Posted Thu, 01 Jan 2015 06:00:00 GMT by Portal Admin

The Layer 2 feature in InterMapper uses information from polling SNMP enabled devices (mainly switches) to determine connections.

Layer 2 won’t add interfaces or devices to the map. The devices should be present on the map, with their interfaces selected in the Interfaces window (including unnumbered interfaces) prior to running the scan for best results. The Edit > Map Settings > Layer 2 features tool allows control over what happens to the map following the scan.

Please note that this can cause your map to be rearranged and require some manual adjustment. The tables and objects used to determine connections include:

RFC1213-MIB
ifTable (1.3.6.1.2.1.2.2)
ipAddrTable (1.3.6.1.2.1.4.20)
ipNetToMediaTable (1.3.6.1.2.1.4.22)

BRIDGE-MIB
dot1dBaseBridgeAddress (1.3.6.1.2.1.17.1.1)
dot1dBaseNumPorts (1.3.6.1.2.1.17.1.2)
dot1qNumVlans (1.3.6.1.2.1.17.7.1.1.4)
dot1dStpDesignatedRoot (1.3.6.1.2.1.17.2.5)
dot1dStpRootCost (1.3.6.1.2.1.17.2.6)
dot1dStpRootPort (1.3.6.1.2.1.17.2.7)
dot1dBasePortTable (1.3.6.1.2.1.17.1.4)
dot1dStpPortTable (1.3.6.1.2.1.17.2.15)
dot1dTpFdbTable (1.3.6.1.2.1.17.4.3)

Q-BRIDGE-MIB
dot1qTpFdbTable (1.3.6.1.2.1.17.7.1.2.2)
dot1qVlanCurrentTable (1.3.6.1.2.1.17.7.1.4.2)

CISCO-CDP-MIB
cdpCacheTable (1.3.6.1.4.1.9.9.23.1.2.1)

LLDP-MIB
lldpRemTable (1.0.8802.1.1.2.1.4.1)
lldpRemManAddrTable (1.0.8802.1.1.2.1.4.2)

CISCO-VTP-MIB
vtpVlanTable (1.3.6.1.4.1.9.9.46.1.3.1)

ENTITY-MIB
entLogicalTable (1.3.6.1.2.1.47.1.2.1)

The algorithms used to determine connections depend on much of the above information being available and generally give best results if the switch is forwarding traffic, since many entries time out in slack periods.

Often information will show up in the Layer 2 window (device list view) that isn’t included on the map, particularly switch-to-switch connections. Information about connections received from one side of a connection needs to be confirmed from the other side or by adjacent devices before it has been validated and can be included in map changes. These are the entries in the Connections (lower right) pane of the Layer 2 view that have asterisks shown to their left.

ref: The Layer 2 View |_____2

Often, by repeating the scan once or twice a day, additional information can be added and can cause further detail to be added to the map.

The layer 2 feature is not a discovery feature in InterMapper, though. It tries to show the layer 2 information that is available in addition to or instead of the default IP-centric view of the network.

For best results with DNS, be sure include DNS server addresses in the Edit > Server Settings > DNS/WINS Settings tool. If a device shows the SNMP sysName value, it means we didn’t get a DNS response for its IP address. Please verify that PTR records are updated on the DNS server so that reverse lookups are possible (or test it from the command-line).

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