WO2012159481A1 - Path maximum transmission unit discovery method and node - Google Patents

Abstract

The present invention provides a path maximum transmission unit (PMTU) discovery method and a node. In the method, a source node sends a message at a specified value not larger than a minimum maximum transmission unit of the system, the message carrying a PMTU detection indication; when receiving the message carrying the PMTU detection indication, an intermediate node forwards the message, and feeds back a packet oversized message to the source node, the packet oversized message carrying an egress MTU of the intermediate node; and the source node determines an MTU value of a PMTU route according to the MTU in the packet oversized message. The method and the node solve the problems in the existing IPV6 protocol that the PMTU discovery efficiency is low, the bandwidth is wasted and the PMTU discovery may be easily attacked.

Description

 Path maximum transmission unit discovery method and node

Technical field

 The present invention relates to the field of data communications, and in particular, to a Path Maximum Transmission Unit (PMTU) discovery method and a node in the IPV6 protocol.

Background technique

 With the depletion of IPv4 addresses, a large number of IPv6 network deployments are gradually being put on the agenda. Compared with the IPv4 protocol stack, an important advancement of the IPv6 protocol stack is the support path Maximum Transmission Unit (PMTU), that is, When the IP V6 packet is sent from the source, the length of the packet must be smaller than the Maximum Transmission Unit (MTU) of the entire path. Therefore, the packet does not need to be fragmented when passing through the intermediate node, which improves the packet of the network device. Forwarding efficiency. The implementation principle of the PMTU is shown in Figure 1. When a packet is sent from the source node, the MTU fragment of the route is used. The default MTU value of the route is the MTU of the outbound interface. If the MTU is compared with the packet when the intermediate node forwards the packet. If the packet size is small, the packet is discarded, and an excessively large packet of the Internet Control Message Protocol Version 6, ICMPv6 error packet is sent to the source node, and the MTU value of the outbound interface is carried. If the source node does not have a packet with a destination address, the source node creates a host route with the destination address of the packet. The MTU value of the route is the MTU value carried in the packet. The host route is compared with the MTU value. If the MTU value becomes smaller, the MTU value of the route is directly modified. After several rounds of interaction, you can learn the minimum MTU of the entire path, that is, the PMTU. When the next retransmission message is sent, it will be fragmented according to the PMTU to ensure that the intermediate node is not fragmented.

At present, the implementation of the PMTU function of the IPv6 protocol stack may require multiple message interactions to complete a single discovery. When there are n nodes, the limit situation sends a message from the first node to the nth node, which requires interaction 2* (n-2) packets can complete a PMTU learning. In fact, the intermediate node needs to receive a forwarding packet and return an ICMPv6 packet with a large packet. In this way, when there are more intermediate nodes, the learning time is longer, and Request For Comments (RFC) specifies the learned PMTU information. The effective time is only 10 minutes. After 10 minutes, it will be deleted, and then the package will be sent later. Need to relearn, there will be a message for a period of time because of MTU The problem is forwarding packets. Therefore, the current PMTU learning mechanism, when the network MTU is decremented hop by hop, the learning convergence of the PMTU is slow, and on the distributed device, the PMTU convergence of the whole machine is slower (because the inter-board communication is also more), these problems are given. The system brings extra overhead and wastes the bandwidth of the system.

 At the same time, there is another attack in the network for learning PMTU. By forging packets and over-receiving packets, the PMTU error is learned, causing network performance degradation or denial of service attacks.

Summary of the invention

 The embodiment of the invention provides a path maximum transmission unit discovery method and a node, which solves the problem that the PMTU discovery efficiency is low, the bandwidth is wasted, and the attack is easy to be attacked in the current IPV6 protocol.

 In order to solve the above problem, an embodiment of the present invention provides a path maximum transmission unit discovery method, including:

 The source node finds whether there is a corresponding PMTU route for the to-be-sent packet. When the PMTU route does not exist, the maximum transmission unit (MTU) value of the PMTU route is set to a specified value. When the MTU value of the found PMTU route is invalid. The MTU value of the PMTU route that is found by the update is a specified value, and the specified value is not greater than the minimum MTU value of the system. When it is determined that the length of the to-be-sent document is greater than the specified value, the specified value is used to Sending a packet to perform fragmentation processing, and sending a PMTU probe packet carrying a PMTU detection indication;

 When receiving the PMTU detection packet, each intermediate node forwards the PMTU detection packet, and sends a packet oversized message to the source node, where the oversized packet carries the intermediate node. MTU value of the outgoing interface;

 The source node receives the oversized packet returned by each intermediate node, and determines the MTU value of the PMTU route according to the MTU value carried in the oversized packet.

