ISDP / CDP problem

Question

Hi guys,I'm facing a very strange problem. I have a Dell N1548P connected via trunk to my Cisco Core 4507.Both have the configuration 'switchport trunk allowed vlan 30,31,32' On my Cisco Core CDP is enabled and on my Dell Switch ISDP is enabled.Both have configured default native vlan 1. On my Cisco I see the Dell when I execute show cdp neighbours but if I execute show isdp neighbours on my Dell it doesn't show me the Cisco Core.If I add VLAN 1 on my Dell Switch on trunk port then I can see the Cisco Core.Actually I thought that the default native vlan 1 do not has to be added to the trunk ports because it is the default native vlan and it seems that on Cisco devices it works but why do I have to add vlan 1 on Dell trunk port?Does anyone have an explanation for that?Thanks!

DELL-Josh Cr · Answer

Hi NetGuy30,

Was VLAN 1 set as the PVID on the trunk? It probably has to do with it being tagged or untagged traffic. Page 877 gives a little more detail on how trunk ports work. https://dell.to/2LuSpv6

NetGuy30 · Answer

Hi Josh, PVID is default VLAN 1. Please have a look on the switchport trunk configuration: Port: Te1/0/4 VLAN Membership Mode: Trunk Mode Member of VLANs : (1),30,31,32 Access Mode VLAN: 1 (default) General Mode PVID: 1 (default) General Mode Ingress Filtering: Enabled General Mode Acceptable Frame Type: Admit All General Mode Dynamically Added VLANs: General Mode Untagged VLANs: 1 General Mode Tagged VLANs: General Mode Forbidden VLANs: Trunking Mode Native VLAN: 1 (default) Trunking Mode Native VLAN Tagging: Disabled Trunking Mode VLANs Enabled: 30,31,32 Private VLAN Host Association: none Private VLAN Mapping: Private VLAN Operational Bindings: Default Priority: 0 Protected: Disabled Do I have to enable 'Trunking Mode Native VLAN Tagging: Disabled'? If so could you please tell me how? Thanks!

DELL-Erman O · Answer

Hello,

I investigated and examined the situation you indicated. I couldn't say directly what caused this situation yet, but until Josh looks at it, can you try the following commands below;

no isdp enable

clear isdp table

clear isdp counters

isdp enable

NetGuy30 · Answer

Hi Erman, Done but same situation like before. How do I enable 'Trunking Mode Native VLAN Tagging: Disabled'? Maybe this causes the problem. Thanx!

DELL-Josh Cr · Answer

You can do it with the following command. switchport trunk allowed vlan remove 1 Page 885 https://dell.to/3a4mco3

NetGuy30 · Answer

Hi Josh, I already removed VLAN 1 from my trunk port.   Could you please tell me how to enable the following: 'Trunking Mode Native VLAN Tagging: Disabled' Thank you!

DELL-Josh Cr · Answer

Try switching to general mode and add the vlan with tagged. Page 875 #switchport general allowed vlan add 1 tagged

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