Packets or Frames

Ok I figured I'd make a post about this because I think sometimes "packets" or "frames" are used interchangeably when they really shouldn't be.

So I'm watching a video on STP and they are saying that the "packets" can continue on an endless loop unless STP is enabled.

Over and over, they use "packets" and not "frames".

I suppose if you want to get technical, the packets are encapsulated within frames but I really think one should use the correct terminology according to the layer in question.

To me, when you're talking about L2 switches and the topic of STP, it's all about frames isn't it? Aren't the frames the actual items that are being switched around endlessly?

When you talk about routers and L3, I don't hear anyone saying routers are forwarding frames, no they are pretty clear in saying packets.

So why are "packets" used when talking about L2 related topics?

Thoughts?

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Comments

DevilWAH

actualy you will hear people say the router strips out the destination mac address from the packet, replaces it with the mac address of the next hop and sends it out the interface...

of course what they mean is that the router replaces the mac address on the frame...

Both routers and switch's really switch frames, a router on an Ethernet segment at least revives a frame and sends out a frame.

I do agree that frames and packets are often used in the wrong terms, but i think often to begin with it makes more scene. most people know a PC has a ip address and you have IP packets. I know people who still find it hard to come to grips with the fact that pc's don't communicate by ip but with there mac address.

I think once you can point out the error of people misplacing the terms then you show you understand.

veritas_libertas

This kind of confusion was very difficult for me during my associate degree studies. I wish authors and instructors/professors would be a little more exact. Then again, I guess I catch myself doing the same thing at times.

networker050184

Its just one of those things you have to get used to. A lot of people just say packet or frame for everything. You could always just go with PDU if you want!

Monkerz

I guess you can look at it like this...

A frame doesn't make it past a networking device, only a packet actually makes it past. The the layer 2 encapsulation is shed, then recreated at every intermediary device. This repackages the packet for "another leg of the journey".

Therefore the packet would be the PDU that is sent in endless loops...

Just my 2 cents.

veritas_libertas

networker050184 wrote: »

You could always just go with PDU if you want!

That would certainly get their attention

alan2308

notgoing2fail wrote: »

So why are "packets" used when talking about L2 related topics?

The same reason that people still can't tell the difference between they're, their, and there. And don't forget your/you're and our/are/hour.

notgoing2fail

haha nice response guys.....

I guess it kinda irks me in that at the end of the day, it really doesn't matter, it's not going to be the end of the world.

But I'm pushing myself to try to be consistent and make sure that I have a solid understanding of all the workings of a network.

When I speak about L2, I will go out of my way to make sure I use "frames", it will help me as well as anyone else who may be confused.

In a way, I kind of find it sloppy. Is it nitpicking? Yeah, I think a tad bit, I mean the author is a CCIE, so clearly he knows the subject and has much more game and credibility than me.

Just something I wanted to bring up and see what you guys thought about it....

DevilWAH

alan2308 wrote: »

The same reason that people still can't tell the difference between they're, their, and there. And don't forget your/you're and our/are/hour.

See may be that why i don't find this a problem. suffering from being a dyslexic, i don't care if some one uses their in place of there.. to me as long as I can understand it then its fine by me

Tihs snetcnee and tihs one are jsut the smae to me.
this sentence and this one are just the same to me.

I never been one who cares for the words used, I don't even really read words, just see the pictures in my head. so if some one said packet being looped around STP, in my head I have a picture of a layer 2 frame, as a picture of a naked packer at in STP is just plain wrong,

notgoing2fail

DevilWAH wrote: »

I never been one who cares for the words used, I don't even really read words, just see the pictures in my head. so if some one said packet being looped around STP, in my head I have a picture of a layer 2 frame, as a picture of a naked packer at in STP is just plain wrong,

Right. I think for the majority of us, we "get" it.

For newbies, I think it can really make learning a bit difficult and for exams, if they wanted to nitpick, they could really get you on this technicality.

