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Do all network devices need to make routing decisions, regardless of communication across networks or within a network?



The Next CEO of Stack OverflowNetwork not participating in OSPF. Does not appear in the routing tablehow IPv4 routing is done for TCP? as TCP is connection oriented but IP is notCan I add a hop by dividing my prefix?routing: understanding the default route vs. prefix length, administrative distance and metricsForce use of gateway for communication on same subnetRouting between vlans with two routersDoes RIP stores information about entire AS?How does routing work across different networks when using a dedicated switch?Optimize Routing TableDoes a gateway need to be designated?










2















From Hunt's TCP/IP Network Adminstration:




Gateways route data between networks, but all network devices, hosts as well as
gateways, must make routing decisions.




Is it correct that routing decisions are made only for communication across different networks?



For communication within a network (whether it is in an internetwork or not),



  • does any device in the network need to make routing decisions?


  • does any device in the network necessarily have a routing table or something similar?


If a device makes routing decision, that that mean the device has a routing table or something similar? If a device has a routing table or something similar, does it make routing decision?



Or, do only gateway devices have to make routing decisions and have routing tables or something similar?



I have these questions because my Linux laptop isn't a gateway in the local wifi network, but has a routing table to my surprise. Is it cecause any device in a network has a routing table? My laptop doesn't seem to connect two networks, because the network for all the loopback addresses and the wifi network can't communicate with each other. But its routing table shows a route for communicating with other devices in the same wifi network, and a default route for all other destinations outside the wifi network.



Thanks.










share|improve this question




























    2















    From Hunt's TCP/IP Network Adminstration:




    Gateways route data between networks, but all network devices, hosts as well as
    gateways, must make routing decisions.




    Is it correct that routing decisions are made only for communication across different networks?



    For communication within a network (whether it is in an internetwork or not),



    • does any device in the network need to make routing decisions?


    • does any device in the network necessarily have a routing table or something similar?


    If a device makes routing decision, that that mean the device has a routing table or something similar? If a device has a routing table or something similar, does it make routing decision?



    Or, do only gateway devices have to make routing decisions and have routing tables or something similar?



    I have these questions because my Linux laptop isn't a gateway in the local wifi network, but has a routing table to my surprise. Is it cecause any device in a network has a routing table? My laptop doesn't seem to connect two networks, because the network for all the loopback addresses and the wifi network can't communicate with each other. But its routing table shows a route for communicating with other devices in the same wifi network, and a default route for all other destinations outside the wifi network.



    Thanks.










    share|improve this question


























      2












      2








      2








      From Hunt's TCP/IP Network Adminstration:




      Gateways route data between networks, but all network devices, hosts as well as
      gateways, must make routing decisions.




      Is it correct that routing decisions are made only for communication across different networks?



      For communication within a network (whether it is in an internetwork or not),



      • does any device in the network need to make routing decisions?


      • does any device in the network necessarily have a routing table or something similar?


      If a device makes routing decision, that that mean the device has a routing table or something similar? If a device has a routing table or something similar, does it make routing decision?



      Or, do only gateway devices have to make routing decisions and have routing tables or something similar?



      I have these questions because my Linux laptop isn't a gateway in the local wifi network, but has a routing table to my surprise. Is it cecause any device in a network has a routing table? My laptop doesn't seem to connect two networks, because the network for all the loopback addresses and the wifi network can't communicate with each other. But its routing table shows a route for communicating with other devices in the same wifi network, and a default route for all other destinations outside the wifi network.



      Thanks.










      share|improve this question
















      From Hunt's TCP/IP Network Adminstration:




      Gateways route data between networks, but all network devices, hosts as well as
      gateways, must make routing decisions.




      Is it correct that routing decisions are made only for communication across different networks?



      For communication within a network (whether it is in an internetwork or not),



      • does any device in the network need to make routing decisions?


      • does any device in the network necessarily have a routing table or something similar?


      If a device makes routing decision, that that mean the device has a routing table or something similar? If a device has a routing table or something similar, does it make routing decision?



      Or, do only gateway devices have to make routing decisions and have routing tables or something similar?



      I have these questions because my Linux laptop isn't a gateway in the local wifi network, but has a routing table to my surprise. Is it cecause any device in a network has a routing table? My laptop doesn't seem to connect two networks, because the network for all the loopback addresses and the wifi network can't communicate with each other. But its routing table shows a route for communicating with other devices in the same wifi network, and a default route for all other destinations outside the wifi network.



      Thanks.







      routing






      share|improve this question















      share|improve this question













      share|improve this question




      share|improve this question








      edited 2 days ago







      Tim

















      asked 2 days ago









      TimTim

      655518




      655518




















          3 Answers
          3






          active

          oldest

          votes


















          7














          Every IP device has a routing table, and therefore makes a routing decision. It may be quite simple with only two entries, but fundamentally, a device needs to decide if the destination is on the directly connected network or not. If not, it forwards the packet to the gateway. For most devices like PCs, there is only a default gateway, but there can be more than one.






          share|improve this answer


















          • 1





            Three entries usually. There's also localhost.

