Will the packet be dropped when the number of hops equals to default TTL?












2















From my understanding, the default TTL represents the maximum number of hops allowed such that the packet may reach the host.




NTP Documentation Archive: ttl - This option is used only with broadcast server and manycast client modes. It specifies the time-to-live ttl to use on broadcast server and multicast server and the maximum ttl for the expanding ring search with manycast client packets




However, it is also mentioned in some answers that the packet is discarded if the TTL is 0 and it will never reach the host. I'm wondering what would happen when the number of hops before the packet was consumed is exactly the same as TTL_DEFAULT (e.g. TTL_DEFAULT is 2 and there are 2 hops before the packet was consumed). Will the packet reach the host, or it will be discarded?










share|improve this question









New contributor




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

























    2















    From my understanding, the default TTL represents the maximum number of hops allowed such that the packet may reach the host.




    NTP Documentation Archive: ttl - This option is used only with broadcast server and manycast client modes. It specifies the time-to-live ttl to use on broadcast server and multicast server and the maximum ttl for the expanding ring search with manycast client packets




    However, it is also mentioned in some answers that the packet is discarded if the TTL is 0 and it will never reach the host. I'm wondering what would happen when the number of hops before the packet was consumed is exactly the same as TTL_DEFAULT (e.g. TTL_DEFAULT is 2 and there are 2 hops before the packet was consumed). Will the packet reach the host, or it will be discarded?










    share|improve this question









    New contributor




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























      2












      2








      2








      From my understanding, the default TTL represents the maximum number of hops allowed such that the packet may reach the host.




      NTP Documentation Archive: ttl - This option is used only with broadcast server and manycast client modes. It specifies the time-to-live ttl to use on broadcast server and multicast server and the maximum ttl for the expanding ring search with manycast client packets




      However, it is also mentioned in some answers that the packet is discarded if the TTL is 0 and it will never reach the host. I'm wondering what would happen when the number of hops before the packet was consumed is exactly the same as TTL_DEFAULT (e.g. TTL_DEFAULT is 2 and there are 2 hops before the packet was consumed). Will the packet reach the host, or it will be discarded?










      share|improve this question









      New contributor




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












      From my understanding, the default TTL represents the maximum number of hops allowed such that the packet may reach the host.




      NTP Documentation Archive: ttl - This option is used only with broadcast server and manycast client modes. It specifies the time-to-live ttl to use on broadcast server and multicast server and the maximum ttl for the expanding ring search with manycast client packets




      However, it is also mentioned in some answers that the packet is discarded if the TTL is 0 and it will never reach the host. I'm wondering what would happen when the number of hops before the packet was consumed is exactly the same as TTL_DEFAULT (e.g. TTL_DEFAULT is 2 and there are 2 hops before the packet was consumed). Will the packet reach the host, or it will be discarded?







      ip ipv4 ipv6 ntp






      share|improve this question









      New contributor




      M. Xu 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 question









      New contributor




      M. Xu 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 question




      share|improve this question








      edited 4 hours ago







      M. Xu













      New contributor




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









      asked 5 hours ago









      M. XuM. Xu

      112




      112




      New contributor




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





      New contributor





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






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






















          1 Answer
          1






          active

          oldest

          votes


















          3














          A TTL of 1 restricts a packet to the local network because a hop to another network will decrement the TTL to 0, then the packet is discarded.



          Every time a packet is processed, the TTL is supposed to be decremented, and then any packets with a TTL of 0 are discarded, but in practice no hosts do it that way. The original idea of TTL is actually Time to Live (in seconds), not a hop count, and each processing of the packet would decrement by the actual time used to process the packet, but the minimum decrement was 1. The idea was to keep upper-layer protocols from receiving stale or duplicate data. This is explained in RFC 791, Internet Protocol, which is for IPv4:




          Time to Live



          The time to live is set by the sender to the maximum time the datagram
          is allowed to be in the internet system. If the datagram is in the
          internet system longer than the time to live, then the datagram must
          be destroyed.



