Skip to main content
12 votes
Accepted

Should I disable STP on my access ports?

You really, really do not want to disable STP where you connect switches to other switches. That is the entire purpose of STP. If you disable STP, and there is a problem, it will really be too late ...
Ron Maupin's user avatar
  • 100k
12 votes
Accepted

Does Switch need its own MAC address?

The basic function of a switch is transparent bridging - for this, it doesn't need any MAC address of its own. However, if you need to talk to a switch - ie. a managed switch - then that switch ...
Zac67's user avatar
  • 85.8k
11 votes
Accepted

Do layer 3 protocols use layer 2 protocols?

Layer 3 (mostly IP) generally relies on the underlying layer-2 network (mostly Ethernet or Wi-Fi) for delivery. Just like a layer-2 network uses layer-1 links to actually move the bits. The ...
Zac67's user avatar
  • 85.8k
9 votes

Manager states we cannot put retail switches on network due to fear of non-STP config and network storm problems. Is this true?

Great question! This is because a layer-2 switching loop can form on the Consumer-grade switching equipment which could produce Broadcast Radiation and impact devices connected to the broadcast ...
TDurden's user avatar
  • 1,241
9 votes

I have a single ethernet switch. Should I use spanning tree?

To add to Zac67's and JFL's answers: In case you decide to enable spanning-tree on the single switch, don't forget to configure the client's and server's switchports as Edge Ports (Cisco speak; ...
Marc 'netztier' Luethi's user avatar
9 votes
Accepted

Fastest spanning tree in multiple-ring topology

MSTP and RSTP converge equally fast, MSTP is the current protocol version. Given the topology in your diagram (ugh!) and its tree depth, no STP variant will converge quickly (if at all). xSTP default ...
Zac67's user avatar
  • 85.8k
8 votes
Accepted

When and where to use Spanning-Tree (Portfast)

Spanning tree only runs between switches, never to standard end hosts. Bear in mind that, under normal circumstances, a port supporting spanning tree will (when it first comes up) run through a ...
rnxrx's user avatar
  • 6,124
8 votes
Accepted

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

Strongly suggested: Configure both port-channel and its members identically (except of course for description and the channel-group and vpc bits). As long as an interface is not configured to be ...
Marc 'netztier' Luethi's user avatar
8 votes
Accepted

Two switches, double connection, no LACP: how does it work?

Most likely, the rapid or the multiple spanning tree protocol RSTP/MSTP has been activated on the 1910 switch. With the unmanaged 1410 switch forwarding STP BPDUs (most do), the 1910 notices a loop to ...
Zac67's user avatar
  • 85.8k
7 votes
Accepted

H3C MST BPDU exchange failing

You have a fundamental problem with your configuration, which is that the configuration digests on core and access switches don't match. [Core-sw]dis stp region-configuration Oper Configuration ...
richardb's user avatar
  • 1,608
7 votes

Is Per Vlan Spanning Tree or RPVST an open standard or can it only be implemented by Cisco?

(R)PVST(+) is a proprietary standard defined by Cisco (or a set thereof). However, there are many other vendors and devices supporting it - you may need to check the specifications of your devices. ...
Zac67's user avatar
  • 85.8k
7 votes
Accepted

spanning tree RootGuard question on vPC switches

Based on the comments I think you are confused about guard root. You configure guard root on the downstream interfaces of all the switches, except the root switch. Basically, you are trying to protect ...
Ron Maupin's user avatar
  • 100k
7 votes

Fastest spanning tree in multiple-ring topology

If you can use Cisco Metro Ethernet switches, you might consider Resilient Ethernet Protocol, which is designed for ring topologies. REP is a protocol used in order to replace the Spanning Tree ...
Ron Trunk's user avatar
  • 67.8k
7 votes

Do I need STP enabled on all switches in a loop?

Generally, a ring is a bad design for Ethernet switches. STP blocks one of the ring links, forming a chain. Traffic between switches on opposite sides need to cross the whole chain, potentially ...
Zac67's user avatar
  • 85.8k
7 votes

Two switches, double connection, no LACP: how does it work?