            – Zan Lynx
            2 days ago











          • @ZanLynx You’re right. I forgot to mention that.

            – Ron Trunk
            2 days ago


















          4














          Theoretically, consider a computer that has an IP address of 192.168.1.3/24 and wants to send some data to the IP address 192.168.2.5/24 then it should make a subnet checking to see if the IP address it wants to reach is in the same network or not; to be able to decide to forward the packet to its gateway or not.



          when you have a subnet mask of /24 which refers in binary to 11111111.11111111.11111111.00000000. Zeros are the places you can modify your IP address in the "same network". If you change anything before zeros start, it means you are changing the network you are in and to be able to communicate with such an IP you need a router between two of them. After all, being able to make this decision is considered as making a routing decision.



          Hope the answer helps.






          share|improve this answer








          New contributor




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



























            1














            Every host needs to decide what to do with the packets it has generated. For a typical single homed host configuration that means one of three things.



            1. Loop them back from the output queue to the input queue and process them locally.

            2. Send them to another host on the same subnet (for example by ARPing for the destination's MAC address)

            3. Send them out of the network by sending them to the default gateway (for example by ARPing for the default gateway's MAC address).

            If you read the early RFCs then they are written on the assumption that this logic will be coded explicitly.



            However modern operating systems (at least full-feature ones) support multi-homing and acting as a router (though the latter is typically disabled by default). So they use an explicit routing table to decide what to do with packets. The interface configurations are used to fill-out default entries in this routing table, but entries can also be added manually.






            share|improve this answer























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              3 Answers
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              active

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              3 Answers
              3






              active

              oldest

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              active

              oldest

              votes






              active

              oldest

              votes









              7














              Every IP device has a routing table, and therefore makes a routing decision. It may be quite simple with only two entries, but fundamentally, a device needs to decide if the destination is on the directly connected network or not. If not, it forwards the packet to the gateway. For most devices like PCs, there is only a default gateway, but there can be more than one.






              share|improve this answer


















              • 1





                Three entries usually. There's also localhost.

                – Zan Lynx
                2 days ago











              • @ZanLynx You’re right. I forgot to mention that.

                – Ron Trunk
                2 days ago















              7














              Every IP device has a routing table, and therefore makes a routing decision. It may be quite simple with only two entries, but fundamentally, a device needs to decide if the destination is on the directly connected network or not. If not, it forwards the packet to the gateway. For most devices like PCs, there is only a default gateway, but there can be more than one.






              share|improve this answer


















              • 1





                Three entries usually. There's also localhost.

                – Zan Lynx
                2 days ago











              • @ZanLynx You’re right. I forgot to mention that.

                – Ron Trunk
                2 days ago













              7












              7








              7







              Every IP device has a routing table, and therefore makes a routing decision. It may be quite simple with only two entries, but fundamentally, a device needs to decide if the destination is on the directly connected network or not. If not, it forwards the packet to the gateway. For most devices like PCs, there is only a default gateway, but there can be more than one.






              share|improve this answer













              Every IP device has a routing table, and therefore makes a routing decision. It may be quite simple with only two entries, but fundamentally, a device needs to decide if the destination is on the directly connected network or not. If not, it forwards the packet to the gateway. For most devices like PCs, there is only a default gateway, but there can be more than one.







              share|improve this answer












              share|improve this answer



              share|improve this answer










              answered 2 days ago









              Ron TrunkRon Trunk

              39.4k33780




              39.4k33780







              • 1





                Three entries usually. There's also localhost.

                – Zan Lynx
                2 days ago











              • @ZanLynx You’re right. I forgot to mention that.

                – Ron Trunk
                2 days ago












              • 1





                Three entries usually. There's also localhost.

                – Zan Lynx
                2 days ago











              • @ZanLynx You’re right. I forgot to mention that.

                – Ron Trunk
                2 days ago







              1




              1





              Three entries usually. There's also localhost.

              – Zan Lynx
              2 days ago





              Three entries usually. There's also localhost.

              – Zan Lynx
              2 days ago













              @ZanLynx You’re right. I forgot to mention that.

              – Ron Trunk
              2 days ago





              @ZanLynx You’re right. I forgot to mention that.

              – Ron Trunk
              2 days ago











              4














              Theoretically, consider a computer that has an IP address of 192.168.1.3/24 and wants to send some data to the IP address 192.168.2.5/24 then it should make a subnet checking to see if the IP address it wants to reach is in the same network or not; to be able to decide to forward the packet to its gateway or not.



              when you have a subnet mask of /24 which refers in binary to 11111111.11111111.11111111.00000000. Zeros are the places you can modify your IP address in the "same network". If you change anything before zeros start, it means you are changing the network you are in and to be able to communicate with such an IP you need a router between two of them. After all, being able to make this decision is considered as making a routing decision.



