Benefits of L3 switching against L2 switching and difference between L3 & L2 switching

nilesh.varade · ‎09-26-2011

Hi,

What would be the benefits for proposing L3 switching in LAN-campus.

Say suppose... there are 4 floors in a building with L3 switches of 4500 series...

All users connects on 4500 series switches and these switches are connected to Core with 10G uplinks to all floors switches in Ring topology.

that means from core_2nd flr-->3rd floor-->4rth floor-->5th flr--> 4rth flr another switch-->3rd flr another sw-->2nd flr Core switch...

above connectivity wud be 10G as backbone...

what wud be benefits such as

1. Technical benefits

2. Security Benefits

3. User Level benefits

4. Performance level benefits

5. Network traffic benefits

And,

which one is beneficial either L2 switching or L3 switching on above scenario...and how??

and differences available in documents for L3 & L2 switching....

Thanks & Regards,

Neel

Marwan ALshawi · ‎09-26-2011

Hi

First of all technically there is no such thing called L3 Switching

Although cisco CEF dose switching based on routing and RIB information but the actual concept of switching is L2 where you have source and destination Mac addresses

In L3 it is routing based on source and destination ip address so L2 is MAC. Tables and switch the traffic/ frames based on the destination Mac to then correct interface

In L3 when I say L3 this Include L3 switch functioning in L3 mode/routing or a router

The forwarding/ routing of traffic/packets is based on the routing table

In your network topology it is nit good design to have it in a ring topology it is better to have it multi tier like access switches in L 2 upmlinks/ trunks tom distribution layer switches and here you will need the L3 functionality to operate L2 with the access switches and L3 routing with the core to route to other networks or blocked such as WAN or Internet block in the network

Each switch can be used as L2 only and if dose support L3 and you need this feUtre you can enable it but it is not must all based on the needs and design

In terms of security, traffic, user benift I would say itnis not related as the use of switch as L2 or L3 is something relate to the design if there are multiple subnets and communication between then required then routing function is required and this can be via a router or L3 switch configured for routing

If it's just flat one subnet/clan no need for L3 routing

Hope this help

If helpful rate

Peter Paluch · ‎09-26-2011

Hello Marwan,

This may be an academic dispute about terminology but I would personally not object against using the term "Layer 3 switch", "Layer 4 switching", "Layer 7 switching".

In fact, I believe that there is no strict definition of the word switching - it is being used in a somewhat free sense, and that may be the reason why some people do not like seeing it related to Layer 3 or higher operations. Traditionally, it has been used with respect to optimized frame delivery using switches, hence the verb. In this original sense, the word switching had two important characteristics:

It was concerned with Layer2 operations, controlled by MAC addresses
It was performed with hardware acceleration, as opposed to software-based bridges

Later, when multilayer switches became more prominent, we kept the familiar word switching to describe the service provided by these multilayer switches - mainly that the services are again performed in hardware - but now, we need to distinguish whether we are talking about Layer2 switching within a single VLAN, or about Layer3 switching between different VLANs. Note how convenient it was to describe everything done by switches as switching - and I believe that this is the reason why it is not objectionable to talk about L2/L3/L4/L7 switching. It is perfectly fine as long as we have the idea of the process behind - that it is controlled by MACs/IPs/transport layer ports/application protocol-specific information, and is performed usually in hardware. When talking about routing, this verb carries the unspoken notion of being performed primarily in software, although that does not need always to be the case.

The words switching and routing are actually infringing on each other's territory, as the devices that once were specific in their nature, purpose and services, have begun to provide integrated services. The terminology is therefore somewhat free, not clearly delineated nor defined, and I believe that it should not be taken too seriously...

Sorry for jumping into this thread with a partially off-topic discussion - I just wanted to provide a different viewpoint.

Best regards,

Peter

Marwan ALshawi · ‎09-26-2011

Peter 5 +

We could add also label switching of MPLS to the discussion

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douhanm · ‎09-26-2011

This is a religious argument really, we have done both

Some argue that smaller L2 domains are good other argue that spanning tree has been around long enough to be stable

Speed wise there are no large differences either since most links are directly connected and BFd handles rapid rotuing protocol notification if your HW supports it

L2 makes it easier to handle moving of devices

L3 seems to be more predictable with path selection and more forgiving for configuration mistakes

And also it depends on your staff what they are used to and familiar with

Matt

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