.. image:: ../../../../_static/openl2m_logo.png =========================== Cisco-SB SNMP VLAN Overview =========================== CBS switches use primarily the *CISCOSB-vlan-MIB* for VLAN definition and interface vlan management. There are some things to note: Switch ports have several modes: * **Access** - ie single untagged frames * **Trunk** - dot1q encapsulated * **General** - access both untagged and tagged frames. We are not sure what the difference is with Trunk, which also allows both untagged and tagged frames. The **port mode** is read from and written to the **vlanPortModeState** mib (.1.3.6.1.4.1.9.6.1.101.48.22.1.1.), where: * 10 = General * 11 = Access * 12 = Trunk **General mode** The untagged vlan is read from and written to the Q-Bridge standard "dot1qVlan" MIB id (dot1qVlan. = ) It appears that the general mode allowed tagged vlans are represented by the standard Q-Bridge "egress port" vlan fields. As we don't support this mode at time of writing, this data is ignored. **Access mode** The untagged vlan is read from and written to "vlanAccessPortModeVlanId" MIB id (vlanAccessPortModeVlanId. = ) **Trunk mode** The untagged vlan on a trunk port is read from and written to vlanTrunkPortModeNativeVlanId. = The vlanTrunkPortModeEntry branch has all vlan memberships. This is a bitmap that is indexed by interface, and grouped by 1024 vlan numbers. E.g. *vlanTrunkModeList1025to2048.14 = * For the interface with ifIndex 14 (likely "GigabitEthernet14"), the bitmap has a 1 for every vlan from 1025 -> 2048 that is enabled on the trunk configuration. Likewise for *vlanTrunkModeList1to1024.*, *vlanTrunkModeList2049to3072.* and *vlanTrunkModeList3073to4094.* .. note:: This is the opposite of the Q-Bridge VLAN bitmaps, where the index is the Vlan ID, and bitmap represents the switch ports that are active on that vlan!