JP2006050405A - Communication network system, communication terminal and nat solving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a burden is applied to management of a router if a configuration of a network connected to the router including a NAT function is changed. <P>SOLUTION: There are provided a first communication network that uses a first IP address, a second communication network that uses a second IP address, and a communication control unit that performs NAT processing between both the communication networks. Each of communication terminals of the first communication network includes: a message generation unit that generates a communication start request message containing a first IP address of the present terminal and described in a data region of an IP packet when starting communicating with another terminal; a route search unit that searches for a transmission route to the other terminal; and an address conversion unit that determines whether the communication control unit is included in the transmission route, and converts the first IP address in the communication start request message into a second IP address of the communication control unit if the communication control unit is included. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a system including a plurality of communication networks connected via a router having a NAT (Network Address Translation) or NAPT (Network Address Port Translation) function.

  Conventionally, when IP packets are communicated between a global network such as the Internet and a local network such as an in-house network, a router having a NAT function is interposed between the two networks, and this router converts the IP packet address. Is known to do. The NAT function focuses on information related to the IP layer in the received IP packet, that is, information described in the header area of the IP packet, and corresponds the source and destination IP addresses in the information to the destination network. The conversion is performed to unify the IP addresses.

  By the way, in an IP telephone service using VoIP (Voice over IP) and a communication service such as a moving image distribution service, SIP (Session Initiation Protocol) or H.264 is used as a voice communication protocol. For example, in the case of SIP, an Invite message is created as the call start request message. This Invite message is described in the data area of the IP packet transmitted to the destination, and the source and destination IP addresses are included in the message.

  However, when an IP packet in which the above Invite message is described is exchanged via a router having a NAT function, the address of the header area of the packet is converted, but the IP address of the Invite message in the data area is not converted. For this reason, there arises a disadvantage that proper communication cannot be performed.

  Techniques for eliminating this inconvenience are described in, for example, Patent Documents 1 and 2 described later. Patent Document 1 discloses a method in which a router having a NAT function and connecting between an internal network and an external network allocates the same address as a public IP address used in the external network to a device connected to the internal network. ing.

Further, in Patent Document 2, an ALG (Application Level Gateway) function defined in RFC 3303 or the like is given to an IP address translation apparatus that connects a network to which IPv4 is applied and a network to which IPv6 is applied. A technique is disclosed in which when an IP address is present in a received SIP message, it is converted into an IP address format corresponding to a destination network.
JP 2003-238991 A JP 2004-165823 A

  According to the above Patent Documents 1 and 2, it can be expected that the above-described inconveniences related to the NAT function are solved by the respective methods. However, in these methods, since the solution means such as address allocation or address conversion is given to the routers connecting the two networks, for example, when the configuration in each network changes due to the increase or decrease in the number of terminals, the router management Each time, the person is required to reset the information about the changed configuration. Further, the communication service between the networks is stopped during the resetting operation, which causes inconvenience for the user.

  The present invention has been made in view of the above problems. In a system in which a plurality of networks are connected by a router having a NAT function, the SIP or H.264 network is used. An object of the present invention is to provide a technique capable of reducing the burden on router management while eliminating the inconvenience when a voice communication protocol such as H.323 is used.

  A communication network system according to the present invention is connected to a first communication network, a second communication network to which a communication protocol different from that of the first communication network is applied, and both the first and second communication networks. And a communication control device that performs address conversion of a header area of an IP packet communicated between the two communication networks, wherein the first communication network includes a plurality of communication terminals assigned with a first IP address. A plurality of internal networks, and a connection device for connecting the plurality of internal networks, wherein the second communication network includes a communication terminal assigned with a second IP address, Each communication terminal of the communication network includes the first IP address of its own terminal when it starts communication with other terminals, and the IP packet A message generation unit that generates a communication start request message described in a data area, a route search unit that searches for a transmission route to the other terminal, and the communication control device is included in the transmission path searched by the route search unit Address conversion for converting the first IP address in the communication start request message generated by the message generation unit into the second IP address of the communication control device when the communication control device is included. And a packet transmission unit that outputs an IP packet in which the communication start request message is described to the transmission path.

