layer 2 connection

Answered Question
Apr 18th, 2010

what does it mean for a customer to have a layer 2 connection?

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Correct Answer by Jon Marshall about 6 years 7 months ago

ccnak1ing wrote:

what does it mean for a customer to have a layer 2 connection?

L2 uses L2 addressing to deliver packets to the destination address. The L2 addressing could be a DLCI with frame-relay, a VPI/VCI with ATM or a mac-address with ethernet.

L3 uses L3 address to deliver packets to the destination address. The L3 addressing is typically an IP address.

L3 is used to get the packet to correct network.

L2 is used to deliver the packet to the correct destination once the packet has got to the right network.

So a layer 2 connection means that on either end of the connection the same subnet/vlan exists. Note subnet/vlan are generally used interchangeably with ethernet because in the vast majority of cases there is a one-to-one correlation between the 2.

WAN connections can be either L2 or L3 depending on the customer requirements.

Jon

Correct Answer by Federico Coto F... about 6 years 7 months ago

As mentioned above a L2 connection could be as complex as involving MPLS, Frame-Relay, PPP, ATM, etc....

Or it can be as simple as a connection between two L2 switches.

For example, if you have two L2 switches connected directly to each other (either as trunk or acceses port, this is a L2 connection).

As well, if you have a computer connected to a port on a switch (unless is a L3 port), the connection is a L2 connection.

The difference between a L3 connection or a L2 connection is that a L3 connection involves routing, and a L2 connection just involves switching.

Federico.

Correct Answer by Reza Sharifi about 6 years 7 months ago

ccnak1ing wrote:

Thanks Giuslar

how about where a mpls vpn is not being used so where there is no CE or SP?

Hi,

In that case than it is simply a vlan (layer-2) with no IP address on that link.

HTH

Reza

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Giuseppe Larosa Sun, 04/18/2010 - 11:04

Hello Ccnak1ing,

a L2 connection service is a type of service where you not interact al Layer3 with SP nodes, like EoMPLS for example:

the CE device on siteA has as Layer3 neighbor your CE node on site B

The SP nodes transport ethernet frames or 802.1Q tagged frames between siteA and siteB.

In contrast with this a L3 service like MPLS VPN involves the service provider node that becomes the L3 neighbor of your CE node in siteA.

In this second case the SP node interacts with the CE node.

Hope to help

Giuseppe

ccnak1ing Sun, 04/18/2010 - 12:23

Thanks Giuslar

how about where a mpls vpn is not being used so where there is no CE or SP?

Correct Answer
Reza Sharifi Sun, 04/18/2010 - 12:27

ccnak1ing wrote:

Thanks Giuslar

how about where a mpls vpn is not being used so where there is no CE or SP?

Hi,

In that case than it is simply a vlan (layer-2) with no IP address on that link.

HTH

Reza

Correct Answer
Federico Coto F... Sun, 04/18/2010 - 12:36

As mentioned above a L2 connection could be as complex as involving MPLS, Frame-Relay, PPP, ATM, etc....

Or it can be as simple as a connection between two L2 switches.

For example, if you have two L2 switches connected directly to each other (either as trunk or acceses port, this is a L2 connection).

As well, if you have a computer connected to a port on a switch (unless is a L3 port), the connection is a L2 connection.

The difference between a L3 connection or a L2 connection is that a L3 connection involves routing, and a L2 connection just involves switching.

Federico.

Correct Answer
Jon Marshall Sun, 04/18/2010 - 12:49

ccnak1ing wrote:

what does it mean for a customer to have a layer 2 connection?

L2 uses L2 addressing to deliver packets to the destination address. The L2 addressing could be a DLCI with frame-relay, a VPI/VCI with ATM or a mac-address with ethernet.

L3 uses L3 address to deliver packets to the destination address. The L3 addressing is typically an IP address.

L3 is used to get the packet to correct network.

L2 is used to deliver the packet to the correct destination once the packet has got to the right network.

So a layer 2 connection means that on either end of the connection the same subnet/vlan exists. Note subnet/vlan are generally used interchangeably with ethernet because in the vast majority of cases there is a one-to-one correlation between the 2.

WAN connections can be either L2 or L3 depending on the customer requirements.

Jon

ccnak1ing Tue, 04/20/2010 - 03:46

Thanks to all contributions, as usual I have a better understanding of this concept now.

Rgds

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