KR20060011656A - System and method for setting packet maximum transmission unit of ipv6 transition tunnel using packet too big message - Google Patents

Abstract

The present invention provides a packet-to-big message format for preventing a packet from being lost by pre-broadcasting a packet too big message including MTU information about an IPv6 packet when using an IPv6 transition tunnel, and using the same, maximum transmission in an IPVIX transition tunnel. A system and method for setting a unit, the method comprising: configuring an Internet Protocol version 6 (IPv6) transition tunnel in an Internet Protocol version 4 (IPv4) network; When setting an MTU for a tunnel interface in an IPv6 transition router, broadcasting a packet too big message to a transmitting node by setting an MTU by reducing the length of an IPv4 header to be encapsulated in a basic MTU of the corresponding interface; And a router corresponding to the transmitting node receives a packet too big message, fragments the packet according to the MTU information, and transmits the packet to the IPv6 transition router.

IPv6, IPv4, Transition, MTU, Packet Too Big, ICMPv6, MTU Discovery

Description

System and Method for setting packet Maximum Transmission Unit of IPv6 transition tunnel using Packet too big message}

1 schematically illustrates a general IPv6 transition network structure;

2a is a diagram of a first step of a general path MTU discovery process;

FIG. 2B is a diagram of steps after the process of FIG. 2A;

2C is a diagram of steps after the process of FIG. 2B;

3 is a flowchart illustrating a conventional path MTU discovery process;

4 is a diagram illustrating a packet to discovery message format delivered during a conventional path MTU discovery process;

5 is a schematic structural diagram of a case where a packet too big message transmitted during a path MTU discovery process is broadcast before packet reception according to the present invention;

FIG. 6 is a schematic diagram illustrating a case where a loop occurs in a process of broadcasting a packet too big message before packet reception, which is delivered during a path MTU discovery process according to the present invention; FIG.

7 is a diagram illustrating a packet to discovery message format delivered in a path MTU discovery process for implementing the present invention;

8 is a flowchart illustrating a process of broadcasting a packet too big message before packet reception according to the first embodiment of the present invention;

9 is a flowchart illustrating a case in which a loop is generated in a process of broadcasting a packet too big message before packet reception according to the second embodiment of the present invention;

FIG. 10 is a flowchart illustrating a case where a loop occurs in a process of broadcasting a packet too big message before packet reception according to a third embodiment of the present invention. FIG.

<Description of the symbols for the main parts of the drawings>

F1: type field F2: code field

F3: Checksum field F4: MTU field

F5: IP datagram field F6: Sequence No. field

The present invention relates to an IPv6 transition mechanism. In particular, when using an IPv6 transition tunnel, an IPV is used by using a packet-to-big message format to prevent packet loss by pre-broadcasting a packet too big message including MTU information about an IPv6 packet. A system and method for setting a maximum transmission unit in a six transition tunnel.

Because there are so many systems on the Internet, the transition from IPv4 to IPv6 cannot happen rapidly. It takes a lot of time for every system on the Internet to switch from IPv4 to IPv6. Therefore, the transition should be made gradually to prevent problems between IPv4 and IPv6 systems.

This strategy was devised by the IETF, which is divided into three transition strategies: double stack, tunneling, and header conversion.

Dual stack means that all hosts have a dual stack protocol before fully migrating to version 6. In other words, IPv4 and IPv6 must be operated simultaneously until all systems on the Internet use IPv6.

Header translation is necessary if most of the Internet uses IPv6 but some systems still use IPv4. If the sender wants to use IPv6 but the receiver does not understand IPv6, the tunneling does not work in this situation because the packet must be in IPv4 format that the receiver can understand, so header conversion is necessary.

The present invention is a technique related to tunneling, and tunneling among the conventional IPv6 transition mechanisms will be described.

Tunneling will be described with reference to FIG. 1.

1 is a diagram schematically illustrating a general IPv6 transition network structure.

As a strategy used when two computers using IPv6 want to communicate with each other and have to traverse an area using IPv4, the packet must have an IPv4 address to pass through this area. IPv6 packets are encapsulated within IPv4 packets when they enter that area and decapsulated when they leave that area. It's like going into one of the tunnels of IPv6 packets and coming out of the other.

