CN101977156B - Method, device and routing equipment for learning maximum transmission unit - Google Patents

Abstract

Translated fromChinese

本发明公开了一种最大传输单元的学习方法、装置及路由设备，该方法包括：接收IPv6报文传输隧道中上游BGP邻居通告的到达IPv6网络的BGP路由信息；该BGP路由信息中携带有上游BGP邻居确定出的到达IPv6网络的路由的第一MTU；对该BGP路由信息携带的BGP路由下一跳对应的第二MTU进行探测；比较第一MTU与第二MTU的大小，将较小值作为确定出的到达IPv6网络的BGP路由的第三MTU并保存；在确定该隧道中还存在下游BGP邻居时，将第三MTU携带在到达该IPv6网络的BGP路由信息中并通告至下游BGP邻居。本发明解决了IPv6报文在传输过程中传输受阻以及被多次分片导致的报文转发效率低的问题。

The invention discloses a maximum transmission unit learning method, device and routing equipment. The method includes: receiving the BGP routing information to reach the IPv6 network notified by the upstream BGP neighbor in the IPv6 message transmission tunnel; the BGP routing information carries the upstream The first MTU of the route to the IPv6 network determined by the BGP neighbor; the second MTU corresponding to the next hop of the BGP route carried by the BGP routing information is detected; the size of the first MTU and the second MTU is compared, and the smaller value As the third MTU of the determined BGP route to the IPv6 network and save it; when it is determined that there is still a downstream BGP neighbor in the tunnel, carry the third MTU in the BGP route information to the IPv6 network and notify the downstream BGP neighbor . The invention solves the problems that the transmission of the IPv6 message is blocked in the transmission process and the message forwarding efficiency is low caused by multiple fragments.

Description

Translated fromChinese

一种最大传输单元的学习方法、装置及路由设备A learning method, device and routing equipment for maximum transmission unit

技术领域technical field

本发明涉及计算机网络通信技术领域，尤其涉及一种最大传输单元MTU的学习方法、装置及路由设备。The present invention relates to the technical field of computer network communication, in particular to a learning method, device and routing equipment of a maximum transmission unit (MTU).

背景技术Background technique

现有互联网协议版本6(IPv6)网络作为下一代网络，目前尚未完全普及，仍然作为孤岛网络分散在互联网协议版本4(IPv4)网络之中。为了实现这些IPv6网络能够通过IPv4网络实现互联互通，一般采用隧道技术，如利用互联网协议版本4-多协议标签交换(IPv4-MPLS)网络提供IPv6报文传输隧道，从而实现IPv6孤岛网络的互联互通，互联网工程任务组(The Internet EngineeringTask Force，IETF)为该方案制定了相应的标准，称其为IPv6运营商边界(IPv6Provider Edge，6PE)方案。The existing Internet Protocol Version 6 (IPv6) network, as the next generation network, has not yet been fully popularized, and is still scattered in the Internet Protocol Version 4 (IPv4) network as an island network. In order to realize the interconnection and intercommunication of these IPv6 networks through the IPv4 network, tunnel technology is generally used, such as using the Internet Protocol Version 4-Multiprotocol Label Switching (IPv4-MPLS) network to provide IPv6 message transmission tunnels, thereby realizing the interconnection and intercommunication of IPv6 isolated island networks , The Internet Engineering Task Force (The Internet Engineering Task Force, IETF) has developed a corresponding standard for this scheme, which is called the IPv6 Provider Edge (IPv6 Provider Edge, 6PE) scheme.

图1所示是采用6PE方案实现IPv6网络互联的一个具体例子，该例子为单个自治域(Autonomous System，AS)内的IPv6网络的互联互通，在图1中，路由设备6PE-1、6PE-2、运营商路由器(Provider，简称P)和6PE-3组成了整个IPv4MPLS网络，其中P设备为网络中IPv4单协议栈路由设备，其他各设备均支持IPv6、IPv4双协议栈。6PE-1、6PE-2、6PE-3之间通过内部边界网关协议(Internal Border Gateway Protocol，IBGP)分发带标签的IPv6路由信息，以6PE-1通告IPv6网络地址S1为例，6PE-1通过多协议内部边界网关协议(Multiprotocol-IBGP，MP-IBGP)协议向6PE-3通告带标签的IPv6路由，网络地址为S1，对应的标签值为L1，6PE-3在收到该标签路由之后，将添加IPv6路由，出标签为L1，下一跳为6PE-1，这样IPv6S3网络中即存在到达S1的IPv6路由了。同样的原理可以实现S1、S2、S3之间IPv6路由互联互通。Figure 1 shows a specific example of using the 6PE solution to realize IPv6 network interconnection. This example is the interconnection and intercommunication of IPv6 networks in a single autonomous domain (Autonomous System, AS). In Figure 1, routing devices 6PE-1, 6PE- 2. The provider router (Provider, referred to as P) and 6PE-3 form the entire IPv4 MPLS network. The P device is an IPv4 single protocol stack routing device in the network, and all other devices support IPv6 and IPv4 dual protocol stacks. 6PE-1, 6PE-2, and 6PE-3 distribute labeled IPv6 routing information through the Internal Border Gateway Protocol (IBGP). Taking 6PE-1 to advertise IPv6 network address S1 as an example, 6PE-1 passes The Multiprotocol-IBGP (MP-IBGP) protocol advertises the labeled IPv6 route to 6PE-3, the network address is S1, and the corresponding label value is L1. After 6PE-3 receives the labeled route, An IPv6 route will be added, the output label is L1, and the next hop is 6PE-1, so that there is an IPv6 route to S1 in the IPv6S3 network. The same principle can realize IPv6 routing interconnection among S1, S2, and S3.

