STP problem ?????????

[raju]

Hi,

We have 5 Qty of 3548 Switches cascaded together using gigabit stack (Switch Model WS-C3548-XL with IOS 12.0 ) . The Giga port 0/1 in Switch-1 is uplink 6509-1 and Giga port 0/2 in Switch-5 is uplink to 6509-2 . HSRP is enabled in both 6509's . Users connected in Switch-1 & Switch-5 don't have any problem whereas users in Switch-2 , Switch-3 & Switch-4 are experiencing problem from time to time like slowness , loss of Network connectivity . Very particularly , printers connected in these three switches can't be pingable sometimes , requires to turn off and turn on the printer . The printers have static IP with gateway of standby IP address . We did some work to isolate the problem. When we shut the uplink to 6509-2 from Switch-5 , it works perfectly means all the Switches in the farm have only one uplink (path ) and vice versa i.e shut the uplink to 6509 from Switch-1 . The problem arises when the Switch farm have two uplinks to both 6509's . Any idea ?.

Thanks

Raju

[milan.kulik]

Hi,

who is the STP root?

What is the connection between the two 6509s?

I think the problem might be following:

One port on in the GigaStack is blocked to breake the STP loop. So some some switches have the L2 path to the HSRP active 6509 which goes through the other 6509. If there is no L2 path between the 6509s, there might be a problem. A similar problem might occure when there is a L2 path, but it takes several hops to get through.

Regards,

Milan

[raju]

Hi,

Thanks . FYI , All the ports in these 5 Switches are assigned to single Vlan say Vlan 100 . Vlan 100 is active in 6509-2 in MSFC side and Vlan 100 is root Vlan in 6509-2 .Both the 6509's are connected through 2 Gigabit ports (ether-channel).

Regards...

[milan.kulik]

Hi,

is there any difference when 6509-1 is HSRP active or 6509-2 is HSRP active?

Regards,

Milan

[raju]

Hi,

I don't notice any difference in performance .My concern is , does any STP configuration or tuning required on 3548 Switches side to have two uplinks to each 6509 . On 6509 side, we have configured root and secondary for each Vlan on both 6509.

Regards.

[milan.kulik]

Hi,

if there is no difference when 6509-1 or 6509-2 is HSRP active or standby, I'd consider the GigaStack as the cause of your problem.

When daisy-chaining the switches via GigaStack all the switches are connected via 1Gbps bus. It might bring a congestion problem while heavy traffic occures.

So I'd try to change your topology:

Either connect each access switch to the 6509s separately (best topology but expensive) or connect the access switches peer-to-peer each to the other, i.e. use always only one port on the GigaStack GBIC.

I'm using following solution in my network:

Connect a pair of access switches together via GigaStack GBICs (i.e. peer-to-peer).

Connect each access switch to a different core switch.

I think this is a reasonable compromise between price and performace requirements.

Regards,

Milan