Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

Catalyst 3750 having more than 128 vlan's

Question: Is is correct that vlan's exceeding 128 runs without spanning-tree.?

BR Simon

1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

Re: Catalyst 3750 having more than 128 vlan's

Simon, Dan,

As Dan has confirmed, these switches have a limitation of 128 running STP instances. If more VLANs exist, the remaining VLANs will not have any STP running in them and, in a redundant network, will lead to switching loops. The VLANs themselves will exist and work but they will not be protected against switching loops.

A STP instance is allocated for a particular active VLAN on a switch, i.e. a VLAN that is allowed at least on one trunk, or having at least one access port, and of course, these ports being up/up. That is the reason why limiting the number of allowed VLANs on trunks, and limiting the number of access ports in diverse VLANs, will help reducing the count of STP instances.

Another solution would be to migrate to MSTP network-wide, and that would be my preferred solution if all switches in your network support MSTP.

Best regards,

Peter

7 REPLIES

Catalyst 3750 having more than 128 vlan's

Hi ,

c3750 has a limit of 1024 vlans. But exceeding 128 will not run without spanning-tree.

Dan

New Member

Catalyst 3750 having more than 128 vlan's

Hi Dan

We agree that 3750 support 1024 (or 1004). However your answer saying that even vlan exceeding 128 runs spanning-tree confuses me.

In my 3750 I have approx. 250 vlan and "show spanning-tree summary" show 128 vlan that ieee STP.

This is the output for one vlan not listet in show spanning-tree summary

3750#sh spanning-tree vlan 2612

Spanning tree instance(s) for vlan 2612 does not exist.

Simon

Catalyst 3750 having more than 128 vlan's

Hi,

Does the vlan 2612 exist ? Can you post a "show vlan id 2612"

Dan

Re: Catalyst 3750 having more than 128 vlan's

Hi ,

I made a quick test on a 3750 and you are right :

SPANTREE_VLAN_SW-2-MAX_INSTANCE: Platform limit of 128 STP instances exceeded.

STP instances = Number of access ports + Sum of all VLANs 
that are carried in each of the trunks

One of the solutions will be limiting the vlans on trunks, as need it.

Dan

New Member

Catalyst 3750 having more than 128 vlan's

3750#sh vlan id 2612

VLAN Name                             Status    Ports

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

2612 adm_ANS_SAfe_RFS10569            active    Gi1/0/25, Gi1/0/26, Gi4/0/2, Gi4/0/3, Po1

VLAN Type  SAID       MTU   Parent RingNo BridgeNo Stp  BrdgMode Trans1 Trans2

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

2612 enet  102612     1500  -      -      -        -    -        0      0

Remote SPAN VLAN

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

Disabled

Primary Secondary Type              Ports

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

sesxsw02swfmgt#

Pls take a look at:

http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps5023/prod_qas09186a00801b0971.html

search for Table 3. Feature Numbers Supported per Stack

Simon

Cisco Employee

Re: Catalyst 3750 having more than 128 vlan's

Simon, Dan,

As Dan has confirmed, these switches have a limitation of 128 running STP instances. If more VLANs exist, the remaining VLANs will not have any STP running in them and, in a redundant network, will lead to switching loops. The VLANs themselves will exist and work but they will not be protected against switching loops.

A STP instance is allocated for a particular active VLAN on a switch, i.e. a VLAN that is allowed at least on one trunk, or having at least one access port, and of course, these ports being up/up. That is the reason why limiting the number of allowed VLANs on trunks, and limiting the number of access ports in diverse VLANs, will help reducing the count of STP instances.

Another solution would be to migrate to MSTP network-wide, and that would be my preferred solution if all switches in your network support MSTP.

Best regards,

Peter

New Member

Catalyst 3750 having more than 128 vlan's

Peter. Thanks for your answer. /Simon

3109
Views
5
Helpful
7
Replies
CreatePlease login to create content