With MLS and L3 switches, why even have routers?

rodman.frowert · ‎09-18-2007

Subject title says it all. I'm guessing that perhaps switches don't have WAN interfaces, so at least ONE router must be used in a network to connect the LAN to the WAN. But if this were the case, wouldn't it make since to go ahead and build switches with these interfaces and get rid of routers all together??

I mean, MLS do routing so much faster than routers... Just trying to figure this one out...

Joseph W. Doherty · ‎09-18-2007

Today, there certainly overlap between L3 switches and routers.

Possibly one reason we still have both is because it's hard to get all the gee wiz features implemented in hardware at a reasonable cost point.

L3 switches are architected more toward raw speed, necessary for multigig bandwidths.

Routers are architected more toward features, since the bandwidth demands are often much lower.

Even when one can do both, i.e. performance with features, this tends to increase the cost relative to boxes marketed just as L3 switches or routers.

E.g.

Compare the new sup32-PISA bandwidth specs doing deep packet inspection vs. sup32 just switching traffic.

rodman.frowert · ‎09-18-2007

Do switches have the ability to connect to WAN's (i.e. can switches be outfitted with serial ports?)

I guess my question is if its possible to build a network without routers and use MLS, L3, and L2 routers only...

Although, as you said, it doesn't sound like this would be the cheapest solution to implement.

Joseph W. Doherty · ‎09-18-2007

"Do switches have the ability to connect to WAN's (i.e. can switches be outfitted with serial ports?)"

Some do, such as the 6500 series.

"I guess my question is if its possible to build a network without routers and use MLS, L3, and L2 routers only... "

Possible?, yes; practical?, it depends.

Richard Burts · ‎09-18-2007

Rodman

You raise an interesting question. I believe that while there is much overlap between routers and layer 3 switches there are still things that one does that the other does not do.

One of the traditional differences was the ability to do WAN. With FlexWan cards on the 6500 there are now some switches that can do serial connections. But most switches can not.

While I am not aware of much difference if you want to run basic dynamic routing protocols (RIP, OSPF, EIGRP) there are some other functionalities that are implemented in IOS routers that are not implemented in layer 3 switches. For example I believe that most switches do not implement NAT.

HTH

Rick

HTH

Rick

rodman.frowert · ‎09-18-2007

Interesting...

I've been studying for the BCMSN for the past few weeks and with all the things I am learning that switches seem to do, I simply figured they are destined to replace routers in the future...

From what I am seeing the 6500 will do just about damn near everything if equipped properly(routing protocols, serial interfaces, hardware NAT) But, of course, I bet that is one expensive switch. The exact thing can be done with one router for a fraction of the cost...

Still pretty cool... ;-)