  The NAT solution according to the present invention is connected to a first communication network, a second communication network to which a communication protocol different from that of the first communication network is applied, and both the first and second communication networks. And a communication control device that performs address conversion of a header area of an IP packet communicated between the two communication networks, wherein the first communication network includes a plurality of communication terminals to which a first IP address is assigned. A system having a plurality of internal networks and a connection device for connecting the plurality of internal networks, wherein the second communication network includes a communication terminal to which a second IP address is assigned. Each communication terminal of the communication network includes the first IP address of its own terminal and the IP packet at the start of communication with another terminal. Generating a communication start request message described in a data area of the network, searching for a transmission path to the other terminal, determining whether or not the communication control apparatus is included in the searched transmission path, and the communication control apparatus Is included, the first IP address in the generated communication start request message is converted into a second IP address of the communication control device, and an IP packet describing the communication start request message is output to the transmission path It is a method of doing.

  According to the present invention, by providing each communication terminal with the IP address conversion function for the data area of the IP packet, even if there is a change in the configuration in each of the first and second communication networks, It can make it difficult to give administrative burden. In addition, each communication terminal determines whether or not IP address conversion needs to be performed according to the transmission path used for communication. Therefore, regardless of whether or not the communication partner is the same network as its own terminal, An appropriate IP packet can be transmitted.

[Example 1]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram illustrating a system configuration of the embodiment. The system of the embodiment is a global area network 10 such as the Internet, a local area network 20 such as an in-house network, and a communication control apparatus connected to both the networks 10 and 20 and having a conventionally known NAT function. A router 101 is provided. The global area network 10 uses a global IP address that is the first or second IP address of the present invention, and the local area network 20 has a first or second IP address different from that used by the global area network 10. Use local IP address.

  As shown in FIG. 1, the global area network 10 includes a plurality of internal networks LAN 200 and LAN 201, a router 100 that connects these two LANs, and an IP phone 300 that is a communication terminal connected to the LAN 200. Is provided. The LAN 200 has a network system with a global IP address of “11.2.0.0/16”, and the LAN 201 has a network system of “10.10.0.0/16”. The IP telephone 300 is a telephone that can use a protocol for voice communication such as SIP or H.323, has “11.22.33.30” as the global IP address of its own terminal, and the router 100 as a default gateway. Is set.

  The router 100 connects the “11.2.0.0/16” LAN 200 and the “10.10.0.0/16” LAN 201 so that they can communicate with each other, and sets “11” as the IP address on the LAN 200 side. .22.33.1 ", as shown in FIG. 1," 10.10.0.1 "is assigned as the IP address on the LAN 201 side. The router 100 is a connection device that does not have a NAT function.

  The other local area network 20 includes a plurality of internal networks LAN 202 and LAN 203, a router 102 connecting these two LANs, an IP phone 301 connected to the LAN 202, and an IP phone 302 connected to the LAN 203. Is provided. The LAN 202 has a network system with a local IP address “192.168.0.0/16”, and the LAN 203 has a network system with “172.16.0.0/16”. Similar to IP phone 300, IP phones 301 and 302 are phones that can use voice communication protocols such as SIP and H.323. The IP phone 301 has “192.168.0.10” as the local IP address of its own terminal, and the IP phone 302 has “172.16.0.10”. In addition, the router 102 is set as a default gateway for the IP phone 301 and the IP phone 302.

  The router 102 connects the “192.168.0.0/16” LAN 202 and the “172.16.0.0/16” LAN 203 so that they can communicate with each other, and the IP address on the LAN 200 side is “192”. .168.0.2 ”, and“ 172.16.0.1 ”is assigned as the IP address on the LAN 203 side. The router 102 is also a connection device that does not have a NAT function, like the router 100 described above.

  The router 101 has a NAT function, and an IP layer portion of an IP packet exchanged between the global area network 10 and the local area network 20, that is, an IP address in the header area of the packet is changed to a global IP address or a local IP address. Convert to The router 101 has “192.168.0.1” as the local IP address and “10.10.0.2” as the global IP address.

  Further, the router 101 has a table as shown in FIG. 2 indicating the connection status of the LAN to each of the routers 101 to 103 in the system and the presence or absence of the NAT function in each of the routers 101 to 103. With reference to this table, for example, when the router 101 receives an IP packet whose destination is the global IP address “10.10.0.2” of its own device, the router 101 performs NAT processing on the IP packet, and It has a function of transferring a packet to the IP phone 301 having the IP address “192.168.0.10” in the “192.168.0.0/16” network of the network 20.

