Layer 2 switch?

[Hanry Zhou]

What is "layer 2 switch"?
and what does managed switch mean? vs. unmanaged switch?

Thanks,
Roger

[Ajit Natarajan]

Layer 2 refers to the OSI reference model.

The OSI (Open System Interconnect) reference model specifies 7 layers:

1. Physical: lowest layer. Deals with physical characteristics such as representation of the data pattern on the wire, etc.

2. Data link: deals with the representation of frames on the wire, in contrast with the physical layer that deals with bits and bytes. Also specifies how data is moved with a single network (single LAN - single subnet in IP terms). DLPI belongs to this layer as do most networking drivers.

3. Network layer: deals with routing of packets between networks (between subnets in IP terms). IP belongs to this layer.

4. Transport layer: deals with connection and connectionless modes of transport (TCP and UDP).

5. Session layer. Deals with management of sessions. No direct TCP/IP equivalent.

6. Presentation layer: deals with encryption of data, and network/host independent data representation formats.

7. Application layer: FTP, telnet, etc.

This description is admittedly brief but you should be able to find a lot of detail on the Internet.

A layer 2 switch (also called bridge) deals with passing frames from one part of a single LAN to another. There is no routing functionality.

Re. managed v. unmanaged: I'm not sure. My guess is a managed switch is one that has management capability, i.e., you can login to the switch and change configuration. An unmanaged switch does not have any configuration capability.

An example of an unmanaged layer 2 switch by this definition would be the hp ProCurve J4097B.

Hope this helps.

Thanks.

Ajit
HP Gigabit Ethernet

[Sridhar Bhaskarla]

Hi Roger,

To make it simple -

A hub provides shared bandwidth to all the hosts connected to it.

A switch provides dedicated bandwidth to each of the hosts connected. This means each host will get full bandwidth.

A layer2 switch works at layer2. The decisions are taken based on the MAC Addresses.

A Layer 3 switch on the other hand is also called "switch router". It can route the packets based on the IP addresses. Each port would act like a router.

Unmanaged switch does not report anything. An example, you cannot get snmp traps or logs etc., Managed switches report the activity. A network management station (such as openview NNM) can be able to monitor the managed switch.

-Sri

[Sergejs Svitnevs]

Layer 2 switch don't know anything about protocols, but just forward data depending on the destination address in the data packet. This address is not the IP address, but the MAC (Media Access Control) address that is unique to each network adapter card.
Managed devices allow the administrator to control various parameters and observe traffic.

Regards,
Sergejs

[Steven E. Protter]

Roger,

take the test already, its not that hard.

Layer 2 has to do with what a switch does and how it fits in with the layers of the network, there is a diagram in the Certification guide.

SEP

[Hanry Zhou]

Steven,

What "test" you are referring to, and what is the "Certified Guide" you are referring to in your email, where I can get it?

Thanks all, and points will be assigned later.

Roger