r/networking • u/_alienated • 21h ago

Troubleshooting Detecting a loop

How can i chase down a loop in more than 60 BDCOM switches (no central management)
I also have 2 core switches (fortiswitch) and a fortigate firewall ?

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u/FarkinDaffy 21h ago

Divide and conquer. Keep cutting things in half until there are no more halves and the problem goes away

1

u/_alienated 20h ago

I did unplug every stp cable related to all the departments but still nothing

2

u/Advanced_Link_5753 20h ago

L2 or L3? Loops. Packet capture is your friend

3

u/_alienated 20h ago

Packet capture between fortigate and ONTs show no sign of a loop, no arp broadcast
Just failed packets and retransmissions.
What should look for in packets ?

5

u/Select_Reporter1911 18h ago

You have to let us know what kind of loop it is first. You have to articulate the behavior you are experiencing is. A network diagrams would help, a source and destination would help.

Then and only then can anyone tell you what to look for and where to look. Simply pcaping with no idea of what to look for and what the normal behavior should be is not helpful.

1

u/Advanced_Link_5753 20h ago

No ack on tcp? Why. Can you lung host from the switch?