How to Discover Layer2 Objects

This task describes how to discover Layer2 objects.

This task includes the following steps:

1. Prerequisite - Set up protocol credentials

   The SNMP protocol is required to discover Layer2 objects. When defining the SNMP protocol credentials, have available the Port and Community authentication parameters.

   For credential information, see Supported Protocols.

2. Prerequisite - Other

   • Make sure that there is SNMP access to all switches in the environment to be discovered. This is a key requirement for fully discovering the Layer2 topology.

3. Run the discovery

   For details on running jobs, refer to "Module/Job-Based Discovery" in the Data Flow Management section of the UCMDB Help.

   Activate the jobs in the following order:

   1. Activate the Host Connection by SNMP job. This job saves SNMP CIs to the CMDB.

      Note Layer2 discovery is based on the connection jobs for the following reasons:

      • The Layer2 connectivity between the switch-port to the host is based on the host MAC address. These MAC addresses are discovered by the network connection jobs (Host Interfaces).
      • The trigger of the Layer2 job is dependent on the type of the discovered switch. The switch class and type is discovered by the Host Networking by SNMP job for the Layer2 module.

   2. Activate the Host Networking by SNMP job. This job discovers host networking topology using SNMP route and system tables. You should run this job on all SNMP agents on the switches that were discovered in the environment. The to-be discovered Layer2 link names are dependent on this discovery. (Layer2 CIs names are the same as the relevant interface name and interface description on the destination network interface adapter which we are discovering.)

   3. Activate the VLANs by SNMP job.

      The trigger for this job is the snmp_of_catalyst_switch query. The Switch CIT is either:

      • an SNMP object

      • an SNMP agent that is connected to a switch

      The SNMP_Net_Dis_Catalyst_Vlans.py script retrieves the VLAN, ELAN name, and VLAN number per ELAN tables.

   4. Activate the VLAN ports by SNMP job.

      The trigger for this job is the catalyst_vlan query. This is a VLAN object that has a connection to:

      • a switch with an SNMP object

      • a switch

      The trigger is placed on the VLAN object instead of on the SNMP itself because the VLAN object must be authenticated with a special community string (and not with the regular community string that was discovered on the SNMP object on the discovered switch). This community string should hold the value <COMMUNITY>@<VLAN NUMBER>. For example, if the community string is public and the discovered VLAN number is 16, the community string is public@16.

      The SNMP_Net_Dis_VMS_catalyst.py script retrieves the Base MAC table and Port number If Index table.

      For details on the SNMP protocol parameters, see SNMP Protocol in the Data Flow Management section of the UCMDB Help.

   5. Activate the Layer2 Topology Bridge-based by SNMP job.

      The trigger for this job is the catalyst_bridge_no_vlan query. This is a Bridge object that has a connection to:

      • a switch with an SNMP object

      • a switch

      Both this job (Layer2 Topology Bridge-based by SNMP) and the following job (Layer2 Topology VLAN-based by SNMP) use the bridgePortDisc.py script. The difference between the jobs in this script is as follows:

      For Cisco network devices.

      • Layer2 Topology Bridge-based by SNMP uses the regular SNMP community authentication. The job is triggered on the Bridge only when the discovered switch has no VLANS.

      • Layer2 Topology VLAN-based by SNMP is triggered on each one of the VLANs discovered on the switch. This job uses the relevant special community authentication, as explained in Activate the VLAN ports by SNMP job., based on the triggered VLAN number.

      For other network devices.

      • Layer2 Topology Bridge-based by SNMP uses the BRIDGE-MIB to discover Layer2 connections.

      • Layer2 Topology VLAN-based by SNMP uses QBRIDGE-MIB or STATISTICS-MIB to discover Layer2 connections.

      Note

      • The Layer2 Topology Bridge-based by SNMP job discovers Layer2 connections per default VLAN. (The default VLAN is #1.) The Layer2 Topology VLAN-based by SNMP job discovers all Layer2 connections for all VLANs, including the default one. Therefore:

        • If you want to discover Layer2 connections for the default VLAN only, you do not need to run the VLANs by SNMP and LVAN ports by SNMP jobs.

        • If you execute the VLANs by SNMP job, and it reports any VLAN CIs connected to the network device, the Layer2 Topology Bridge-based by SNMP job does not discover Layer2 connections because the device is excluded from the job's trigger TQL query. To discover Layer2 connections on a device with discovered VLANs, you must use the Layer2 Topology VLAN-based by SNMP job.

        • If you dispatch the Bridge-based Layer2 job on the bridge of a switch that holds VLANs, only the default VLAN Layer2 topology is discovered.

      • The Layer2 Topology Bridge-based/VLAN-based by SNMP jobs only report switches to host Layer2 connections. To report switch to switch, you must also run the Process Layer2 Saved Files job.

   6. Activate the Layer2 Topology VLAN-based by SNMP job.

      The trigger for this job is the catalyst_vlan_with_bridge query. This is a VLAN object with a value in its bridge_mac attribute. It should also have a connection to either:

      • a switch with an SNMP object

      • a switch

      For details on the bridgePortDisc.py script, see Activate the Layer2 Topology Bridge-based by SNMP job..