Understanding hubs and switches












3















Newbie here. I'm trying to understand how hubs and switches work.
I read that hubs only forwards to all ports but a switch only forwards to the port it needs to.



So, If I connect 3 computers to the same hub, and use PC1 to ping PC2, then all the 3 computers will receive the ping?



But if I connect 3 computers to the same switch and used PC1 to ping PC 2, then only PC1 and PC2 sees the ping because switches only forward it to the correct port. Is that correct?










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  • 2





    Did you mean "hub" in the second paragraph?

    – Ron Trunk
    11 hours ago











  • yes thanks just edited it

    – The_Bear
    10 hours ago











  • Does anybody actually use hubs anymore? (I mean besides my co-worker, who installed them because he could get them dirt-cheap from an electronics recycler.)

    – Mark
    6 hours ago











  • Hubs are useful for Wireshark and the like, where promiscuous mode sniffing of a common broadcast domain is desirable.

    – mckenzm
    2 hours ago
















3















Newbie here. I'm trying to understand how hubs and switches work.
I read that hubs only forwards to all ports but a switch only forwards to the port it needs to.



So, If I connect 3 computers to the same hub, and use PC1 to ping PC2, then all the 3 computers will receive the ping?



But if I connect 3 computers to the same switch and used PC1 to ping PC 2, then only PC1 and PC2 sees the ping because switches only forward it to the correct port. Is that correct?










share|improve this question









New contributor




The_Bear is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
















  • 2





    Did you mean "hub" in the second paragraph?

    – Ron Trunk
    11 hours ago











  • yes thanks just edited it

    – The_Bear
    10 hours ago











  • Does anybody actually use hubs anymore? (I mean besides my co-worker, who installed them because he could get them dirt-cheap from an electronics recycler.)

    – Mark
    6 hours ago











  • Hubs are useful for Wireshark and the like, where promiscuous mode sniffing of a common broadcast domain is desirable.

    – mckenzm
    2 hours ago














3












3








3


1






Newbie here. I'm trying to understand how hubs and switches work.
I read that hubs only forwards to all ports but a switch only forwards to the port it needs to.



So, If I connect 3 computers to the same hub, and use PC1 to ping PC2, then all the 3 computers will receive the ping?



But if I connect 3 computers to the same switch and used PC1 to ping PC 2, then only PC1 and PC2 sees the ping because switches only forward it to the correct port. Is that correct?










share|improve this question









New contributor




The_Bear is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.












Newbie here. I'm trying to understand how hubs and switches work.
I read that hubs only forwards to all ports but a switch only forwards to the port it needs to.



So, If I connect 3 computers to the same hub, and use PC1 to ping PC2, then all the 3 computers will receive the ping?



But if I connect 3 computers to the same switch and used PC1 to ping PC 2, then only PC1 and PC2 sees the ping because switches only forward it to the correct port. Is that correct?







switch ping






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The_Bear is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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share|improve this question









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Check out our Code of Conduct.









share|improve this question




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edited 10 hours ago







The_Bear













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asked 11 hours ago









The_BearThe_Bear

283




283




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The_Bear is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.






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Check out our Code of Conduct.








  • 2





    Did you mean "hub" in the second paragraph?

    – Ron Trunk
    11 hours ago











  • yes thanks just edited it

    – The_Bear
    10 hours ago











  • Does anybody actually use hubs anymore? (I mean besides my co-worker, who installed them because he could get them dirt-cheap from an electronics recycler.)

    – Mark
    6 hours ago











  • Hubs are useful for Wireshark and the like, where promiscuous mode sniffing of a common broadcast domain is desirable.

    – mckenzm
    2 hours ago














  • 2





    Did you mean "hub" in the second paragraph?

    – Ron Trunk
    11 hours ago











  • yes thanks just edited it

    – The_Bear
    10 hours ago











  • Does anybody actually use hubs anymore? (I mean besides my co-worker, who installed them because he could get them dirt-cheap from an electronics recycler.)

    – Mark
    6 hours ago











  • Hubs are useful for Wireshark and the like, where promiscuous mode sniffing of a common broadcast domain is desirable.

    – mckenzm
    2 hours ago








2




2





Did you mean "hub" in the second paragraph?

– Ron Trunk
11 hours ago





Did you mean "hub" in the second paragraph?