  IP phone 300 to IP phone 302 have the same configuration. For example, taking IP phone 301 as an example, as shown in FIG. 1, when communication with another terminal is started, A message generation unit 31 that generates a communication start request message that includes an IP address and is described in the data area of the IP packet, a route search unit 32 that searches for a transmission route to another terminal, and a transmission searched by the route search unit 32 It is determined whether or not a router having a NAT function is included in the route, and when included, an address conversion unit 33 that performs an address conversion process to be described later on the communication start request message generated by the message generation unit 31, and a communication start A packet transmission unit 34 for outputting an IP packet in which the request message is described to the transmission path. The route search unit 32 of the present embodiment has the same information as the table of FIG. 2 that the router 101 has, and searches for a transmission route based on this table.

  The operation procedure of the system of the embodiment will be described with reference to the flowchart shown in FIG. Here, it is assumed that each of IP phone 300 to IP phone 302 uses SIP as a protocol for voice communication. First, the case where the IP phone 301 of the local area network 20 makes a call with the IP phone 300 of the global area network 10 will be described as an example.

  When IP phone 301 starts a call with IP phone 300, message generator 31 of IP phone 301 generates an Invite message, which is a communication start request message in accordance with SIP (step S1). At this time, the route search unit 32 searches the transmission route to the IP telephone 300 as the communication partner with reference to the table of FIG. 2 (step S2). The search procedure will be described with reference to the flowchart shown in FIG.

  The route search unit 32 of the IP phone 301 searches the table in FIG. 2 for a router connected to the internal network corresponding to the IP address “11.22.33.10” of the IP phone 300 that is the communication partner (step A1). Here, the internal network corresponding to “11.22.3.10” of the IP phone 300 refers to the LAN 11.2 of the “11.22.0.0/16” system, and from the table of FIG. It can be seen that the connected router is the router 100 (step A2).

  Subsequently, the route search unit 32 confirms that the other internal network connected to the router 100 is the “10.10.0.0/16/16”-system LAN 201 (step A3). A router connected to other than the router 100 detects that it is the router 101 (step A4).

  Further, it is detected from the table of FIG. 2 that the router 101 is also connected to the “192.168.0.0/16” LAN 202 where the IP phone 301 as its own terminal exists (step A5). . From the above search results, the route search unit 32 of the IP phone 301 recognizes that the transmission route from the own terminal to the IP phone 300 is “LAN 202 → router 101 → LAN 201 → router 100 → LAN 200” (step A6). ).

  FIG. 5 shows a search procedure for a transmission path when the IP phone 301 makes a call with the IP phone 302 in the local area network 20. The route search unit 32 of the IP telephone 301 is an internal network corresponding to “172.16.0.10” that is the IP address of the IP telephone 302 that is the communication partner, that is, the “172.16.0.0/16” system. The router connected to the LAN 203 is searched from the table of FIG. 2 (step B1).

  As a result, it is detected that the router 102 is connected to the LAN 203 (step B2). Further, the router 102 has “192.168.0.0/16” in which the IP phone 301 as its own terminal exists. A connection to the local LAN 202 is detected (step B3). From the above search results, the route search unit 32 recognizes that the transmission route from the IP phone 301 to the IP phone 302 is “LAN 202 → router 102 → LAN 203” (step B4).

  When the transmission route is searched by the route search unit 32 in the above procedure, the address conversion unit 33 is activated, and the table of FIG. 2 indicates whether or not the transmission route includes a router having the NAT function. Based on the determination (FIG. 3: step S3). Here, it can be seen from the table of FIG. 2 that the router having the NAT function is the router 101, so the address translation unit 33 determines whether or not the router 101 is on the transmission path. .

  Specifically, for example, in a call between the IP phone 301 and the IP phone 300 described with reference to FIG. 4, it is determined that the router 101 is included in the transmission path (step S3: Yes), and transmission is in progress. That NAT processing is performed. Further, in the case of a call between the IP phone 301 and the IP phone 302 described with reference to FIG. 5, since the router 101 is not passed (step S3: No), it is recognized that NAT processing is not performed during transmission.