          This field must be decreased at each point that the internet header is
          processed to reflect the time spent processing the datagram. Even if
          no local information is available on the time actually spent, the
          field must be decremented by 1. The time is measured in units of
          seconds (i.e. the value 1 means one second). Thus, the maximum time
          to live is 255 seconds or 4.25 minutes. Since every module that
          processes a datagram must decrease the TTL by at least one even if it
          process the datagram in less than a second, the TTL must be thought of
          only as an upper bound on the time a datagram may exist. The
          intention is to cause undeliverable datagrams to be discarded, and to
          bound the maximum datagram lifetime.



          Some higher level reliable connection protocols are based on
          assumptions that old duplicate datagrams will not arrive after a
          certain time elapses. The TTL is a way for such protocols to have an
          assurance that their assumption is met.




          When IPv6 was created, the authors understood that TTL was not being used the way it was documented. For IPv6, the TTL was changed to Hop Limit to reflect how the TTL was actually being used. See RFC 2460




          Hop Limit



          8-bit unsigned integer. Decremented by 1 by each node that forwards
          the packet. The packet is discarded if Hop Limit is decremented to
          zero.




          -and what routers are supposed to do when receiving an IPv6 packet:




          if the IPv6 Hop Limit is less than or equal to 1 { send an ICMP Time
          Exceeded -- Hop Limit Exceeded in Transit message to the Source
          Address and discard the packet
          }




          -and where IPv6 recognizes that the IPv4 implementations of TTL were flawed:




          8.2 Maximum Packet Lifetime



          Unlike IPv4, IPv6 nodes are not required to enforce maximum packet
          lifetime. That is the reason the IPv4 "Time to Live" field was renamed
          "Hop Limit" in IPv6. In practice, very few, if any, IPv4
          implementations conform to the requirement that they limit packet
          lifetime, so this is not a change in practice. Any upper-layer
          protocol that relies on the internet layer (whether IPv4 or IPv6) to
          limit packet lifetime ought to be upgraded to provide its own
          mechanisms for detecting and discarding obsolete packets.







          I'm wondering what would happen when the number of hops before the
          packet was consumed is exactly the same as TTL_DEFAULT (e.g.
          TTL_DEFAULT is 2 and there are 2 hops before the packet was consumed).
          Will the packet reach the host, or it will be discarded?




          In practice, for an IPv4 packet with a TTL of 1, the packet will reach and be processed by the destination on the same LAN. For a TTL of 2, the packet will reach and be processed by a host one hop from the local LAN (second LAN). And so on.



          That means if the destination of a packet with a TTL of 2 is two (router) hops from the local LAN, the second router will decrement the TTL on the packet to 0 and discard the packet before it reaches the destination (third) LAN.






          share|improve this answer























            Your Answer








            StackExchange.ready(function() {
            var channelOptions = {
            tags: "".split(" "),
            id: "496"
            };
            initTagRenderer("".split(" "), "".split(" "), channelOptions);

            StackExchange.using("externalEditor", function() {
            // Have to fire editor after snippets, if snippets enabled
            if (StackExchange.settings.snippets.snippetsEnabled) {
            StackExchange.using("snippets", function() {
            createEditor();
            });
            }
            else {
            createEditor();
            }
            });

            function createEditor() {
            StackExchange.prepareEditor({
            heartbeatType: 'answer',
            autoActivateHeartbeat: false,
            convertImagesToLinks: false,
            noModals: true,
            showLowRepImageUploadWarning: true,
            reputationToPostImages: null,
            bindNavPrevention: true,
            postfix: "",
            imageUploader: {
            brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
            contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
            allowUrls: true
            },
            noCode: true, onDemand: true,
            discardSelector: ".discard-answer"
            ,immediatelyShowMarkdownHelp:true
            });


            }
            });






            M. Xu is a new contributor. Be nice, and check out our Code of Conduct.










            draft saved

            draft discarded


















            StackExchange.ready(
            function () {
            StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fnetworkengineering.stackexchange.com%2fquestions%2f56950%2fwill-the-packet-be-dropped-when-the-number-of-hops-equals-to-default-ttl%23new-answer', 'question_page');
            }
            );

            Post as a guest















            Required, but never shown

























            1 Answer
            1






            active

            oldest

            votes








            1 Answer
            1






            active

            oldest

            votes









            active

            oldest

            votes






            active

            oldest

            votes









            3














            A TTL of 1 restricts a packet to the local network because a hop to another network will decrement the TTL to 0, then the packet is discarded.



