Switches

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Layer 2 Switches

These are standard switches that are only able to operate on the Data Link Layer.

Management IP

Layer 2 switches don’t perform packet routing and don’t build a routing table. That creates a problem if we want to configure a Layer 2 switch using Telnet or SSH. Thankfully, there’s a workaround!

We can assign an IP address to a SVI to allow remote connections to the switch’s CLI. SVIs are more commonly used with Layer 3/Multilayer Switches, so read up on them below if you need to.

• (config)#interface vlan1
• (config-if)#ip address ip-address netmask
• (config-if)#no shutdown
• (config-if)#exit
  • Simply configure an IP address on the SVI as you would on a multilayer switch, and enable the interface if necessary.
• (config)#ip default-gateway ip-address
  • Configure a default gateway. Depending on the configuration of VLANs, the switch may not be able to communicate with the device trying to configure it without one.

Layer 3/Multilayer Switches

Switches with some IP routing capability. You can sort of think of these as a router with many more interfaces, although they aren’t quite as graceful at IP routing as a dedicated router… You’ll see what I mean when you try configuring one.

The primary reason for multilayer switches is to route traffic between multiple VLANs within a network, without having to use a separate router in a Router-on-a-Stick configuration.

IP Routing

Allows a multilayer switch to route layer 3 traffic through appropriately configured interfaces like a router would.

1. enable IP routing with ip routing in global configuration
2. configure interfaces with no switchport to use as routed ports (only need this for trunk ports)

SVIs

SVI = Switch Virtual Interface

Use these in a layer 3/multilayer switch to route multiple VLANs through a single trunk port

1. Ensure that all necessary VLANs exist on the switch
   1. check with show vlan brief
   2. Create new VLAN(s) with vlan (vlan-number) if necessary
2. select the first VLAN as an interface
   1. int (vlan-id)
3. assign the VLAN an IP address, typically the last usable in the subnet:
   1. ip address (ip-address)
4. repeat for all VLANs