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Community Member

L3 Switch Vs Router

I am newbie to Layer3 Switching, Please some one tell me the advantage / uses of L3 switches over router. Also please tell me whether can I use the L3 switch as router for WAN connectity.

Thanks in Advance.

5 REPLIES
Bronze

Re: L3 Switch Vs Router

Hi

A network device that forwards traffic based on layer 3 information at very high speeds. Traditionally, routers, which inspect layer 3, were considerably slower than layer 2 switches. In order to increase routing speeds, many "cut-through" techniques were used, which perform an "inspect the first packet at layer 3 and send the rest at layer 2" type of processing. Ipsilon's IP Switch and Cabletron's SecureFast switches were pioneers in cut-through switching.

As more routing lookup functions were moved from software into the ASIC chips, layer 3 switches could inspect each packet just like a router at high speed without using proprietary cut-through methods. If a layer 3 switch supports packet-by-packet inspection and supports routing protocols, it is called a "routing switch" or "switch router," which simply means "fast router." For example, Cisco calls its high-end routers Gigabit Switch Routers.

The more deeply a packet is examined, the more forwarding decisions can be made based upon type of traffic, quality of service and so on. To get to this information means digging into the packet's headers to ferret out the data, which takes processing time. To understand how the packets are formed, see TCP/IP abc's. The following shows what is examined at each layer. See layer 3, layer 2 switch, Web switch and virtual LAN.

I hope this solve your problem, Please rate this post

-Minu

Community Member

Re: L3 Switch Vs Router

Thanks for your imme reply. can u guide me how to configure the L3 switch for internet connection (The ISP Using RJ45 media)

Bronze

Re: L3 Switch Vs Router

You can either create a layer 3 port by using the command:

no switchport

and then put an IP address on it, or you can create an SVI and tag the ISP connection with that vlan. Here are some examples of the first option:

conf t

int f0/1

no switchport

description [ISP]

ip address 1.1.1.1 255.255.255.252

no cdp enable

no shut

end

or the second option:

conf t

vlan 3

name [ISP]

int vlan 3

description [ISP]

ip address 1.1.1.1 255.255.255.252

no shut

int f0/1

switchport mode access

switchport nonegotiate

switchport access vlan 3

no cdp enable

spanning-tree portfast

spanning-tree guard root

spanning-tree bpduguard enable

no shut

end

Hope this helps.

Gold

Re: L3 Switch Vs Router

A point to the above discussion comes up in this case where you want to use a switch to talk to a ISP. Only some of the larger switches can run NAT. You will need to use a router if you do not have enough public IP's from your ISP.

Cisco Employee

Re: L3 Switch Vs Router

Excellent point by Tim.

Please refer the below URL for Network Address Translation Catalyst Switch Support Matrix:

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a008011c629.shtml

Regards,

Arul

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