In this case, the maximum transmission unit (hereinafter referred to as 'MTU') for IPv6 packets can only be reduced by the length of the IPv4 header (20 bytes), and in the IPv6 network, packets transmitted differently from the IPv4 network are divided into intermediate nodes. Since it is not possible, path MTU discovery must be performed at the source node.

To go through an IPv6 transition tunnel, you must add 20 bytes of IPv4 header to the IPv6 packet. In this encapsulation process, the packet size becomes the size of 20 bytes added to the IPv6 packet size.

If all MTUs in the Ethernet network are set to 1500, which is the default value, packets with an IPv6 packet size of 1500 bytes will pass through the IPv6 transition tunnel and will be 1520 bytes. In IPv6, no packet can be repartitioned at an intermediate node, so path MTU discovery must be performed.

The above phenomenon will be described in detail with reference to the drawings.

FIG. 2A is a diagram of a first step of a general path MTU discovery process, FIG. 2B is a diagram of a step after the process of FIG. 2A, and FIG. 2C is a diagram of a step of the process after FIG. 2B. The processes of Figures 2A, 2B and 2C are detailed in RFC1981.

If node A sends 1500 bytes of packet to node B, MTU of node B and node C (1480 bytes) is set smaller than 1500 bytes of packet size to be transmitted. Retransmit by dividing by packet size. The node A extracts packet size information (1480 bytes) from the MTU field in the packet too big message and then transmits a packet in units of 1480 bytes.

However, if the MTU of the D node is 1460, the C node transmits a packet too big message to the sender to split the packet into smaller packet sizes.

The node A extracts packet size information (1460 bytes) from the MTU field in the packet too big message and then transmits a packet in units of 1460 bytes.

The process can be developed in the following flow.

3 is a flowchart illustrating a conventional path MTU discovery process.

When a node receives a packet from a previous node (S1), it compares whether the packet size is larger than the set MTU (S2), and forwards the packet to the next node if the packet is the same size or smaller packet as the MTU (S6). ).

If the packet is larger than the MTU, the packet too big message is transmitted to the previous node (sending side) (S3).

The packet too big message will be described later with reference to FIG. 4.

The previous node (sending side) fragments the packet by the packet maximum transmission unit recorded in the MTU field in the packet too big message (S4), and retransmits the packet (S5).

Before describing the packet too big message, let's look at the basic Internet Control Message Protocol (ICMP) message format.

ICMP applied in the present invention means ICMPv6, and in order to understand ICMPv6, an understanding of ICMPv4 should be preceded.

In the following description of ICMPv4, the Internet Control Message Protocol (ICMPv4) (ICMPv4) is a protocol designed to supplement error control and support mechanisms, which are disadvantages of the IP protocol. Likewise, it can be divided into error-reporting messages and query messages.

Category Type Message Error reporting messages 3 Destination unreachable 4 Source quench 11 Time exceeded 12 Parameter problem 5 Redirection Query messages 8 or 0 Echo request or reply 13 or 14 Timestamp request or reply 17 or 18 Address mask request or reply 10 or 9 Router solicitation or advertisement

ICMPv6 has the same strategy and objectives as ICMPv4 and is a modified version to better adapt to IPv6. In addition, some protocols that were independent of version 4 (ARP, IGMP, etc.) were merged into ICMPv6.

Although the general format of ICMP messages is different for each message type, the first 4 bytes are commonly used as a field called Type.

Type refers to the type of message, and code is a field used when you need to display detailed information within the message.

The packet too big message is a type added in version 6. Two things happen when a router receives a datagram that is larger than the maximum transmission unit size of the network that the datagram must pass. First, the router discards the datagram. It then sends an ICMP error packet to the source, where the message sent is a packet too big message.

4 is a diagram illustrating a packet to discovery message format delivered during a conventional path MTU discovery process.

Referring to FIG. 4, the packet too big message has a value of 2 in the type field F1, the code field F2 has only one zero value, there is a checksum field F3, and the MTU field ( F4) informs the sender of the packet of the maximum size accepted by the network and includes an IP datagram field.

In the prior art, the path MTU discovery process itself discards all packets from the next node until the packet too big message is returned from the next node after the first packet is transmitted, and then retransmits the packet. Packets can be a load on the network, and there is a problem that transmission delay occurs due to the time taken for this process itself.

