Layer 3 Switch vs. Router

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feverlax

Limp Gawd
Joined
Mar 1, 2005
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What are the benefits of using a Layer 3 switch as opposed to a router for distributing traffic? Basically the building I work in has a fiber line coming in which then gets connected to a Level 3 switch (NetVanta 1534) which is then connected to all the ethernet ports and what not. Why would they choose to use this device as opposed to a router? Or just a regular Layer 2 switch?

Thanks!
 
You need to route between vlans, to use a router to do this you will be limited by the routers link speed, a layer 2 switch can't route so a layer 3 switch in some cases is the best option.

I assume this is some kind of LAN extensions and not a leased internet line.
 
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Are you even sure they use the Layer 3 features?
Most (all?) manged switches are Layer 3, therefore if you want a managed switch, you're probably going to have a Layer 3 device.

We have all managed procurve l3 switches, but don't use a single routing service on any of them.
 
I'm not entirely sure what features they are using. I do know that they are upgrading the switches in place now to the NetVanta 1534 Layer 3 "lite" switches to allow them to do MAC address filtering, block rogue DHCP devices and provide remote management and other security features. I was mostly just wondering if they were really cost efficient for our needs
 
Right now, L3 switches from the "mainline brands" (HP/Dell/Cisco) are not really cost efficient. Using L2 switches + routers is usually less costly. Lately, companies like Adtran and Allied Telesis have been selling switches with L3 features that aren't terribly expensive. But there is usually a question of whether people "trust" those switches.
 
Most layer 3 switches will do basic routing. They can do static routes, maybe some simple routing with RIP. Some can do access lists and other router type functions.

A true router is going to do a lot more. Larger, more complex access lists, support for more routing protocols, like EIGRP, BGP, OSPF.

If you're routing between 2 internal subnets, probably a basic layer 3 switch is fine. Larger networks need bigger switches. If you're connecting to an ISP and running BGP, you'll want a true router.

Routers also support more connection types. A switch will do Ethernet, and if you buy an expensive enough switch, maybe ATM, either PVCs or (rarely) LANE.

A router will do connections via T-1, T3, DSL, serial, ethernet, ATM, etc... You can usually use a router for VPN connections, NAT, etc...
 
I think you left out the one "big problem" for L3 switches - they can't usually do NAT. I think that's the main reason most people still need a router even if they have an L3 switch.
 
I've never touched a Cisco 6500 but do they do NAT?

From the top of my head I recall a 3750 being able to do BGP, EIGRP, ACLs and possibly Tunnels (don't quote me on the last two).

I do agree on the different media types. Also, the cost of routers (depending on the model) could be cheaper than a Layer 3 switch.
 
I've never touched a Cisco 6500 but do they do NAT?
Click to expand...
Yes, but that's the only cisco switch that can do NAT. Furthermore, if you can afford a 6500, you won't be worried about whether you need a router or not =)
 
In my org we only use 3800s, CAT 3750s, CAT 4500s, 7600s, and ASRs. What's the average price range on a 6500, CSR, 7000 and XSRs?
 
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