5.3 Assigning an IP to a Switch

Basics​

If you don’t have physical access to a managed switch but need to access it, the switch will need an IP address so you can access it remotely.

You should know the following terms:

  • Telnet
  • Secure SHell (SSH)
  • Simple Network Management Protocol (SNMP)
  • Redundancies
  • Network loop
  • Spanning Tree Protocol
  • Root switch
  • Bridge Protocol Data Units (BPDU)

You can access switches remotely with an IP address through network protocols, such as: 

  • Telnet, a legacy protocol that uses a text-based interface to create a virtual terminal.
  • SSH, (Secure SHell). A more secure protocol, in which data is encrypted, that allows administrators to log into remote devices and execute commands.
  • SNMP (Simple Network Management Protocol). SNMP is embedded in many network devices, such as routers, switches, servers, firewalls, and wireless access points.

Managed switches should have a static IP address assigned to them, which you can do through the switches configuration page. Check your switch vendor’s documentation for specific directions on how to configure the switches in your network. For one example, review Assigning a Static IP Address from Cisco, or for more detailed information on configuring a Cisco switch using Telnet, review How to configure Cisco switch: A step-by-step guide with commands by Tim Keary for comparitech. 

Network Loops and the Spanning Tree Protocol (STP)

The ports on a switch can be set to either forward or block data. All of the ports on a switch that are set to forward data are considered the Spanning Tree. It is common practice to create some redundancies between switches in the case that there is an issue with a switch, port, or cable. These redundancies can keep your network up and running in case of some kind of failure.

When you create more than one path on your network between two devices, you do run the risk of ending up with a network loop. This may also occur when there are multiple connections between two switches or two different ports on the same switch are connected to each other. The effect of a network loop is that data can be broadcast out through every port of a switch, or that data can continue to loop between switches, theoretically forever. This can flood your network and greatly reduce performance.

The Spanning Tree Protocol is designed to stop or shut down network loops. It uses an algorithm that monitors your network and shuts down redundant links. The algorithm determines a root switch, or root bridge in older terminology, that becomes the focal point in the network from which the other switches on your network compare data. All of the switches on your network will routinely exchange information on an ongoing basis, comparing data they receive from different switches using Bridge Protocol Data Units, or BPDU.

You may not intentionally cause a network loop. If you have configured a managed switch that controls the devices in a classroom or an office, but someone adds an unmanaged switch beyond that without your knowledge, they may inadvertently create a network loop.

Some indications you may have a network loop issue include network latency, dropped pings, or devices that try to connect to the network but are unable to authenticate. You might also have phones that are unable to register or that have poor audio quality. If you walk into a closet and see every light lit up on a switch, it’s likely there is a double patch. This condition seems to occur in phone systems frequently.

Here are additional resources you may find useful:

Complete the following task or self-assessment:

  • Use the resources provided to either assign an IP address to a switch or review the IP address already assigned to a switch.