Accordingly, the present invention has been made to solve the above problems, broadcast the packet too big message at the time of IPv6 transition tunnel generation or system initialization in advance to perform the path MTU discovery process, such a broadcast packet The goal is to provide an algorithm that does not loop in this network.

According to the present invention, a packet-to-big message format includes: a type field defining a message format; Code fields to subdivide types within the same type; Checksum field for message error checking; An MTU field indicating a packet maximum transmission unit; IP datagram field for actual data; And the value of the code field is 1, the sequence No. provided for comparison with a previously received packet too big message. Contains a field.

In order to achieve the above object, a system for setting a maximum packet transmission unit in an IP-VIX transition tunnel using the packet-to-big message format according to the present invention comprises: Internet Protocol version 6 (IPv6) in an Internet Protocol version 4 (IPv4) network; When a transit tunnel is configured, when setting up the MTU for this tunnel interface, broadcast the packet too big message to the sending node by setting the MTU by reducing the length of the IPv4 header to be encapsulated in the base MTU of that interface. IPv6 transition router; And receiving at least one packet too big message broadcast and transmitted from the IPv6 transition router, fragmenting the packet according to the corresponding MTU information, and broadcasting at least one packet too big message to a previous node corresponding to the sender. It includes the sending IPv6 router.

In addition, the method for setting the maximum packet transmission unit in the IPVIX transition tunnel using the packet-to-big message format according to the present invention for achieving the above object, Internet Protocol version IPv6 (Internet Protocol version 4) in the IPv4 (Internet Protocol version 4) network 6) a transition tunnel is configured; When setting an MTU for a tunnel interface in an IPv6 transition router, broadcasting a packet too big message to a transmitting node by setting an MTU by reducing the length of an IPv4 header to be encapsulated in a basic MTU of the corresponding interface; And a router corresponding to the transmitting node receives the packet too big message, fragments the packet according to the corresponding MTU information, and transmits the packet to the IPv6 transition router.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention.

When configuring an IPv6 transition network, you set up a tunnel to a transition router that performs encapsulation for IPv6 transitions. The MTU for this tunnel interface is the IPv4 header to be encapsulated in the default MTU (1500 bytes for Ethernet) of that interface. It should be set to decrease by the length of 20 bytes.

At this point, the transition router broadcasts an IPv6 packet too big message to all other interfaces on which IPv6 packets will be received except for the tunnel interface.

The router receiving the packet packet too big message processes the packet too big message as shown in FIG. 5.

5 is a schematic block diagram of a case where a packet too big message transmitted during a path MTU discovery process is broadcast before packet reception according to the present invention.

Referring to FIG. 5, when an IPv6 transition router broadcasts a packet too big message to the transmitting nodes, the router receives the packet too big message and transmits the packet too big message to the router corresponding to the transmitting node.

On the other hand, there is no problem in such a network structure, but in a structure in which a loop is generated as shown in FIG.

The system can determine whether the loop occurs when the system administrator or the operator configures the network. Therefore, the packet too big message is repeated by setting the code field values in the packet too big message to different values depending on whether the loop occurs. Can be prevented from being transmitted.

FIG. 6 is a schematic diagram illustrating a case where a loop occurs in a process of broadcasting a packet too big message transmitted during a path MTU discovery process before packet reception according to the present invention.

In the structure in which the loop is generated as shown in FIG. 6, the ICMPv6 packet too big message structure needs to be modified. Looking at the packet too big message structure shown in FIG. 4, since the value of the code field is always 0, the receiver may consider the value of the code field. There was no need. Therefore, the value of the code field can be distinguished from 0 and 1 so that the packet too big message broadcasting method is different in the case of 0 and 1.

In this case, the value of the code field may be set to other values other than 0 and 1, and the present invention will be described by using 0 and 1 as an example.

7 is a diagram illustrating a packet to discovery message format delivered during a path MTU discovery process for implementing the present invention.

Referring to FIG. 7, the type field F1 indicates a value of 2 to indicate a packet too big message type, and the code field F2 indicates a value of 0 or 1 so as to know whether a packet too big message is broadcast. When the checksum field F3, the MTU field F4 and the IP datagram field F5 are provided in the same manner as before, and the value of the code field F2 is 1, a sequence number is added. This allows you to check whether the packet too big message being broadcast is a packet too big message previously received.