 Optionally, the method further includes

 When the length of the to-be-sent packet is not greater than the specified value, the packet to be sent is directly sent; and, when the source node finds the corresponding PMTU route and the PMTU for the to-be-sent packet When the MTU value of the route is valid, and the length of the to-be-sent packet is not greater than the valid MTU value, the to-be-sent packet is directly sent.

Optionally, the packet carries the PMTU detection indication in the following manner: The hop-by-hop option header is carried in the hop-by-hop option header, and the option carries an option, which is a PMTU detection indication, and the option is a route alert option or a new option.

 Optionally, the above method may also have the following features.

 When the source node does not find the corresponding PMTU route and establishes the PMTU route, the method further includes: establishing a PMTU cache entry corresponding to the established PMTU route; when the MTU value of the found PMTU route is invalid When the PMTU route is updated, the method further includes: updating a PMTU cache entry corresponding to the updated PMTU route;

 And setting an MTU of the established or updated PMTU cache entry to an MTU of the egress node found by the source node;

 The step of determining, by the source node, the MTU value of the corresponding PMTU route according to the MTU value carried in the oversized packet includes:

 After receiving the oversized packet returned by the intermediate node, the source node extracts the MTU value in the oversized packet and searches for the corresponding PMTU cache entry, if the extracted MTU value is smaller than the PMTU cache. The MTU value in the entry replaces the MTU value in the PMTU cache entry with the extracted MTU value, and does not process if the extracted MTU value is not less than the MTU value in the PMTU cache entry;

 After processing the oversized packet returned by all the intermediate nodes, the source node uses the MTU value of the PMTU to discover.

 Optionally, the above method may also have the following features.

 After receiving the oversized packet, the source node discards the oversized packet if the corresponding PMTU cache entry is not found.

 Optionally, the above method may also have the following features.

 Set learning time, effective time and aging time;

 After the source node sends the packet carrying the PMTU detection indication, the source node sets the corresponding PMTU cache entry to the learning state.

If the source node completes the MTU value discovery of the PMTU route in the learning time from the learning state, setting the state of the PMTU cache entry to a valid state, if The source node does not complete the MTU value discovery of the PMTU route, and sets the state of the PMTU cache entry to an aging state; when the valid state starts to exceed the valid time, the PMTU cache entry is set to an aging state; When the aging time is exceeded, the PMTU cache entry and its corresponding PMTU route are deleted.

 Optionally, the above method may also have the following features.

 The source node performs fragmentation processing on the MTU value of the PMTU route when the source node finds the corresponding PMTU route and the PMTU route corresponding to the PMTU route of the PMTU route is aging. Sending a packet carrying the PMTU detection indication, and setting a corresponding PMTU cache entry to a learning state;

 When the PMTU cache entry corresponding to the PMTU route is in a learning state or a valid state, the packet is processed by the MTU value of the PMTU route, and the packet is sent.

 The embodiment of the present invention further provides a node, including a message sending unit and a message receiving unit, where:

 The message sending unit is configured to: when the node is used as a source node, find, for the to-be-transmitted message, whether there is a corresponding path maximum transmission unit (PMTU) route, and when there is no need to establish a PMTU route, set the PMTU route. The maximum transmission unit (MTU) value is a specified value. When the MTU value of the found PMTU route is invalid, the MTU value of the found PMTU route is updated to a specified value, and the specified value is not greater than the minimum MTU value of the system. When it is determined that the length of the to-be-sent packet is greater than the specified value, the packet is fragmented by the specified value, and the PMTU detection packet carrying the PMTU detection indication is sent;

 The packet receiving unit is configured to: when receiving an oversized packet returned by each intermediate node, determine an MTU value of the corresponding PMTU route according to the MTU value carried in the oversized packet.

 Optionally, the foregoing node may also have the following features.

