Difference between Serial and Ethernet ports on a router?

[xyyz]

I'm studying for my CCNA... and I haven't found anything that explains the difference between these two ports.

I've been told that the serial ports are "programmable" ... why this is an advantage I dunno.

Initially, my understanding was that routing tables were send over the serial links... but what if a router has all ethernet ports... the ethernet ports must also deal with routing protocols right?

I'm really confused here... at one point I also thought that serial links only dealt with routing tables... but then I was told that they can send data too.

Another thing... someone told me that an s0 always connected to an s1, but in a book it shows an s0 connecting to an s0. Can an s0 connect to another s0?

I have the following resources...

Sybex's CCNA book (Lemelle or something)
Cisco Network Academy CCNA material

Any and all help will be greatly appreciated.

 

[Damaged]

Okay. Let's try and get your thoughts straightened out here.

First, while serial ports may be programmable it doesn't matter for what you're learning here, so set that thought aside for now.

The thing that you need to realize is that no matter what the port, whether it be serial, ethernet, HSSI, FDDI, what-fsck-ever, it is simply a physical standard (layer 1) for transfering data. PERIOD. That's all you really need to view these things as right now.

Can an S0 connect to another S0? Sure. Why not. Think about it once. You have rtr1 and rtr2. Both could have an interface named S0. If you want a serial connection of some sort b/w them and each has only one serial interace then, yes, you can certainly connect an S0 to an S0. These are simply logical names for device interfaces. Heck, you can connect an S0 to an SE3/0/1:0. Doesn't matter as long as they are compatible serial types (e.g. DS-0s, DS-1s, etc.)

Make a little more sense now, or not?

 

[CTR]

I think when somebody told you that an S0 always connects to an S1, they might have been trying to tell you that serial is a point-to-point link, as opposed to Ethernet which is a shared medium. That is the only scrap of helpful advice I can construe from that statement.

This might help you as well in thinking about serial as a physical media: Instead of just saying "serial" you should think of it as "synchronous serial" when dealing with T1's, T3's, etc. Because you can have an asynchronous serial interface and that would not be able to communicate to a synchronous serial interface for obvious reasons.

And think of routing protocols as just plain ol' data. No different than IP, IPX, ICMP, SNA, or anything else as far as interfaces are concerned. IGRP, RIP, and BGP are basically just protocls that happen to transfer routing information instead of html data or mp3's or whatever.

Hope that helps you some.

 

[spidey07]

Good explanation fellas.

I always tried to think on everthing an an interface. All interfaces are progammable meaning you can set criteria for each.

Maybe it would be best if you simply draw a box. Call this box a router. Draw lines out of the box. These lines correspond to your interfaces no matter what kind they are (serial, enet, etc). Really think of a router in its most simple form...it routes traffic from one physical network to another. A physical network could be an ethernet, a FDDI ring, Frame-Relay, or serial, or whatever.

Routing tables are completely internal to each router. It is through routing protocols that routers share and agree on this information to form a complete picture of reachability. So really routing protocols can run on any interface, it is really just the routers talking to each other.

good luck!