Where is the TCN? It should send one!

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vpnwarrior
Posts: 10
Joined: Sat Oct 07, 2023 10:03 pm

Where is the TCN? It should send one!

Post by vpnwarrior » Sun Sep 22, 2024 2:50 am

Hello,

When a blocked port on a switch becomes a root port in case of direct link failure, it sends a TCN to the root bridge. When the port goes into forwarding, it also sends a TCN.
However in Wireshark, the output says only one TCN is sent when the port goes into forwarding and that can't be.

Anyone knows about this behavior? I am using virl, I thought these were accurate?

Thank you,
Last edited by vpnwarrior on Tue Sep 24, 2024 12:22 am, edited 1 time in total.

vpnwarrior
Posts: 10
Joined: Sat Oct 07, 2023 10:03 pm

Re: One TCN instead of two TCNs?

Post by vpnwarrior » Tue Sep 24, 2024 12:21 am

When a switch with a blocked port becomes the new root port because its root port went down, normally the directly connected switch should send a TCN to the root bridge.
However the output of wireshark does not show any notification from that switch when it should, doesn't make sense.

Does anybody have an idea what the TCN doesn't show up in the output?

Thank you,

Uldis (UD)
Posts: 5148
Joined: Wed Mar 15, 2017 4:44 pm
Location: London
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Re: Where is the TCN? It should send one!

Post by Uldis (UD) » Tue Sep 24, 2024 6:31 pm

First advice to test such stuff is real switches, and CCNA learning course
Virtual switches have some restrictions to get what you described...
So real switch is your solution, and of course knowledge of CCNA :)

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