下面描述IPv6报文如何在MPLS网络中传输，6PE-3在收到目的地址为S1的IPv6报文时，将查找本地IPv6路由表，确认下一跳为6PE-1，且出标签为L1(该报文由6PE-1分发)，之后6PE-3为该IPv6报文封装上标签L1，同时查找下一跳6PE-1的出口。根据MPLS转发表确定要达到6PE-1，需要插入标签T1(为6PE-3到6PE-1的MPLS隧道标签)，并转发至P，此时原来的IPv6报文将包含双层标签，内层标签为IPv6路由标签(L1)，而外层标签为MPLS隧道标签(T1)。P在收到该报文之后，它不关心报文中封装的是IPv4数据还是IPv6数据，根据外层标签T1确定该报文将转发至6PE-1，并交换标签T1为T2，此时报文的标签栈变为T2/L1。6PE-1在收到该报文之后，将弹出标签T2，同时根据IPv6标签L1确定转发至正确的网段。The following describes how IPv6 packets are transmitted in the MPLS network. When 6PE-3 receives an IPv6 packet whose destination address is S1, it will search the local IPv6 routing table to confirm that the next hop is 6PE-1, and the outgoing label is L1( The message is distributed by 6PE-1), and then 6PE-3 encapsulates the IPv6 message with a label L1, and at the same time searches for the exit of the next hop 6PE-1. According to the MPLS forwarding table, it is determined that to reach 6PE-1, label T1 (MPLS tunnel label from 6PE-3 to 6PE-1) needs to be inserted and forwarded to P. At this time, the original IPv6 message will contain double-layer labels, and the inner layer The label is an IPv6 routing label (L1), and the outer label is an MPLS tunnel label (T1). After P receives the packet, it does not care whether the packet encapsulates IPv4 data or IPv6 data. It determines that the packet will be forwarded to 6PE-1 according to the outer label T1, and switches the label T1 to T2. At this time, the packet The label stack becomes T2/L1. After receiving the message, 6PE-1 pops out the label T2 and determines to forward it to the correct network segment according to the IPv6 label L1.

上述IPv6报文在传输中容易碰到两个问题，一方面，IPv4网络中的设备P在转发报文时将执行最大传输单元(Maximum Transmission Unit，MTU)检查即检查该报文长度是否超过出接口的MTU，若当前接收的报文的长度超过其出接口的MTU时，P由于无法识别IPv6报文而只能丢弃该报文；另一方面，即使报文的长度未超过P出接口的MTU，由P成功转发至6PE-1，6PE-1根据该报文的标签L1以及IPv6路由确认转发至某个出接口，若当前报文的长度超过6PE-1出接口的MTU时，6PE-1将为该IPv6报文再次执行分片，这样导致IPv6报文在经隧道传输过程被多次分片，降低了报文转发效率。The above-mentioned IPv6 message is easy to encounter two problems during transmission. On the one hand, the device P in the IPv4 network will perform a Maximum Transmission Unit (Maximum Transmission Unit, MTU) check when forwarding a message, that is, to check whether the length of the message exceeds the output limit. If the length of the currently received packet exceeds the MTU of its outgoing interface, P can only discard the packet because it cannot recognize the IPv6 packet; on the other hand, even if the length of the packet does not exceed the MTU of the outgoing interface of P MTU, successfully forwarded by P to 6PE-1, 6PE-1 confirms forwarding to an outgoing interface according to the label L1 of the packet and IPv6 routing, if the length of the current packet exceeds the MTU of the outgoing interface of 6PE-1, 6PE- 1 Fragmentation will be performed on the IPv6 packet again, which will cause the IPv6 packet to be fragmented multiple times during tunnel transmission, reducing the packet forwarding efficiency.

图2所示是采用6PE方案实现IPv6网络互联的另外一个具体例子，该例子为跨多个自治域的IPv6网络的互联互通，图2中AS1由6PE-1、P和自治系统边界路由器(Autonomous System Border Router，ASBR)1组成，AS2由ASBR2和6PE-2组成(ASBR2和6PE-2之间还可以包括若干P设备，在图2中未示意出)，IPv6S1通过6PE-1连接自治域AS1，IPv6S2连接自治域AS2，6PE-1和ASBR1之间建立MP-IBGP连接，6PE-1将带标签的IPv6路由通告给ASBR1，ASBR1与ASBR2之间建立多协议BGP协议(Multiprotocol Extensions BGP，MP-EBGP)连接，ASBR1将6PE-1的带标签IPv6路由通过MP-EBGP通告至ASBR-2，ASBR2与6PE-2建立MP-IBGP连接，ASBR2再将ASBR1通告的带标签IPv6路由通过MP-IBGP通告至6PE-2，这样6PE-2即可学习到6PE-1的带标签Ipv6路由，S2和S1相互学习到各自的IPv6路由。Figure 2 shows another specific example of using the 6PE solution to realize IPv6 network interconnection. This example is the interconnection and intercommunication of IPv6 networks across multiple autonomous domains. In Figure 2, AS1 is composed of 6PE-1, P and Autonomous System System Border Router, ASBR)1, AS2 is composed of ASBR2 and 6PE-2 (a number of P devices can be included between ASBR2 and 6PE-2, which is not shown in Figure 2), IPv6S1 is connected to the autonomous domain AS1 through 6PE-1 , IPv6S2 is connected to autonomous domain AS2, an MP-IBGP connection is established between 6PE-1 and ASBR1, 6PE-1 advertises the labeled IPv6 route to ASBR1, and a multiprotocol BGP protocol (Multiprotocol Extensions BGP, MP- EBGP) connection, ASBR1 advertises the labeled IPv6 route of 6PE-1 to ASBR-2 through MP-EBGP, ASBR2 establishes an MP-IBGP connection with 6PE-2, and ASBR2 advertises the labeled IPv6 route advertised by ASBR1 through MP-IBGP to 6PE-2, so that 6PE-2 can learn the labeled IPv6 route of 6PE-1, and S2 and S1 can learn their own IPv6 routes from each other.

