色情琪琪电影网:Using SNMP to Find a Port Number from a MAC Addres

Introduction

This document describes how to use Simple Network Management Protocol (SNMP) to obtain the port number on a Cisco Catalyst switch from which you know the MAC address.

Prerequisites

Requirements

Readers of this document should have knowledge of these topics:

• How to get VLANs from a Catalyst switch with use of SNMP

• How to use community string indexing with SNMP

• General use of the SNMP get command and walk command

Components Used

This document applies to Catalyst switches that run regular Catalyst OS (CatOS) or Cisco IOS® Software. The software supports the BRIDGE-MIB and the IF-MIB.

The information in this document is based on these software and hardware versions:

• Catalyst 3524XL that runs Cisco IOS Software Release 12.0(5)WC5a

• Net-SNMP version 5.0.6

  Note: To obtain this software, refer to Net-SNMP .

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.

Conventions

For more information on document conventions, refer to the Cisco Technical Tips Conventions.

Background

For more information on how to query the content-addressable memory (CAM) table, VLANs, and all related MIBs, such as the CISCO-VTP-MIB and the BRIDGE-MIB, refer to the Background section of the document How To Get Dynamic CAM Entries (CAM Table) for Catalyst Switches Using SNMP.

Details of the MIB Variables, Which Includes Object Identifiers (OIDs)

.1.3.6.1.2.1.17.4.3.1.1dot1dTpFdbAddress OBJECT-TYPE-- FROM BRIDGE-MIB-- TEXTUAL CONVENTION MacAddressSYNTAX          OCTET STRING (6)MAX-ACCESS      read-onlySTATUS          MandatoryDESCRIPTION    "A unicast MAC address for which the bridge has forwardingand/or filtering information."::= { iso(1) org(3) dod(6) internet(1) mgmt(2) mib-2(1) dot1dBridge(17) dot1dTp(4)dot1dTpFdbTable(3) dot1dTpFdbEntry(1) 1 }.1.3.6.1.2.1.17.4.3.1.2dot1dTpFdbPort OBJECT-TYPE-- FROM BRIDGE-MIBSYNTAX          IntegerMAX-ACCESS      read-onlySTATUS          MandatoryDESCRIPTION    "Either the value "0", or the port number of the port on whicha frame having a sourceaddress equal to the value of the corresponding instance ofdot1dTpFdbAddress has been seen.A value of "0" indicates that the port number has not been learned,but that the bridge doeshave some forwarding/filtering information about this address (that is,in the StaticTable).Implementors are encouraged to assign the port value to thisobject whenever it islearned, even for addresses for which the corresponding value ofdot1dTpFdbStatus is not learned(3)."::= { iso(1) org(3) dod(6) internet(1) mgmt(2) mib-2(1) dot1dBridge(17) dot1dTp(4)dot1dTpFdbTable(3) dot1dTpFdbEntry(1) 2 }.1.3.6.1.2.1.2.2.1.1ifIndex OBJECT-TYPESYNTAX      InterfaceIndexMAX-ACCESS  read-onlySTATUS      currentDESCRIPTION      "A unique value, greater than zero, for each interface.  Itis recommended that values are assigned contiguouslystarting from 1.  The value for each interface sub-layermust remain constant at least from one re-initialization ofthe entity‘s network management system to the next re-initialization."::= { ifEntry 1 }.1.3.6.1.2.1.17.1.4.1.2dot1dBasePortIfIndex OBJECT-TYPESYNTAX  INTEGERACCESS  read-onlySTATUS  mandatoryDESCRIPTION"The value of the instance of the ifIndex object,defined in MIB-II, for the interface correspondingto this port."::= { dot1dBasePortEntry 2 }.1.3.6.1.2.1.31.1.1.1.1ifName OBJECT-TYPESYNTAX      DisplayStringMAX-ACCESS  read-onlySTATUS      currentDESCRIPTION    "The textual name of the interface.  The value of thisobject should be the name of the interface as assigned bythe local device and should be suitable for use in commandsentered at the device‘s `console‘.  This might be a textname, such as `le0‘ or a simple port number, such as `1‘,depending on the interface naming syntax of the device.  Ifseveral entries in the ifTable together represent a singleinterface as named by the device, then each will have thesame value of ifName.  Note that for an agent which respondsto SNMP queries concerning an interface on some other(proxied) device, then the value of ifName for such aninterface is the proxied device‘s local name for it.If there is no local name, or this object is otherwise notapplicable, then this object contains a zero-length string."::= { ifXEntry 1 }

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.

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.

1. Issue this command in order to use VLAN 1 to obtain the MAC address table:

   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.

   This command uses community string indexing. The command also uses dot1dTpFdbAddress, which has OID .1.3.6.1.2.1.17.4.3.1.1. If you have loaded the MIBs onto your network management system (NMS), you can use the object name instead of the OID. Issue this command instead:

   snmpwalk -c public@1 crumpy dot1dTpFdbAddress     

   Note: You can also use the object names in Steps 2–5.

2. Issue this command to determine the bridge port number for VLAN 1:

   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    …    

   Note: VLAN 1 is dot1dTpFdbPort , or .1.3.6.1.2.1.17.4.3.1.2.

3. Issue this command to map the bridge port to the ifIndex, OID .1.3.6.1.2.1.2.2.1.1:

   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

   This command queries the dot1dBasePortIfIndex, which has OID .1.3.6.1.2.1.17.1.4.1.2.

4. 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    ifMIB.ifMIBObjects.ifXTable.ifXEntry.ifName.8 = Fa0/7    ifMIB.ifMIBObjects.ifXTable.ifXEntry.ifName.9 = Fa0/8    ifMIB.ifMIBObjects.ifXTable.ifXEntry.ifName.10 = Fa0/9    ifMIB.ifMIBObjects.ifXTable.ifXEntry.ifName.11 = Fa0/10    ifMIB.ifMIBObjects.ifXTable.ifXEntry.ifName.12 = Fa0/11    ifMIB.ifMIBObjects.ifXTable.ifXEntry.ifName.13 = Fa0/12    ifMIB.ifMIBObjects.ifXTable.ifXEntry.ifName.14 = Fa0/13    ifMIB.ifMIBObjects.ifXTable.ifXEntry.ifName.15 = Fa0/14    …

5. 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:

     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                

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 sample output:

crumpy# show macDynamic Address Count:                 58Secure Address Count:                  2Static Address (User-defined) Count:   0System Self Address Count:             51Total MAC addresses:                   111Maximum MAC addresses:                 8192Non-static Address Table:Destination Address  Address Type  VLAN  Destination Port-------------------  ------------  ----  -------------------0000.0c07.ac08       Dynamic          1  FastEthernet0/10001.021b.5091       Dynamic          1  FastEthernet0/10001.0348.4d5a       Dynamic          1  FastEthernet0/10001.0348.ddbf       Dynamic          1  FastEthernet0/10001.972d.dfae       Dynamic          1  FastEthernet0/10002.55c6.cfe7       Dynamic          1  FastEthernet0/10002.7d61.d400       Dynamic          1  FastEthernet0/1