Dumb question but why not use routers instead of switches?

I don't fully understand why in a network switches are used since they only do layer 2 switching and it seems that routers are more intelligent to route packets.

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Kaminsky

Basic idea:

Layer 2 switches collect multiple host traffic and bring their traffic into the network from that local area. Routers move traffic around edges of areas and provide the core of the network. More powerfull/expensive switches can also concentrate switch traffic and route them in larger networks as can more powerfull/expensive routers do for the smaller routers.

Turgon

SurferdudeHB wrote: »

I don't fully understand why in a network switches are used since they only do layer 2 switching and it seems that routers are more intelligent to route packets.

One school attempts to do precisely that when it's practical to reduce the potential of spanning-tree conplexities and other L2 issues. Constraints include port density of routers vs switches and L3 lookups as opposed to ASIC switched frames. Remember that many switches today are L3 capable.

Handbrake

If a switch runs on L3 why do we still call it a sw?

human151

they are referred to as multilayer switches. You can make any port into a routing port by using the "no switchport" command.

in many situations you just do not need the capabilities of a router.

SurferdudeHB

So what's the difference between MAC forwarding and IP routing? Is MAC address intended for LAN's specifically?

Forsaken_GA

You could theoretically use the mac address as a layer 3 address if the layer 3 protocol was coded to handle it (there are ipv6 addressing scheme's that do that, in fact), but in the ip4 world, yes, the mac address is layer 2 relevant, which is why you need things like arp, rarp, and proxy arp

tiersten

Work out what the price would be for a 24 port router which can do wire speed switching between all ports

tech-airman

SurferdudeHB wrote: »

I don't fully understand why in a network switches are used since they only do layer 2 switching and it seems that routers are more intelligent to route packets.

SurferdudeHB,

Think of it in terms of IP addressing, you know, your favorite subject, subnetting.

With a basic unmanaged Layer 2 switch, like a Cisco/Linksys switch, you can plug two computers into the switch that are in the same IP subnet as follows...

[Comp1 = 192.168.1.1/24]---[Unmanaged Switch]---[Comp2 = 192.168.1.4/24]

Now, let's look at the same situation using a router instead of an unmanaged switch...

[Comp1 = 192.168.1.1/24]---{192.168.1.2/24}[router]{192.168.2.3/24}---[Comp2 = 192.168.2.4/24]

So in the situation of the Unmanaged Switch scenario, you only use two IP addresses. In the situation of a router: 1) you need to have two separate subnets on both sides of the router 2) you need an IP address for each router interface 3) you need one IP address for each computer. So even in this simple scenario, you will need four (4) IP addresses just for two computers on opposite side of a router.

Now if you want to add another computer to a router, you'd need: 1) another router interface 2) resubnet another subnetwork for the new computer, e.g. 192.168.3.0/24 3) assign a new host address to the new computer, e.g. 192.168.3.2/24.

As you can see, the workload just gets higher and higher if you used a router instead of a switch.

Are you starting to see the relative benefit of a switch compared to a router?

SurferdudeHB

tech-airman wrote: »
SurferdudeHB,

Think of it in terms of IP addressing, you know, your favorite subject, subnetting.

With a basic unmanaged Layer 2 switch, like a Cisco/Linksys switch, you can plug two computers into the switch that are in the same IP subnet as follows...
[Comp1 = 192.168.1.1/24]---[Unmanaged Switch]---[Comp2 = 192.168.1.4/24]
Now, let's look at the same situation using a router instead of an unmanaged switch...
[Comp1 = 192.168.1.1/24]---{192.168.1.2/24}[router]{192.168.2.3/24}---[Comp2 = 192.168.2.4/24]
So in the situation of the Unmanaged Switch scenario, you only use two IP addresses. In the situation of a router: 1) you need to have two separate subnets on both sides of the router 2) you need an IP address for each router interface 3) you need one IP address for each computer. So even in this simple scenario, you will need four (4) IP addresses just for two computers on opposite side of a router.

Now if you want to add another computer to a router, you'd need: 1) another router interface 2) resubnet another subnetwork for the new computer, e.g. 192.168.3.0/24 3) assign a new host address to the new computer, e.g. 192.168.3.2/24.

As you can see, the workload just gets higher and higher if you used a router instead of a switch.

Are you starting to see the relative benefit of a switch compared to a router?

Yes I see, that make sense, thank you.

And subnetting is so... fun

thenjduke

Routers do not send Broadcast Traffic and think about the OSI layer.

dynamik

thenjduke wrote: »

Routers do not send Broadcast Traffic and think about the OSI layer.

By default

ncsugrad2002

K, everyone else has made this complicated.

I'll make it simple.

Switches=hardware based. Think fast.

Routers=software based. Think not so fast. They have routing tables to go through for every packet, blah blah blah.

There's more to it than this. But having a 48 port router isn't such a good idea..not to mention it's expensive

(although cisco actually did something similiar with their lowest level L3 switches, haha.. I'll find the model # sometime)

JavonR

ncsugrad2002 wrote: »

K, everyone else has made this complicated.

I'll make it simple.

Switches=hardware based. Think fast.

Routers=software based. Think not so fast. They have routing tables to go through for every packet, blah blah blah.

There's more to it than this. But having a 48 port router isn't such a good idea..not to mention it's expensive

(although cisco actually did something similiar with their lowest level L3 switches, haha.. I'll find the model # sometime)

Dang, beat me to it.

But I would also like to reinforce, switches = very fast, routers = not so fast.

thenjduke

dynamik wrote: »

By default

Yes forgot the by default

Silly DHCP Relay agents.

Turgon

phoeneous wrote: »

Not entirely true. Frame Relay actually has a broadcast command.

Frame Relay Commands

As does ATM although we need to be careful here about confusing the broadcast behavior of routers with that of WAN technologies.