IPv6报文的转发则是通过建立三个MPLS隧道来实现的，如图2示中的T3(6PE-1和ASBR1之间的隧道)、T2(ASBR1和ASBR2之间的隧道)和T1(ASBR2和6PE-2之间的隧道)，6PE-2在收到到达S1的IPv6报文之后，将会先通过隧道T1将报文转发至ASBR2，ASBR2再通过隧道T2转发至ASBR1，ASBR1则通过MPLS隧道T3将报文转发至6PE-1，从而实现IPv6报文的转发。由于6PE-2不需要知道如何到达ASBR1和6PE-1，它只需要将报文转发至ASBR2，剩余的转发操作则有ASBR2来执行，报文转发至ASBR2时，ASBR2会进行MTU检查，如果报文的长度超过其出接口的MTU，那么需要执行分片后转发，类似地，ASBR2和6PE-2在转发过程也同样需要进行MTU的检查，这样可能导致IPv6报文在经隧道传输过程被多次分片，降低了报文转发效率。另外，报文在经由AS1和AS2中的P设备转发至边界路由设备时，也有可能因为其长度大于P设备出接口的MTU而使得P设备直接丢弃该报文，使得IPv6报文的传输过程受阻导致IPv6网络之间无法实现互通。The forwarding of IPv6 packets is realized by establishing three MPLS tunnels, such as T3 (tunnel between 6PE-1 and ASBR1), T2 (tunnel between ASBR1 and ASBR2) and T1 (tunnel between ASBR2) as shown in Figure 2. and 6PE-2), after 6PE-2 receives the IPv6 packet arriving at S1, it will first forward the packet to ASBR2 through tunnel T1, and ASBR2 will forward it to ASBR1 through tunnel T2, and ASBR1 will pass MPLS Tunnel T3 forwards the packets to 6PE-1, thereby realizing the forwarding of IPv6 packets. Since 6PE-2 does not need to know how to reach ASBR1 and 6PE-1, it only needs to forward the packet to ASBR2, and ASBR2 will perform the remaining forwarding operations. When the packet is forwarded to ASBR2, ASBR2 will check the MTU. If the length of the packet exceeds the MTU of its outgoing interface, it needs to be forwarded after fragmentation. Similarly, ASBR2 and 6PE-2 also need to check the MTU during the forwarding process, which may cause IPv6 packets to be duplicated during tunnel transmission. Sub-fragmentation reduces packet forwarding efficiency. In addition, when the packet is forwarded to the border routing device via the P devices in AS1 and AS2, the P device may directly discard the packet because its length is greater than the MTU of the outgoing interface of the P device, which hinders the transmission process of the IPv6 packet. As a result, IPv6 networks cannot communicate with each other.

发明内容Contents of the invention

本发明实施例提供一种最大传输单元MTU的学习方法、装置及路由设备，用以解决在现有6PE技术中IPv6报文在传输过程中由于长度大小超过路由设备出接口MTU导致传输受阻以及被多次分片导致的报文转发效率低的问题。The embodiment of the present invention provides a maximum transmission unit (MTU) learning method, device and routing equipment, which are used to solve the problem that in the existing 6PE technology, the transmission of IPv6 messages is blocked and blocked due to the length exceeding the MTU of the outgoing interface of the routing equipment during transmission. The problem of low packet forwarding efficiency caused by multiple fragments.

本发明实施例提供的一种最大传输单元的学习方法，包括：A method for learning a maximum transmission unit provided in an embodiment of the present invention includes:

对于IPv4网络中形成的IPv6报文传输隧道中的每个运行边界网关协议BGP的路由设备执行下述操作：For each routing device running Border Gateway Protocol BGP in the IPv6 packet transmission tunnel formed in the IPv4 network, perform the following operations:

接收IPv6报文传输隧道中上游边界网关协议BGP邻居通告的到达IPv6网络的BGP路由信息；所述BGP路由信息中携带有所述上游BGP邻居确定出的到达IPv6网络的路由的第一MTU；Receiving the BGP routing information to reach the IPv6 network notified by the upstream Border Gateway Protocol BGP neighbor in the IPv6 message transmission tunnel; the BGP routing information carries the first MTU of the route to the IPv6 network determined by the upstream BGP neighbor;

对接收的所述BGP路由信息携带的到达该IPv6网络的BGP路由下一跳对应的第二MTU进行探测；Detecting the second MTU corresponding to the next hop of the BGP route to the IPv6 network carried by the received BGP routing information;

比较所述第一MTU与探测到的第二MTU的大小，将两者中的较小值作为确定出的到达IPv6网络的BGP路由的第三MTU并保存；Comparing the size of the first MTU and the detected second MTU, using the smaller value of the two as the third MTU of the BGP route determined to reach the IPv6 network and saving;

确定所述隧道中是否还存在下游BGP邻居，若存在，将所述第三MTU携带在到达该IPv6网络的BGP路由信息中并通告至所述下游BGP邻居；若不存在，则结束MTU的学习过程。Determine whether there is still a downstream BGP neighbor in the tunnel, if it exists, carry the third MTU in the BGP routing information arriving at the IPv6 network and notify it to the downstream BGP neighbor; if not, end the learning of the MTU process.

本发明实施例提供的一种最大传输单元的学习装置，包括：An apparatus for learning a maximum transmission unit provided in an embodiment of the present invention includes:

BGP路由信息接收单元，用于接收IPv6报文传输隧道中上游边界网关协议BGP邻居通告的到达IPv6网络的BGP路由信息；所述BGP路由信息中携带有所述上游BGP邻居确定出的到达IPv6网络的路由的第一MTU；The BGP routing information receiving unit is configured to receive the BGP routing information to reach the IPv6 network notified by the upstream Border Gateway Protocol BGP neighbor in the IPv6 message transmission tunnel; the BGP routing information carries the reachable IPv6 network determined by the upstream BGP neighbor The first MTU of the route;

MTU探测单元，用于对接收的所述BGP路由信息携带的到达该IPv6网络的BGP路由下一跳对应的第二MTU进行探测；The MTU detection unit is used to detect the second MTU corresponding to the next hop of the BGP route carried by the received BGP routing information to reach the IPv6 network;

比较单元，用于将比较所述第一MTU与探测到的第二MTU的大小，将两者中较小值作为确定出的到达IPv6网络的BGP路由的第三MTU并保存；The comparison unit is used to compare the size of the first MTU and the detected second MTU, and save the smaller value as the determined third MTU of the BGP route to the IPv6 network;

路由通告单元，用于确定所述隧道中是否还存在下游BGP邻居，若存在，将所述第三MTU携带在到达该IPv6网络的BGP路由信息中并通告至所述下游BGP邻居。A route notification unit, configured to determine whether there are downstream BGP neighbors in the tunnel, and if so, carry the third MTU in the BGP routing information to the IPv6 network and notify the downstream BGP neighbors.