The packet sending unit is further configured to: determine whether the length of the to-be-sent packet is less than or equal to the specified value, and directly send the to-be-sent when the length of the to-be-sent packet is not greater than the specified value And when the node is the source node, when the corresponding PMTU route is found for the to-be-sent packet, and the MTU value of the PMTU route is valid, and the length of the to-be-sent packet is not When the valid MTU value is greater than the valid MTU value, the to-be-sent packet is directly sent.

 Optionally, the foregoing node may also have the following features.

 The packet sending unit is configured to carry the PMTU detection indication in the following manner: carrying a hop-by-hop option header in the ^^ text, the hop-by-hop option header carries an option, where the option carries a PMTU detection indication, The option is the route alert option or a new option.

 Optionally, the foregoing node may also have the following features.

 The message sending unit is further configured to: when a PMTU route is established by not finding a corresponding PMTU route, establishing a PMTU cache entry corresponding to the established PMTU route, when the MTU value of the found PMTU route is invalid When the PMTU route is updated, updating the PMTU cache entry corresponding to the updated PMTU route; and setting the MTU value of the PMTU cache entry to the MTU of the outbound node found by the source node;

 The message receiving unit is configured to determine an MTU value of the corresponding PMTU route according to the following manner:

 After receiving the oversized packet returned by the intermediate node, extracting the MTU value in the oversized packet and searching for the corresponding PMTU cache entry, if the extracted MTU value is smaller than the MTU in the PMTU cache entry. And replacing the MTU value in the PMTU cache entry with the extracted MTU value, and if the extracted MTU value is not less than the MTU value in the PMTU cache entry, not processing;

 After processing the oversized packet returned by all the intermediate nodes, the MTU value of the corresponding PMTU route is updated by using the MTU value of the PMTU cache entry, and the MTU value of the PMTU route is found.

 Optionally, the foregoing node may also have the following features.

 After receiving the oversized packet, the packet receiving unit discards the oversized packet if the corresponding PMTU cache entry is not found.

 Optionally, the foregoing node may also have the following features.

The sending unit of the message is further configured to: set the learning time, the effective time, and the aging time; after sending the packet carrying the PMTU detection indication, set the corresponding PMTU cache entry to the learning state; If the MTU value discovery of the PMTU route is completed within the learning time from the learning state, the state of the PMTU cache entry is set to a valid state, and if the MTU value discovery of the PMTU route is not completed, the PMTU is The status of the cache entry is set to the aging state;

 Setting the PMTU cache entry to an aging state when the valid time is exceeded from the valid state;

 Deleting the PMTU cache entry and the PMTU route when the aging time is exceeded from the aging state;

 When the node is the source node, the corresponding PMTU route is found for the to-be-sent packet, and the MTU value of the PMTU route is valid, and the length of the to-be-sent packet is greater than the MTU value of the PMTU route:

 When the PMTU cache entry corresponding to the PMTU route is in an aging state, the packet is processed by using the MTU value of the PMTU route, and the packet carrying the PMTU detection indication is sent, and the corresponding PMTU cache entry is set to the learning state. ;

 When the PMTU cache entry corresponding to the PMTU route is in a learning state or a valid state, the MTU value of the PMTU route is fragmented and sent.

 Optionally, the foregoing node may also have the following features.

 The node further includes a forwarding processing unit, and the forwarding processing unit is configured to: when receiving the packet carrying the PMTU detection indication, when the node is not the destination node of the packet, forwarding the packet, and sending the packet is too large The packet is sent to the source node of the packet, and the oversized packet carries the MTU of the outbound interface found on the node.

 In the embodiment of the present invention, the PMTU discovery process solves the problem of data packet loss in the PMTU learning process, reduces the number of packet interactions in the PMTU learning process, and learns the packet loss problem after the PMTU ages, and also solves the PMTU learning process. Security issues in the classroom have improved the efficiency and reliability of PMTU learning.

BRIEF abstract

 Figure 1 is a schematic diagram of an IPv6 path MTU discovery;

2 is a schematic diagram of a format of a hop-by-hop option; Figure 3 is a schematic diagram of the format of the route alert option;

 4 is a schematic diagram of an option format defined in an embodiment of the present invention;

 FIG. 5 is a diagram of a state transition of a PMTU cache entry provided by an embodiment; FIG.

 6 is a schematic diagram of PMTU discovery provided by an embodiment of the present invention;

 7 is a flowchart of a source node sending process provided by an embodiment;

 FIG. 8 is a flowchart of a source node receiving process provided by an embodiment.

