Advanced Networking - L3 switches vs Routers

• L3 switch do switching at layer 3 by preserving the source and destination mac and preserving the TTL value of the IP header of the 1st routed packet, so the first packet is routed using normal routing lookup, but after that all packet are switched.

• Switches doesnt support some QoS features.

• Switches don't support NAT

• The forwarding on switches is done on ASIC (Application Specific Integrated Circuits) which is done in hardware rather than a software. Forwarding in Routers are done with Software.

• Routers support different WAN technologies (such as modules) while switches do not.
•  Routers do normal routing lookup, but by introducing fast switching and CEF, packets are also now switched on a router.
• Routers were devices that connected the LAN to the WAN and switches were just LAN devices and you may add a layer 3 switch to the lan if you had some vlans and didn't want to use a router.
• Routers seem to support more traffic monitoring features, such as netflow and nbar where as Layer 3 switches don't seem to have that kind of support.... until you get to the 6500

• The hardware inside a Layer 3 switch merges that of traditional switches and routers, replacing some of a router's software logic with hardware to offer better performance in some situations.
• Layer 3 switches often cost less than traditional routers. Designed for use within local networks, a Layer 3 switch will typically not possess the WAN ports and wide area network features a traditional router will always have.