            Every time a packet is processed, the TTL is supposed to be decremented, and then any packets with a TTL of 0 are discarded, but in practice no hosts do it that way. The original idea of TTL is actually Time to Live (in seconds), not a hop count, and each processing of the packet would decrement by the actual time used to process the packet, but the minimum decrement was 1. The idea was to keep upper-layer protocols from receiving stale or duplicate data. This is explained in RFC 791, Internet Protocol, which is for IPv4:




            Time to Live



            The time to live is set by the sender to the maximum time the datagram
            is allowed to be in the internet system. If the datagram is in the
            internet system longer than the time to live, then the datagram must
            be destroyed.



            This field must be decreased at each point that the internet header is
            processed to reflect the time spent processing the datagram. Even if
            no local information is available on the time actually spent, the
            field must be decremented by 1. The time is measured in units of
            seconds (i.e. the value 1 means one second). Thus, the maximum time
            to live is 255 seconds or 4.25 minutes. Since every module that
            processes a datagram must decrease the TTL by at least one even if it
            process the datagram in less than a second, the TTL must be thought of
            only as an upper bound on the time a datagram may exist. The
            intention is to cause undeliverable datagrams to be discarded, and to
            bound the maximum datagram lifetime.



            Some higher level reliable connection protocols are based on
            assumptions that old duplicate datagrams will not arrive after a
            certain time elapses. The TTL is a way for such protocols to have an
            assurance that their assumption is met.




            When IPv6 was created, the authors understood that TTL was not being used the way it was documented. For IPv6, the TTL was changed to Hop Limit to reflect how the TTL was actually being used. See RFC 2460




            Hop Limit



            8-bit unsigned integer. Decremented by 1 by each node that forwards
            the packet. The packet is discarded if Hop Limit is decremented to
            zero.




            -and what routers are supposed to do when receiving an IPv6 packet:




            if the IPv6 Hop Limit is less than or equal to 1 { send an ICMP Time
            Exceeded -- Hop Limit Exceeded in Transit message to the Source
            Address and discard the packet
            }




            -and where IPv6 recognizes that the IPv4 implementations of TTL were flawed:




            8.2 Maximum Packet Lifetime



            Unlike IPv4, IPv6 nodes are not required to enforce maximum packet
            lifetime. That is the reason the IPv4 "Time to Live" field was renamed
            "Hop Limit" in IPv6. In practice, very few, if any, IPv4
            implementations conform to the requirement that they limit packet
            lifetime, so this is not a change in practice. Any upper-layer
            protocol that relies on the internet layer (whether IPv4 or IPv6) to
            limit packet lifetime ought to be upgraded to provide its own
            mechanisms for detecting and discarding obsolete packets.







            I'm wondering what would happen when the number of hops before the
            packet was consumed is exactly the same as TTL_DEFAULT (e.g.
            TTL_DEFAULT is 2 and there are 2 hops before the packet was consumed).
            Will the packet reach the host, or it will be discarded?




            In practice, for an IPv4 packet with a TTL of 1, the packet will reach and be processed by the destination on the same LAN. For a TTL of 2, the packet will reach and be processed by a host one hop from the local LAN (second LAN). And so on.



            That means if the destination of a packet with a TTL of 2 is two (router) hops from the local LAN, the second router will decrement the TTL on the packet to 0 and discard the packet before it reaches the destination (third) LAN.






            share|improve this answer




























              3














              A TTL of 1 restricts a packet to the local network because a hop to another network will decrement the TTL to 0, then the packet is discarded.