  When recognizing that NAT processing is performed during transmission, such as communication between the IP phone 301 and the IP phone 300, the address converting unit 33 uses the IP address of its own terminal included in the Invite message generated by the message generating unit 31. That is, the IP address of the caller is converted to the global IP address of the router 101 (step S4). Further, when the NAT process is not performed during transmission as in the communication between the IP telephone 301 and the IP telephone 302, the process proceeds to a packet transmission process described later without performing address conversion.

  Using the example of the Invite message shown in FIG. 6, the procedure of the address conversion process in step S4 will be described. The illustrated example is an Invite message generated during communication from IP phone 301 to IP phone 300. As described above, in the case of passing through the router 101 having the NAT function, the IP address “192.168..192” of the information “From:” 301 ”<sip: 301@192.168.0.10>” describing the caller is described. 0.10 ”is converted into“ 10.10.0.2 ”which is the global IP address of the router 101. If the transmission path does not pass through the router 101, the IP address of the call source is not converted from “192.168.0.10”.

  The packet transmission unit 34 describes the Invite message whose address has been converted in Step S4 or the Invite message that does not require address conversion in the data area of the IP packet, and outputs this to the transmission path (Step S5). ).

  According to the embodiment described above, since each of the IP phones 300 to 302 has an address conversion function for Invite messages, even if there is a change in the LAN configuration within the global area network 10 or the local area network 20, The burden on managing the router 101 that performs NAT processing between both networks can be reduced. In addition, since each IP phone 300 to 302 determines in advance whether or not NAT processing is performed on the transmission path, it is possible to perform appropriate address conversion according to the transmission path. As a result, in each internal network, it becomes easy to realize the addition of a LAN by a router such as the router 100 or 102 that does not have a NAT function.

[Example 2]
In the first embodiment described above, the route search unit 32 searches for a transmission route based on the table of FIG. 2, but instead of this search method, a trace route (Trace Trace) based on a conventionally known ICMP (Internet Control Message Protocol) is used. (Route) command search processing can be employed. The procedure will be described below as a second embodiment. The system configuration of this embodiment is the same as that shown in FIG. 1, but each IP phone 300-302 has the table shown in FIG. 7, that is, the IP address and NAT assigned to each router 100-102. Information indicating the presence or absence of a function is given.

  A route search procedure according to this embodiment will be described. First, along the sequence diagram shown in FIG. 8, a case will be described in which IP phone 301 in local area network 20 makes a call with IP phone 300 existing in the other global area network 10. IP phone 301 sends an IP packet with a TTL (Time To Live) value set to “1” to “11.22.33.30”, which is the IP address of IP phone 300 that is the communication partner. This IP packet is sent to the router 102 which is the default gateway of the IP telephone 301 (step S11).

  When the router 102 receives the IP packet transmitted from the IP telephone 301, it subtracts “1” from the set TTL value “1”. As a result, the TTL value in the router 102 becomes “0”. When the router 102 recognizes that the TTL value has become “0”, it discards the IP packet in accordance with ICMP (step S 12), and notifies the sender of the IP phone 301 of the discard in accordance with ICMP. A Time Exceeded Message, which is a type 3 message, is transmitted to the IP address “192.168.0.10” of the IP phone 301 based on the table of FIG. 7 (step S13). By receiving the Time Exceeded Message from the router 102, the IP phone 301 grasps that the router 102 exists in the transmission path to the IP phone 300 that is the communication partner (step S14).

  Next, IP phone 301 sends an IP packet obtained by adding TTL value “1”, that is, an IP packet having TTL value “2” to IP address “11.22.33.30” of IP phone 300 of the communication partner. Send it out. This IP packet is first sent to the router 102, which is the default gateway, in the same manner as in step S11 (step S15).

  When receiving the IP packet from the IP telephone 301, the router 102 deducts the TTL value by “1”, and transmits the IP packet having the TTL value “1” to the router 101 (step S16). When the router 101 receives the IP packet sent from the router 102, it subtracts “1” from the TTL value. Thereby, since the TTL value becomes “0”, the router 101 discards the IP packet (step S17), and transmits the Time Exceeded Message described above to the IP phone 301 via the router 102 (steps S18 and S19). ).