It's just something that I think if a CCIE is teaching a course, he/she should try to go out of their way to help reduce any possible confusion....

alan2308

DevilWAH wrote: »

See may be that why i don't find this a problem. suffering from being a dyslexic, i don't care if some one uses their in place of there.. to me as long as I can understand it then its fine by me

Tihs snetcnee and tihs one are jsut the smae to me.
this sentence and this one are just the same to me.

I never been one who cares for the words used, I don't even really read words, just see the pictures in my head. so if some one said packet being looped around STP, in my head I have a picture of a layer 2 frame, as a picture of a naked packer at in STP is just plain wrong,

There's a huge difference between dyslexia and plain laziness. You're still typing in complete sentences with correct punctuation. I'd be a lot less likely to notice it then.

But attention to detail matters, especially in this field. If you don't believe me, send out a batch of sloppy resumes or fat finger a single digit in an IP address.

chmorin

alan2308 wrote: »

or fat finger a single digit in an IP address.

Been there, done that.

DevilWAH

I tell you the one that really gets me is

Layer 3 Switch...

hold on though... a switch is a device that runs at layer 2 of the OSI and "switchs frames"

A router is a device that runs at layer 3 and "routes" packets

So the term a layer 3 switch in my mind is plain wrong! should they not be called ethernet routers? but even this is wrong as they also switch..

how about "multi layer ethernet networking devices"

notgoing2fail

DevilWAH wrote: »

I tell you the one that really gets me is

Layer 3 Switch...

hold on though... a switch is a device that runs at layer 2 of the OSI and "switchs frames"

A router is a device that runs at layer 3 and "routes" packets

So the term a layer 3 switch in my mind is plain wrong! should they not be called ethernet routers? but even this is wrong as they also switch..

how about "multi layer ethernet networking devices"

Yeah, since "switch" implies layer 2. And by calling it a L3 Switch, you're basically saying, "L3 Layer 2".

Of course calling a device an "L3 Switch" has a cool factor sound to it.

As someone mentioned up above, there is a slight "laziness or sloppiness" to it. I suppose if one were to pay $300-400 for a video tutorial, you'd really want to make sure that authors are using the right terms.

I just feel bad for the new guys who take their words for it hook line and sinker. Video authors shouldn't assume the audience will just "get it", because that's bad practice.

I'm telling you, one day some poor fool is going to get an exam question like this:

A) A layer 2 device can switch packets at wire speed
b) A router is a device that reduces broadcast domains
c) All switches have the capability to route packets
d) none of the above

Some poor chap is going to pick "A".

Then the exam simulator is going to say, "GOTCHYA!" A layer 2 device switches frames, not packets! hahaha.....

networker050184

Switching does not imply layer 2. Routing is packet switching. I think you guys are definitely going over board. Especially with assumptions.

notgoing2fail

networker050184 wrote: »

Switching does not imply layer 2. Routing is packet switching. I think you guys are definitely going over board. Especially with assumptions.

I thought routing was packet forwarding?

networker050184

notgoing2fail wrote: »

I thought routing was packet forwarding?

Thats just it, more than one way to skin a cat. Doesn't mean one way is wrong.

notgoing2fail

networker050184 wrote: »

Thats just it, more than one way to skin a cat. Doesn't mean one way is wrong.

I thought that you could get away with "packet switching" when you have routers with actual switching capabilities like with IP CEF enabled.

If you turn off IP CEF/ip route cache and all processing is done at the route processor, is it fair to say that packets are now forwarded since they are never switched at the switching engine?

chmorin

networker050184 wrote: »

Thats just it, more than one way to skin a cat. Doesn't mean one way is wrong.

Could this be a case of a square is a rectangle, but a rectangle is not a square?

Muaahhahah. This is one of those topics that if you think to hard about it, you are going to get confused. Break out packet tracer and follow the packet from hop to hop. You get to see what changes in the frame and packet if I remember correctly.

networker050184

Switching has nothing to do with the layer. Its just a name for having a packet/frame come in one interface and have it "switched" out another interface. That is all it means. Nothing to do with the routers architecture.

chX

I read once something similar to:

The process of receiving a packet on one interface, making a decision about what to do with it, and emitting it on another interface is not routing, it's switching.