              Every time a packet is processed, the TTL is supposed to be decremented, and then any packets with a TTL of 0 are discarded, but in practice no hosts do it that way. The original idea of TTL is actually Time to Live (in seconds), not a hop count, and each processing of the packet would decrement by the actual time used to process the packet, but the minimum decrement was 1. The idea was to keep upper-layer protocols from receiving stale or duplicate data. This is explained in RFC 791, Internet Protocol, which is for IPv4:




              Time to Live



              The time to live is set by the sender to the maximum time the datagram
              is allowed to be in the internet system. If the datagram is in the
              internet system longer than the time to live, then the datagram must
              be destroyed.



              This field must be decreased at each point that the internet header is
              processed to reflect the time spent processing the datagram. Even if
              no local information is available on the time actually spent, the
              field must be decremented by 1. The time is measured in units of
              seconds (i.e. the value 1 means one second). Thus, the maximum time
              to live is 255 seconds or 4.25 minutes. Since every module that
              processes a datagram must decrease the TTL by at least one even if it
              process the datagram in less than a second, the TTL must be thought of
              only as an upper bound on the time a datagram may exist. The
              intention is to cause undeliverable datagrams to be discarded, and to
              bound the maximum datagram lifetime.



              Some higher level reliable connection protocols are based on
              assumptions that old duplicate datagrams will not arrive after a
              certain time elapses. The TTL is a way for such protocols to have an
              assurance that their assumption is met.




              When IPv6 was created, the authors understood that TTL was not being used the way it was documented. For IPv6, the TTL was changed to Hop Limit to reflect how the TTL was actually being used. See RFC 2460




              Hop Limit



              8-bit unsigned integer. Decremented by 1 by each node that forwards
              the packet. The packet is discarded if Hop Limit is decremented to
              zero.




              -and what routers are supposed to do when receiving an IPv6 packet:




              if the IPv6 Hop Limit is less than or equal to 1 { send an ICMP Time
              Exceeded -- Hop Limit Exceeded in Transit message to the Source
              Address and discard the packet
              }




              -and where IPv6 recognizes that the IPv4 implementations of TTL were flawed:




              8.2 Maximum Packet Lifetime



              Unlike IPv4, IPv6 nodes are not required to enforce maximum packet
              lifetime. That is the reason the IPv4 "Time to Live" field was renamed
              "Hop Limit" in IPv6. In practice, very few, if any, IPv4
              implementations conform to the requirement that they limit packet
              lifetime, so this is not a change in practice. Any upper-layer
              protocol that relies on the internet layer (whether IPv4 or IPv6) to
              limit packet lifetime ought to be upgraded to provide its own
              mechanisms for detecting and discarding obsolete packets.







              I'm wondering what would happen when the number of hops before the
              packet was consumed is exactly the same as TTL_DEFAULT (e.g.
              TTL_DEFAULT is 2 and there are 2 hops before the packet was consumed).
              Will the packet reach the host, or it will be discarded?




              In practice, for an IPv4 packet with a TTL of 1, the packet will reach and be processed by the destination on the same LAN. For a TTL of 2, the packet will reach and be processed by a host one hop from the local LAN (second LAN). And so on.



              That means if the destination of a packet with a TTL of 2 is two (router) hops from the local LAN, the second router will decrement the TTL on the packet to 0 and discard the packet before it reaches the destination (third) LAN.






              share|improve this answer


























                3












                3








                3







                A TTL of 1 restricts a packet to the local network because a hop to another network will decrement the TTL to 0, then the packet is discarded.



                Every time a packet is processed, the TTL is supposed to be decremented, and then any packets with a TTL of 0 are discarded, but in practice no hosts do it that way. The original idea of TTL is actually Time to Live (in seconds), not a hop count, and each processing of the packet would decrement by the actual time used to process the packet, but the minimum decrement was 1. The idea was to keep upper-layer protocols from receiving stale or duplicate data. This is explained in RFC 791, Internet Protocol, which is for IPv4:




                Time to Live



                The time to live is set by the sender to the maximum time the datagram
                is allowed to be in the internet system. If the datagram is in the
                internet system longer than the time to live, then the datagram must
                be destroyed.



