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vlans should be forwarding

mikecowdell
Level 1
Level 1

‎03-04-2013 08:36 AM - edited ‎03-07-2019 12:02 PM


We run spanning tree on our network and I'm having some issues with one of our distribution switches which is the secondary uplink for access layer switches. For some reason it isn't forwarding on a few interfaces. We upgraded the code to 12.2(58)SE2 hoping that would solve the problem, but we're getting the same results.  I put the results of the 2 different switches.  switch-ds4 is the switch we're seeint issues on.  switch-ds2 is also a distribution switch and the secondary uplink for access layer swtitches.  I'm learning, but I'm not an expert at all when it comes to networking.  Any thoughts/tips would be much appreciated.

Switch Ports Model              SW Version            SW Image
------ ----- -----              ----------            ----------
*    1 24    WS-C2960G-24TC-L   12.2(58)SE2           C2960-LANBASEK9-M

switch-ds4#show int trunk

Port        Mode             Encapsulation  Status        Native vlan
Gi0/1       on               802.1q         trunking      1
Gi0/2       on               802.1q         trunking      1
Gi0/3       on               802.1q         trunking      1
Gi0/22      on               802.1q         trunking      1
Gi0/24      on               802.1q         trunking      1

Port        Vlans allowed on trunk
Gi0/1       1,124,607
Gi0/2       1,49-50,52,607
Gi0/3       1,55,63,607
Gi0/22      1,124,607
Gi0/24      1,49-50,52,55,63,124,607

Port        Vlans allowed and active in management domain
Gi0/1       1,124,607
Gi0/2       1,49-50,52,607
Gi0/3       1,55,63,607
Gi0/22      1,124,607
Gi0/24      1,49-50,52,55,63,124,607

Port        Vlans in spanning tree forwarding state and not pruned
Gi0/1       none
Gi0/2       none
Gi0/3       1,55,63,607
Gi0/22      none
Gi0/24      1,49-50,52,55,63,124,607

It should look something like this DS switch:

switch-ds2#sho int trunk

Port        Mode         Encapsulation  Status        Native vlan
Gi1/0/1     on           802.1q         trunking      1
Gi1/0/2     on           802.1q         trunking      1
Gi1/0/3     on           802.1q         trunking      1
Gi1/0/4     on           802.1q         trunking      1
Gi1/0/5     on           802.1q         trunking      1
Gi1/0/6     on           802.1q         trunking      1
Gi1/0/7     on           802.1q         trunking      1
Gi1/0/8     on           802.1q         trunking      1
Gi1/0/9     on           802.1q         trunking      1
Gi1/0/10    on           802.1q         trunking      1

Port        Vlans allowed on trunk
Gi1/0/1     1,46,48-50,52,54-56,63,124,607
Gi1/0/2     1,49-50,52,55,63,124,607
Gi1/0/3     1,49-50,52,54-56,63,124,607
Gi1/0/4     1,49-50,52,55-56,124,607
Gi1/0/5     1,46,49-50,52,55-56,124,607
Gi1/0/6     1,46,49-50,52,54-56,124,607
Gi1/0/7     1,48-50,52,55-56,124,607
Gi1/0/8     1,55,124,607
Gi1/0/9     1-4094
Gi1/0/10    1-4094

Port        Vlans allowed and active in management domain
Gi1/0/1     1,46,49-50,52,54-56,63,124,607
Gi1/0/2     1,49-50,52,55,63,124,607
Gi1/0/3     1,49-50,52,54-56,63,124,607
Gi1/0/4     1,49-50,52,55-56,124,607
Gi1/0/5     1,46,49-50,52,55-56,124,607
Gi1/0/6     1,46,49-50,52,54-56,124,607
Gi1/0/7     1,49-50,52,55-56,124,607
Gi1/0/8     1,55,124,607
Gi1/0/9     1,46,49-50,52,54-56,63,124,607
Gi1/0/10    1,46,49-50,52,54-56,63,124,607

