Simple Network Management Protocol (SNMP) | 195Figure 16-6 shows the output for an Aggregator. All hex pairs are 00, indicating that no ports are assignedto VLAN 10. In Figure 16-7, Port 0/2 is added to VLAN 10 as untagged. And the first hex pair changesfrom 00 to 04.Figure 16-7. Displaying Ports in a VLAN using SNMPThe value 40 is in the first set of 7 hex pairs, indicating that these ports are in Stack Unit 0. The hex value40 is 0100 0000 in binary. As described above, the left-most position in the string represents Port 1. Thenext position from the left represents Port 2 and has a value of 1, indicating that Port 0/2 is in VLAN 10.The remaining positions are 0, so those ports are not in the VLAN.Note that the table contains none of the other information provided by the show vlan command, such as portspeed or whether the ports are tagged or untagged.Fetching Dynamic MAC Entries Using SNMPThe Aggregator supports the RFC 1493 dot1d table for the default VLAN and the dot1q table for all otherVLANs.Note: The 802.1q Q-BRIDGE MIB defines VLANs with regard to 802.1d, as 802.1d itself does not definethem. As a switchport must belong to a VLAN (the default VLAN or a configured VLAN), all MAC addresslearned on a switchport are associated with a VLAN. For this reason, the Q-Bridge MIB is used for MACaddress query. Moreover, specific to MAC address query, dot1dTpFdbTable is indexed by MAC addressonly for a single forwarding database, while dot1qTpFdbTable has two indices —VLAN ID and MACaddress —to allow for multiple forwarding databases and considering that the same MAC address islearned on multiple VLANs. The VLAN ID is added as the first index so that MAC addresses can be readby VLAN, sorted lexicographically. The MAC address is part of the OID instance, so in this case,lexicographic order is according to the most significant octet.[Dell Force10 system output]FTOS(conf)#do show vlan id 10Codes: * - Default VLAN, G - GVRP VLANsQ: U - Untagged, T - Taggedx - Dot1x untagged, X - Dot1x taggedG - GVRP tagged, M - Vlan-stackNUM Status Description Q Ports10 Inactive U Tengig 0/2[Unix system output]> snmpget -v2c -c mycommunity 10.11.131.185 .1.3.6.1.2.1.17.7.1.4.3.1.2.1107787786SNMPv2-SMI::mib-2.17.7.1.4.3.1.2.1107787786 = Hex-STRING: 40 00 00 00 00 00 00 00 00 00 0000 00 00 00 0000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0000 00 00 00 00 00 00 00 00
