What is the difference between a managed and unmanaged switch?
Unmanaged switches — These switches have no configuration interface or options. They are plug-and-play. They are typically the least expensive switches, found in home, SOHO, or small businesses. They can be desktop or rack mounted.
Managed switches — These switches have one or more ways, or interfaces, to modify the operation of the switch. Common management methods include: a serial console or Command Line Interface accessed via telnet or Secure Shell; an embedded Simple Network Management Protocol SNMP agent allowing management from a remote console or management station; a web interface for management from a web browser. Examples of configuration changes that one can do from a managed switch include: enable features such as Spanning Tree Protocol; set port speed; create or modify VLANs, etc.
Two sub-classes of managed switches are marketed today:
Smart (or intelligent) switches — These are managed switches with a limited set of management features. Likewise "web-managed" switches are switches which fall in a market niche between unmanaged and managed. For a price much lower than a fully managed switch they provide a web interface (and usually no CLI access) and allow configuration of basic settings, such as VLANs, port-speed and duplex.
Enterprise Managed (or fully managed) switches - These have a full set of management features, including Command Line Interface, SNMP agent, and web interface. They may have additional features to manipulate configurations, such as the ability to display, modify, backup and restore configurations. Compared with smart switches, enterprise switches have more features that can be customized or optimized, and are generally more expensive than "smart" switches. Enterprise switches are typically found in networks with larger number of switches and connections, where centralized management is a significant savings in administrative time and effort. A Stackable switch is a version of enterprise-managed switch.
I would explain in more personal detail, but the wiki explains it pretty well.
Most managed switches offer you features like:
- View the bridging table to see which MAC addresses are associated with a given port
- View error statistics for each port
- View packet transmit / receive statistics for each port
- Set duplex / speed negotiation (or lack thereof) on a per-port basis
- View power-over-Ethernet status and current draw for each port (if applicable)
Typically there is a TELNET, serial, and / or web-based interface to interact with the switch.
Many managed switches allow you to poll the device with the SNMP protocol to use the information described above in graphs, alerts, etc. (Beware-- some low end managed switches, like the Dell 27xx series, don't have SNMP functionality!)
Most managed switches today support things like 802.1D spanning tree, 802.1q VLANs, and 802.3ad link aggregation, and the management interface allows you to configure these various features. You can typically setup port VLAN memberships, link aggregation groups, and control spanning tree parameters all from a web or command-line interface.
A goodly number of managed switches have taken to emulating the Cisco command-line interface (HP ProCurve, Dell PowerConnect to name a couple) such that someone with Cisco-specific knowledge can easily configure those switches.
If you are debating whether it is worth it to upgrading to managed switches, here are some criteria:
Security. Do you need the ability to switch on and off ports, match ports with MAC addresses, and set up VLANS?
Performance. Do you need to monitor and shape traffic of individual ports or switches? Do your clients have real-time performance needs (SLA's or metrics that you must meet)? Do you have VOIP set up and want better QoS features on the local network?
Management. Would you like the ability to be able to easily see network performance across various clients? Have extra assistance with troubleshooting connectivity or other issues? Integrate your switches into your SNMP management tool for log file correlation?
Random Features. Do you have the need for link aggregation or the other random features offered only by managed switches?
One additional thing: Most managed switches allow some form of port binding (so that you can use multiple NICs in a device to effectively multiply the bandwidth to the switch. Also, VLAN support is often not found on unmanaged switches, but are common on managed ones.
Unmanaged switches have a set behavior that works from the time they're powered on until they're powered off.
Managed switches normally have settings that can be modified remotely. This might include turning ports on or off, managing port speeds, throttling, segmenting and more.