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Difference between using serial cable and Ethernet cable between routers?

I’ve just started routing and I’m curious to why we use serial cables instead fastethernet .

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We don't's pretty rare.

Original Poster3 points · 6 days ago

Which one?

Serial connections.

It's pretty rare to use these days unless you're on a budget or have specific requirements you need to meet.

Pretty much the reason why Frame Relay was removed from the CCNA and and Serial connections are hardly mentioned in the books.

Original Poster6 points · 6 days ago

Makes sense my books a little old

Firstly I have the most recent cert guide and it's still referencing the lease lines and serial.

Secondly you should really be using the newest books because things are always changing

Original Poster1 point · 5 days ago

I plan to get up to date

Doesn't really matter what you use's good to know about the different types of connections.

Once they are connected, it's all about learning the overlying technology that passes through them.

They still have their place...for example, my company still uses T1s for OBM.

Serial cable is a dead technology, from what ive learned from my icnd1

I use it every day for server to server low bandwidth communications. It's more secure than IP and once it's set up you don't really have to do anything with it.

2 points · 5 days ago

It's more secure than IP

It’s still IP at layer 3. The difference is at layer 2, Ethernet vs hdlc/ppp.

A T1 is, but this isn't. It's encrypted data across a serial link. No IP involved at all.

What do you mean by:

It's more secure than IP

Is this because of the reliability? I am just very curious.

It's a point to point connection, no way to intercept or capture the traffic.

But a cross-over cable (without a device between the servers) with ethernet using IP does the same thing right?

It could. Depends on how your program is written I guess.
Our database is only accessible to the serial interface, you can't get to it over ip as there is nothing listening for it on the ip interface.

Ah okay, that is a very specific situation and baked in the application. ;)

So you are securing on layer 1 :P

I'm just the network guy. Tell me what needs to be done and I'll make it happen.
The dev guys deserve all the credit for taking the customer requirements and making it possible.

2 years of school and we were constantly using serial connections in our labs. In my head I was like "this can't really be what they use today" and lo and behold, it's absolutely not.

Would have been a lot more beneficial to learn more about fiber, school had no budget to upgrade lab gear though.

Meow 🐈🐈Meow 🐱🐱 Meow Meow🍺🐈🐱Meow A+!
7 points · 6 days ago

The point is more about learning about a non-ethernet interface type. All the complexity of fiber is all in the layer 1 stuff so it isn't really all that worth it from a lab point of view.

But non-ethernet interfaces aren't really used today, at least not inside an enterprise, maybe at an ISP level (no experience there).

In the course (granted, a while back) their use case for serial links was dedicated lines between branch sites. If they wanted to bring that into the modern day, they should focus more on IPsec, but I suppose that's more of a security topic to them

Or scrap serial and introduce VXLAN

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3 points · 6 days ago

Eh serial still has its place, especially for voip or for legacy / rural networks. The ccna mostly just teaches it for awareness and to show the difference in behaviour. It probably won’t be in future updates down the road. VXLAN awareness would probably be in the next round too.

As for schools using serials in labs, I’m guessing it is mostly them just being cheap, trying to make the lab a bit harder, or they are just used to it and don’t care that much.

The last time I used serial connections was also the last time I used frame relay. I was working for a power company about 13 years ago.

Part of the reason you hear about it is, in Packet Tracer they do alot with serial cable connections because it works in the program. Ethernet has some bugs in packet tracer when connecting routers together. That's about the only reason :)

Original Poster1 point · 5 days ago

Yh I tried ethernet between two routers with a static route, maybe I misconfig or maybe error, I plan to try again later

CCNA R&S, Sec+, Net+, A+
3 points · 6 days ago

Serial is still alive. PRIs are commonly used for telephony, although more people are moving to SIP and cloud PBX.

CCNA-Makes Phones Do Things
3 points · 5 days ago

My org has several sites running multilink PPP still because it's all they can get for some remote offices.

3 points · 6 days ago

Any context to the question?

Do you mean stacking cables or something like 9600 baud 9 pin OG serial?

Original Poster1 point · 5 days ago

I just wondered why in my rev book it's mentioned serial cable but in my class we used ethernet, but now I know

Not a serial cable, but I have used a serial link for some of my labs using a WIC-1DSU-T1 module and a t1 crossover cable made out of cat5e.

CCNA-Makes Phones Do Things
1 point · 5 days ago

Serial's a lot less common nowadays, but for a long time was the standard handoff for WAN links.

1 point · 4 days ago

about 992 MBps at Gigabit speeds :) -- assuming you crank the clock rate to 8000000

but it is harder to stretch those twisted pair cables down the street and across the ocean :)


The only reason you would connect two routers together with a serial cable is in a lab environment so you can practice working with Legacy Connections and a real CSU/DSU. Normally you would use the appropriate WIC.

PPP and variants (PPPoE and MLP) are still in the exam objectives, so they are "fair game"

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