Questions tagged [spanning-tree]

For questions about Spanning Tree Protocol (STP), a common protocol to prevent bridge loops at OSI layer-2.

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10
votes
3answers
40k views

Spanning tree Default Priority Values

This question is a repost of the same question in The Cisco Learning Network; however, the answers are unique to Stack Exchange. I have always accepted that the defualt priority value of STP (802.1d) ...
5
votes
2answers
320 views

Why FastEthernet STP Link Selected over EtherChannel?

What are the possible reasons why STP would choose to use a FastEthernet link over an EtherChannel? Below is a network diagram where this is happening.
19
votes
5answers
18k views

Should portfast be used on a port potentially connecting to an unmanaged switch?

I understand the basics of how spanning tree works and why you would want to use portfast on user access ports. When dealing with a topology with a large number of dumb switches under desks and ...
16
votes
3answers
66k views

How is the root bridge elected in STP?

How does STP/RSTP determine which bridge is the root bridge, and how are paths to the root bridge selected?
11
votes
2answers
18k views

Preventing STP loops in etherchannels configurations

What is the best practice when configuring etherchannel on Cisco switches to prevent a STP loop/broadcast storm when etherchannel is mis-configured? I had an instance where 2 ports on a switch were ...
11
votes
2answers
2k views

How did I break (half of) my network?

I'm looking for some post-event advice so this event doesn't happen again. We have a network core of two Cisco 4500x switches, configured for VSS redundancy. From those, we have iSCSI devices, our ...
4
votes
1answer
406 views

Strange flooding during installing new switch in network

This is very strange issue i am noticing. In our datacenter we have every switch in rack has cisco vPC configured in short whole datacenter running vPC so there is no loop for spanning-tree anywhere ...
-3
votes
4answers
13k views

How Layer-2 data will be fragmented?

Got a doubt while studying about LLC layer. From Network layer I came to know that IP fragmentation will be done, For L4 TCP will segment the data. Here, the question is Protocols starting from Layer-...
4
votes
1answer
4k views

spanning-tree port type edge trunk on port-channel vs physical interface

If i configure spanning-tree port type edge trunk on physical interface instead of port-channel does that work? Or i have to do spanning-tree port type edge trunk on port-channel ? Example: ...
8
votes
1answer
2k views

Native Vlan Cisco Catalyst and Layer 3 switch

I have run into an interesting issue setting the native VLAN between one of my Cisco Catalyst 2960 and my Layer 3 switch (third party). Here is the setup, the layer three switch is set up to run on ...
5
votes
2answers
2k views

Juniper trunking with two links (not using LAG)

Some reason I'm drawing a blank on this. Let's say I have two EX switches connected together with 2 links to each other (xe-0/1/0 and xe-0/1/1 on both switches). I can easily setup a trunk on one of ...
3
votes
1answer
291 views

What happens when a BPDU message age reaches "max age"

I read that every time a BPDU is forwarded by a switch, the message age is incremented by 1. Also the switch will wait "max age" - "message age" for a new BPDU. I'd like to know what happens if a ...
3
votes
1answer
545 views

Spanning tree - port roles and status during root bridge election

Regarding my studies I would like to confirm the three statements below about spanning tree. When a switch boot or spanning tree is enabled on a switch, the switch ports pass into blocking state 20 ...
3
votes
0answers
2k views

RSTP ignores VLANs and even "Non-STP" ports?

I have 18 Edge-corE ES4324 switches running 2.5.1.8 (and a single 3-com 2948-SFP Plus running 01.00.01) deployed initially as 2 physically separate networks, running side by side for the most part. ...
2
votes
2answers
919 views

RSTP recovery time with Ethernet ring

I am trying to test Rapid Spanning Tree on an Ethernet ring. Most of what I found does not seem to apply to my specific situation, but I am happy to be pointed elsewhere. Specifically, I have one ...