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  1. cisco noob fly351's Avatar
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    #26
    Quote Originally Posted by chmorin View Post
    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.
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  3. Senior Member alan2308's Avatar
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    #27
    Quote Originally Posted by chmorin View Post
    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."
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  4. Senior Member notgoing2fail's Avatar
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    #28
    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?
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  5. cisco noob fly351's Avatar
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    #29
    Quote Originally Posted by chX View Post
    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.
    Last edited by fly351; 06-30-2010 at 02:46 PM. Reason: grammer...
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  6. Senior Member notgoing2fail's Avatar
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    #30
    Quote Originally Posted by alan2308 View Post
    And here's one more for everyone to chew on. A switch "bridges."


    Oh nice one!!!!
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  7. Went to the dark side.... Moderator networker050184's Avatar
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    #31
    Jeez people its just a term. Packet switching = routing, bridging = switching etc.
    An expert is a man who has made all the mistakes which can be made.
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  8. The Bringer of Light DevilWAH's Avatar
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    #32
    switching and a switch are two different things, as is a router and routing..

    switching and routing are technologies

    on the other hand a SWITCH and a ROUTER are names of devices, and with in networking they use to have a defination, Switch was layer 2 and Router was layer 3.

    In effect both switching and routing are the same thing, they both read a source address of some type or another and look up where it has to go in a table and forward it out a exit interface to the next device.

    the term SWITCH was used to designate a device that did this at layer 2, and a Router did this at layer 3.

    Now however there is so much over lap that they dont really exist as seperate devices any more.

    I do think it can be confusing to people new to networking to hear the teams layer 3 switch or multi layer switch.

    May be its just cause I rember when a ROuter was a ROUTER and a Switch was a SWITCH.. hehe
    • If you can't explain it simply, you don't understand it well enough. Albert Einstein
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  9. Senior Member notgoing2fail's Avatar
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    #33
    I have the book on IP CEF. I have to get it, there's a page where the author talks about not confusing the way a router switches and a switch switches.

    That it is confusing but the processes are different.

    I'll have to find it and see exactly what the author meant....
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  10. Senior Member notgoing2fail's Avatar
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    #34
    Here's the introduction to Cisco Express Forwarding book.


    How does a router switch a packet? What is the difference between routing a packet, switching a frame, and packet switching?
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  11. Senior Member notgoing2fail's Avatar
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    #35
    OMG you guys are going to get a kick out of this. I just received my SWITCH book today and how timely is this! The author goes into a quick review on layer 2/3 switches. I pulled out just a couple sentences here but you can find it on page 8 and 9.

    What a doosie!!!! You're going to fall off your chair!!!!!


    Here's what the author says: My comments are in blue.


    Layer 2 switches are capable of switching packets based only on MAC addresses.
    I thought frames contained MAC address info? Not packets. Packets are Layer 3. Frames are Layer 2 and Segments are Layer 4.

    So how can a packet contain MAC info in order to be switched?



    The term Layer 2 switching implies that frames forwarded by the switch are not modified in any way.
    Ok I can give the author this one. Usually packets are forwarded and frames are switched. But I'll throw a bone here.


    Layer 2 only switches are not capable of routing frames based on IP address and are limited to forwarding frames only based on MAC addresss.
    Of course not, frames don't contain any L3 address, so of course you can't route on IP. Again, he mentions frames are forwarded, not switched.....



    Layer 2 switches might support features that read Layer 3 information of a frame for specific features.
    Since when does a frame (a data-link layer) contain Layer 3 info?



    Seriously, holy sh**, the author is ALL OVER THE PLACE.

    Forget nitpicking, you guys have to admit, that's one confusing paragraph he wrote!!!!
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  12. Went to the dark side.... Moderator networker050184's Avatar
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    #36
    Makes sense to me. I think you are just nit picking way too much man.
    An expert is a man who has made all the mistakes which can be made.
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  13. cisco noob fly351's Avatar
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    #37
    My comments are in red

    Quote Originally Posted by notgoing2fail View Post
    Here's what the author says: My comments are in blue.

    Layer 2 switches are capable of switching packets based only on MAC addresses.
    I thought frames contained MAC address info? Not packets. Packets are Layer 3. Frames are Layer 2 and Segments are Layer 4.

    So how can a packet contain MAC info in order to be switched?


    Yes, the frame header contains the MAC address but the frame contains the Packet. What you quoted says "capable of switching packets", not that the packet contains the MAC address.


    Layer 2 switches might support features that read Layer 3 information of a frame for specific features.
    Since when does a frame (a data-link layer) contain Layer 3 info?

    Doesn't QoS operate at Layer 2 and 3?
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  14. Senior Member notgoing2fail's Avatar
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    #38
    Quote Originally Posted by networker050184 View Post
    Makes sense to me. I think you are just nit picking way too much man.