Preferred embodiment of the invention

 Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that, in the case of no conflict, the features in the embodiments and the embodiments in the present application may be arbitrarily combined with each other.

 In the embodiment of the present invention, the source node sends the packet with the specified value of the maximum transmission unit that is not greater than the smallest transmission unit, and the packet carries the PMTU detection indication. When the intermediate node receives the packet carrying the PMTU detection indication, the intermediate node forwards the packet. And the feedback packet is oversized to the source node, and the oversized packet carries the MTU of the outbound interface of the intermediate node, and the source node determines the MTU value of the PMTU route according to the MTU in the oversized packet.

 An embodiment of the present invention provides a path maximum transmission unit discovery method, including:

 The source node finds whether there is a corresponding PMTU route for the to-be-sent packet. If the MTU value of the PMTU route is invalid or not found, the MTU value of the PMTU route is established or updated. The specified value is not greater than the minimum value of the system. The maximum transmission unit performs fragmentation processing on the packet with a specified value, and sends a packet carrying the PMTU detection indication.

 When receiving the packet carrying the PMTU detection indication, each intermediate node forwards the packet, and sends a packet oversized message to the source node, where the oversized packet carries the intermediate node and is found. MTU of the outgoing interface;

 The source node receives the oversized packet returned by each intermediate node, and determines the MTU value of the corresponding PMTU route according to the MTU value carried in the oversized packet.

The source node finds a corresponding PMTU route and sends the PMTU route to the to-be-sent packet. The value is sent directly to the to-be-sent packet. If the MTU value of the corresponding PMTU route is not found, and the length of the to-be-sent packet is not greater than the specified value, the direct transmission is performed. The message to be sent is mentioned. This can avoid PMTU learning when small messages are used, reducing the waste of system routing and PMTU storage space.

 The PMTU detection indication is carried in the following manner: The hop-by-hop option header is carried in the packet, and the hop-by-hop option header carries an option, where the option carries a PMTU detection indication, and the option is a route alert option. Or add options. The sent message includes the following information: the basic message header, the hop-by-hop option header containing the PMTU detection indication, and the fragmented message to be sent.

 In the IPv6 basic protocol stack, a hop-by-hop option header is defined. The format of this option is shown in Figure 2. Its main function is to require every node in the packet transmission process to check. The hop-by-hop option message can carry one or more TLV (Type-Length-Value, type-length-data) encoding options. One of the most important options is the route alert option. This route alert option is required to pass The router, but the destination address is not the packet processing of the router. The format is as shown in Figure 3. The 2-byte data (network sequence) is currently defined as follows: 0 indicates that the message is an MLD (Multicast Detect). Listener found agreement) message

 1 indicates that the message is an RSVP (Resource Reservation Protocol) message.

 2 indicates that the message is an active network protocol message.

 3-65535 Reserved to be assigned

 In the embodiment of the present invention, a route alert data is newly defined, and any one of 3-65535 is used, for example, as a PMTU detection indication, indicating that the packet is a PMTU detection packet.

 You can also use the new option to carry the PMTU detection indication. For example, you can define an option that is parallel to the route alert. This option is also an option for the hop-by-hop option. The option format is also TLV. As shown in Figure 4, the type can be Choose one from the current reservation, such as 8 and so on.

 If the source node does not find the corresponding PMTU route or the MTU value of the found PMTU route is invalid, the PMTU cache entry corresponding to the PMTU route is also established or updated, and the MTU value of the PMTU cache entry is set. Describe the MTU of the egress node found by the source node;

Determining, by the source node, the MTU value of the corresponding PMTU route according to the MTU value carried in the packet oversized packet includes: After receiving the oversized packet returned by the intermediate node, the source node extracts the MTU value in the oversized packet and searches for the corresponding PMTU cache entry, if the extracted MTU value is smaller than the PMTU cache. The MTU value in the entry replaces the MTU value in the PMTU cache entry with the extracted MTU value, and does not process if the extracted MTU value is not less than the MTU value in the PMTU cache entry;

 After processing all the intermediate nodes, the source node updates the MTU value of the corresponding PMTU route by using the MTU value of the PMTU cache entry, and completes the MTU value discovery of the PMTU route.

