Why is the BGP base on TCP 1027 rather than 179?











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Why is the BGP foreign address port 1027?



I use BGP to connect Router1 and Router2, but when I show the TCP progress:



Router1>show tcp brief 
TCB Local Address Foreign Address (state)
4E976890 10.0.0.1.179 10.0.0.2.1027 ESTABLISHED


We say the BGP is based on TCP port 179. Why is Router2's BGP on port 1027?










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    up vote
    5
    down vote

    favorite












    Why is the BGP foreign address port 1027?



    I use BGP to connect Router1 and Router2, but when I show the TCP progress:



    Router1>show tcp brief 
    TCB Local Address Foreign Address (state)
    4E976890 10.0.0.1.179 10.0.0.2.1027 ESTABLISHED


    We say the BGP is based on TCP port 179. Why is Router2's BGP on port 1027?










    share|improve this question


























      up vote
      5
      down vote

      favorite









      up vote
      5
      down vote

      favorite











      Why is the BGP foreign address port 1027?



      I use BGP to connect Router1 and Router2, but when I show the TCP progress:



      Router1>show tcp brief 
      TCB Local Address Foreign Address (state)
      4E976890 10.0.0.1.179 10.0.0.2.1027 ESTABLISHED


      We say the BGP is based on TCP port 179. Why is Router2's BGP on port 1027?










      share|improve this question















      Why is the BGP foreign address port 1027?



      I use BGP to connect Router1 and Router2, but when I show the TCP progress:



      Router1>show tcp brief 
      TCB Local Address Foreign Address (state)
      4E976890 10.0.0.1.179 10.0.0.2.1027 ESTABLISHED


      We say the BGP is based on TCP port 179. Why is Router2's BGP on port 1027?







      cisco router bgp






      share|improve this question















      share|improve this question













      share|improve this question




      share|improve this question








      edited Nov 26 at 10:09









      jonathanjo

      8,9661630




      8,9661630










      asked Nov 26 at 9:43









      three-blocks

      3306




      3306






















          3 Answers
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          up vote
          9
          down vote



          accepted










          One side of the connection will have an arbitrary port number, the other will be on 179.



          Cisco Press "BGP Fundamentals" has a good explanation (link)




          the neighbor with the higher IP address manages the connection. The router initiating the request uses a dynamic source port, but the destination port is always 179.



          Example 1-1 shows an established BGP session using the command show tcp brief to display the active TCP sessions between routers. Notice that the TCP source port is 179 and the destination port is 59884 on R1, and the ports are opposite on R2.




          Example 1-1: Established BGP session

          RP/0/0/CPU0:R1# show tcp brief | exc "LISTEN|CLOSED"
          PCB VRF-ID Recv-Q Send-Q Local Address Foreign Address State
          0x088bcbb8 0x60000000 0 0 10.1.12.1:179 10.1.12.2:59884 ESTAB

          R2# show tcp brief
          TCB Local Address Foreign Address (state)
          EF153B88 10.1.12.2. 59884 10.1.12.1.179 ESTAB


          This is just the same as any other TCP connection: the passive open side sits and waits on a well-known port number; the active open side uses an arbitary port. This makes it much easier to manage many-to-many TCP links.






          share|improve this answer






























            up vote
            4
            down vote













            TCP source vs. destination ports.



            To give a different example: HTTP servers listen on TCP port 80. So when you are connecting to a web server, you will automatically use TCP/80 as the destination port. However, the source port is a random one above 1024.



            The exact same thing happens with BGP - the client (the router initiating the connection) will connect to TCP destination port 179. But the source port for that connection will be a random high port.






            share|improve this answer








            New contributor




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

























              up vote
              2
              down vote













              In general, the BGP use TCP 179 port as the BGP service. the client connect BGP service port there is no limit.



              such as the SSH server use 22 as its port, there is no limit for the client port.






              share|improve this answer





















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                3 Answers
                3






                active

                oldest

                votes








                3 Answers
                3






                active

                oldest

                votes









                active

                oldest

                votes






                active

                oldest

                votes








                up vote
                9
                down vote



                accepted










                One side of the connection will have an arbitrary port number, the other will be on 179.