If the value of the code field F2 is 0, in this case, the packet too big message is processed in the same manner as before regardless of the sequence number.

Hereinafter, a process of broadcasting a packet too big message in the system of the structure shown in FIG. 5 will be described.

8 is a flowchart illustrating a process of broadcasting a packet too big message before packet reception according to the first embodiment of the present invention.

Referring to FIG. 8, first, an IPv6 transition network is configured, and system initialization for establishing a tunnel in a transition router that performs encapsulation for IPv6 transition is performed (S11).

At this time, when setting the MTU for this tunnel interface, the initialization process should be set to reduce the length (20 bytes) of the IPv4 header to be encapsulated from the default MTU (1500 bytes in Ethernet) of the interface.

As soon as this process is completed, the IPv6 transition router broadcasts a packet too big message to the previous node corresponding to the sender (S12).

After receiving the packet too big message, the node compares the MTU value included in the packet too big message with the path MTU value set in the node, and if the value is different, corrects the path MTU value and fragments the packet according to this value. S13), a packet is transmitted to the IPv6 transition router.

Meanwhile, a process of broadcasting a packet too big message in a structure in which a loop occurs may be divided into two embodiments.

Two embodiments of the present invention provide a method of adding a sequence number to suppress the occurrence of a loop, in which a sequence number is changed for every packet too big message to be broadcast in an IPv6 transition router, and packet too at a router in each node. When a big message is received, the sequence number is increased by one.

First, an embodiment of the former will be described.

9 is a flowchart illustrating a case where a loop is generated in the process of broadcasting a packet too big message before packet reception according to the second embodiment of the present invention.

First, an IPv6 transition network is configured, and system initialization for establishing a tunnel in a transition router performing encapsulation for IPv6 transition is performed (S21).

At this time, when setting the MTU for this tunnel interface, the initialization process should be set to reduce the length (20 bytes) of the IPv4 header to be encapsulated from the default MTU (1500 bytes in Ethernet) of the interface.

As soon as this process is completed, the IPv6 transition router sets the code field (F2) of the packet too big message to 1 and gives the sequence number to broadcast the packet too big message to the previous node corresponding to the sender (S22). ).

The node receiving the packet too big message checks the code field (F2) and if the code field is 0, it broadcasts the packet too big message regardless of the sequence number in the same manner as the conventional method.

However, if the code field F2 is checked and the code field is 1, the sequence number is checked (S23), and the sequence number is compared with the sequence number of the packet too big message previously received (S24).

If the sequence number is the same, compare the MTU value included in the packet too big message with the path MTU value set in the node, and if the value is different, modify the path MTU value and fragment the packet according to this value. Transmit (S25).

If the sequence number is different, the packet too big message is regarded as a previously received packet too big message (discard) (S26).

Through this process, if the packet too big message is pre-broadcasted to the sender node before the packet is transmitted, the packet too big message is returned. Then, the packet is repartitioned to solve the loss during retransmission.

Hereinafter, the latter embodiment will be described.

FIG. 10 is a flowchart illustrating a case where a loop is generated in a process of broadcasting a packet too big message before packet reception according to the third embodiment of the present invention.

First, an IPv6 transition network is configured, and system initialization for establishing a tunnel in a transition router performing encapsulation for IPv6 transition is performed (S31).

At this time, when setting the MTU for this tunnel interface, the initialization process should be set to reduce the length (20 bytes) of the IPv4 header to be encapsulated from the default MTU (1500 bytes in Ethernet) of the interface.

As soon as this process is completed, the IPv6 transition router sets the code field (F2) of the packet too big message to 1 and gives the sequence number to broadcast the packet too big message to the previous node corresponding to the sender (S32). ).

The node receiving the packet too big message checks the code field (F2) and if the code field is 0, it broadcasts the packet too big message regardless of the sequence number in the same manner as the conventional method.

However, if the code field F2 is checked and the code field is 1, the sequence No. is checked (S33) to compare whether the sequence No. is larger than the sequence No. of the packet too big message previously received (S34).

If the sequence No. is larger than the sequence no. Of the packet too big message previously received, compare the MTU value included in the packet too big message with the path MTU value set in the node, and if the value is different, correct the path MTU value (S35). , Sequence No. After increasing the value of the field by 1 (S36), the packet is fragmented and transmitted to the IPv6 transition router (S37).