– Ron Trunk
11 hours ago













yes thanks just edited it

– The_Bear
10 hours ago





yes thanks just edited it

– The_Bear
10 hours ago













Does anybody actually use hubs anymore? (I mean besides my co-worker, who installed them because he could get them dirt-cheap from an electronics recycler.)

– Mark
6 hours ago





Does anybody actually use hubs anymore? (I mean besides my co-worker, who installed them because he could get them dirt-cheap from an electronics recycler.)

– Mark
6 hours ago













Hubs are useful for Wireshark and the like, where promiscuous mode sniffing of a common broadcast domain is desirable.

– mckenzm
2 hours ago





Hubs are useful for Wireshark and the like, where promiscuous mode sniffing of a common broadcast domain is desirable.

– mckenzm
2 hours ago










3 Answers
3






active

oldest

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4















If I connect 3 computers to the same hub, and use PC1 to ping PC2, then all the 3 computers will receive the ping?




PC2 and PC3 receive the echo request, and PC1 and PC3 receive the echo reply. A sender's signal is repeated to the other ports but not back the sender.



However, receive depends on the point of view: since the echo request doesn't address PC3's MAC, its NIC physically receives the frame but drops it right away - the encapsulated packet isn't received by the IP stack.




But if I connect 3 computers to the same switch and used PC1 to ping PC 2, then only PC1 and PC2 sees the ping because switches only forward it to the correct port. Is that correct?




Yes. Ping uses IP and IP requires ARP before sending an IP packet (containing an echo request or anything else). ARP causes the switch to learn PC1's and PC2's MAC addresses, so the switch forwards the frames with the echo request/reply to just the intended destinations.






share|improve this answer



















  • 1





    What if its the first time that it is being pinged on the switch, as the switch wont have the Mac Address, so does PC3 also receive it too?

    – The_Bear
    8 hours ago











  • @The_Bear Yes, when a switch encounters a new MAC address destination, it floods all the other ports and waits for a response.

    – Veskah
    6 hours ago



















3














A hub is simply like a powered cable, where every signal is repeated out all the other interfaces.



A switch is really a high-density bridge. The simplest switches will learn which devices are on which interfaces, and they will then forward frames for a particular device to the interface where the devices is connected. Although, a switch will flood broadcast, and unknown unicast frames out every other interface



Hubs (layer-1 devices) repeat every signal, even garbage, but switches (layer-2 devices) work with frames (dropping damaged frames).






share|improve this answer


























  • So I'm right in saying that if I connect 3 PC's to a switch and use PC1 to ping PC2, only PC1 and PC2 will see the ping, PC3 won't?

    – The_Bear
    10 hours ago













  • If the switch has not yet learned the destination interface, it will flood the frame to all the other interfaces. It learns very quickly because it only takes one frame from a host for it to learn where the host is.

    – Ron Maupin
    10 hours ago











  • So does that mean when the ping is first sent, all the ports will receive it in the switch but if it is pinged again it will only go to PC2?

    – The_Bear
    8 hours ago






  • 1





    Maybe. As @Zac67 points out, the source host may need to ARP for the destination address, and that will suffice to populate the MAC address table, but the table entries do time out, so it may need to happen again. A host will maintain an ARP table for destinations, and its entries also time out, but that is not coordinated with any other host or the switch MAC address table. You cannot say at any given time if a switch MAC address table has an entry for the destination.

    – Ron Maupin
    8 hours ago











  • No. The previous ARP already updates the switch's MAC table, so the first ping already goes to PC2 only.

    – Zac67
    8 hours ago



















2














Ethernet has evolved over time, and has some archaic standards that no longer matter all that much.



Originally Ethernet used what was known as a half-duplex signalling standard, which is like having a 1-lane road with vehicles that can travel in either direction on it.



When endpoint devices try to transmit at the same time on a half-duplex hub network, this causes a collision event, which requires both devices to pause for a random period of time and try again. Some of the more expensive early hubs from the 1990s such as from Cabletron had a collision light that would show when a collision occurred.



As more devices are added to a half-duplex hub network, the risk of data collisions increases, and overall throughput declines because so much time is being wasted by colliding, waiting, trying again, colliding, waiting, trying again..



Generally an Ethernet cable cannot be longer than 100 meters, and there cannot be more than 4 hubs between two devices, because 500 meters is the distance limit of the collision detection system when two devices try to transmit at the same time but their data packets collide.



