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Strange NX-OS behaviour (CDP between N7K VDCs)

Hello guys,

I wasn't quite sure where to start that topic, but decided to drop it here as I found this specific related to Nexus 7000.

Right, so the scenario is as follow:

[N7K-1-1]------[N7K-2-1]

          |       \ /        |

          |       / \        |

          |     /     \      |

[N7K-1-2]------[N7K-2-2]

These links are all physical, doubled, port-channel links, terminated on M2XL module.

Native vlan I've been using in Core is 3967, and it does traverse tagged (vlan dot1Q tag native in global config).

For some reason, I am unable to get two cdp neighborship between N7K-1-1 and N7K1-2 (which are both on same physical chassis but in different vDCs). Everything else works just fine (L2/L3). I have L3 OSPF adjacency working just fine there.

N7K1-1 can see N7K2-1 & 2 with absolutely the same configuration. The configuration I've got is as follow:

!

vlan dot1Q tag native

!

vlan 3967

  name native_3967

!

interface port-channel3

  description Po3-N7K-1-1-N7K-1-2-Po3

  switchport

  switchport mode trunk

  switchport trunk native vlan 3967

  switchport trunk allowed vlan 202,3967

  logging event port link-status

  logging event port trunk-status

!

#show port-channel summary interface po3 | egrep ^3

3     Po3(SU)     Eth      LACP      Eth6/3(P)    Eth6/4(P)

interface Ethernet6/3

  description Po3-N7K-1-1-N7K-1-2-Eth6/3

  switchport

  switchport mode trunk

  switchport trunk native vlan 3967

  switchport trunk allowed vlan 202,3967

  channel-group 3 mode active

  no shutdown

The configuration is 1:1 on the otherside.

Now, the interesting part, absolutely the same configuration, applied on links to N7K1-1/1-2 - works just fine. CDP traverses and everything is good..I found, empirically, that if I add vlan 1 to the trunk - CDP pops-up...

What do I miss...?

Here are some more additional snippets, which might help:

Ethernet6/3 is up

    CDP enabled on interface

    Refresh time is 60 seconds

    Hold time is 180 seconds

!

# show int eth 6/3 switchport

Name: Ethernet6/3

  Switchport: Enabled

  Switchport Monitor: Not enabled

  Operational Mode: trunk

  Access Mode VLAN: 1 (default)

  Trunking Native Mode VLAN: 3967 (native_3967)

  Trunking VLANs Allowed: 202,3967

  FabricPath Topology List Allowed: 0

  Administrative private-vlan primary host-association: none

  Administrative private-vlan secondary host-association: none

  Administrative private-vlan primary mapping: none

  Administrative private-vlan secondary mapping: none

  Administrative private-vlan trunk native VLAN: none

  Administrative private-vlan trunk encapsulation: dot1q

  Administrative private-vlan trunk normal VLANs: none

  Administrative private-vlan trunk private VLANs: none

  Operational private-vlan: none

!

# show int po3 switchport

Name: port-channel3

  Switchport: Enabled

  Switchport Monitor: Not enabled

  Operational Mode: trunk

  Access Mode VLAN: 1 (default)

  Trunking Native Mode VLAN: 3967 (native_3967)

  Trunking VLANs Allowed: 202,3967

  FabricPath Topology List Allowed: 0

  Administrative private-vlan primary host-association: none

  Administrative private-vlan secondary host-association: none

  Administrative private-vlan primary mapping: none

  Administrative private-vlan secondary mapping: none

  Administrative private-vlan trunk native VLAN: none

  Administrative private-vlan trunk encapsulation: dot1q

  Administrative private-vlan trunk normal VLANs: none

  Administrative private-vlan trunk private VLANs: none

  Operational private-vlan: none

# show cdp neighbors interface ethernet 6/3 - 4

Note: CDP Neighbor entry not found

# show cdp neighbors interface ethernet 6/1 - 2

Device-ID          Local Intrfce  Hldtme Capability  Platform      Port ID

N7K2-1             Eth6/1         139    R S I s   N7K-C7009     Eth6/1       

N7K2-1             Eth6/2         139    R S I s   N7K-C7009     Eth6/2

interface Ethernet6/1

  switchport

  switchport mode trunk

  switchport trunk native vlan 3967

  switchport trunk allowed vlan 2-3967

  channel-group 1 mode active

  no shutdown

# show int eth 6/1 switchport

Name: Ethernet6/1

  Switchport: Enabled

  Switchport Monitor: Not enabled

  Operational Mode: trunk

  Access Mode VLAN: 1 (default)

  Trunking Native Mode VLAN: 3967 (native_3967)

  Trunking VLANs Allowed: 2-3967

  FabricPath Topology List Allowed: 0

  Administrative private-vlan primary host-association: none

  Administrative private-vlan secondary host-association: none

  Administrative private-vlan primary mapping: none

  Administrative private-vlan secondary mapping: none

  Administrative private-vlan trunk native VLAN: none

  Administrative private-vlan trunk encapsulation: dot1q

  Administrative private-vlan trunk normal VLANs: none

  Administrative private-vlan trunk private VLANs: none

  Operational private-vlan: none

# show run int po1

interface port-channel1

  description Po1-esmdrrv1-esmdrrv2-Po1

  switchport

  switchport mode trunk

  switchport trunk native vlan 3967

  switchport trunk allowed vlan 2-3967

  logging event port link-status

  logging event port trunk-status

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Strange NX-OS behaviour (CDP between N7K VDCs)

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