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STP Strange issue

The_guroo_2
Level 2
Level 2

Guys a very starnge issue

i have three switches two 3550 and one 2950....there are no configs on the swicth at all i conected them and as ecxpected 2950 became root bridge but the funny thing is that other two swicthes ports are as under.

The way i have conected is that 2950 is conected with both 3550 (each link to each swicth) and then 3550 is conected to otehr 3550 (with one link)

This is the config of 3550 (both of them)

I am very confused why there is no link in blocking mode (Desg) ports are forwarding at both 3550 which is opposite to the theaory of STP. All three swicthes have PVST config............can someone plz clarify

Interface        Role Sts Cost      Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/1            Root FWD 19        128.1    P2p

Fa0/3            Desg FWD 19        128.3    P2p

Interface        Role Sts Cost      Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/1            Root FWD 19        128.1    P2p

Fa0/3            Desg FWD 19        128.3    P2p

3 Replies 3

andrew.prince
Level 10
Level 10

Post the output from the 2950

Sent from Cisco Technical Support iPad App

Interface        Role Sts Cost      Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/10            Desg FWD 19        128.1    P2p

Fa0/11            Desg FWD 19        128.3    P2p

so 2950 is conected to 2X 3550 and 3550 is conected to each other............its just a triangle.......the tsrange thing is there is no blocking ie ALTR..vv strange

Please post the output of below commands from all the three devices :

show cdp neigh

sh int trunk

sh spanning int

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