11-17-2018 06:01 AM - edited 03-08-2019 04:38 PM
Hi
I am running some spanning tree loop issue on my switches
We have 2 sites connected with metro ethernet link
On each site we have cisco 3850 stack switches
On each site we have 2 links from different service providers connecting site A and site B switches
We are making trunk link between between Site A and Site B
So we have 2 trunks
1 trunks is on ISP A and 1 on ISP B
We have enabled rstp on both switches
We prefer isp1 over isp2 so we increased cost on isp2 link on site B switch
So ideally isp2 link shoud go into Alt path Blocking state
But non of the link is going on blocking state
And i see output of
#show spanning tree
Both trunks on both switches are in Desg/forwarding
Means non of the port on both switches are in forwarding which is causing loop in network and ports on site B switch are flapping
I would need some assistance please
11-17-2018 08:04 AM - edited 11-17-2018 08:07 AM
Hello
You could utlilise a flex link which will put the specified isp b link into a backup link so to use the isp a as the primary link This should negate your switching looP
int x/x
description primary isp a
switchport backup interface xxx ( isp b)
11-17-2018 11:31 AM
11-18-2018 09:01 AM
11-18-2018 11:29 AM
Hello
shayan_2k@hotmail.com wrote:
i see link says P2P and other one says Shr
Check the speed/duplex settings usually you see this when the port is running half duplex
11-19-2018 12:22 PM
i tried changing speed and duplex full but didnt worked
also i tried flex interface but i think this command is not supported on 16.3.6
switch is not accepting switchport backup interface gx/x
11-19-2018 12:58 PM
11-19-2018 02:13 PM
Do you see BPDU sending and receiving at the switchport?
LAB-SW-01#sh spanning-tree interface g1/0/24 detail | i BPDU BPDU: sent 123888, received 5045088
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