Port        Vlans in spanning tree forwarding state and not pruned
Gi1/0/1     1,46,49-50,52,54-56,63,124,607
Gi1/0/2     1,49-50,52,55,63,124,607
Gi1/0/3     1,49-50,52,54-56,63,124,607
Gi1/0/4     1,49-50,52,55-56,124,607
Gi1/0/5     1,46,49-50,52,55-56,124,607
Gi1/0/6     1,46,49-50,52,54-56,124,607
Gi1/0/7     1,49-50,52,55-56,124,607
Gi1/0/8     1,55,124,607
Gi1/0/9     46,54-56,63
Gi1/0/10    54-56,63,124

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0 Helpful
3 Replies 3

Wilson Bonilla
Level 3
Level 3

‎03-04-2013 08:48 AM

Hello Mike,

Could you post the output of the command.

Show spanning-tree interface gig 0/1 then gig 0/2.

Show run interface gig 0/1.

Show cdp neigh gig 0/1

By any chance do you have a topology diagram that can be posted.

Mostly these interfaces are redundant paths, redundant paths are stanby, not forwarding data, spanning -tree will not forward vlans across those ports in other to prevent loops in the network. This is totally normal and expected, otherwise if the ports where forwarding you should be experiencing high profile issues.

Regards.

Wilson B.

0 Helpful

mikecowdell
Level 1
Level 1
In response to Wilson Bonilla

‎03-04-2013 10:37 AM

Thanks for the reply.  The access layer switches are all blocking on the the secondary uplinks, but every DS switch (primary and secondary) are forwarding because they only have 1 link.

us68-b50rm0-ds4-fac#Show spanning-tree interface gig 0/1

Vlan                Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
VLAN0001            Altn BLK 3004      128.1    P2p
VLAN0124            Altn BLK 3004      128.1    P2p
VLAN0607            Altn BLK 3004      128.1    P2p
us68-b50rm0-ds4-fac#Show spanning-tree interface gig 0/2

Vlan                Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
VLAN0001            Altn BLK 3004      128.2    P2p
VLAN0049            Altn BLK 3004      128.2    P2p
VLAN0050            Altn BLK 3004      128.2    P2p
VLAN0052            Altn BLK 3004      128.2    P2p
VLAN0607            Altn BLK 3004      128.2    P2p
us68-b50rm0-ds4-fac#Show run interface gig 0/1
Building configuration...

Current configuration : 147 bytes
!
interface GigabitEthernet0/1
description us68-b50rm0-as2-fac
switchport trunk allowed vlan 1,124,607
switchport mode trunk
no mdix auto
end

us68-b50rm0-ds4-fac#Show cdp neigh gig 0/1
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
                  S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone,
                  D - Remote, C - CVTA, M - Two-port Mac Relay

Device ID        Local Intrfce     Holdtme    Capability  Platform  Port ID
us68-b50rm0-as2-fac.lehi.micron.com
                 Gig 0/1           137              S I   WS-C2960- Gig 0/2
us68-b50rm0-ds4-fac#

0 Helpful

Wilson Bonilla
Level 3
Level 3
In response to mikecowdell

‎03-04-2013 12:17 PM

Mike,

The topology is redundant; at some point there must be a blocking port and it appears that DS4 is the one with the highes cost to the root switch since it's the one blocking gig0/1 ... /22

Port       Vlans in spanning tree forwarding state and not pruned

Gi0/1       none

Gi0/2       none

Gi0/3       1,55,63,607

Gi0/22      none

Gi0/24      1,49-50,52,55,63,124,607

Spanning-tree calculates what is the cost of the port to reach the root switch by doing calculations it's able to find out the ports with the better cost and identify the worst as well, it appears that DS4 ports gig0/1,2 and 22 are the worst so they are blocking all vlans to avoid layer two loops.

If this is not the desire result, you may need to change costs, verify root switch for your network.

Regards.

Wilson B.

0 Helpful
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