,



It used to be that hubs were the inexpensive network component while switches were really expensive, because a hub isn't really much more than a collection of amplifier circuits while a switch includes actual processing to decode and analyze packets, and also splits the collision domains into separate territories.



Though it also used to be that you had to use a special cable called a crossover cable to interconnect endpoint devices or to make hub-to-hub connections. We don't care about any of this anymore because all devices include a way to make any connection a normal or crossover, known as Auto-MDIX.



,



Since some time around 2005, the bottom fell out of the switch market, and switches became cheaper and cheaper until we reached a point where hubs basically disappeared and we now use switches for everything.



The original design spec for 100 meter cables and 4 hubs per collision domain still exist, but it's now basically irrelevant because hubs are no longer in use. We now effectively have an isolated collision domain between every endpoint and its matching switch port.



Due to this you could probably make a half-duplex twisted pair Ethernet cable 500 meters long between a device and a switch port, and it would work fine. Doing this violates the cable length of the original signalling specification which cannot imagine hubs not being used, but 500 meters is compatible with the original half-duplex collision detection method, should the switch port and endpoint device both transmit and collide.



,



But even the collision domain has become irrelevant, due to later twisted pair wiring standards changing from half-duplex to full duplex. What this means is that there is now an isolated path available for sending from one end to the other, in both directions.



In this configuration, a collision is not even possible when a single endpoint connects to a single switch port, and so a twisted pair cable could likely far exceed the 500 meter limit of the collision detection mechanism, and still work.



Though we are now deviating quite far from the original Ethernet design specification and we will instead start running up against electromagnetic limits with capacitance and inductance causing signal degradation.






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    3 Answers
    3






    active

    oldest

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    3 Answers
    3






    active

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    oldest

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    oldest

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    4















    If I connect 3 computers to the same hub, and use PC1 to ping PC2, then all the 3 computers will receive the ping?




    PC2 and PC3 receive the echo request, and PC1 and PC3 receive the echo reply. A sender's signal is repeated to the other ports but not back the sender.



    However, receive depends on the point of view: since the echo request doesn't address PC3's MAC, its NIC physically receives the frame but drops it right away - the encapsulated packet isn't received by the IP stack.




    But if I connect 3 computers to the same switch and used PC1 to ping PC 2, then only PC1 and PC2 sees the ping because switches only forward it to the correct port. Is that correct?




    Yes. Ping uses IP and IP requires ARP before sending an IP packet (containing an echo request or anything else). ARP causes the switch to learn PC1's and PC2's MAC addresses, so the switch forwards the frames with the echo request/reply to just the intended destinations.






    share|improve this answer



















    • 1





      What if its the first time that it is being pinged on the switch, as the switch wont have the Mac Address, so does PC3 also receive it too?

      – The_Bear
      8 hours ago











    • @The_Bear Yes, when a switch encounters a new MAC address destination, it floods all the other ports and waits for a response.

      – Veskah
      6 hours ago
















    4















    If I connect 3 computers to the same hub, and use PC1 to ping PC2, then all the 3 computers will receive the ping?




    PC2 and PC3 receive the echo request, and PC1 and PC3 receive the echo reply. A sender's signal is repeated to the other ports but not back the sender.



    However, receive depends on the point of view: since the echo request doesn't address PC3's MAC, its NIC physically receives the frame but drops it right away - the encapsulated packet isn't received by the IP stack.




    But if I connect 3 computers to the same switch and used PC1 to ping PC 2, then only PC1 and PC2 sees the ping because switches only forward it to the correct port. Is that correct?




    Yes. Ping uses IP and IP requires ARP before sending an IP packet (containing an echo request or anything else). ARP causes the switch to learn PC1's and PC2's MAC addresses, so the switch forwards the frames with the echo request/reply to just the intended destinations.






    share|improve this answer



















    • 1





      What if its the first time that it is being pinged on the switch, as the switch wont have the Mac Address, so does PC3 also receive it too?

      – The_Bear
      8 hours ago











    • @The_Bear Yes, when a switch encounters a new MAC address destination, it floods all the other ports and waits for a response.

      – Veskah
      6 hours ago














    4












    4








    4








    If I connect 3 computers to the same hub, and use PC1 to ping PC2, then all the 3 computers will receive the ping?




    PC2 and PC3 receive the echo request, and PC1 and PC3 receive the echo reply. A sender's signal is repeated to the other ports but not back the sender.



