Pardon me if these two questions simply illustrate my ignorance:
I have two clusters of 3524XL switches; one on the 3rd floor of my building, one on the 5th.
Each cluster is, in turn, connected via gigabit SX to a 3750E in our central network room on the 4th floor.
The 5th floor cluster has 5 switches, all connected to each other via gigabit SX GBICs and 2m fiber patch cords.
The 3rd floor cluster has 3 switches, all connected to each other via gigabit SX GBICs and 2m fiber patch cords.
The configuration of the GBIC ports on all switches is identical:
dot1Q trunking mode, no portfast, no flow control, 802.1p priority:0
The 1st GBIC port on switch 1 is connected to the 2nd GBIC on the switch 2
The 1st GBIC port on switch 2 is connected to the 2nd GBIC on the switch 3
The single difference between the two clusters is that I have a 3750E connected to the last switch in the 3rd floor cluster.
Its SFP settings are the same as the GBICs in regard to speed, no portfast and no flow control.
When I look at the topology of the two clusters in CNA, the links between all of the 5th floor switches show as being in FWD state.
In the 3rd floor cluster, however, the link between switch 2 and switch 3, and the link between switch 3 and the 3750 show as being in the blocked state.
1) Should I be concerned?
2) What are the possible causes and possible solutions?
For security reasons, you should definitely stay away from using VLAN 1 for user traffic. VLAN 1 is used for control protocols like: PAGP, CDP, VTP, etcâ¦
Here is a link to a white paper that describes the security risks.
Also, make the most powerful and centralized switch your STP root, so in your case the 3750 is a better choice.
My question is where is the L2 boundary? If the 3750E has SVI (interface VLAN) for your 3524XL's, I think your problem is you didn't specify the 3750E to be the spanning tree root.
In the spanning tree root election process, it will choose the lowest MAC address as it's root. In your case, it is possible that the spanning tree negotiated to use one of the 3524XL as the root switch (since they are older, and the MAC can be lower).
The potential problem is if the 3524XL is the root, it will takes too much CPU on these switch, since they are old (EOL) and has a slower CPU.