 The source node, when receiving the feedback packet of the destination node, determines that the packet that has been returned by all the intermediate nodes has been processed. The feedback packet of the destination node may be a packet oversized message or other indication packet, indicating that the probe arrives at the terminal. If the packet is too large, the packet may be sent to the source node to notify the source node of the PMTU to reach the destination. The specified MTU value, for example, 0, indicating that the packet is too large is the destination node. Returned, of course, the MTU value can also be any value. The source node determines the PMTU detection to reach the end point by the same source address in the text returned by the destination node and the destination address detected by the source node.

 If the source node receives the packet with a large packet, if the corresponding PMTU cache entry is not found, the source node discards the oversized packet. This method can prevent illegal packet attacks. Because the PMTU cache entry of the embodiment of the present invention is generated before the PMTU probe message, if it is a legal message, the PMTU cache entry can be found according to the returned packet oversized message. If it is not found, it can be considered as an illegal message.

 The learning time, the effective time, and the aging time are also set for the PMTU cache entry. After the source node sends the packet carrying the PMTU detection indication, the corresponding PMTU cache entry is set to the learning state.

 If the source node completes the MTU value discovery of the PMTU route from the learning time starting from the learning state, setting the state of the PMTU cache entry to a valid state, if the source node does not complete the PMTU route The MTU value is found to set the state of the PMTU cache entry to an aging state;

Setting the PMTU cache entry to an aging state when the valid state starts to exceed the valid time; The PMTU cache entry and the PMTU route are deleted when the aging time is exceeded from the aging state. The transition between states is shown in Figure 5.

 The source node finds a corresponding PMTU route for the to-be-sent packet, and the PMTU path is fragmented by the MTU value of the PMTU route when the PMTU cache entry corresponding to the PMTU route is in an aging state. Processing, sending a packet carrying the PMTU detection indication, and setting the corresponding PMTU cache entry to a learning state;

 When the PMTU cache entry corresponding to the PMTU route is in a learning state or a valid state, the packet is processed by the MTU value of the PMTU route, and the packet is sent.

As shown in FIG. 6, it is a schematic diagram of PMTU discovery according to an embodiment of the present invention.

 Take three intermediate nodes as an example, including:

 If the source node does not exist or the MTU value of the found PMTU route is invalid, the packet is fragmented by the specified value, and the packet is sent. The packet carries the PMTU detection indication. In this embodiment, the specified value is the minimum. Maximum transmission unit 1280;

 When receiving the packet carrying the PMTU detection indication, the intermediate node R1 forwards the packet, and returns a packet with a large packet to the source node, and the packet has an outgoing interface MTU value of 1450;

 The intermediate node R2, when receiving the packet carrying the PMTU detection indication forwarded by the R1, forwards the packet, and returns a packet with a large packet to the source node, and the packet has an outgoing interface MTU value of 1400;

 The intermediate node R3, when receiving the packet carrying the PMTU detection indication forwarded by the R2, forwards the packet, and returns a packet with a large packet to the source node, and the packet has an outgoing interface MTU value of 1300;

 When receiving the packet carrying the PMTU detection indication forwarded by the R3, the destination node processes the packet, and returns a packet with a large packet to the source node, carrying the MTU value =0;

 The source node processes the large packets of each packet and obtains the MTU of the PMTU route as 1300.

An embodiment of the present invention provides a PMTU discovery method, including:

Step 1: The source node performs >3⁄4 text transmission; As shown in Figure 7, it includes:

 When the source node sends out an IPv6 packet, the route is checked. The PMTU route is found and the MTU value of the PMTU route is valid. That is, the minimum MTU of the system is <= route ΜΎΌ<= the MTU of the outbound interface of the node, and the MTU value of the PMTU route is taken. It is the maximum transmission unit of the fragment (FMTU for short); it determines whether the length of the packet to be sent is less than or equal to the FMTU, and if so, directly sends the packet, and if not, sends the fragment according to the FMTU;

 If the corresponding PMTU route is not found, the specified value is the FMTU. In this embodiment, the minimum MTU value of the system is 1280. The length of the packet to be sent is less than or equal to the FMTU. If yes, the packet is sent directly. If no, the PMTU route and the PMTU cache entry are generated, the MTU value of the PMTU route is set to the specified value, the MTU value of the PMTU cache entry is set to the MTU value of the outbound interface of the source node, and the PMTU probe packet is constructed, according to the FMTU. Fragment transmission, and set the state of the PMTU cache entry to the learning state;

 If the corresponding PMTU route is found but the MTU value of the PMTU route is invalid, the specified value is the FMTU. In this embodiment, the minimum MTU value of the system is 1280, and the length of the to-be-sent packet is less than or equal to the FMTU. If yes, the PMTU route and the PMTU cache entry are updated. The MTU value of the PMTU route is set to the specified value, and the MTU value of the PMTU cache entry is set to the MTU value of the outbound interface of the source node to construct the PMTU. The probe packet is sent according to the FMTU; the PMTU cache entry status is set to the learning state.