    However, receive depends on the point of view: since the echo request doesn't address PC3's MAC, its NIC physically receives the frame but drops it right away - the encapsulated packet isn't received by the IP stack.




    But if I connect 3 computers to the same switch and used PC1 to ping PC 2, then only PC1 and PC2 sees the ping because switches only forward it to the correct port. Is that correct?




    Yes. Ping uses IP and IP requires ARP before sending an IP packet (containing an echo request or anything else). ARP causes the switch to learn PC1's and PC2's MAC addresses, so the switch forwards the frames with the echo request/reply to just the intended destinations.






    share|improve this answer














    If I connect 3 computers to the same hub, and use PC1 to ping PC2, then all the 3 computers will receive the ping?




    PC2 and PC3 receive the echo request, and PC1 and PC3 receive the echo reply. A sender's signal is repeated to the other ports but not back the sender.



    However, receive depends on the point of view: since the echo request doesn't address PC3's MAC, its NIC physically receives the frame but drops it right away - the encapsulated packet isn't received by the IP stack.




    But if I connect 3 computers to the same switch and used PC1 to ping PC 2, then only PC1 and PC2 sees the ping because switches only forward it to the correct port. Is that correct?




    Yes. Ping uses IP and IP requires ARP before sending an IP packet (containing an echo request or anything else). ARP causes the switch to learn PC1's and PC2's MAC addresses, so the switch forwards the frames with the echo request/reply to just the intended destinations.







    share|improve this answer












    share|improve this answer



    share|improve this answer










    answered 10 hours ago









    Zac67Zac67

    28.3k21457




    28.3k21457








    • 1





      What if its the first time that it is being pinged on the switch, as the switch wont have the Mac Address, so does PC3 also receive it too?

      – The_Bear
      8 hours ago











    • @The_Bear Yes, when a switch encounters a new MAC address destination, it floods all the other ports and waits for a response.

      – Veskah
      6 hours ago














    • 1





      What if its the first time that it is being pinged on the switch, as the switch wont have the Mac Address, so does PC3 also receive it too?

      – The_Bear
      8 hours ago











    • @The_Bear Yes, when a switch encounters a new MAC address destination, it floods all the other ports and waits for a response.

      – Veskah
      6 hours ago








    1




    1





    What if its the first time that it is being pinged on the switch, as the switch wont have the Mac Address, so does PC3 also receive it too?

    – The_Bear
    8 hours ago





    What if its the first time that it is being pinged on the switch, as the switch wont have the Mac Address, so does PC3 also receive it too?

    – The_Bear
    8 hours ago













    @The_Bear Yes, when a switch encounters a new MAC address destination, it floods all the other ports and waits for a response.

    – Veskah
    6 hours ago





    @The_Bear Yes, when a switch encounters a new MAC address destination, it floods all the other ports and waits for a response.

    – Veskah
    6 hours ago











    3














    A hub is simply like a powered cable, where every signal is repeated out all the other interfaces.



    A switch is really a high-density bridge. The simplest switches will learn which devices are on which interfaces, and they will then forward frames for a particular device to the interface where the devices is connected. Although, a switch will flood broadcast, and unknown unicast frames out every other interface



    Hubs (layer-1 devices) repeat every signal, even garbage, but switches (layer-2 devices) work with frames (dropping damaged frames).






    share|improve this answer


























    • So I'm right in saying that if I connect 3 PC's to a switch and use PC1 to ping PC2, only PC1 and PC2 will see the ping, PC3 won't?

      – The_Bear
      10 hours ago













    • If the switch has not yet learned the destination interface, it will flood the frame to all the other interfaces. It learns very quickly because it only takes one frame from a host for it to learn where the host is.

      – Ron Maupin
      10 hours ago











    • So does that mean when the ping is first sent, all the ports will receive it in the switch but if it is pinged again it will only go to PC2?

      – The_Bear
      8 hours ago






    • 1





      Maybe. As @Zac67 points out, the source host may need to ARP for the destination address, and that will suffice to populate the MAC address table, but the table entries do time out, so it may need to happen again. A host will maintain an ARP table for destinations, and its entries also time out, but that is not coordinated with any other host or the switch MAC address table. You cannot say at any given time if a switch MAC address table has an entry for the destination.

      – Ron Maupin
      8 hours ago











    • No. The previous ARP already updates the switch's MAC table, so the first ping already goes to PC2 only.

