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LansoirThemtq
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inquire about the default behavior of the switch

Fri Mar 03, 2023 6:18 am

As a beginner in MikroTik switch configuration, I would like to inquire about the default behavior of the switch in a specific scenario. I have set up VLANs on the switch, but I'm unsure what happens to communication on the switch if the router goes offline or is completely turned off. Will the connected devices still be able to communicate with each other, despite the router being offline? Or will the switch maintain the communication on the switch, causing all devices to remain on their respective VLANs and be unable to communicate with each other?

Any guidance or assistance would be greatly appreciated.
 
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mkx
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Re: inquire about the default behavior of the switch

Fri Mar 03, 2023 12:12 pm

Switch (with or without VLANs) normally doesn't require a running router for its own operations. Which is switching ethernet frames between ports (according to VLAN configuration if it has VLAN configuration set and enabled).

Router offers IP services to connected networks. In the narrow meaning only routing of packets between interfaces according to routing table, many routers offer other IP services vital to LANs (e.g. DHCP service, DNS service, ...). So if router goes away, LAN hosts can experience problems. But that won't be due to switch.

Mind that quite a few switch models (Mikrotik's CRS line included if running ROS) can offer certain IP services. In this case things get a bit more complicated when one wants to asses consequences of missing certain networking device. But MT switch, running SwOS, doesn't offer any of IP services (apart from management GUI) so this paragraph probably doesn't apply in your case.
 
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k6ccc
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Re: inquire about the default behavior of the switch

Fri Mar 03, 2023 5:53 pm

Everything I write here assumes the switch is strictly operating as a switch - the case if using SwitchOS.

I'm assuming your question involves a situation where a switch has multiple VLANs and a trunk to a router that among other tasks, routes traffic between VLANs. This is exactly my situation at home.
If there are multiple devices plugged into ports on the switch on for example VLAN 101, those devices do not need the router in order to communicate with each other. Similarly, multiple devices on VLAN 102 will be able to communicate with each other without needing the router. However devices on VLAN 101 can not communicate with devices on VLAN 102 without going through the router. So if the router fails or is disconnected, devices on VLAN 101 will not be able to communicate with devices on VLAN 102, even though they are plugged into the same switch (but on different VLANs). Easy way to think of it, each VLAN in a managed switch can be thought of as a separate switch. That's not entirely true, but for practical purposes, it can be thought of that way.

Note that besides routing between different VLANs, the devices plugged into the switch may well need the router for other services besides routing between VLANs or other LANs that do not involve the switch. For example, DHCP, DNS, Internet connection, etc. Some of those other services may prevent connectivity even though the devices are on the same VLAN on the switch. For example, if you use DHCP and the router fails, any new devices on the switch won't get an IP address.

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