  The IP telephone 301 that has received the Time Exceeded Message from the router 101 has the router 101 as the next hop of the router 102 on the transmission path to the IP telephone 300 that is the communication partner (step S20). From the table, it is understood that this router 101 has the NAT function (step S21). At this point, the IP telephone 301 recognizes that the IP packet to the IP telephone 300 is subjected to NAT processing, and thus ends the transmission of the IP packet by the above-described trace route command. Thereafter, the IP phone 301 performs the address conversion described in the first embodiment (FIG. 3: step S4) on the Invite message described in the IP packet to the IP phone 300.

  A case where the IP phone 301 communicates with the IP phone 302 of the local area network 20 will be described with reference to the sequence diagram of FIG. First, IP phone 301 transmits an IP packet in which the TTL value is set to “1” to IP address “172.16.0.10” of IP phone 302 of the communication partner. This IP packet is sent to the router 102, which is the default gateway of the IP telephone 301, in the same manner as described above (step S21).

  The router 102 that has received the IP packet from the IP telephone 301 subtracts “1” from the TTL value, so that the TTL value becomes “0”. Therefore, the IP packet is discarded (step S22). ICMP Time Exceeded Message is transmitted (step S23). When the IP telephone 301 receives the Time Exceeded Message from the router 102, it can be seen that the IP telephone 301 passes through the router 102 on the transmission path (step S24).

  Next, IP phone 301 adds the TTL value and transmits the IP packet set to “2” to IP phone 302. This packet is also sent to the router 102 (step S25), and the router 102 that has received the packet transmits the IP packet having the TTL value “1” by subtracting the TTL value “1” to the IP telephone 302. (Step S26).

  Upon receiving the IP packet from the router 102, the IP phone 302 recognizes that this packet has been sent to its own terminal, discards the packet (step S27), and receives an Echo Reply Message, which is a type 0 message in ICMP. Is transmitted to the IP telephone 301 via the router 102 (steps S28 and S29). The IP phone 301 that has received the Echo Reply Message from the IP phone 302 passes only the router 102 in the route to the IP phone 302 (step S30), and the router 102 does not use NAT from the table of FIG. (Step S31). As a result, IP phone 301 determines not to convert the IP address for the Invite message described in the IP packet to IP phone 302.

  According to the second embodiment, the route search performed by the route search unit 32 of each telephone employs the above-described method based on the trace route command. Therefore, the LAN configuration of the internal network such as the global area network 10 or the local area network 20 is used. Even if changes, this change can be flexibly dealt with when searching for a route.

  In each of the embodiments described above, the router 101 has been described as having a NAT function. However, the present invention is not limited to NAT but may be NAPT (Network Address Port Translation).

It is a block diagram which shows the system configuration | structure of the Example by this invention. It is explanatory drawing for demonstrating the table in Example 1. FIG. 3 is a flowchart illustrating an operation procedure according to the first exemplary embodiment. 3 is a flowchart illustrating a route determination procedure according to the first embodiment. 3 is a flowchart illustrating a route determination procedure according to the first embodiment. FIG. 6 is an explanatory diagram for explaining an address conversion process according to the first embodiment. FIG. 10 is an explanatory diagram for explaining a table in the second embodiment. It is a sequence diagram which shows the path | route determination procedure in Example 2. FIG. It is a sequence diagram which shows the path | route determination procedure in Example 2. FIG.

Explanation of symbols

10 Global Area Network 20 Local Area Network 100-103 Router 200-203 LAN
300 to 302 IP phone 31 Message generation unit 32 Route search unit 33 Address conversion unit 34 Packet transmission unit

Claims (9)