      – Zac67
      8 hours ago
















    3














    A hub is simply like a powered cable, where every signal is repeated out all the other interfaces.



    A switch is really a high-density bridge. The simplest switches will learn which devices are on which interfaces, and they will then forward frames for a particular device to the interface where the devices is connected. Although, a switch will flood broadcast, and unknown unicast frames out every other interface



    Hubs (layer-1 devices) repeat every signal, even garbage, but switches (layer-2 devices) work with frames (dropping damaged frames).






    share|improve this answer


























    • So I'm right in saying that if I connect 3 PC's to a switch and use PC1 to ping PC2, only PC1 and PC2 will see the ping, PC3 won't?

      – The_Bear
      10 hours ago













    • If the switch has not yet learned the destination interface, it will flood the frame to all the other interfaces. It learns very quickly because it only takes one frame from a host for it to learn where the host is.

      – Ron Maupin
      10 hours ago











    • So does that mean when the ping is first sent, all the ports will receive it in the switch but if it is pinged again it will only go to PC2?

      – The_Bear
      8 hours ago






    • 1





      Maybe. As @Zac67 points out, the source host may need to ARP for the destination address, and that will suffice to populate the MAC address table, but the table entries do time out, so it may need to happen again. A host will maintain an ARP table for destinations, and its entries also time out, but that is not coordinated with any other host or the switch MAC address table. You cannot say at any given time if a switch MAC address table has an entry for the destination.

      – Ron Maupin
      8 hours ago











    • No. The previous ARP already updates the switch's MAC table, so the first ping already goes to PC2 only.

      – Zac67
      8 hours ago














    3












    3








    3







    A hub is simply like a powered cable, where every signal is repeated out all the other interfaces.



    A switch is really a high-density bridge. The simplest switches will learn which devices are on which interfaces, and they will then forward frames for a particular device to the interface where the devices is connected. Although, a switch will flood broadcast, and unknown unicast frames out every other interface



    Hubs (layer-1 devices) repeat every signal, even garbage, but switches (layer-2 devices) work with frames (dropping damaged frames).






    share|improve this answer















    A hub is simply like a powered cable, where every signal is repeated out all the other interfaces.



    A switch is really a high-density bridge. The simplest switches will learn which devices are on which interfaces, and they will then forward frames for a particular device to the interface where the devices is connected. Although, a switch will flood broadcast, and unknown unicast frames out every other interface



    Hubs (layer-1 devices) repeat every signal, even garbage, but switches (layer-2 devices) work with frames (dropping damaged frames).







    share|improve this answer














    share|improve this answer



    share|improve this answer








    edited 11 hours ago

























    answered 11 hours ago









    Ron MaupinRon Maupin

    64.6k1367120




    64.6k1367120













    • So I'm right in saying that if I connect 3 PC's to a switch and use PC1 to ping PC2, only PC1 and PC2 will see the ping, PC3 won't?

      – The_Bear
      10 hours ago













    • If the switch has not yet learned the destination interface, it will flood the frame to all the other interfaces. It learns very quickly because it only takes one frame from a host for it to learn where the host is.

      – Ron Maupin
      10 hours ago











    • So does that mean when the ping is first sent, all the ports will receive it in the switch but if it is pinged again it will only go to PC2?

      – The_Bear
      8 hours ago






    • 1





      Maybe. As @Zac67 points out, the source host may need to ARP for the destination address, and that will suffice to populate the MAC address table, but the table entries do time out, so it may need to happen again. A host will maintain an ARP table for destinations, and its entries also time out, but that is not coordinated with any other host or the switch MAC address table. You cannot say at any given time if a switch MAC address table has an entry for the destination.

      – Ron Maupin
      8 hours ago











    • No. The previous ARP already updates the switch's MAC table, so the first ping already goes to PC2 only.

      – Zac67
      8 hours ago



















    • So I'm right in saying that if I connect 3 PC's to a switch and use PC1 to ping PC2, only PC1 and PC2 will see the ping, PC3 won't?

      – The_Bear
      10 hours ago













    • If the switch has not yet learned the destination interface, it will flood the frame to all the other interfaces. It learns very quickly because it only takes one frame from a host for it to learn where the host is.

      – Ron Maupin
      10 hours ago











    • So does that mean when the ping is first sent, all the ports will receive it in the switch but if it is pinged again it will only go to PC2?