In S34, the sequence No. of the packet too big message previously received by the sequence No. If not greater than, i.e., equal to or less than, it is regarded as a packet too big message previously received and discarded a packet too big message (S38).

Through this process, if the packet too big message is pre-broadcasted to the sender node before the packet is transmitted, the packet too big message is returned. Then, the packet is repartitioned to solve the loss during retransmission.

Although not described in the first embodiment, the second embodiment and the third embodiment, when the path MTU is set, it is maintained for a certain period of time. After this time, the path MTU value disappears and is changed to the MTU value of the original interface. When the conventional path MTU discovery is performed again, some packets are discarded.

To prevent this, a packet too big message having a code field (F2) value 1 may be periodically transmitted.

In RFC1981, the minimum packet too big message interval is limited to 5 minutes. Therefore, the present invention preferably transmits a packet too big message having a code field value of 1 every 5 minutes.

The present invention can be more effective when the packet passing through the IPv6 transition tunnel is applied to the frequent access network. It also has features that can be used in tunnels such as IPv6-in-IPv6.

Although the preferred embodiments of the present invention have been described in detail above, those skilled in the art will appreciate that the present invention may be modified without departing from the spirit and scope of the invention as defined in the appended claims. It will be appreciated that modifications or variations may be made. Therefore, changes in the future embodiments of the present invention will not be able to escape the technology of the present invention.

As described above, according to the present invention, packet forwarding is delayed and sometimes dropped in the conventional method in which a packet too big message is transmitted after a packet is transmitted by pre-broadcasting a packet too big message when configuring an IPv6 transition network. You can solve the problem.

Claims (20)

