What are the other operations performed by a switch which are outside the VLAN's boundaries.

Is Logical (VLAN) Segregation is exactly same as breaking a switching network physically via a Router?

  • Please, never, ever use all-caps, even in a title. It is rude. – Ron Maupin Mar 20 '20 at 14:38
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    What is behind your question? Are you trying to design a Metro Ethernet network? Are you trying to choose specific hardware? – Ron Trunk Mar 20 '20 at 15:31
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can post and accept your own answer. – Ron Maupin Dec 17 '20 at 16:16

Using VLANs on a switch is the same thing as having multiple, unconnected switches. It takes a router to route packets between VLANs.

With a layer-2 switch, you need an external router for a device on one VLAN to communicate with a device on a different VLAN. Routers route packets between networks, while switches switch frames on the same network.

A layer-3 switch can be configured to route packets between VLANs because a layer-3 switch has a router built into it.

  • Thanks Ron; I am pretty much aware of routing, switching and itne-vlan routing. – tech savvy Mar 20 '20 at 14:45
  • Then I am not sure of your question. Each VLAN is the same thing as a separate, unconnected switch. – Ron Maupin Mar 20 '20 at 14:47
  • STP and RSTP runs outside VLAN's right? (not talking about PVSTP/+) here. Is there any other switch operations or consideration one should take care designing switching network? Perspective of my question is in not in access network but in transport network(WAN) – tech savvy Mar 20 '20 at 15:00
  • WANs have nothing to do with VLANs. Routers terminate layer-2, and a VLAN is a layer-2 construct. If you have a layer-2 switch, and you create separate VLANs on the switch, then each VLAN is an island, unless you have a router to route packets between them. A router will strip off the layer-2 frames from the packets, losing any layer-2 information. That happens as the packets are routed to the WAN. – Ron Maupin Mar 20 '20 at 15:05
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    Extending layer-2 over distances is a very, very bad idea. We live in a layer-3 world, and there is almost nothing today that requires that. In any case, extending layer-2 across any distance is the same as having it locally. You just extend the layer-2 problems (broadcast storms, STP convergence, etc. ) across a larger footprint. In any case, you really do not use different subnets on a VLAN, you would have multiple VLANs for that. A layer-2 transport network would be layer-3 separated. Perhaps you should edit your question with a drawing showing what you mean. – Ron Maupin Mar 20 '20 at 15:37

It seems you're asking about the control-plane of Ethernet networks. Yes, there are other, optional features of modern Ethernet-based networks, and especially for wireless networks. These aren't strictly necessary, and many Ethernet networks don't use or support any of these features.

For the wired kind, some other examples you may be looking for are:

  • LLDP
  • LACP
  • 802.1ag CFM (now part of 802.1Q)
  • SPB and PBB (not widely-adopted, but once considered to be revolutionary replacements for STP)

Some of these features were once envisioned to be ubiquitous, but have only found niche use, too. LACP is pretty much only used for link aggregation (LAG) but it has troubleshooting / OAM value, and to be honest, many network management and migration chores would be easier if LACP were used more broadly.

I hope this helps somewhat answer your question and point to some of the other technologies we don't commonly work with, but that are considered to be "beneath layer-3."

  • Yes,seems to be a bit closer to my inquiry... – tech savvy Mar 20 '20 at 15:31
  • @techsavvy, although those are link-only protocols that will not cross an interface. – Ron Maupin Mar 20 '20 at 15:37

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