              Hope the answer helps.






              share|improve this answer








              New contributor




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
























                4














                Theoretically, consider a computer that has an IP address of 192.168.1.3/24 and wants to send some data to the IP address 192.168.2.5/24 then it should make a subnet checking to see if the IP address it wants to reach is in the same network or not; to be able to decide to forward the packet to its gateway or not.



                when you have a subnet mask of /24 which refers in binary to 11111111.11111111.11111111.00000000. Zeros are the places you can modify your IP address in the "same network". If you change anything before zeros start, it means you are changing the network you are in and to be able to communicate with such an IP you need a router between two of them. After all, being able to make this decision is considered as making a routing decision.



                Hope the answer helps.






                share|improve this answer








                New contributor




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






















                  4












                  4








                  4







                  Theoretically, consider a computer that has an IP address of 192.168.1.3/24 and wants to send some data to the IP address 192.168.2.5/24 then it should make a subnet checking to see if the IP address it wants to reach is in the same network or not; to be able to decide to forward the packet to its gateway or not.



                  when you have a subnet mask of /24 which refers in binary to 11111111.11111111.11111111.00000000. Zeros are the places you can modify your IP address in the "same network". If you change anything before zeros start, it means you are changing the network you are in and to be able to communicate with such an IP you need a router between two of them. After all, being able to make this decision is considered as making a routing decision.



                  Hope the answer helps.






                  share|improve this answer








                  New contributor




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










                  Theoretically, consider a computer that has an IP address of 192.168.1.3/24 and wants to send some data to the IP address 192.168.2.5/24 then it should make a subnet checking to see if the IP address it wants to reach is in the same network or not; to be able to decide to forward the packet to its gateway or not.



                  when you have a subnet mask of /24 which refers in binary to 11111111.11111111.11111111.00000000. Zeros are the places you can modify your IP address in the "same network". If you change anything before zeros start, it means you are changing the network you are in and to be able to communicate with such an IP you need a router between two of them. After all, being able to make this decision is considered as making a routing decision.



                  Hope the answer helps.







                  share|improve this answer








                  New contributor




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









                  share|improve this answer



                  share|improve this answer






                  New contributor




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









                  answered 2 days ago









                  metinmetin

                  664




                  664




                  New contributor




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





                  New contributor





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






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





















                      1














                      Every host needs to decide what to do with the packets it has generated. For a typical single homed host configuration that means one of three things.



                      1. Loop them back from the output queue to the input queue and process them locally.

                      2. Send them to another host on the same subnet (for example by ARPing for the destination's MAC address)

                      3. Send them out of the network by sending them to the default gateway (for example by ARPing for the default gateway's MAC address).

                      If you read the early RFCs then they are written on the assumption that this logic will be coded explicitly.



                      However modern operating systems (at least full-feature ones) support multi-homing and acting as a router (though the latter is typically disabled by default). So they use an explicit routing table to decide what to do with packets. The interface configurations are used to fill-out default entries in this routing table, but entries can also be added manually.






                      share|improve this answer



























                        1














                        Every host needs to decide what to do with the packets it has generated. For a typical single homed host configuration that means one of three things.



                        1. Loop them back from the output queue to the input queue and process them locally.

                        2. Send them to another host on the same subnet (for example by ARPing for the destination's MAC address)

                        3. Send them out of the network by sending them to the default gateway (for example by ARPing for the default gateway's MAC address).

                        If you read the early RFCs then they are written on the assumption that this logic will be coded explicitly.



                        However modern operating systems (at least full-feature ones) support multi-homing and acting as a router (though the latter is typically disabled by default). So they use an explicit routing table to decide what to do with packets. The interface configurations are used to fill-out default entries in this routing table, but entries can also be added manually.






                        share|improve this answer

























                          1












                          1








                          1







                          Every host needs to decide what to do with the packets it has generated. For a typical single homed host configuration that means one of three things.



                          1. Loop them back from the output queue to the input queue and process them locally.

                          2. Send them to another host on the same subnet (for example by ARPing for the destination's MAC address)

                          3. Send them out of the network by sending them to the default gateway (for example by ARPing for the default gateway's MAC address).

                          If you read the early RFCs then they are written on the assumption that this logic will be coded explicitly.



                          However modern operating systems (at least full-feature ones) support multi-homing and acting as a router (though the latter is typically disabled by default). So they use an explicit routing table to decide what to do with packets. The interface configurations are used to fill-out default entries in this routing table, but entries can also be added manually.






                          share|improve this answer













                          Every host needs to decide what to do with the packets it has generated. For a typical single homed host configuration that means one of three things.



                          1. Loop them back from the output queue to the input queue and process them locally.

                          2. Send them to another host on the same subnet (for example by ARPing for the destination's MAC address)

                          3. Send them out of the network by sending them to the default gateway (for example by ARPing for the default gateway's MAC address).

                          If you read the early RFCs then they are written on the assumption that this logic will be coded explicitly.



                          However modern operating systems (at least full-feature ones) support multi-homing and acting as a router (though the latter is typically disabled by default). So they use an explicit routing table to decide what to do with packets. The interface configurations are used to fill-out default entries in this routing table, but entries can also be added manually.







                          share|improve this answer












                          share|improve this answer



                          share|improve this answer










                          answered 7 hours ago









                          Peter GreenPeter Green

                          8,08721229




                          8,08721229



























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