                This field must be decreased at each point that the internet header is
                processed to reflect the time spent processing the datagram. Even if
                no local information is available on the time actually spent, the
                field must be decremented by 1. The time is measured in units of
                seconds (i.e. the value 1 means one second). Thus, the maximum time
                to live is 255 seconds or 4.25 minutes. Since every module that
                processes a datagram must decrease the TTL by at least one even if it
                process the datagram in less than a second, the TTL must be thought of
                only as an upper bound on the time a datagram may exist. The
                intention is to cause undeliverable datagrams to be discarded, and to
                bound the maximum datagram lifetime.



                Some higher level reliable connection protocols are based on
                assumptions that old duplicate datagrams will not arrive after a
                certain time elapses. The TTL is a way for such protocols to have an
                assurance that their assumption is met.




                When IPv6 was created, the authors understood that TTL was not being used the way it was documented. For IPv6, the TTL was changed to Hop Limit to reflect how the TTL was actually being used. See RFC 2460




                Hop Limit



                8-bit unsigned integer. Decremented by 1 by each node that forwards
                the packet. The packet is discarded if Hop Limit is decremented to
                zero.




                -and what routers are supposed to do when receiving an IPv6 packet:




                if the IPv6 Hop Limit is less than or equal to 1 { send an ICMP Time
                Exceeded -- Hop Limit Exceeded in Transit message to the Source
                Address and discard the packet
                }




                -and where IPv6 recognizes that the IPv4 implementations of TTL were flawed:




                8.2 Maximum Packet Lifetime



                Unlike IPv4, IPv6 nodes are not required to enforce maximum packet
                lifetime. That is the reason the IPv4 "Time to Live" field was renamed
                "Hop Limit" in IPv6. In practice, very few, if any, IPv4
                implementations conform to the requirement that they limit packet
                lifetime, so this is not a change in practice. Any upper-layer
                protocol that relies on the internet layer (whether IPv4 or IPv6) to
                limit packet lifetime ought to be upgraded to provide its own
                mechanisms for detecting and discarding obsolete packets.







                I'm wondering what would happen when the number of hops before the
                packet was consumed is exactly the same as TTL_DEFAULT (e.g.
                TTL_DEFAULT is 2 and there are 2 hops before the packet was consumed).
                Will the packet reach the host, or it will be discarded?




                In practice, for an IPv4 packet with a TTL of 1, the packet will reach and be processed by the destination on the same LAN. For a TTL of 2, the packet will reach and be processed by a host one hop from the local LAN (second LAN). And so on.



                That means if the destination of a packet with a TTL of 2 is two (router) hops from the local LAN, the second router will decrement the TTL on the packet to 0 and discard the packet before it reaches the destination (third) LAN.






                share|improve this answer













                A TTL of 1 restricts a packet to the local network because a hop to another network will decrement the TTL to 0, then the packet is discarded.



                Every time a packet is processed, the TTL is supposed to be decremented, and then any packets with a TTL of 0 are discarded, but in practice no hosts do it that way. The original idea of TTL is actually Time to Live (in seconds), not a hop count, and each processing of the packet would decrement by the actual time used to process the packet, but the minimum decrement was 1. The idea was to keep upper-layer protocols from receiving stale or duplicate data. This is explained in RFC 791, Internet Protocol, which is for IPv4:




                Time to Live



                The time to live is set by the sender to the maximum time the datagram
                is allowed to be in the internet system. If the datagram is in the
                internet system longer than the time to live, then the datagram must
                be destroyed.



                This field must be decreased at each point that the internet header is
                processed to reflect the time spent processing the datagram. Even if
                no local information is available on the time actually spent, the
                field must be decremented by 1. The time is measured in units of
                seconds (i.e. the value 1 means one second). Thus, the maximum time
                to live is 255 seconds or 4.25 minutes. Since every module that
                processes a datagram must decrease the TTL by at least one even if it
                process the datagram in less than a second, the TTL must be thought of
                only as an upper bound on the time a datagram may exist. The
                intention is to cause undeliverable datagrams to be discarded, and to
                bound the maximum datagram lifetime.



