How we discover Vlan Memship

We already should have vlan information at this time.

We call SnmpConnector()._get_port_vlan_membership()

Q-Bridge MIB

The Q-Bridge “dot1qPvid” entry maps every switch port (i.e. port-id) to the untagged vlan on that port.

self.get_snmp_branch('dot1qPvid')

So here is the first time we need the mapping from port-id to interface-id (see Vlan discovery) to read or set the untagged vlan on an interface.

Some devices may not implement the above dot1qPvid mib, so we can also look at the “CurrentVlan” branch of the Q-Bridge MIB.

# THIS IS LIKELY NOT PROPERLY HANDLED !!!
# read the current vlan untagged port mappings
# retval = self.get_snmp_branch(dot1qVlanCurrentUntaggedPorts)
# if retval < 0:
#    self.add_warning(f"Error getting 'Q-Bridge-Vlan-Untagged-Interfaces' ({dot1qVlanCurrentUntaggedPorts})")
#    return retval

# read the current vlan egress port mappings, tagged and untagged
retval = self.get_snmp_branch('dot1qVlanCurrentEgressPorts')

dot1qVlanCurrentEgressPorts.<vlan-id> has a sub-oid for each vlan, where the value is a bitmap of all ports active on this vlan, in either tagged on untagged mode.

dot1qVlanCurrentUntaggedPorts.<vlan-id> then only returns the untagged ports, again indexed by vlan id, and the return value is the bitmap of ports active.

IEEE Q-Bridge MIB

This MIB defines a similar structure to the Q-Bridge MIB. Some devices implement this MIB (or both).

As mentioned in the vlan discovery section, you can learn Vlans, static or dynamic, from ieee8021QBridgeVlanStatus.<vlan-id>

Then you can get names from ieee8021QBridgeVlanStaticName.<vlan-id>

Like Q-Bridge, you can read tagged and untaggeded ports in vlan from ieee8021QBridgeVlanCurrentEgressPorts.<vlan-id>

And get the list of untagged ports from ieee8021QBridgeVlanCurrentUntaggedPorts.<vlan-id>

Note that all the ‘list’ entries return bitmap values that have the bit set for the corresponding Port-ID, i.e. not the ifIndex! You have map the port-id back to the proper interface ifIndex!