Wikipedia:Reference desk/Archives/Computing/2023 September 2
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September 2
[edit]STP understanding
[edit]I am trying to get my head around understanding how STP (spanning tree) really works and what is the best way to know if I have a loop in my network. Could someone please help me out by explaining how everything is connected and how to identify a loop in a network by the symptoms only? (like if I don't have a cloud controller available atm, i.e, Unifi, etc). Please make it simple but technical. Thank you everyone! MissBono [Yes?] 17:11, 2 September 2023 (UTC) MissBono [Yes?] 17:11, 2 September 2023 (UTC)
- If you have loops in your ethernet network, the broadcasts will keep on broadcasting, round and around in the loop and then everywhere connected. You may notice that your ethernet interfaces are going at 100%. If you have mixed speeds, then it may be limited by the slowest link in the loop, or perhaps by a slow switch. Users on the network will get a slow response time. You may have to enable SNMP clients on your network devices and run some software to look at the numbers going on the interfaces. You should be able to observe the counts of broadcast packets are dominating the traffic. If you have been recording this data over time, you can see a sudden jump in the traffic when something changed. THen you might be able to tell from the time what that was. Graeme Bartlett (talk) 00:02, 4 September 2023 (UTC)
- I think "STP" refers specifically to the Spanning Tree Protocol. It works like a group of people entering and exploring a maze of corridors connected to each other at forks. If an explorer reaches a dead end, they backtrack. If they are at a fork leading to unexplored corridors, they pick a corridor and mark it as explored. If they are at a fork leading to only explored corridors, they treat it as a dead end. Eventually, the whole reachable part of the maze will have been explored and no member of the group will have gone into a loop, since that would necessarily require them to enter a corridor that had already been marked. Now imagine that next to marking unexplored corridors, the explorer marks the corridor through which they arrived at an unexplored corridor as being essential. At the end, all reachable points can be reached through essential corridors, and as before, the essential corridors do not contain a loop. So together they form a spanning tree. In the protocol, the second part – eliminating inessential corridors – is a separate phase achieved differently to optimize performance, but the idea is fundamentally the same: from the root, each node should be reachable in one way only, so one access is picked as being preferred and the other accesses are eliminated. --Lambiam 09:41, 4 September 2023 (UTC)
- Standard procedure for troubleshooting: Describe your network in considerably more detail: the more you tell us, the more likely we may be able to help you. Are you in charge? Did it use to work? Or did it never work properly? What are the obvious symptoms of the problem? Can you pinpoint the time/day when it started to malfunction? Is it consistent or intermittent? Has someone important recently left in a hurry? Most importantly, What Changed? Are there even change logs? Maybe someone stuck in an unauthorised mis-configured router somewhere? Agree totally with checking/installing SNMP monitoring everywhere, although it can be notoriously insecure.[1][2] MinorProphet (talk) 23:14, 4 September 2023 (UTC)
- I think "STP" refers specifically to the Spanning Tree Protocol. It works like a group of people entering and exploring a maze of corridors connected to each other at forks. If an explorer reaches a dead end, they backtrack. If they are at a fork leading to unexplored corridors, they pick a corridor and mark it as explored. If they are at a fork leading to only explored corridors, they treat it as a dead end. Eventually, the whole reachable part of the maze will have been explored and no member of the group will have gone into a loop, since that would necessarily require them to enter a corridor that had already been marked. Now imagine that next to marking unexplored corridors, the explorer marks the corridor through which they arrived at an unexplored corridor as being essential. At the end, all reachable points can be reached through essential corridors, and as before, the essential corridors do not contain a loop. So together they form a spanning tree. In the protocol, the second part – eliminating inessential corridors – is a separate phase achieved differently to optimize performance, but the idea is fundamentally the same: from the root, each node should be reachable in one way only, so one access is picked as being preferred and the other accesses are eliminated. --Lambiam 09:41, 4 September 2023 (UTC)