C6509 / 2.1.1.10 :
Gi6/1 [full, 1000M] => Po100 [auto, auto]
2 PANI / WS-C6509 / 2.1.1.12 :
Po100 [auto, auto] => Po110 [auto, auto]
3 BUMI / WS-C6509 / 2.1.1.13 :
Po110 [auto, auto] => Po120 [auto, auto]
4 AGNI / WS-C6509 / 2.1.1.11 :
Po120 [auto, auto] => Gi8/12 [full, 1000M] Destination 0001.0000.0304 found on AGNI[WS-C6509] (2.1.1.11) Layer 2 trace completed.
Router#
Tip For additional information about Cisco Catalyst 6500 Series Switches (including configuration examples and troubleshooting information), see the documents listed on this page:
http://www.cisco.com/en/US/products/hw/switches/ps708/tsd_products_support_series_home.html
Participate in the Technical Documentation Ideas forum