Most switches comes with Spanning Tree (STP) enabled by default. This protocols will detect the loop and disable one of the link to break it. The new switch you connect either has STP disabled or a ...
JFL's user avatar
  • 19.7k
6 votes
Accepted

Cisco: err-disabled due to loop - but there are NO redundant physical paths/ wires/ connections

I think this might be related to a bug. This issue is documented in Cisco bug ID CSCea46385. To resolve the issue, you need to add the no keepalive command to the interface. Hope this helps you on ...
SleepyMan's user avatar
  • 2,016
6 votes
Accepted

Does the System ID Extension ever affect root bridge election?

Benjamin Dales answer is certainly correct for switches running standards based spanning tree. For switches using per VLAN STP however: yes, it can very well make a difference. Granted, under rather ...
Daniel's user avatar
  • 1,071
6 votes
Accepted

Building too large for ethernet runs

Fiber is not so expensive unless you are getting fleeced. Indeed, it can be cheaper than copper cabling. It's also the right solution to long runs. Given the installation costs, it's likewise foolish ...
Ecnerwal's user avatar
  • 2,746
6 votes

Best way to connect VLANs / STP / LAG

VLANs are a way of partitioning a given network into distinct layer 2 segments as if you'd be using separate switches, so you don't have your whole network bunched together. The advantage of VLANs ...
Zac67's user avatar
  • 85.8k
6 votes

Does Switch need its own MAC address?

Yes, if your switch supports spanning-tree protocol(either legacy spanning tree protocol, rapid-pvst+ or MST) your switch will have a mac address since spanning-tree protocol uses bridgeID to elect ...
Muhammad Nasir Akram's user avatar
6 votes
Accepted

How does STP convergence work?

I don't understand how a bridge decides that it is not connected to another bridge performing STP. If it doesn't hear BPDUs, then there's no bridge connected. How long will it until it decides ...
Ron Trunk's user avatar
  • 67.8k
6 votes
Accepted

Network Redundancy with LACP Trunking

Scenario A: Switch 1 has ports 1+2 trunked together via LACP. They are plugged into Switch 2 ports 1+2. Both links will be used, but a single flow will only use one link. There is a hashing ...
Ron Maupin's user avatar
  • 100k
6 votes

I have a single ethernet switch. Should I use spanning tree?

As explained by Zac67 answer STP is normally only useful when connecting several switches together. However there's other related features than can be useful on a standalone switch. BPDU Guard will ...
JFL's user avatar
  • 19.7k
6 votes

designated ports and root ports in STP

In short and simplified, a designated port is a forwarding port that leads away from the root bridge (from the priority perspective). The other end of a designated port is a root port (assuming P2P). ...
Zac67's user avatar
  • 85.8k
6 votes

Is Spanning Tree Protocol Needed?

Two links between two switches form a mesh: there are multiple paths between the switches. With default/no configuration, these links cause a bridge loop, bringing down your network (broadcasts ...
Zac67's user avatar
  • 85.8k
6 votes
Accepted

Why do Designated Ports in STP still send BPDUs if the otherside of the link is blocking?

BPDUs are still sent because the switch topology could change, and it will then be detected. For example, if the root port on the switch with the blocked port either goes down or loses a path to the ...
Ron Maupin's user avatar
  • 100k
6 votes

Network topology with big spanning tree diameter

I guess you aren't familiar with the infamous "All Systems Down" article from 2003. [ archive ] I can't find the original CIO article, and it was never archived. In simple terms, spanning-...
Ricky's user avatar
  • 32.4k
6 votes

Why does STP choose the lowest bridge ID as the root bridge?

Why should we choose the switch which has "the lowest" bridge ID to be the root bridge,not "the highest" ? Because that is the standard, and it has been for decades, so it is not ...
Ron Maupin's user avatar
  • 100k

Only top scored, non community-wiki answers of a minimum length are eligible