      – The_Bear
      8 hours ago






    • 1





      Maybe. As @Zac67 points out, the source host may need to ARP for the destination address, and that will suffice to populate the MAC address table, but the table entries do time out, so it may need to happen again. A host will maintain an ARP table for destinations, and its entries also time out, but that is not coordinated with any other host or the switch MAC address table. You cannot say at any given time if a switch MAC address table has an entry for the destination.

      – Ron Maupin
      8 hours ago











    • No. The previous ARP already updates the switch's MAC table, so the first ping already goes to PC2 only.

      – Zac67
      8 hours ago

















    So I'm right in saying that if I connect 3 PC's to a switch and use PC1 to ping PC2, only PC1 and PC2 will see the ping, PC3 won't?

    – The_Bear
    10 hours ago







    So I'm right in saying that if I connect 3 PC's to a switch and use PC1 to ping PC2, only PC1 and PC2 will see the ping, PC3 won't?

    – The_Bear
    10 hours ago















    If the switch has not yet learned the destination interface, it will flood the frame to all the other interfaces. It learns very quickly because it only takes one frame from a host for it to learn where the host is.

    – Ron Maupin
    10 hours ago





    If the switch has not yet learned the destination interface, it will flood the frame to all the other interfaces. It learns very quickly because it only takes one frame from a host for it to learn where the host is.

    – Ron Maupin
    10 hours ago













    So does that mean when the ping is first sent, all the ports will receive it in the switch but if it is pinged again it will only go to PC2?

    – The_Bear
    8 hours ago





    So does that mean when the ping is first sent, all the ports will receive it in the switch but if it is pinged again it will only go to PC2?

    – The_Bear
    8 hours ago




    1




    1





    Maybe. As @Zac67 points out, the source host may need to ARP for the destination address, and that will suffice to populate the MAC address table, but the table entries do time out, so it may need to happen again. A host will maintain an ARP table for destinations, and its entries also time out, but that is not coordinated with any other host or the switch MAC address table. You cannot say at any given time if a switch MAC address table has an entry for the destination.

    – Ron Maupin
    8 hours ago





    Maybe. As @Zac67 points out, the source host may need to ARP for the destination address, and that will suffice to populate the MAC address table, but the table entries do time out, so it may need to happen again. A host will maintain an ARP table for destinations, and its entries also time out, but that is not coordinated with any other host or the switch MAC address table. You cannot say at any given time if a switch MAC address table has an entry for the destination.

    – Ron Maupin
    8 hours ago













    No. The previous ARP already updates the switch's MAC table, so the first ping already goes to PC2 only.

    – Zac67
    8 hours ago





    No. The previous ARP already updates the switch's MAC table, so the first ping already goes to PC2 only.

    – Zac67
    8 hours ago











    2














    Ethernet has evolved over time, and has some archaic standards that no longer matter all that much.



    Originally Ethernet used what was known as a half-duplex signalling standard, which is like having a 1-lane road with vehicles that can travel in either direction on it.



    When endpoint devices try to transmit at the same time on a half-duplex hub network, this causes a collision event, which requires both devices to pause for a random period of time and try again. Some of the more expensive early hubs from the 1990s such as from Cabletron had a collision light that would show when a collision occurred.



    As more devices are added to a half-duplex hub network, the risk of data collisions increases, and overall throughput declines because so much time is being wasted by colliding, waiting, trying again, colliding, waiting, trying again..



    Generally an Ethernet cable cannot be longer than 100 meters, and there cannot be more than 4 hubs between two devices, because 500 meters is the distance limit of the collision detection system when two devices try to transmit at the same time but their data packets collide.



    ,



    It used to be that hubs were the inexpensive network component while switches were really expensive, because a hub isn't really much more than a collection of amplifier circuits while a switch includes actual processing to decode and analyze packets, and also splits the collision domains into separate territories.



    Though it also used to be that you had to use a special cable called a crossover cable to interconnect endpoint devices or to make hub-to-hub connections. We don't care about any of this anymore because all devices include a way to make any connection a normal or crossover, known as Auto-MDIX.



    ,



    Since some time around 2005, the bottom fell out of the switch market, and switches became cheaper and cheaper until we reached a point where hubs basically disappeared and we now use switches for everything.