 Step 2: The intermediate node receives the packet, and determines whether the packet carries the PMTU detection indication. If yes, the packet is forwarded, and then the source node returns an ICMPv6 packet oversized message, and the MTU returned by the packet is too large. The MTU of the outbound interface that is found on the intermediate node, that is, the MTU value of the outgoing interface. If no, it is processed according to the normal process, forwarded or processed locally.

 Wherein, it is determined according to the following manner whether to carry the PMTU detection indication:

During the packet forwarding process, the intermediate node finds that the IPv6 packet carries the hop-by-hop option header, and then sends the packet to the IPv6 protocol stack for processing. The IPv6 protocol stack parses the hop-by-hop option header to further determine whether the route alert option is included, and then determines whether the route alert option is the type of the defined PMTU learning. If yes, the packet carries the PMTU detection indication. Of course, if the new option is used to carry the PMTU indication, it is determined whether the new option is carried in the message. Step 3: After receiving the packet carrying the PMTU detection indication, the destination node is similar to the intermediate node. The difference is that the packet is not forwarded to the source node and is returned to the ICMPv6 packet of the source node. The MTU value is 0.

 Step 4: The source node receives the packet with too large a packet, and determines the PMTU route according to the MTU value in the oversized packet.

 As shown in Figure 8, it includes:

 The source node receives the packet with a large packet, and extracts the MTU value in the packet with the oversized packet. The PMTU cache entry is searched according to the destination address of the original packet that generated the packet with too large packet. If not found, the attack is considered as attack 4艮文, discard the 4 艮文.

 If the corresponding PMTU cache entry is found, and the MTU obtained in the oversized packet is not 0.

(Indicating that the packet returned by the intermediate node is too large), and the PMTU cache entry learning state does not time out, then the MTU size in the MTU and the PMTU cache entry is determined. If the extracted MTU is smaller than the MTU in the PMTU cache entry, then Replace the MTU in the PMTU cache entry with the removed MTU. If the MTU is not smaller than the MTU in the PMTU cache entry, it will not be processed. If the MTU of the packet is too large, the MTU is 0 (indicating that the packet returned by the destination node) The large message, the probe has reached the end point, the MTU of the corresponding PMTU route is updated by the MTU of the PMTU cache entry, and the PMTU cache entry status is set to a valid state to complete the PMTU discovery.

 Step 5: After the source node learns the PMTU, it sends the packet according to the learned PMTU.

 When the PMTU is valid, the PMTU cache entry enters the aging state; and if the PMTU cache entry learning state times out, the feedback message returned by the destination node has not been received (for example, no packet with an MTU of 0 is received). The PMTU has not been learned yet, and the PMTU cache entry enters an aging state;

 After entering the aging state, if the flow continues to be sent, the PMTU sends the PMTU detection indication according to the FMTU. The PMTU cache entry enters the learning state and repeats the above PMTU learning process. The aging state times out, indicating that there is no packet during the aging period. Send, delete the PMTU cache entry and the corresponding PMTU route. The aging timer can be used for timing.

The PMTU discovery is performed in the embodiment of the present invention, and the data packet loss in the PMTU learning process is solved. The packet problem reduces the number of packet interactions in the PMTU learning process and the problem of packet loss after PMTU aging. It also solves the security problem in the PMTU learning process and improves the efficiency and reliability of PMTU learning.

 Obviously, those skilled in the art should understand that the above modules or steps can be implemented by a general-purpose computing device, which can be concentrated on a single computing device or distributed over a network composed of multiple computing devices. Alternatively, they may be implemented by program code executable by the computing device, such that they may be stored in the storage device by the computing device, or they may be fabricated into individual integrated circuit modules, or multiple of them Modules or steps are made in a single integrated circuit module. Thus, embodiments of the invention are not limited to any particular combination of hardware and software.