                Cisco Press "BGP Fundamentals" has a good explanation (link)




                the neighbor with the higher IP address manages the connection. The router initiating the request uses a dynamic source port, but the destination port is always 179.



                Example 1-1 shows an established BGP session using the command show tcp brief to display the active TCP sessions between routers. Notice that the TCP source port is 179 and the destination port is 59884 on R1, and the ports are opposite on R2.




                Example 1-1: Established BGP session

                RP/0/0/CPU0:R1# show tcp brief | exc "LISTEN|CLOSED"
                PCB VRF-ID Recv-Q Send-Q Local Address Foreign Address State
                0x088bcbb8 0x60000000 0 0 10.1.12.1:179 10.1.12.2:59884 ESTAB

                R2# show tcp brief
                TCB Local Address Foreign Address (state)
                EF153B88 10.1.12.2. 59884 10.1.12.1.179 ESTAB


                This is just the same as any other TCP connection: the passive open side sits and waits on a well-known port number; the active open side uses an arbitary port. This makes it much easier to manage many-to-many TCP links.






                share|improve this answer



























                  up vote
                  9
                  down vote



                  accepted










                  One side of the connection will have an arbitrary port number, the other will be on 179.



                  Cisco Press "BGP Fundamentals" has a good explanation (link)




                  the neighbor with the higher IP address manages the connection. The router initiating the request uses a dynamic source port, but the destination port is always 179.



                  Example 1-1 shows an established BGP session using the command show tcp brief to display the active TCP sessions between routers. Notice that the TCP source port is 179 and the destination port is 59884 on R1, and the ports are opposite on R2.




                  Example 1-1: Established BGP session

                  RP/0/0/CPU0:R1# show tcp brief | exc "LISTEN|CLOSED"
                  PCB VRF-ID Recv-Q Send-Q Local Address Foreign Address State
                  0x088bcbb8 0x60000000 0 0 10.1.12.1:179 10.1.12.2:59884 ESTAB

                  R2# show tcp brief
                  TCB Local Address Foreign Address (state)
                  EF153B88 10.1.12.2. 59884 10.1.12.1.179 ESTAB


                  This is just the same as any other TCP connection: the passive open side sits and waits on a well-known port number; the active open side uses an arbitary port. This makes it much easier to manage many-to-many TCP links.






                  share|improve this answer

























                    up vote
                    9
                    down vote



                    accepted







                    up vote
                    9
                    down vote



                    accepted






                    One side of the connection will have an arbitrary port number, the other will be on 179.



                    Cisco Press "BGP Fundamentals" has a good explanation (link)




                    the neighbor with the higher IP address manages the connection. The router initiating the request uses a dynamic source port, but the destination port is always 179.



                    Example 1-1 shows an established BGP session using the command show tcp brief to display the active TCP sessions between routers. Notice that the TCP source port is 179 and the destination port is 59884 on R1, and the ports are opposite on R2.




                    Example 1-1: Established BGP session

                    RP/0/0/CPU0:R1# show tcp brief | exc "LISTEN|CLOSED"
                    PCB VRF-ID Recv-Q Send-Q Local Address Foreign Address State
                    0x088bcbb8 0x60000000 0 0 10.1.12.1:179 10.1.12.2:59884 ESTAB

                    R2# show tcp brief
                    TCB Local Address Foreign Address (state)
                    EF153B88 10.1.12.2. 59884 10.1.12.1.179 ESTAB


                    This is just the same as any other TCP connection: the passive open side sits and waits on a well-known port number; the active open side uses an arbitary port. This makes it much easier to manage many-to-many TCP links.






                    share|improve this answer














                    One side of the connection will have an arbitrary port number, the other will be on 179.



                    Cisco Press "BGP Fundamentals" has a good explanation (link)




                    the neighbor with the higher IP address manages the connection. The router initiating the request uses a dynamic source port, but the destination port is always 179.



                    Example 1-1 shows an established BGP session using the command show tcp brief to display the active TCP sessions between routers. Notice that the TCP source port is 179 and the destination port is 59884 on R1, and the ports are opposite on R2.




