Get the Port Number on Which a MAC Address Has Been Learned
Step-by-Step Instructions
Complete the steps in this section in order to use SNMP to get the port number on which a MAC address has been learned. Consider that the port number is in VLAN1.
Note: In the commands in this section:
- public is the read community string.
- @1 is the VLAN 1 part of the read community string.
- crumpy is the device host name.
Note: You can also use the IP address for this host name.
Note: The Conclusion section uses the values that appear in italics in the command output.
- Retrieve the VLANs. Use the snmpwalk command on the vtpVlanState object (.1.3.6.1.4.1.9.9.46.1.3.1.1.2 ):
Note: This command uses community string indexing. The command also uses vtpVlanState, which has OID.1.3.6.1.4.1.9.9.46.1.3.1.1.2. If you have loaded the MIBs to your network management system (NMS), you can use the object name instead of the OID. Issue this command instead:%snmpwalk -c public crumpy .1.3.6.1.4.1.9.9.46.1.3.1.1.2 CISCO-VTP-MIB::vtpVlanState.1.1 = INTEGER: operational(1) CISCO-VTP-MIB::vtpVlanState.1.3 = INTEGER: operational(1) CISCO-VTP-MIB::vtpVlanState.1.7 = INTEGER: operational(1) CISCO-VTP-MIB::vtpVlanState.1.10 = INTEGER: operational(1) ...
Note: You can also use the object names in steps 2 through 6.%snmpwalk -c public@1 crumpy vtpVlanState
- Issue this command in order to obtain the MAC address table by considering that the port belongs to VLAN1:
Note: Provide the appropriate VLAN number after the community string. In this example, it is VLAN1.snmpwalk -c public@1 crumpy .1.3.6.1.2.1.17.4.3.1.1 17.4.3.1.1.0.0.12.7.172.8 = Hex: 00 00 0C 07 AC 08 17.4.3.1.1.0.1.2.27.80.145 = Hex: 00 01 02 1B 50 91 17.4.3.1.1.0.1.3.72.77.90 = Hex: 00 01 03 48 4D 5A 17.4.3.1.1.0.1.3.72.221.191 = Hex: 00 01 03 48 DD BF ...
The command lists all MAC addresses that have been learned on all ports that belong to VLAN 1. - Issue this command to determine the bridge port number for VLAN 1:
Note: VLAN 1 is dot1dTpFdbPort , or .1.3.6.1.2.1.17.4.3.1.2.snmpwalk -c public@1 crumpy .1.3.6.1.2.1.17.4.3.1.2 17.4.3.1.2.0.0.12.7.172.8 = 13 17.4.3.1.2.0.1.2.27.80.128 = 13 17.4.3.1.2.0.1.2.27.80.145 = 13 17.4.3.1.2.0.1.2.163.145.225 = 13 ...
- Issue this command to map the bridge port to the ifIndex, OID .1.3.6.1.2.1.2.2.1.1:
This command queries the dot1dBasePortIfIndex, which has OID .1.3.6.1.2.1.17.1.4.1.2.snmpwalk -c public@1 crumpy .1.3.6.1.2.1.17.1.4.1.2 17.1.4.1.2.13 = 2 17.1.4.1.2.14 = 3 17.1.4.1.2.15 = 4 17.1.4.1.2.16 = 5
- Use the walk command with ifName in order to correlate the ifIndex value with a correct port name.
Issue this command:
Note: The ifName has OID .1.3.6.1.2.1.31.1.1.1.1.
snmpwalk -c public@1 crumpy .1.3.6.1.2.1.31.1.1.1.1 ifMIB.ifMIBObjects.ifXTable.ifXEntry.ifName.1 = VL1 ifMIB.ifMIBObjects.ifXTable.ifXEntry.ifName.2 = Fa0/1 ifMIB.ifMIBObjects.ifXTable.ifXEntry.ifName.3 = Fa0/2 ifMIB.ifMIBObjects.ifXTable.ifXEntry.ifName.4 = Fa0/3 ifMIB.ifMIBObjects.ifXTable.ifXEntry.ifName.5 = Fa0/4 ifMIB.ifMIBObjects.ifXTable.ifXEntry.ifName.6 = Fa0/5 ifMIB.ifMIBObjects.ifXTable.ifXEntry.ifName.7 = Fa0/6 ...
- Link a MAC address to the port on which the address was learned.
- From Step 1, the MAC address is:
17.4.3.1.1.0.0.12.7.172.8 = Hex: 00 00 0C 07 AC 08
- From Step 2, the bridge port tells that the MAC address belongs to bridge port number 13:
17.4.3.1.2.0.0.12.7.172.8 = 13
- From Step 3, the bridge port number 13 has ifIndex number 2:
17.1.4.1.2.13 = 2
- From Step 4, the ifIndex 2 corresponds to port Fast Ethernet 0/1:
ifMIB.ifMIBObjects.ifXTable.ifXEntry.ifName.2 = Fa0/1
- From Step 1, the MAC address is:
Conclusion
The MAC address 00 00 0C 07 AC 08 is learned on port Fa0/1.
Compare this conclusion with output from:
- The show cam dynamic command for CatOS switches
- The show mac command for Cisco IOS Software switches
Here is the sample output:
crumpy# show mac Dynamic Address Count: 58 Secure Address Count: 2 Static Address (User-defined) Count: 0 System Self Address Count: 51 Total MAC addresses: 111 Maximum MAC addresses: 8192 Non-static Address Table: Destination Address Address Type VLAN Destination Port ------------------- ------------ ---- ------------------- 0000.0c07.ac08 Dynamic 1 FastEthernet0/1 0001.021b.5091 Dynamic 1 FastEthernet0/1 0001.0348.4d5a Dynamic 1 FastEthernet0/1 0001.0348.ddbf Dynamic 1 FastEthernet0/1 0001.972d.dfae Dynamic 1 FastEthernet0/1 0002.55c6.cfe7 Dynamic 1 FastEthernet0/1 0002.7d61.d400 Dynamic 1 FastEthernet0/1 …
original: http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a00801c9199.shtml
