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Question

Cisco small home network

Mar 14, 2017 3:38AM PDT

How do I get different sub nets to connect with one router and two switches?

Discussion is locked

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Answer
By assigning ranges, etc.
Mar 14, 2017 7:59AM PDT

You design your network which I can't do for you. Today's switched hubs mean there is no gain on a home sized network by making sub nets. I can't imagine why I'd do this on a home network except to practice.

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Answer
Depends on your gear...
Mar 17, 2017 4:57PM PDT

If your router is Cisco and you don't care about separation, you can just plug your router into one switch, then plug the second switch into the first. Then on the router add the IP of your second subnets gateway as a secondary address on the the LAN interface.

If you care about traffic separation of the subnets, you will need to have either two LAN ports available on your router, each serving as a gateway for different subnets and connected to one of the two switches. In this design you won't want to connect the switches to each other.

Or, you will need manageable switches on which you can create additional VLANs, and a trunk between them. Additionally you would need to create 802.1q sub-interfaces on your router's LAN port and connect it to a VLAN trunk port on your switch. A term for this design is router on a stick.

This article provides a more detailed explanation.

https://learningnetwork.cisco.com/docs/DOC-23481

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Wait a second.
Mar 17, 2017 5:18PM PDT

In a switched hub, all this is automatic. When I see subnets the teacher is usually ignoring how modern gear works.

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Not automatic at all.
Mar 17, 2017 6:03PM PDT

None of what I described is automatic, it would all need to be configured.

A hub and a switch are in fact two different pieces of equipment. Hubs are old technology and aren't sold anymore, but you may occasionally come across one in the wild.

Basically a hub would take traffic it received on any port and send it out all it's other ports. A switch maintains a table of MAC addresses of all the different pieces of equipment connected to it and which MAC address is on which physical port. It looks at the destination MAC address of traffic coming in a port and sees if that address is on another port, if it knows about it it sends the traffic to only that port. There are some traffic types that are sent out all the ports, except the one it was received on, on a switch, those being broadcasts and multicasts. Most of the switches that are available in retail stores are what are termed, dumb switches. This means they can't be managed or changed in any manner. More advanced "managed" switches allow it's configuration to change. These switches allow for the creation of VLANs. A VLAN is just a grouping of physical ports, and ports on a specific VLAN can only send and receive traffic to other ports on the same VLAN. You can think of it like multiple switches in one physical box.

IP addressing runs at a different layer. If a client is trying to reach another machine, it sends out an ARP request. This is basically a mapping of an IP address to a MAC address. If the IP the client is trying to reach is on a different subnet, the ARP will be for the IP address that is configured as it's gateway IP so it can send traffic to the router. So if you had two IPs on different subnets assigned to a single router port, clients on both subnets would see the same MAC address for their gateway IP in their ARP tables.

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Now we're talking.
Mar 18, 2017 8:24AM PDT

I haven't seen a HUB in over a decade. In fact I keep one in our engineering collection because it's useful for packet sniffing.

All the other switches are switches and subnets would only be an exercise with no gain.