    I know, it's my OCD kicking in.....
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  15. Senior Member notgoing2fail's Avatar
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    #39
    Quote Originally Posted by fly351 View Post
    My comments are in red




    Yes, the frame header contains the MAC address but the frame contains the Packet. What you quoted says "capable of switching packets", not that the packet contains the MAC address.



    Doesn't QoS operate at Layer 2 and 3?



    Ok for the first one, it could lead to different interpretations. My POV was that the author meant that the switch can make decisions on the "packet" based on the MAC address. Especially for Layer 2 switch, I don't know if a switch is capable of reading passed the frame and into the packet itself?


    For the second one, QoS operates on both layers yes. CoS for layer 2 and DSCP/IntServ for layer 3.

    So I'm ok with a switch reading layer 2 (CoS) frame info. But to say that a switch reads layer 3 frame info is nonsense. It's just sloppy authoring. There's no such thing as a layer 3 frame!!!
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  16. Went to the dark side.... Moderator networker050184's Avatar
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    #40
    So if there is no Layer 3 info in the frame how is it routed when the L2 header is stripped off?
    An expert is a man who has made all the mistakes which can be made.
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  17. Senior Member notgoing2fail's Avatar
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    #41
    Quote Originally Posted by networker050184 View Post
    So if there is no Layer 3 info in the frame how is it routed when the L2 header is stripped off?
    No that's not what I meant, what you just said is what I was trying to convey.

    That layer 3 strips off frame info, therefore you are left with packet or datagram.

    What I'm trying to say is that a packet can be contained within a frame on layer 2, but frames don't exist on layer 3.
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  18. Went to the dark side.... Moderator networker050184's Avatar
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    #42
    What if its a frame being tunneld over IP or MPLS? I think you need to just let it go man
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  19. Senior Member notgoing2fail's Avatar
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    #43
    Quote Originally Posted by networker050184 View Post
    What if its a frame being tunneld over IP or MPLS? I think you need to just let it go man
    Then you have got yourself a good point. That is interesting indeed....

    I have not thought about tunneling...
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  20. The Bringer of Light DevilWAH's Avatar
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    #44
    and how about a packet capture/anaylizer program like wire shark??

    should this not be a frame capture application
    • If you can't explain it simply, you don't understand it well enough. Albert Einstein
    • An arrow can only be shot by pulling it backward. So when life is dragging you back with difficulties. It means that its going to launch you into something great. So just focus and keep aiming.
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  21. Member HardDisk's Avatar
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    #45
    Let me get this straight.

    A layer 4 Segment is "routed" once it is encapsulated within an IP Packet aka DataGram.

    An IP Packet is "switched" once it is encapsulated within an Ethernet Frame.

    So can I then say that a TCP Segment is both "routed" and "switched"? (rhetorical question).

    Enjoyed this post with my morning coffee. Thanks
    Last edited by HardDisk; 07-02-2010 at 12:17 PM.
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  22. The Bringer of Light DevilWAH's Avatar
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    #46
    Quote Originally Posted by HardDisk View Post
    Let me get this straight.

    A layer 4 Segment is "routed" once it is encapsulated within an IP Packet aka DataGram.

    An IP Packet is "switched" once it is encapsulated within an Ethernet Frame.

    So can I then say that a TCP Segment is both "routed" and "switched"? (rhetorical question).

    Enjoyed this post with my morning coffee. Thanks

    Well only routed and switched if it passes across a router. if its only passes across a layer 2 network it is never routed

    I wonder how may new network people we have discouraged so far from getting in to this field
    • If you can't explain it simply, you don't understand it well enough. Albert Einstein
    • An arrow can only be shot by pulling it backward. So when life is dragging you back with difficulties. It means that its going to launch you into something great. So just focus and keep aiming.
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  23. cisco noob fly351's Avatar
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    #47
    Quote Originally Posted by DevilWAH View Post
    I wonder how may new network people we have discouraged so far from getting in to this field
    hahaha I am sure this thread is got some new people going
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  24. Member HardDisk's Avatar
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    #48
    If you made it past the fact that the ISO created the OSI model and that ironically somehow ISO stands for "International Organization for Standardization" then you've got what it takes.
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  25. Senior Member notgoing2fail's Avatar
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    #49
    Quote Originally Posted by DevilWAH View Post
    Well only routed and switched if it passes across a router. if its only passes across a layer 2 network it is never routed

    I wonder how may new network people we have discouraged so far from getting in to this field

    Right, you can say if the destination IP address is local to the subnet it's just switched...


    Let's hope no one turns away from this field because of this thread. I really think it's a thread worth discussing.

    Why shy away from it? Let's get to the bottom of things, is it nitpicking? Yes.....

    But it's also a little fun too ...... I can't be the only one that's a little curious how the terms are thrown around loosely....
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  26. cisco noob fly351's Avatar
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    #50
    They might be loosely thrown around, but at the same time... if someone is working on their CCNP I hope they can understand the difference I can see where someone would get confused at the CCENT/CCNA level, but if you can grasp the different encapsulations then it shouldn't be to confusing.
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