本发明实施例提供的路由设备，包括本发明实施例提供的上述最大传输单元的学习装置。The routing device provided in the embodiment of the present invention includes the above-mentioned apparatus for learning the maximum transmission unit provided in the embodiment of the present invention.

本发明实施例的有益效果包括：The beneficial effects of the embodiments of the present invention include:

本发明实施例提供的最大传输单元的学习方法、装置及路由设备，对于IPv4网络中形成的IPv6报文传输隧道中的每个运行BGP的路由设备，执行下述操作即：接收上游BGP邻居通告的到达IPv6网络的BGP路由信息；该BGP路由信息携带有该上游BGP邻居确定出的到达IPv6网络的路由的第一MTU；对接收的BGP路由信息携带的到达该IPv6网络的BGP路由下一跳对应的第二MTU进行探测；比较第一MTU与探测到的第二MTU的大小，将两者中较小值作为确定出的到达IPv6网络的BGP路由的第三MTU并保存；如果还存在下游BGP邻居，则将第三MTU携带在到达该IPv6网络的BGP路由信息中并通告至下游BGP邻居，直至该隧道中的每个运行BGP的路由设备都学习到了到达该IPv6网络的BGP路由对应的MTU。本发明实施例在支持BGP协议的运营商边界设备和自治系统边界路由之间通过BGP路由传递MTU的值，使得传输IPv6报文的隧道的终点即连接另一IPv6网络的运营商边界设备可以计算出到达目的IPv6网络的路由中各跳的MTU的最小值，并将其作为发送IPv6报文是否需要进行分片的依据，经过上述过程之后，在该隧道的终点收到发往该IPv6网络的IPv6报文时，将该报文的大小与自身保存的MTU的大小进行比较，决定是否需要分片，如果进行分片，分片后的报文的长度是到达该IPv6网络的路由中各跳MTU的最小值，因此，对于通过IPv4网络实现IPv6网络的互联互通的应用场景尤其是跨多个IPv4自治域实现IPv6网络的互联互通的应用场景来说，不论IPv4网络中传输IPv6报文的隧道需要跨越多少中间设备(例如P设备)或边界设备，任何中间设备或者边界设备，都不会因为IPv6报文长度的大小超出了该路由设备出接口的MTU的大小而丢弃该IPv6报文，从而避免了现有6PE技术出现的IPv6报文的传输受阻的情况，并且在该隧道的终点对收到的IPv6报文进行分片操作后，该隧道中其他路由设备也不会再执行报文的分片操作，提高了IPv6报文在隧道中转发效率。The MTU learning method, device and routing device provided by the embodiments of the present invention, for each routing device running BGP in the IPv6 message transmission tunnel formed in the IPv4 network, perform the following operations: receive the upstream BGP neighbor notification The BGP routing information to reach the IPv6 network; the BGP routing information carries the first MTU of the route to the IPv6 network determined by the upstream BGP neighbor; the next hop of the BGP route to the IPv6 network carried by the received BGP routing information The corresponding second MTU is detected; compare the size of the first MTU and the detected second MTU, and save the smaller value of the two as the third MTU of the determined BGP route to the IPv6 network; if there is still a downstream The BGP neighbor carries the third MTU in the BGP routing information reaching the IPv6 network and notifies it to the downstream BGP neighbor until each routing device running BGP in the tunnel has learned the BGP routing corresponding to the IPv6 network. MTU. In the embodiment of the present invention, the value of the MTU is transmitted through the BGP route between the operator's border device supporting the BGP protocol and the autonomous system border route, so that the end point of the tunnel that transmits the IPv6 message, that is, the operator's border device connected to another IPv6 network, can calculate The minimum value of the MTU of each hop in the route to the destination IPv6 network, and use it as the basis for whether fragmentation is required to send IPv6 packets. After the above process, the end of the tunnel receives the IPv6 network For an IPv6 message, compare the size of the message with the size of the MTU saved by itself to determine whether fragmentation is required. If fragmentation is performed, the length of the fragmented message is the length of each hop in the route to the IPv6 network. The minimum value of the MTU. Therefore, for the application scenario of realizing the interconnection and intercommunication of the IPv6 network through the IPv4 network, especially the application scenario of realizing the interconnection and intercommunication of the IPv6 network across multiple IPv4 autonomous How many intermediate devices (such as P devices) or border devices need to be crossed, any intermediate device or border device will not discard the IPv6 packet because the size of the IPv6 packet length exceeds the MTU size of the outgoing interface of the routing device, thereby It avoids the situation that the transmission of IPv6 packets that occurs in the existing 6PE technology is blocked, and after the end point of the tunnel fragments the received IPv6 packets, other routing devices in the tunnel will no longer execute the fragmentation of the packets. Fragmentation operation improves the forwarding efficiency of IPv6 packets in the tunnel.