Industrial applicability

 In the embodiment of the present invention, the PMTU discovery process solves the problem of data packet loss in the PMTU learning process, reduces the number of packet interactions in the PMTU learning process, and learns the packet loss problem after the PMTU ages, and also solves the PMTU learning process. Security issues in the classroom have improved the efficiency and reliability of PMTU learning.

Claims

Claim  1. A path maximum transmission unit (PMTU) discovery method, comprising:  The source node finds whether there is a corresponding PMTU route for the to-be-sent packet. When the PMTU route does not exist, the maximum transmission unit (MTU) value of the PMTU route is set to a specified value. When the MTU value of the found PMTU route is invalid. The MTU value of the PMTU route that is found by the update is a specified value, and the specified value is not greater than the minimum MTU value of the system. When it is determined that the length of the to-be-sent document is greater than the specified value, the specified value is used to Sending a packet to perform fragmentation processing, and sending a PMTU probe packet carrying a PMTU detection indication;  When receiving the PMTU detection packet, each intermediate node forwards the PMTU detection packet, and sends a packet oversized message to the source node, where the oversized packet carries the intermediate node. MTU value of the outgoing interface;  The source node receives the oversized packet returned by each intermediate node, and determines the MTU value of the PMTU route according to the MTU value carried in the oversized packet.  2. The method of claim 1 further comprising  When it is determined that the length of the to-be-sent packet is not greater than the specified value, directly sending the to-be-sent packet; and,  When the source node finds the corresponding PMTU route for the to-be-transmitted message, and the MTU value of the PMTU route is valid, and the length of the to-be-sent packet is not greater than the valid MTU value, directly sending the to-be-sent Send a message.  3. The method of claim 1, wherein the message carries the PMTU detection indication in the following manner:  The hop-by-hop option header is carried in the hop-by-hop option header, and the option carries the PMTU detection indication, and the option is a route alert option or a new option.  4. The method of claim 1, wherein When the source node does not find the corresponding PMTU route and establishes the PMTU route, the method further includes: establishing a PMTU cache entry corresponding to the established PMTU route; when the MTU value of the found PMTU route is invalid When the PMTU route is updated, the method further includes: updating a PMTU cache entry corresponding to the updated PMTU route; And setting the MTU value of the established or updated PMTU cache entry to the MTU of the egress node found by the source node;  The step of determining, by the source node, the MTU value of the corresponding PMTU route according to the MTU value carried in the oversized packet includes:  After receiving the oversized packet returned by the intermediate node, the source node extracts the MTU value in the oversized packet and finds the corresponding PMTU cache entry, when the extracted MTU value is smaller than the PMTU. When the MTU value in the entry is cached, the MTU value in the PMTU cache entry is replaced by the extracted MTU value, and is not processed when the extracted MTU value is smaller than the MTU value in the PMTU cache entry;  After processing the oversized packet returned by all the intermediate nodes, the source node uses the MTU value of the PMTU to discover.  5. The method of claim 4, further comprising:  After the source node receives the packet oversized message, if the corresponding PMTU cache entry is not found, the packet is discarded.  6. The method of claim 4, further comprising:  Set learning time, effective time and aging time;  After the source node sends the packet carrying the PMTU detection indication, the source node sets the corresponding PMTU cache entry to the learning state.  If the source node completes the MTU value discovery of the PMTU route during the learning time from the learning state, setting the state of the PMTU cache entry to a valid state, if the source node does not complete the PMTU route The MTU value is found to set the state of the PMTU cache entry to an aging state;  Setting the PMTU cache entry to an aging state when the valid state is exceeded;  When the aging time exceeds the aging time, the PMTU cache entry and its corresponding PMTU route are deleted. 