When configuring a transition tunnel to configure an IPv6 transition network in an IPv4 network, When setting the maximum trasmission unit (MTU) for the tunnel interface, the MTU is set by subtracting a specific value related to the IPv4 network from the basic MTU, and then a packet too big message including the set MTU value is broadcast to another router. IPv6 transition router; And A packet including at least one IPv6 router that fragments a packet to be transmitted according to MTU information included in a packet too big message transmitted by the IPv6 transition router and broadcasts the received packet too big message to another router. Maximum transmission unit setting system. If an Internet Protocol version 6 (IPv6) transition tunnel is configured in an Internet Protocol version 4 (IPv4) network, when setting the MTU for this tunnel interface, the length of the IPv4 header to be encapsulated in the default MTU of that interface is established. An IPv6 transition router for shortening an MTU by broadcasting a packet too big message to a transmitting node; And At least one transmission that receives a packet too big message that is broadcast and transmitted from an IPv6 transition router, fragments the packet according to the MTU information, and broadcasts a packet too big message to a previous node corresponding to the sender. A system for setting a packet maximum transmission unit in an IPVIX transition tunnel using a packet-to-big message format including a side IPv6 router. The method of claim 2, wherein the packet too big message A type field defining a message format; A code field subdivided according to a network structure in which a loop does not occur in the same type (type) and a network in which the loop occurs; Checksum field for message error checking; An MTU field indicating a packet maximum transmission unit; IP datagram field for actual data; And If the value of the code field is the value that will be present in the network where the loop occurs, the sequence No. provided for comparison with the previously received packet too big message. A system for setting a maximum packet transmission unit in an IPVIX transition tunnel using a packet-to-big message format comprising a field. The method of claim 2, The IPv6 transition router, A system for setting a maximum packet transmission unit in an IPVIX transition tunnel using a packet-to-big message format characterized by periodically broadcasting a packet too big message. The method of claim 2, The IPv6 transition router, In a network structure in which no loop occurs, the code field value in the packet too big message is set to the first value, and in the network structure in which the loop occurs, the code field value in the packet too big message is set to the second value. A system for setting a maximum packet transmission unit in an IPVIX transition tunnel using a packet-to-big message format. The method of claim 2, wherein The at least one IPv6 router, If the code field value in the received packet too big message is the first value, broadcast the packet too big message. If the code field value in the received packet too big message is the second value, the sequence No. Check the value of the field to determine whether it is a previously received packet too big message, and if it is determined that it is a newly received packet too big message, the packet is fragmented according to the MTU information and corresponding to the sender. A system for setting a maximum packet transmission unit in an IPVIX transition tunnel using a packet-to-big message format characterized by broadcasting a packet too big message to a previous node. The method of claim 6, wherein The at least one IPv6 router, If the code field value in the received packet too big message is the first value, broadcast the packet too big message. If the code field value in the received packet too big message is the second value, the sequence No. Checks the value of the field to determine whether it is a previously received packet too big message, and if determined to be the same as a previously received packet too big message, discards the packet too big message. A system for setting the maximum packet transmission unit in an IPVIX transition tunnel using a message format. Configuring an Internet Protocol version 6 (IPv6) transition tunnel in an Internet Protocol version 4 (IPv4) network; When setting an MTU for a tunnel interface in an IPv6 transition router, broadcasting a packet too big message to a transmitting node by setting an MTU by reducing the length of an IPv4 header to be encapsulated in a basic MTU of the corresponding interface; And The router corresponding to the transmitting node receives the packet too big message, fragments the packet according to the MTU information, and transmits the packet to the IPv6 transition router using the packet-to-big message format. How to set the maximum packet transmission unit in. 9. The method of claim 8, wherein the IPv6 transition router broadcasts a packet too big message at regular intervals. 9. The router of claim 8, wherein the router corresponding to the transmitting node is And transmitting a packet too big message to a previous node corresponding to a transmitting side. Configuring an Internet Protocol version 6 (IPv6) transition tunnel in an Internet Protocol version 4 (IPv4) network; When setting the MTU for a tunnel interface in an IPv6 transition router, set the MTU by reducing the length of the IPv4 header to be encapsulated in the default MTU of the interface, set the code field of the packet too big message to 1, and give the sequence number the sending side. Broadcasting a packet too big message to a previous node corresponding to the corresponding node; receiving a packet too big message, checking a code field and checking a sequence number if the code field is 1; Comparing the sequence No. with the sequence No. of the packet too big message previously received; And If the sequence number is the same, compare the MTU value included in the packet too big message with the path MTU value set in the node, and if the value is different, modify the path MTU value and fragment the packet according to this value. A method for setting a maximum packet transmission unit in an IPVIX transition tunnel using a packet-to-big message format including transmitting. 12. The method of claim 11, wherein the IPv6 transition router broadcasts a packet too big message at regular intervals. 12. The packet of claim 11, wherein the node receiving the packet too big message checks the code field and if the code field is 0, broadcasts a packet too big message regardless of the sequence number in the same manner as the conventional method. A method of setting a maximum packet transmission unit in an IPVs transition tunnel using a two-big message format. 12. The method of claim 11, further comprising discarding a packet too big message as a previously received packet too big message if the sequence number is different. How to set the transmission unit. 12. The router of claim 11, wherein the router corresponding to the transmitting node is And transmitting a packet too big message to a previous node corresponding to a transmitting side. Configuring an Internet Protocol version 6 (IPv6) transition tunnel in an Internet Protocol version 4 (IPv4) network; When setting the MTU for a tunnel interface in an IPv6 transition router, set the MTU by reducing the length of the IPv4 header to be encapsulated in the default MTU of the interface, set the code field of the packet too big message to 1, and give the sequence number the sending side. Broadcasting a packet too big message to a previous node corresponding to the corresponding node; receiving a packet too big message, checking a code field and checking a sequence number if the code field is 1; Comparing whether the sequence No. is larger than the sequence No. of the packet too big message previously received; And If the sequence number is large, compare the MTU value included in the packet too big message with the path MTU value set in the node, and if the value is different, correct the path MTU value, and packet fragment the packet according to the IPv6 transition router. A method for setting a maximum packet transmission unit in an IPVIX transition tunnel using a packet-to-big message format including transmitting. 17. The method of claim 16, wherein the IPv6 transition router broadcasts a packet too big message at regular intervals. 17. The packet of claim 16, wherein the node receiving the packet too big message checks the code field and if the code field is 0, broadcasts a packet too big message regardless of the sequence number in the same manner as the conventional method. A method of setting a maximum packet transmission unit in an IPVs transition tunnel using a two-big message format. 17. The method of claim 16, further comprising discarding a packet too big message as a previously received packet too big message if the sequence number is the same or smaller. How to set the maximum packet transmission unit. 17. The router of claim 16, wherein the router corresponding to the sending node is And transmitting a packet too big message to a previous node corresponding to a transmitting side.

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