附图说明Description of drawings

图1为现有技术中6PE方案实现IPv6网络互联的网络连接示意图之一；Fig. 1 is one of the network connection schematic diagrams of realizing IPv6 network interconnection in the 6PE scheme in the prior art;

图2为现有技术中6PE方案实现IPv6网络互联的网络连接示意图之二；Fig. 2 is the second schematic diagram of the network connection of IPv6 network interconnection realized by the 6PE scheme in the prior art;

图3为本发明实施例提供的最大传输单元的学习方法的流程图；FIG. 3 is a flow chart of a method for learning a maximum transmission unit provided by an embodiment of the present invention;

图4为自定义团体属性的格式示意图；FIG. 4 is a schematic diagram of the format of a custom community attribute;

图5为本发明实施例提供的第一个具体实例的网络连接示意图；FIG. 5 is a schematic diagram of a network connection of a first specific example provided by an embodiment of the present invention;

图6为本发明实施例提供的最大传输单元的学习装置的结构示意图。FIG. 6 is a schematic structural diagram of an apparatus for learning an MTU provided by an embodiment of the present invention.

具体实施方式Detailed ways

下面结合附图，对本发明实施例提供的一种最大传输单元(MTU)的学习方法、装置及路由设备进行详细地说明。A method, device, and routing device for learning a maximum transmission unit (MTU) provided by embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

本发明实施例提供的MTU学习方法，如图3所示，包括如下步骤：The MTU learning method provided by the embodiment of the present invention, as shown in Figure 3, includes the following steps:

S301、接收IPv6报文传输隧道中上游BGP邻居通告的到达IPv6网络的BGP路由信息；该BGP路由信息中携带有该上游BGP邻居确定出的到达IPv6网络的路由的第一MTU；S301. Receive the BGP routing information to the IPv6 network notified by the upstream BGP neighbor in the IPv6 packet transmission tunnel; the BGP routing information carries the first MTU of the route to the IPv6 network determined by the upstream BGP neighbor;

S302、对接收的BGP路由信息携带的到达该IPv6网络的BGP路由下一跳的第二MTU进行探测；S302. Detect the second MTU of the next hop of the BGP route to the IPv6 network carried in the received BGP routing information;

S303、比较所述第一MTU与探测到的第二MTU的大小，将两者中较小值作为确定出的到达IPv6网络的BGP路由的第三MTU并保存；S303. Compare the size of the first MTU and the detected second MTU, and save the smaller value of the two as the determined third MTU of the BGP route to the IPv6 network;

S304、确定IPv6报文传输隧道中是否还存在下游BGP邻居；若存在，执行下述步骤S305；若不存在，结束本流程；S304. Determine whether there is still a downstream BGP neighbor in the IPv6 packet transmission tunnel; if it exists, perform the following step S305; if it does not exist, end this process;

S305、将第三MTU携带在到达该IPv6网络的BGP路由信息中并通告至下游BGP邻居。S305. Carry the third MTU in the BGP routing information arriving at the IPv6 network and notify the downstream BGP neighbors.

上述步骤S301中，IPv6报文传输隧道指的是连接两个IPv6网络的IPv4-MPLS网络提供的IPv6报文传输通道。In the above step S301, the IPv6 packet transmission tunnel refers to the IPv6 packet transmission channel provided by the IPv4-MPLS network connecting two IPv6 networks.

上述步骤S301和步骤S305中，在到达IPv6网络的BGP路由信息中携带第一MTU或携带第三MTU，可以通过下述方式实现：自定义BGP路由信息中的扩展团体属性，将第一MTU或第三MTU的值封装在所述扩展团体属性的Value字段中。In the above step S301 and step S305, carrying the first MTU or carrying the third MTU in the BGP routing information reaching the IPv6 network can be realized in the following manner: customizing the extended community attribute in the BGP routing information, setting the first MTU or The value of the third MTU is encapsulated in the Value field of the extended community attribute.

扩展团体属性(Extended Communities Attribute)是BGP路由信息中的路由属性中的一类，其格式如图4所示，自定义团体属性，可以自定义其中的type字段(扩展团体属性的类型)为MTU，将第一MTU或者第三MTU的值封装在自定义的扩展团体属性的Value字段中。Extended Communities Attribute (Extended Communities Attribute) is a type of routing attributes in BGP routing information. Its format is shown in Figure 4. To customize community attributes, you can customize the type field (the type of extended communities attribute) as MTU , encapsulate the value of the first MTU or the third MTU in the Value field of the custom extended community attribute.

较佳地，在本发明实施例中，还需要同时保存本次MTU学习过程中得到的第一MTU和第二MTU也与到达IPv6网络的BGP路由信息，以便后续MTU发生变化时，可以及时根据保存的第一MTU和第二MTU对保存的第三MTU进行更新。Preferably, in the embodiment of the present invention, it is also necessary to save the first MTU and the second MTU obtained in the MTU learning process and the BGP routing information to reach the IPv6 network at the same time, so that when the subsequent MTU changes, it can be timely based on The stored first MTU and the second MTU update the stored third MTU.

下面结合两个具体的实例，对本发明实施例提供的MTU学习方法进行详细地说明。The MTU learning method provided by the embodiment of the present invention will be described in detail below in conjunction with two specific examples.

第一个实例：First instance:

本实例采用图5所示的单自治域内IPv6网络互联的网络拓扑，运营商边界设备R1与IPv6S1网络相连，运营商边界设备R2与IPv6S2网络相连，同时R1和R2同属于IPv4-MPLS网络，为了实现将IPv6S2网络的IPv6报文发送至IPv6S1网络，需要在报文发送之前，执行BGP协议的路由设备R1和R2按照下面的流程分别执行MTU学习的步骤：This example adopts the network topology of IPv6 network interconnection in a single autonomous domain as shown in Figure 5. The operator border device R1 is connected to the IPv6S1 network, and the carrier border device R2 is connected to the IPv6S2 network. At the same time, R1 and R2 belong to the IPv4-MPLS network. To realize sending the IPv6 message of the IPv6S2 network to the IPv6S1 network, before the message is sent, the routing devices R1 and R2 that implement the BGP protocol respectively perform the steps of MTU learning according to the following process:

步骤1、R1向IPv6报文传输隧道中其上游的BGP邻居即R2通告到达IPv6S1网络的BGP路由信息，在通告的BGP路由中携带有R1确定出的到达IPv6S1网络的路由的MTU1；Step 1, R1 notifies its upstream BGP neighbor in the IPv6 message transmission tunnel, that is, R2, the BGP routing information to reach the IPv6S1 network, and the BGP route notified carries the MTU1 of the route to the IPv6S1 network determined by R1;

在本步骤1中，由于R1是直接与IPv6S1网络相连的运营商边界设备，MTU1的值，R1可以通过获取R1中与到达IPv6S1网络的路由对应的出接口的MTU的值得到MTU1。In thisstep 1, since R1 is an operator border device directly connected to the IPv6S1 network, the value of MTU1, R1 can obtain MTU1 by obtaining the value of the MTU of the outgoing interface corresponding to the route to the IPv6S1 network in R1.

