11-09-2019 06:50 AM - edited 11-09-2019 06:51 AM
Hi all,
note that this is not a real life scenario, I'm just tinkering with my home lab.
SWA_C2950_24P#show interfaces trunk
Port Mode Encapsulation Status Native vlan
Fa0/11 on 802.1q trunking 1
Fa0/12 on 802.1q trunking 1
Fa0/21 on 802.1q trunking 1
Fa0/22 on 802.1q trunking 1
Port Vlans allowed on trunk
Fa0/11 10,20,30
Fa0/12 10,20,30
Fa0/21 10,20,30
Fa0/22 10,20,30
Port Vlans allowed and active in management domain
Fa0/11 10,20,30
Fa0/12 10,20,30
Fa0/21 10,20,30
Fa0/22 10,20,30
Port Vlans in spanning tree forwarding state and not pruned
Fa0/11 10,20,30
Fa0/12 10,20,30
Fa0/21 10,20,30
Fa0/22 10,20,30
SWA_C2950_24P#show cdp neighbors
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone
Device ID Local Intrfce Holdtme Capability Platform Port ID
SWC_C3550_24P Fas 0/21 169 S I WS-C3550-2Fas 0/21
SWC_C3550_24P Fas 0/22 169 S I WS-C3550-2Fas 0/22
SWB_C2950_48P Fas 0/12 179 S I WS-C2950G-Fas 0/22
SWB_C2950_48P Fas 0/11 179 S I WS-C2950G-Fas 0/21
Question is, how does CDP keep collecting infos from the peers? Isn't CDP supposed to use the native VLAN?
Solved! Go to Solution.
11-09-2019 03:23 PM
Hello,
Even if you don't specifically allow Vlan 1 on the trunk, it is still passing through the trunk. You cannot remove it from the trunk.
11-09-2019 10:02 AM
11-09-2019 10:52 AM
Oh. Well, that makes sense. I'm studying for the CCNP SWITCH exam and all Q&A tests give much emphasis on how neighboring devices can't talk anymore via CDP [or VTP] if the native VLAN is not allowed on the trunk. Look at this one:
https://ciscoexam.online/CCNP/300-115/1488
Here the accepted correct answer is "The native VLAN is not present on the trunk."
However, my tests show that both CDP and VTP keep working as usual even if I don't allow the native VLAN through the trunk. CDP information is still received and VLANs are still propagated to VTP clients.
Actually I haven't found any mention of this behavior on my study material, it's just that pretty much any tests collection you may find around will always tell you that both CDP and VTP rely on the native VLAN to operate properly. It looks like this isn't really the case though.
11-09-2019 03:23 PM
Hello,
Even if you don't specifically allow Vlan 1 on the trunk, it is still passing through the trunk. You cannot remove it from the trunk.
11-10-2019 08:24 AM
11-10-2019 08:43 AM
11-10-2019 08:45 AM
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