Routing is what OSPF, BGP, RIP, etc, do. Which is populating the routing table with information which can be used to make a switching decision.

Interesting way to look at it.

fly351

DevilWAH wrote: »

I tell you the one that really gets me is

Layer 3 Switch...

hold on though... a switch is a device that runs at layer 2 of the OSI and "switchs frames"

A router is a device that runs at layer 3 and "routes" packets

So the term a layer 3 switch in my mind is plain wrong! should they not be called ethernet routers? but even this is wrong as they also switch..

how about "multi layer ethernet networking devices"

I am pretty sure a Layer 3 switch is still considered a switch because of how it compiles a TCAM table, which a router does not. Single table look ups vs multi-table look ups.

fly351

chX wrote: »

I read once something similar to:

- Switching is receiving a frame/packet/whatever on one interface, making a decision about what to do with it and sending it out another inteface, and;

- Routing is what OSPF, BGP, RIP, etc, do. Which is filling the routing table with information which can be used to make a switching decision.

Interesting way to look at it.

But if you look at what you just said... basically that boils down to...

"Switching forwards"
"Routing forwards"

So what is the difference?

chmorin

fly351 wrote: »

But if you look at what you just said... basically that boils down to...

"Switching forwards"
"Routing forwards"

So what is the difference?

The end does not define the means.

Switching and routing have different tools and different algorithms associated with each set in order to accomplish the task that they are assigned. A hub forwards too, but it certainly is no router. It is the decision making process that decides the term.

chX

fly351 wrote: »

But if you look at what you just said... basically that boils down to...

"Switching forwards"
"Routing forwards"

So what is the difference?

I've edited my post a little bit.

At the end of the day I see it as:

A layer 2 Ethernet switch (since you can have ATM/FR/MPLS switches, right?) moves frames around a LAN based on Layer2 addressing.

A router separates and interconnects networks and stops broadcasts (by default). It can make switching decisions based on routing information it acquires.

A layer 3 switch is a layer 2 switch with routing capabilities, or perhaps you could say a router with a lot more ports.

That's my fairly narrow view, purely from the networking I've been exposed to so far.

fly351

chmorin wrote: »

The end does not define the means.

Switching and routing have different tools and different algorithms associated with each set in order to accomplish the task that they are assigned. A hub forwards too, but it certainly is no router. It is the decision making process that decides the term.

lol I understand that

I was trying to chX to respond.

alan2308

chmorin wrote: »

The end does not define the means.

Switching and routing have different tools and different algorithms associated with each set in order to accomplish the task that they are assigned. A hub forwards too, but it certainly is no router. It is the decision making process that decides the term.

Actually, a hub repeats. And here's one more for everyone to chew on. A switch "bridges."

notgoing2fail

Ok, let's take "packets" and "frames" out of the equation.

What is the definition of switching and forwarding? What is the difference?

Does one provide more intelligence than the other? Is one more CPU intensive?

Is switching or forwarding a feature readily available on any router or switch?

fly351

chX wrote: »

I've edited my post a little bit.

At the end of the day I see it as:

A layer 2 Ethernet switch (since you can have ATM/FR/MPLS switches, right?) moves frames around a LAN based on Layer2 addressing.

A router separates and interconnects networks and stops broadcasts (by default). It can make switching decisions based on routing information it acquires.

A layer 3 switch is a layer 2 switch with routing capabilities, or perhaps you could say a router with a lot more ports.

That's my fairly narrow view, purely from the networking I've been exposed to so far.

That's pretty much correct. What I was trying to point out is that switching and routing are similar because they forward based on table look ups (aka routing tables, CAM tables, TCAM, ACLs, etc...) Layer 3 switching combines these tables into a TCAM so it performs a single table look up. Layer 2 switches do forward based on a table lookup.

notgoing2fail

alan2308 wrote: »

And here's one more for everyone to chew on. A switch "bridges."

Oh nice one!!!!

networker050184

Jeez people its just a term. Packet switching = routing, bridging = switching etc.