R1将MTU1的值携带在自定义的扩展团体属性中，具体方法参见前述步骤S301的说明。R1 carries the value of MTU1 in the self-defined extended community attribute. For the specific method, refer to the description of the foregoing step S301.

步骤2、R2接收到该BGP路由信息之后，对该BGP路由信息携带的到达IPv6S1网络的路由的BGP路由下一跳对应的MTU2进行探测；Step 2. After receiving the BGP routing information, R2 detects the corresponding MTU2 of the BGP routing next hop of the route to the IPv6S1 network carried by the BGP routing information;

R2从接收的BGP路由信息中提取该BGP路由的下一跳的IP地址，BGP路由的下一跳是BGP路由信息中路由属性的一种，用于指明到达该路由前缀对应的网络(IPv6S1网络)需要将报文转发至BGP下一跳的路由设备(即R1)。R2 extracts the IP address of the next hop of the BGP route from the received BGP routing information. The next hop of the BGP route is a type of routing attribute in the BGP routing information, which is used to indicate the network (IPv6S1 network) corresponding to the prefix of the route. ) need to forward the packet to the routing device (that is, R1) of the BGP next hop.

根据该BGP路由的下一跳(R1)的IP地址，R2可自动探测该下一跳对应的MTU值。具体可采用现有的自动探测方法，例如通过发送Internet控制报文协议(Internet Control Message Protocol，ICMP)报文来发现MTU2，如果该传输隧道中R1和R2之间的路径上还连接有若干P设备或其他路由设备，探测MTU2的过程，即确定从R2经过若干P设备或其他路由设备到达R1的路径中各跳的MTU值的最小值。具体探测方法属于现有技术，在此不再赘述。According to the IP address of the next hop (R1) of the BGP route, R2 can automatically detect the MTU value corresponding to the next hop. Specifically, the existing automatic detection method can be used, for example, by sending an Internet Control Message Protocol (Internet Control Message Protocol, ICMP) message to discover MTU2, if there are several P The process of detecting MTU2 by a device or other routing devices is to determine the minimum value of the MTU value of each hop in the path from R2 to R1 through several P devices or other routing devices. The specific detection method belongs to the prior art, and will not be repeated here.

步骤3、R2比较MTU1和MTU2两者的大小，将两者中的较小值确定为到达IPv6S1网络的BGP路由对应的MTU3并保存。Step 3. R2 compares the sizes of MTU1 and MTU2, and determines the smaller value of the two as the corresponding MTU3 of the BGP route to the IPv6S1 network and saves it.

MTU3可以与到达IPv6S1网络的BGP路由一起保存于路由表中，以便在后续在转发该路由的IPv6报文时，可以根据MTU3的大小判断是否需要对报文进行分片的操作。MTU3 can be stored in the routing table together with the BGP route to the IPv6S1 network, so that when the IPv6 message of this route is forwarded later, it can be judged whether the message needs to be fragmented according to the size of MTU3.

步骤4、R2判断该隧道中是否存在下游BGP邻居，由于R2是与IPv6S2网络相连的运营商边界设备，其不存在BGP邻居，因此流程到此结束。Step 4. R2 judges whether there is a downstream BGP neighbor in the tunnel. Since R2 is an operator border device connected to the IPv6S2 network, it does not have a BGP neighbor, so the process ends here.

在经过上述步骤1～4之后，R2中保存的是到达IPv6S1网络的路由各跳MTU的最小值，R2收到IPv6S2网络发送至IPv6S1网络的IPv6报文后，将该报文的大小与保存的MTU3的大小进行比较，决定是否需要分片，如果进行分片，分片后的报文的长度是到达IPv6S1网络的路由的MTU的最小值，因此，在R2和R1之间的P设备不会因为报文长度的大小超出了该路由出接口的MTU的大小而丢弃报文，在R1中，也不会再执行报文的分片操作，提高了报文的转发效率。After theabove steps 1 to 4, R2 saves the minimum value of the MTU of each hop of the route to the IPv6S1 network. After receiving the IPv6 message sent from the IPv6S2 network to the IPv6S1 network, R2 compares the size of the message with the saved Compare the size of MTU3 to decide whether fragmentation is required. If fragmentation is performed, the length of the fragmented message is the minimum value of the MTU of the route to the IPv6S1 network. Therefore, the P device between R2 and R1 will not If the packet is discarded because the packet length exceeds the MTU size of the outgoing interface of the route, R1 will not perform fragmentation of the packet, which improves the packet forwarding efficiency.

第二个实例：Second instance:

本实例采用图2所示的跨自治域的IPv6网络互联的网络拓扑，其中IPv6S1网络通过AS1、AS2与IPv6S2网络相连，AS1由6PE-1、P和ASBR1组成，AS2由ASBR2和6PE-2组成，AS1和AS2都属于IPv4-MPLS网络，6PE-1和6PE-2是运营商边界设备。This example adopts the network topology of inter-autonomous domain IPv6 network interconnection shown in Figure 2, in which the IPv6S1 network is connected to the IPv6S2 network through AS1 and AS2, AS1 is composed of 6PE-1, P and ASBR1, and AS2 is composed of ASBR2 and 6PE-2 , both AS1 and AS2 belong to the IPv4-MPLS network, and 6PE-1 and 6PE-2 are carrier border devices.

