Mastering the basics

bbarrick

I'm slowly working my way through Odom's book here, I don't want to miss anything. I figure if I master the basics, it will make the rest a that much easier to understand.

I'm on Chapter 5 reading about multiplexing in TCP/UDP and I just want to make sure I have something clear from the previous chapters.

Frames aren't used unless a packet is sent through a router to a subnet or internet connection and HDLC frames are used on a leased lines that use HDLC protocols?

Frames contain the source/destination IP address, packets contain source/destination MAC address right?

SharkDiver

These are simply the names of the data units in the different OSI Layers
Bits = Layer 1
Frames = Layer 2
Packets = Layer 3
Segments = Layer 4
I would think that your last sentence is backwards. Packets contain the source and destination IP Addresses being they are Layer 3. Frames contain the source and destination MAC addresses being they are Layer 2.

NetworkVeteran

I agree you should be clear on L2 vs. L3 before moving to more advanced topics.

Frames contain the source/destination IP address, packets contain source/destination MAC address right?

Not quite, mate. You have this backwards. Frames = L2 = MAC addresses and Packets = L3 = IP addresses, typically.. I say that since it's still possible to run a network that doesn't use Ethernet at L2 or IP at L3.

Frames aren't used unless a packet is sent through a router to a subnet or internet connection

In a typical network, both frames and packets are used in just about every message.

HDLC frames are used on a leased lines that use HDLC protocols?

HDLC and PPP are both options. Note, Cisco's HDLC implementation is non-standardized and lacks authentication support.

bbarrick

NetworkVeteran wrote: »

I agree you should be clear on L2 vs. L3 before moving to more advanced topics.


Not quite, mate. You have this backwards. Frames = L2 = MAC addresses and Packets = L3 = IP addresses, typically.. I say that since it's still possible to run a network that doesn't use Ethernet at L2 or IP at L3.

Ok, that was simple I know but just a clarification I needed. Makes more sense now. Odom frequently uses different terms for the same thing, I understand that it's probably an industry wide thing to do but for a total beginner it can make your head spin.

In a typical network, both frames and packets are used in just about every message.

Ok, even in some of the diagrams where it shows a frame leaving the network from a router onto the internet he calls it an IP packet each step of the way. I'm assuming this is just another term for frame? My thinking was that since the computer/router can determine whether or not the destination address is local or not there would be no need for a frame and it would just forward the packet onto it's destination as a packet. But if it was headed for the default gateway to go to a destination not on the same network it would need the frame...I will reread all of this again a few times most likely. I knew I'd be able to get some different wording here to help me understand it.

HDLC and PPP are both options. Note, Cisco's HDLC implementation is non-standardized and lacks authentication support.

Does PPP use the typical ethernet protocol?

NetworkVeteran

bbarrick wrote:

he calls it an IP packet each step of the way. I'm assuming this is just another term for frame?

Nope! L3 runs over L2. Thus, you have a Frame or a Frame+Packet. The terms 'frame' and 'packet' are not interchangeable at all. I recall Odom being fairly good at saying what he means, although all technical books contain errata. It may be worth checking out his errata page and using a pencil to update the chapters you're reading if you're getting confused.

My thinking was that since the computer/router can determine whether or not the destination address is local or not there would be no need for a frame

IP doesn't know anything about cabling, transceivers, line encoding, CSMA/CD, etc. so it alone would be insufficient to transfer date from one station to another. L3 needs L2 and L2 needs L1.

Does PPP use the typical ethernet protocol?

PPP doesn't use Ethernet and Ethernet doesn't use PPP. They are each different L2 protocols.

bbarrick

NetworkVeteran wrote: »

Nope! L3 runs over L2. Thus, you have a Frame or a Frame+Packet. The terms 'frame' and 'packet' are not interchangeable at all. I recall Odom being fairly good at saying what he means, although all technical books contain errata. It may be worth checking out his errata page and using a pencil to update the chapters you're reading if you're getting confused.

I'm sure he still is, I have a tendency to make simple things more complex than they are when I'm first starting out. Taking this into context I will take another look at this. The diagram does show a pc sending an IP packet to through three routers but I'm guessing the reader should assume that the packet is being encapsulated into a frame.

IP doesn't know anything about cabling, transceivers, line encoding, CSMA/CD, etc. so it alone would be insufficient to transfer date from one station to another. L3 needs L2 and L2 needs L1.

Makes sense.

PPP doesn't use Ethernet and Ethernet doesn't use PPP. They are each different L2 protocols.[/QUOTE]

So far he hasn't touched on PPP at all, he mentioned it along with HDLC and went on to discuss HDLC frames and that was it. I'm really enjoying this book, I'm just a beginner to all of this but the pieces are coming together. Thanks for the help.

bbarrick

I had all of this written down in my notes correctly, I had just gotten a little mixed up as I read further along. I'm going to go back when I'm done with the 5th chapter and rewrite my notes. The test exam for the first four chapters I can pass with a perfect score. Knowing which pins certain devices transmit and receive on was rather easy for me, some of the terms and their proper definitions are a little fuzzy but I think if I keep studying the way I have I'll have the basics down well enough that I can move on. I want to take the CCENT test with the confidence that I can almost ace it rather than feeling a bit unsure of whether I can pass at all.