With IPHost Network Monitor you can run simple snmp requests against a Cisco device in your network.
vlanTrunkPortVlansXmitJoined4k
vlan Trunk Port Vlans Xmit Joined4k
1.3.6.1.4.1.9.9.46.1.6.1.1.25
A string of octets containing one bit per VLAN for VLANS with VlanIndex values of 3072 through 4095 in the management domain on this trunk port. The first octet corresponds to VLANs with VlanIndex values of 3072 through 3079; the second octet to VLANs 3080 through 3087; etc. The most significant bit of each octet corresponds to the lowest value VlanIndex in that octet. If the bit corresponding to a VLAN is set to '1', then this VLAN is presently being forwarded on this trunk port, i.e., it is not pruned; if the bit is set to '0', then this VLAN is presently not being forwarded on this trunk port, either because it is pruned or for some other reason.
Back to CISCO-VTP-MIB MIB page.
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