为了实现将IPv6S2网络的IPv6报文发送至IPv6S1网络，需要在报文发送之前，各执行BGP协议的路由设备按照下面的流程分别执行MTU学习的步骤：In order to send IPv6 messages from the IPv6S2 network to the IPv6S1 network, each routing device that implements the BGP protocol needs to perform the steps of MTU learning according to the following procedures before the message is sent:

步骤1′、6PE-1向ASBR1通告到达IPv6S1网络的BGP路由信息，在通告的BGP路由中携带有6PE-1确定出的到达该IPv6S1网络的路由的MTU1；Step 1', 6PE-1 notifies ASBR1 of the BGP routing information to reach the IPv6S1 network, carrying the MTU1 of the route to the IPv6S1 network determined by 6PE-1 in the BGP route of the notification;

与步骤S501相似，6PE-1通过路由信息中的扩展团体属性携带MTU1；6PE-1向ASBR1通告的BGP路由信息中还包括该BGP路由的下一跳的信息，该BGP下一跳的信息为6PE-1的地址。Similar to step S501, 6PE-1 carries MTU1 through the extended community attribute in the routing information; the BGP routing information notified by 6PE-1 to ASBR1 also includes the next hop information of the BGP route, and the BGP next hop information is 6PE-1's address.

步骤2′、ASBR1根据接收的BGP路由信息中的BGP下一跳的地址，对该BGP路由下一跳对应的MTU2进行探测；Step 2', ASBR1 detects the MTU2 corresponding to the next hop of the BGP route according to the address of the BGP next hop in the received BGP routing information;

步骤3′、ASBR1比较MTU1和MTU2的大小，将两者之中较小值作为该BGP路由的MTU3值并保存。Step 3', ASBR1 compares the size of MTU1 and MTU2, and saves the smaller value of the two as the MTU3 value of the BGP route.

步骤4′、ASBR1确定该隧道中还存在下游BGP邻居ASBR2；Step 4', ASBR1 determines that there is also a downstream BGP neighbor ASBR2 in the tunnel;

步骤5′、ASBR1向ASBR2通告到达IPv6S1网络的BGP路由信息，在该BGP路由信息中携带ASBR1确定出的到达该IPv6S1网络的路由的MTU3。Step 5', ASBR1 notifies ASBR2 of the BGP routing information to the IPv6S1 network, and the BGP routing information carries the MTU3 of the route to the IPv6S1 network determined by ASBR1.

步骤6′、ASBR2接收该BGP路由信息之后，与ASBR1的处理方式类似，根据该BGP路由信息中的BGP下一跳(ASBR1)的地址，对该BGP路由下一跳对应的MTU4进行探测，ASBR2比较MTU4和MTU3的大小，将两者之中较小值作为该BGP路由的MTU5并保存。ASBR2确定该隧道中还存在下游BGP邻居6PE-2，继续向6PE-2通告到达IPv6S1网络的BGP路由信息，在该BGP路由信息中携带ASBR2确定出的到达该IPv6S1网络的路由的MTU5。Step 6', after ASBR2 receives the BGP routing information, similar to the processing method of ASBR1, according to the address of the BGP next hop (ASBR1) in the BGP routing information, the MTU4 corresponding to the next hop of the BGP routing is detected, and ASBR2 Compare the sizes of MTU4 and MTU3, and save the smaller value as the MTU5 of the BGP route. ASBR2 determines that there is still a downstream BGP neighbor 6PE-2 in the tunnel, and continues to notify 6PE-2 of the BGP routing information to reach the IPv6S1 network, and the BGP routing information carries the MTU5 of the route to the IPv6S1 network determined by ASBR2.

步骤7′、6PE-2接收该BGP路由信息之后，与ASBR2的处理方式类似，根据该BGP路由信息中的BGP下一跳(ASBR2)的地址，对该BGP路由下一跳对应的MTU6进行探测；6PE-2比较MTU5和MTU6的大小，将两者之中较小值作为该BGP路由的MTU7并保存。由于6PE-2是与IPv6S2网络直接相连的运营商边界设备，因此，MTU学习的流程到此结束。After Step 7', 6PE-2 receives the BGP routing information, similar to the processing method of ASBR2, according to the address of the BGP next hop (ASBR2) in the BGP routing information, the MTU6 corresponding to the next hop of the BGP routing is detected ; 6PE-2 compares the size of MTU5 and MTU6, and saves the smaller value as the MTU7 of the BGP route. Since 6PE-2 is an operator border device directly connected to the IPv6S2 network, the process of MTU learning ends here.

经过上述流程之后，6PE-2中保存的是到达IPv6S1网络的路由的各跳MTU中的最小值，6PE-2收到IPv6S2网络发送至IPv6S1网络的IPv6报文后，将该报文的大小与保存的MTU7的大小进行比较，决定是否需要分片，如果进行分片，分片后的报文的长度是到达IPv6S1网络的路由中各跳的MTU的最小值，因此，在6PE-2和6PE-1之间的P设备不会因为报文长度的大小超出了该路由出接口的MTU的大小而丢弃该IPv6报文，并且在ASBR2、ASBR1和6PE-1中，也不会再执行报文的分片操作，提高了报文的转发效率。After the above process, 6PE-2 stores the minimum value of the MTU of each hop of the route to the IPv6S1 network. After receiving the IPv6 message sent from the IPv6S2 network to the IPv6S1 network, 6PE-2 compares the size of the message with Compare the size of the saved MTU7 to determine whether fragmentation is required. If fragmentation is performed, the length of the fragmented message is the minimum value of the MTU of each hop in the route to the IPv6S1 network. Therefore, in 6PE-2 and 6PE The P device between -1 will not discard the IPv6 packet because the packet length exceeds the MTU size of the outgoing interface of the route, and will not execute the packet in ASBR2, ASBR1, and 6PE-1 Fragmentation operation improves packet forwarding efficiency.