                    Example 1-1: Established BGP session

                    RP/0/0/CPU0:R1# show tcp brief | exc "LISTEN|CLOSED"
                    PCB VRF-ID Recv-Q Send-Q Local Address Foreign Address State
                    0x088bcbb8 0x60000000 0 0 10.1.12.1:179 10.1.12.2:59884 ESTAB

                    R2# show tcp brief
                    TCB Local Address Foreign Address (state)
                    EF153B88 10.1.12.2. 59884 10.1.12.1.179 ESTAB


                    This is just the same as any other TCP connection: the passive open side sits and waits on a well-known port number; the active open side uses an arbitary port. This makes it much easier to manage many-to-many TCP links.







                    share|improve this answer














                    share|improve this answer



                    share|improve this answer








                    edited Nov 26 at 10:06

























                    answered Nov 26 at 9:58









                    jonathanjo

                    8,9661630




                    8,9661630






















                        up vote
                        4
                        down vote













                        TCP source vs. destination ports.



                        To give a different example: HTTP servers listen on TCP port 80. So when you are connecting to a web server, you will automatically use TCP/80 as the destination port. However, the source port is a random one above 1024.



                        The exact same thing happens with BGP - the client (the router initiating the connection) will connect to TCP destination port 179. But the source port for that connection will be a random high port.






                        share|improve this answer








                        New contributor




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






















                          up vote
                          4
                          down vote













                          TCP source vs. destination ports.



                          To give a different example: HTTP servers listen on TCP port 80. So when you are connecting to a web server, you will automatically use TCP/80 as the destination port. However, the source port is a random one above 1024.



                          The exact same thing happens with BGP - the client (the router initiating the connection) will connect to TCP destination port 179. But the source port for that connection will be a random high port.






                          share|improve this answer








                          New contributor




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




















                            up vote
                            4
                            down vote










                            up vote
                            4
                            down vote









                            TCP source vs. destination ports.



                            To give a different example: HTTP servers listen on TCP port 80. So when you are connecting to a web server, you will automatically use TCP/80 as the destination port. However, the source port is a random one above 1024.



                            The exact same thing happens with BGP - the client (the router initiating the connection) will connect to TCP destination port 179. But the source port for that connection will be a random high port.






                            share|improve this answer








                            New contributor




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









                            TCP source vs. destination ports.



                            To give a different example: HTTP servers listen on TCP port 80. So when you are connecting to a web server, you will automatically use TCP/80 as the destination port. However, the source port is a random one above 1024.



                            The exact same thing happens with BGP - the client (the router initiating the connection) will connect to TCP destination port 179. But the source port for that connection will be a random high port.







                            share|improve this answer








                            New contributor




                            Bogd 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




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









                            answered Nov 26 at 14:45









                            Bogd

                            411




                            411




                            New contributor




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





                            New contributor





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






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






















                                up vote
                                2
                                down vote













                                In general, the BGP use TCP 179 port as the BGP service. the client connect BGP service port there is no limit.



                                such as the SSH server use 22 as its port, there is no limit for the client port.






                                share|improve this answer

























                                  up vote
                                  2
                                  down vote













                                  In general, the BGP use TCP 179 port as the BGP service. the client connect BGP service port there is no limit.



                                  such as the SSH server use 22 as its port, there is no limit for the client port.






                                  share|improve this answer























                                    up vote
                                    2
                                    down vote










                                    up vote
                                    2
                                    down vote









                                    In general, the BGP use TCP 179 port as the BGP service. the client connect BGP service port there is no limit.



                                    such as the SSH server use 22 as its port, there is no limit for the client port.






                                    share|improve this answer












                                    In general, the BGP use TCP 179 port as the BGP service. the client connect BGP service port there is no limit.



                                    such as the SSH server use 22 as its port, there is no limit for the client port.







                                    share|improve this answer












                                    share|improve this answer



                                    share|improve this answer










                                    answered Nov 26 at 9:53









                                    aircraft

                                    544111




                                    544111






























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