    The original design spec for 100 meter cables and 4 hubs per collision domain still exist, but it's now basically irrelevant because hubs are no longer in use. We now effectively have an isolated collision domain between every endpoint and its matching switch port.



    Due to this you could probably make a half-duplex twisted pair Ethernet cable 500 meters long between a device and a switch port, and it would work fine. Doing this violates the cable length of the original signalling specification which cannot imagine hubs not being used, but 500 meters is compatible with the original half-duplex collision detection method, should the switch port and endpoint device both transmit and collide.



    ,



    But even the collision domain has become irrelevant, due to later twisted pair wiring standards changing from half-duplex to full duplex. What this means is that there is now an isolated path available for sending from one end to the other, in both directions.



    In this configuration, a collision is not even possible when a single endpoint connects to a single switch port, and so a twisted pair cable could likely far exceed the 500 meter limit of the collision detection mechanism, and still work.



    Though we are now deviating quite far from the original Ethernet design specification and we will instead start running up against electromagnetic limits with capacitance and inductance causing signal degradation.






    share|improve this answer




























      2














      Ethernet has evolved over time, and has some archaic standards that no longer matter all that much.



      Originally Ethernet used what was known as a half-duplex signalling standard, which is like having a 1-lane road with vehicles that can travel in either direction on it.



      When endpoint devices try to transmit at the same time on a half-duplex hub network, this causes a collision event, which requires both devices to pause for a random period of time and try again. Some of the more expensive early hubs from the 1990s such as from Cabletron had a collision light that would show when a collision occurred.



      As more devices are added to a half-duplex hub network, the risk of data collisions increases, and overall throughput declines because so much time is being wasted by colliding, waiting, trying again, colliding, waiting, trying again..



      Generally an Ethernet cable cannot be longer than 100 meters, and there cannot be more than 4 hubs between two devices, because 500 meters is the distance limit of the collision detection system when two devices try to transmit at the same time but their data packets collide.



      ,



      It used to be that hubs were the inexpensive network component while switches were really expensive, because a hub isn't really much more than a collection of amplifier circuits while a switch includes actual processing to decode and analyze packets, and also splits the collision domains into separate territories.



      Though it also used to be that you had to use a special cable called a crossover cable to interconnect endpoint devices or to make hub-to-hub connections. We don't care about any of this anymore because all devices include a way to make any connection a normal or crossover, known as Auto-MDIX.



      ,



      Since some time around 2005, the bottom fell out of the switch market, and switches became cheaper and cheaper until we reached a point where hubs basically disappeared and we now use switches for everything.



      The original design spec for 100 meter cables and 4 hubs per collision domain still exist, but it's now basically irrelevant because hubs are no longer in use. We now effectively have an isolated collision domain between every endpoint and its matching switch port.



      Due to this you could probably make a half-duplex twisted pair Ethernet cable 500 meters long between a device and a switch port, and it would work fine. Doing this violates the cable length of the original signalling specification which cannot imagine hubs not being used, but 500 meters is compatible with the original half-duplex collision detection method, should the switch port and endpoint device both transmit and collide.



      ,



      But even the collision domain has become irrelevant, due to later twisted pair wiring standards changing from half-duplex to full duplex. What this means is that there is now an isolated path available for sending from one end to the other, in both directions.



      In this configuration, a collision is not even possible when a single endpoint connects to a single switch port, and so a twisted pair cable could likely far exceed the 500 meter limit of the collision detection mechanism, and still work.



      Though we are now deviating quite far from the original Ethernet design specification and we will instead start running up against electromagnetic limits with capacitance and inductance causing signal degradation.






      share|improve this answer


























        2












        2








        2







        Ethernet has evolved over time, and has some archaic standards that no longer matter all that much.



        Originally Ethernet used what was known as a half-duplex signalling standard, which is like having a 1-lane road with vehicles that can travel in either direction on it.



        When endpoint devices try to transmit at the same time on a half-duplex hub network, this causes a collision event, which requires both devices to pause for a random period of time and try again. Some of the more expensive early hubs from the 1990s such as from Cabletron had a collision light that would show when a collision occurred.



        As more devices are added to a half-duplex hub network, the risk of data collisions increases, and overall throughput declines because so much time is being wasted by colliding, waiting, trying again, colliding, waiting, trying again..



        Generally an Ethernet cable cannot be longer than 100 meters, and there cannot be more than 4 hubs between two devices, because 500 meters is the distance limit of the collision detection system when two devices try to transmit at the same time but their data packets collide.