A first communication network, a second communication network to which a communication protocol different from that of the first communication network is applied, and communication between the first communication network and the second communication network. A communication control device that performs address conversion of the header area of the IP packet to be performed,
The first communication network includes a plurality of internal networks having a plurality of communication terminals assigned with a first IP address, and a connection device for connecting the plurality of internal networks.
The second communication network has a communication terminal assigned a second IP address;
Each communication terminal of the first communication network is
A message generation unit that generates a communication start request message including the first IP address of the own terminal and described in the data area of the IP packet at the start of communication with another terminal;
A route search unit for searching for a transmission route to the other terminal;
It is determined whether or not the communication control device is included in the transmission route searched by the route search unit, and when the communication control device is included, the first IP in the communication start request message generated by the message generation unit An address conversion unit for converting an address into a second IP address of the communication control device;
A communication network system, comprising: a packet transmission unit that outputs an IP packet in which the communication start request message is described to the transmission path. The second communication network includes a plurality of internal networks having a plurality of communication terminals assigned a second IP address, and a connection device for connecting the plurality of internal networks.
Each communication terminal of the second communication network is
A message generation unit that generates a communication start request message including the second IP address of the own terminal and described in the data area of the IP packet at the start of communication with another terminal;
A route search unit for searching for a transmission route to the other terminal;
It is determined whether the communication control device is included in the transmission route searched by the route search unit, and when the communication control device is included, the second IP in the communication start request message generated by the message generation unit An address conversion unit for converting an address into a first IP address of the communication control device;
The communication network system according to claim 1, further comprising: a packet transmission unit that outputs an IP packet describing the communication start request message to the transmission path.   3. The route search unit according to claim 1, wherein the route search unit searches for the transmission route based on information relating the connection devices and the communication control device to a network connected to the devices. Communication network system.   The path search unit sequentially transmits IP packets by gradually increasing a TTL (Time To Live) value to the other terminals to be communicated in accordance with ICMP (Internet Control Message Protocol), and the transmission 3. The communication network system according to claim 1, wherein the transmission path is searched by receiving an ICMP message indicating that the TTL value exceeds the time for the IP packet that has been transmitted. A first communication network, a second communication network to which a communication protocol different from that of the first communication network is applied, and communication between the first communication network and the second communication network. A communication terminal assigned with a first IP address in the first communication network in a system comprising a communication control device that performs address conversion of a header area of an IP packet to be performed,
A message generation unit that generates a communication start request message including the first IP address of the own terminal and described in the data area of the IP packet at the start of communication with another terminal;
A route search unit for searching for a transmission route to the other terminal;
It is determined whether or not the communication control device is included in the transmission route searched by the route search unit, and when the communication control device is included, the first IP in the communication start request message generated by the message generation unit An address conversion unit for converting an address into a second IP address of the communication control device;
A communication terminal, comprising: a packet transmission unit that outputs an IP packet describing the communication start request message to the transmission path. A first communication network, a second communication network to which a communication protocol different from that of the first communication network is applied, and communication between the first communication network and the second communication network. A communication control device that performs address conversion of the header area of the IP packet to be transmitted, wherein the first communication network includes a plurality of internal networks having a plurality of communication terminals assigned with a first IP address, A connection device for connecting the internal networks of the second communication network, wherein the second communication network includes a communication terminal to which a second IP address is assigned.
Each communication terminal of the first communication network is
At the start of communication with another terminal, a communication start request message including the first IP address of the own terminal and described in the data area of the IP packet is generated, a transmission path to the other terminal is searched, and the searched transmission It is determined whether or not the communication control device is included in the route, and when the communication control device is included, the first IP address in the generated communication start request message is set to the second IP address of the communication control device. A NAT resolution method, wherein the IP packet describing the communication start request message is output to the transmission path. The second communication network of the system has a plurality of internal networks having a plurality of communication terminals assigned a second IP address, and a connection device for connecting the plurality of internal networks;
Each communication terminal of the second communication network is
At the start of communication with another terminal, a communication start request message including the second IP address of the own terminal and described in the data area of the IP packet is generated, a transmission path to the other terminal is searched, and the searched transmission It is determined whether or not the communication control device is included in the path, and when the communication control device is included, the second IP address in the generated communication start request message is set to the first IP address of the communication control device. 7. The NAT resolution method according to claim 6, wherein the IP packet describing the communication start request message is output to the transmission path.   The said each communication terminal searches the said transmission path | route based on the information which linked | related the said each connection apparatus and the said communication control apparatus, and the network connected to this each apparatus, The said transmission path | route is characterized by the above-mentioned. NAT resolution method.   Each communication terminal sequentially transmits IP packets by gradually increasing a TTL (Time To Live) value to the other terminals to be communicated in accordance with ICMP (Internet Control Message Protocol), and the transmission 8. The NAT resolution method according to claim 6, wherein the transmission path is searched by receiving an ICMP message indicating that the TTL value exceeds the time for the IP packet that has been transmitted.

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