                Some higher level reliable connection protocols are based on
                assumptions that old duplicate datagrams will not arrive after a
                certain time elapses. The TTL is a way for such protocols to have an
                assurance that their assumption is met.




                When IPv6 was created, the authors understood that TTL was not being used the way it was documented. For IPv6, the TTL was changed to Hop Limit to reflect how the TTL was actually being used. See RFC 2460




                Hop Limit



                8-bit unsigned integer. Decremented by 1 by each node that forwards
                the packet. The packet is discarded if Hop Limit is decremented to
                zero.




                -and what routers are supposed to do when receiving an IPv6 packet:




                if the IPv6 Hop Limit is less than or equal to 1 { send an ICMP Time
                Exceeded -- Hop Limit Exceeded in Transit message to the Source
                Address and discard the packet
                }




                -and where IPv6 recognizes that the IPv4 implementations of TTL were flawed:




                8.2 Maximum Packet Lifetime



                Unlike IPv4, IPv6 nodes are not required to enforce maximum packet
                lifetime. That is the reason the IPv4 "Time to Live" field was renamed
                "Hop Limit" in IPv6. In practice, very few, if any, IPv4
                implementations conform to the requirement that they limit packet
                lifetime, so this is not a change in practice. Any upper-layer
                protocol that relies on the internet layer (whether IPv4 or IPv6) to
                limit packet lifetime ought to be upgraded to provide its own
                mechanisms for detecting and discarding obsolete packets.







                I'm wondering what would happen when the number of hops before the
                packet was consumed is exactly the same as TTL_DEFAULT (e.g.
                TTL_DEFAULT is 2 and there are 2 hops before the packet was consumed).
                Will the packet reach the host, or it will be discarded?




                In practice, for an IPv4 packet with a TTL of 1, the packet will reach and be processed by the destination on the same LAN. For a TTL of 2, the packet will reach and be processed by a host one hop from the local LAN (second LAN). And so on.



                That means if the destination of a packet with a TTL of 2 is two (router) hops from the local LAN, the second router will decrement the TTL on the packet to 0 and discard the packet before it reaches the destination (third) LAN.







                share|improve this answer












                share|improve this answer



                share|improve this answer










                answered 2 hours ago









                Ron MaupinRon Maupin

                65.2k1368122




                65.2k1368122






















                    M. Xu is a new contributor. Be nice, and check out our Code of Conduct.










                    draft saved

                    draft discarded


















                    M. Xu is a new contributor. Be nice, and check out our Code of Conduct.













                    M. Xu is a new contributor. Be nice, and check out our Code of Conduct.












                    M. Xu is a new contributor. Be nice, and check out our Code of Conduct.
















                    Thanks for contributing an answer to Network Engineering Stack Exchange!


                    • Please be sure to answer the question. Provide details and share your research!

                    But avoid



                    • Asking for help, clarification, or responding to other answers.

                    • Making statements based on opinion; back them up with references or personal experience.


                    To learn more, see our tips on writing great answers.




                    draft saved


                    draft discarded














                    StackExchange.ready(
                    function () {
                    StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fnetworkengineering.stackexchange.com%2fquestions%2f56950%2fwill-the-packet-be-dropped-when-the-number-of-hops-equals-to-default-ttl%23new-answer', 'question_page');
                    }
                    );

                    Post as a guest















                    Required, but never shown





















































                    Required, but never shown














                    Required, but never shown












                    Required, but never shown







                    Required, but never shown

































                    Required, but never shown














                    Required, but never shown












                    Required, but never shown







                    Required, but never shown







                    Popular posts from this blog

                    Liste der Baudenkmale in Friedland (Mecklenburg)

                    Single-Malt-Whisky

                    Czorneboh