        ,



        It used to be that hubs were the inexpensive network component while switches were really expensive, because a hub isn't really much more than a collection of amplifier circuits while a switch includes actual processing to decode and analyze packets, and also splits the collision domains into separate territories.



        Though it also used to be that you had to use a special cable called a crossover cable to interconnect endpoint devices or to make hub-to-hub connections. We don't care about any of this anymore because all devices include a way to make any connection a normal or crossover, known as Auto-MDIX.



        ,



        Since some time around 2005, the bottom fell out of the switch market, and switches became cheaper and cheaper until we reached a point where hubs basically disappeared and we now use switches for everything.



        The original design spec for 100 meter cables and 4 hubs per collision domain still exist, but it's now basically irrelevant because hubs are no longer in use. We now effectively have an isolated collision domain between every endpoint and its matching switch port.



        Due to this you could probably make a half-duplex twisted pair Ethernet cable 500 meters long between a device and a switch port, and it would work fine. Doing this violates the cable length of the original signalling specification which cannot imagine hubs not being used, but 500 meters is compatible with the original half-duplex collision detection method, should the switch port and endpoint device both transmit and collide.



        ,



        But even the collision domain has become irrelevant, due to later twisted pair wiring standards changing from half-duplex to full duplex. What this means is that there is now an isolated path available for sending from one end to the other, in both directions.



        In this configuration, a collision is not even possible when a single endpoint connects to a single switch port, and so a twisted pair cable could likely far exceed the 500 meter limit of the collision detection mechanism, and still work.



        Though we are now deviating quite far from the original Ethernet design specification and we will instead start running up against electromagnetic limits with capacitance and inductance causing signal degradation.






        share|improve this answer













        Ethernet has evolved over time, and has some archaic standards that no longer matter all that much.



        Originally Ethernet used what was known as a half-duplex signalling standard, which is like having a 1-lane road with vehicles that can travel in either direction on it.



        When endpoint devices try to transmit at the same time on a half-duplex hub network, this causes a collision event, which requires both devices to pause for a random period of time and try again. Some of the more expensive early hubs from the 1990s such as from Cabletron had a collision light that would show when a collision occurred.



        As more devices are added to a half-duplex hub network, the risk of data collisions increases, and overall throughput declines because so much time is being wasted by colliding, waiting, trying again, colliding, waiting, trying again..



        Generally an Ethernet cable cannot be longer than 100 meters, and there cannot be more than 4 hubs between two devices, because 500 meters is the distance limit of the collision detection system when two devices try to transmit at the same time but their data packets collide.



        ,



        It used to be that hubs were the inexpensive network component while switches were really expensive, because a hub isn't really much more than a collection of amplifier circuits while a switch includes actual processing to decode and analyze packets, and also splits the collision domains into separate territories.



        Though it also used to be that you had to use a special cable called a crossover cable to interconnect endpoint devices or to make hub-to-hub connections. We don't care about any of this anymore because all devices include a way to make any connection a normal or crossover, known as Auto-MDIX.



        ,



        Since some time around 2005, the bottom fell out of the switch market, and switches became cheaper and cheaper until we reached a point where hubs basically disappeared and we now use switches for everything.



        The original design spec for 100 meter cables and 4 hubs per collision domain still exist, but it's now basically irrelevant because hubs are no longer in use. We now effectively have an isolated collision domain between every endpoint and its matching switch port.



        Due to this you could probably make a half-duplex twisted pair Ethernet cable 500 meters long between a device and a switch port, and it would work fine. Doing this violates the cable length of the original signalling specification which cannot imagine hubs not being used, but 500 meters is compatible with the original half-duplex collision detection method, should the switch port and endpoint device both transmit and collide.



        ,



        But even the collision domain has become irrelevant, due to later twisted pair wiring standards changing from half-duplex to full duplex. What this means is that there is now an isolated path available for sending from one end to the other, in both directions.



        In this configuration, a collision is not even possible when a single endpoint connects to a single switch port, and so a twisted pair cable could likely far exceed the 500 meter limit of the collision detection mechanism, and still work.



        Though we are now deviating quite far from the original Ethernet design specification and we will instead start running up against electromagnetic limits with capacitance and inductance causing signal degradation.







        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered 6 hours ago









        Dale MahalkoDale Mahalko

        21215




        21215






















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