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New Member

What's difference between STP instance and STP logical ports ?

In cisco document ,3750 can support 128 STP instance. 6509 with sup720 can support up to 13000 logical interfaces in PVST+ mode. Why 3750 said STP instance and 6509 said logical interfaces ? What's difference between them ?

If there are four port belong to vlan 20,is there one instance and four logical interface ?

thanks!

2 REPLIES

Re: What's difference between STP instance and STP logical ports

Not very sure if this is what you want to know

In PVST, switch runs one "instance" of STP per VLAN. So on a L2 switch, this means that you can have 128 separate "instances" of STP running at a time.

The term "logical interface" refers to VLAN interfaces which we create for interVLAN routing

For your 4 ports in VLAN 20, switch will run one "instance" of STP for VLAN 20. One your core / distribution switch you will create one "logical interface" for VLAN 20

New Member

Re: What's difference between STP instance and STP logical ports

thanks for your reply.

When I said "logical interface",I mean STP logical interface.

I can't understand why 3750 STP limit is expressed by STP instance and 6509/4500 STP limit is expressed by STP logical interface .

In cisco document

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a00800951ac.shtml#resource_error

The total represents the sum of all logical ports across all instances of STP for the different VLANs. Make sure that this number does not exceed the maximum number supported for each Supervisor Engine type.

Note: The formula to compute the sum of logical ports on the switch is:

(number of non-ATM trunks * number of active Vlans on that trunk)

+ 2*(number of ATM trunks * number of active Vlans on that trunk)

+ number of non-trunking ports

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