7. The method of claim 6 further comprising: When the source node finds the corresponding PMTU route for the to-be-transmitted message and the PMTU cache entry corresponding to the PMTU route of the PMTU route is in an aging state, the MTU value of the PMTU route is used to fragment the packet. Processing, sending a packet carrying the PMTU detection indication, and setting the corresponding PMTU cache entry to a learning state;  When the PMTU cache entry corresponding to the PMTU route is in a learning state or a valid state, the packet is processed by the MTU value of the PMTU route, and the packet is sent.  8. A node, comprising a message sending unit and a message receiving unit, wherein:  The message sending unit is configured to: when the node is used as a source node, find, for the to-be-transmitted message, whether there is a corresponding path maximum transmission unit (PMTU) route, and when there is no need to establish a PMTU route, set the PMTU route. The maximum transmission unit (MTU) value is a specified value. When the MTU value of the found PMTU route is invalid, the MTU value of the found PMTU route is updated to a specified value, and the specified value is not greater than the minimum MTU value of the system. When it is determined that the length of the to-be-sent packet is greater than the specified value, the packet is fragmented by the specified value, and the PMTU detection packet carrying the PMTU detection indication is sent;  The packet receiving unit is configured to: when receiving an oversized packet returned by each intermediate node, determine an MTU value of the corresponding PMTU route according to the MTU value carried in the oversized packet.  9. The node according to claim 8, wherein  The packet sending unit is further configured to: determine whether the length of the to-be-sent packet is less than or equal to the specified value, and directly send the to-be-sent when the length of the to-be-sent packet is not greater than the specified value And the MTU value of the PMTU route is valid, and the length of the to-be-sent packet is not greater than the valid MTU, when the node is the source node, and the corresponding PMTU route is found for the to-be-sent packet. The value is sent directly to the to-be-sent message.  10. The node according to claim 8, wherein  The packet sending unit is configured to carry the PMTU detection indication by: carrying a hop-by-hop option header in the packet, where the hop-by-hop option header carries an option, where the option carries the PMTU detection indication, The option is a route alert option or a new option. 11. The node according to claim 8, wherein The message sending unit is further configured to: when a PMTU route is established by not finding a corresponding PMTU route, establishing a PMTU cache entry corresponding to the established PMTU route, when the MTU value of the found PMTU route is invalid When the PMTU route is updated, the PMTU cache entry corresponding to the updated PMTU route is updated;  And setting an MTU value of the PMTU cache entry to the egress node of the source node MTU;  The message receiving unit is configured to determine an MTU value of the corresponding PMTU route according to the following manner:  After receiving the oversized packet returned by the intermediate node, extracting the MTU value in the oversized packet and finding the corresponding PMTU cache entry, if the extracted MTU value is smaller than the PMTU cache entry. The MTU value is used to replace the MTU value in the PMTU cache entry with the extracted MTU value, and if the extracted MTU value is not less than the MTU value in the PMTU cache entry, it is not processed;  After processing the oversized packet returned by all the intermediate nodes, the MTU value of the corresponding PMTU route is updated by using the MTU value of the PMTU cache entry, and the MTU value of the PMTU route is found.  12. The node according to claim 11, wherein  After receiving the oversized packet, the packet receiving unit discards the oversized packet if the corresponding PMTU cache entry is not found.  13. The node according to claim 11, wherein  The sending unit of the message is further configured to: set a learning time, an effective time, and an aging time; after sending the message carrying the PMTU detection indication, setting the corresponding PMTU cache entry to a learning state; If the MTU value discovery of the PMTU route is completed within the learning time from the learning state, the state of the PMTU cache entry is set to a valid state, and if the MTU value discovery of the PMTU route is not completed, the The state of the PMTU cache entry is set to an aging state; when the valid state is exceeded, the PMTU cache entry is set to an aging state; Deleting the PMTU cache entry and its corresponding PMTU route when the aging time is exceeded from the aging state;  When the node is the source node, the corresponding PMTU route is found for the to-be-sent packet, and the MTU value of the PMTU route is valid, and the length of the to-be-sent packet is greater than or equal to the MTU value of the PMTU route:  When the PMTU cache entry corresponding to the PMTU route is in an aging state, the packet is processed by using the MTU value of the PMTU route, and the packet carrying the PMTU detection indication is sent, and the corresponding PMTU cache entry is set to the learning state. ;  When the PMTU cache entry corresponding to the PMTU route is in a learning state or a valid state, the packet is processed by the MTU value of the PMTU route, and the packet is sent.  The node according to claim 8, further comprising a forwarding processing unit, wherein the forwarding processing unit is configured to: when receiving the packet carrying the PMTU detection indication, when the node is not the destination node of the packet And forwarding the packet, and sending a packet with a large packet to the source node of the packet, where the oversized packet carries the MTU of the outbound interface found on the node.