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Unexpected traffic on Nexus 5000 trunk port.

Steve Hart
Level 1
Level 1

Hi all,

I have an interesting issue that may be a little hard to explain.

So I took a laptop with wireshark and plugged it into a nexus 5000 port that is configured as a trunk with 3 vlans allowed on it. The laptop was seeing all kinds of traffic on the wire, most of it was not involving my laptop.

For example: Server A VLAN 10= 10.10.10.1  Server B VLAN 20= 10.20.20.1 and wireshark laptop is plugged into a trunk port which is allowing those vlan's. The vlan's are routable.

10.10.10.3 is seeing the entire conversation when 10.10.10.1 backs up 10.20.20.1 even though it has no reason to see it. It is as if the trunk is spanning traffic to the laptop port. No span is setup however. It's really weird. This is not just broadcast traffic, but actual tcp taffic between Server A and B.

Why would a trunk port see traffic between 2 other servers talking to each other on the vlan.

Thanks for any info.

Trunk port configuration below:

Interface Ethernet 141/1/3

switchport mode trunk

switchport trunk allowed vlan 10, 20

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