在上述两个实例中，如果连接IPv6S1网络的R1或者6PE-1发现到达IPv6网络的路由对应的出接口的MTU1出现变化后，会向其下游邻居R2或ASBR1通告携带有更新后的MTU1的BGP路由信息，R2或ASBR1接收到该BGP路由信息后，会发现当前接收的BGP路由信息中的MTU1与保存的MTU1值不相等，这时，比较更新后的MTU1与本地保存的MTU2的大小确定两者之中的较小值，并在确定出的较小值与保存的MTU3不相等时，并使用该较小值更新保存的MTU3；如果是ASBR1，由于其还存在下游邻居ASBR2，那么还需要将更新后的MTU3携带在到达该IPv6的BGP路由信息中并通告至ASBR2，ASBR2接收到该路由信息后，执行类似的操作，直至MTU的计算在整个隧道中得到更新。In the above two examples, if R1 or 6PE-1 connected to the IPv6S1 network finds that the MTU1 of the outgoing interface corresponding to the route to the IPv6 network has changed, it will notify its downstream neighbor R2 or ASBR1 of BGP carrying the updated MTU1 After receiving the BGP routing information, R2 or ASBR1 will find that the MTU1 in the currently received BGP routing information is not equal to the saved MTU1 value. At this time, compare the updated MTU1 with the locally saved MTU2 to determine the two The smaller value among them, and when the determined smaller value is not equal to the saved MTU3, use the smaller value to update the saved MTU3; if it is ASBR1, because it also has a downstream neighbor ASBR2, then it needs to The updated MTU3 is carried in the BGP routing information reaching the IPv6 and notified to ASBR2. After receiving the routing information, ASBR2 performs similar operations until the calculation of the MTU is updated in the entire tunnel.

在上述两个实例中，R2、ASBR1、ASBR2或6PE-2还可以在首次学习MTU的过程结束后，周期性对到达该IPv6网络的BGP路由下一跳对应的MTU进行自动探测，并根据自动探测的结果，对MTU学习的结果进行更新。以ASBR1为例，ASBR1在当前探测到的MTU2与保存的MTU2不相等时，则需要将当前探测到的MTU2的值与保存的该路由对应的MTU1值进行比较确定两者中的较小值，并当两者中的较小值与保存的MTU3不相等时，使用该较小值更新保存的MTU3，将更新后的MTU3携带在达到IPv6S1网络的BGP路由信息中并通告至ASBR2，ASBR2收到后，按照前述更新方法对保存的MTU进行更新，直至连接IPv6S2网络的运营商边界设备6PE-2也更新了其保存的MTU7。In the above two examples, R2, ASBR1, ASBR2 or 6PE-2 can also periodically automatically detect the MTU corresponding to the next hop of the BGP route to the IPv6 network after the first learning of the MTU The detection result updates the MTU learning result. Take ASBR1 as an example. When the currently detected MTU2 is not equal to the saved MTU2, ASBR1 needs to compare the currently detected MTU2 value with the saved MTU1 value of the route to determine the smaller value of the two. And when the smaller value of the two is not equal to the saved MTU3, use the smaller value to update the saved MTU3, carry the updated MTU3 in the BGP routing information reaching the IPv6S1 network and notify it to ASBR2, and ASBR2 receives it Afterwards, the saved MTU is updated according to the aforementioned updating method until the operator edge device 6PE-2 connected to the IPv6S2 network also updates its saved MTU7.

基于同一发明构思，本发明实施例还提供了一种MTU学习装置及路由设备，由于该装置及设备解决问题的原理与前述一种MTU学习方法相似，因此该装置和路由设备的实施可以参见方法的实施，重复之处不在赘述。Based on the same inventive concept, the embodiment of the present invention also provides an MTU learning device and a routing device. Since the problem-solving principle of the device and device is similar to the aforementioned MTU learning method, the implementation of the device and routing device can be found in the method The implementation of the implementation, the repetition is not repeated.

本发明实施例提供的一种最大传输单元MTU的学习装置，如图6所示，包括：An apparatus for learning a maximum transmission unit MTU provided in an embodiment of the present invention, as shown in FIG. 6 , includes:

BGP路由信息接收单元601，用于接收IPv6报文传输隧道中上游边界网关协议BGP邻居通告的到达IPv6网络的BGP路由信息；所述BGP路由信息中携带有所述上游BGP邻居确定出的到达IPv6网络的路由的第一MTU；The BGP routinginformation receiving unit 601 is configured to receive the BGP routing information to reach the IPv6 network notified by the upstream Border Gateway Protocol BGP neighbor in the IPv6 packet transmission tunnel; the BGP routing information carries the reach IPv6 determined by the upstream BGP neighbor The first MTU of the route of the network;

MTU探测单元602，用于对接收的所述BGP路由信息携带的到达该IPv6网络的BGP路由下一跳对应的第二MTU进行探测；TheMTU detection unit 602 is configured to detect the second MTU corresponding to the next hop of the BGP route to the IPv6 network carried by the received BGP routing information;

比较单元603，用于将比较所述第一MTU与探测到的第二MTU的大小，将两者中较小值作为确定出的到达IPv6网络的BGP路由的第三MTU并保存；Thecomparison unit 603 is used to compare the size of the first MTU and the detected second MTU, and save the smaller value of the two as the determined third MTU of the BGP route to the IPv6 network;

路由通告单元604，用于确定所述隧道中是否还存在下游BGP邻居，若存在，将所述第三MTU携带在到达该IPv6的BGP路由信息中并通告至所述下游BGP邻居。Theroute notification unit 604 is configured to determine whether there is a downstream BGP neighbor in the tunnel, and if so, carry the third MTU in the BGP routing information reaching the IPv6 and notify the downstream BGP neighbor.

进一步地，上述路由通告单元604，用于自定义BGP路由信息中的扩展团体属性，将自定义的扩展团体属性的类型字段设置为MTU；将第三MTU的值封装在所述扩展团体属性的Value字段中。Further, theroute notification unit 604 is configured to customize the extended community attribute in the BGP routing information, and set the type field of the self-defined extended community attribute to MTU; encapsulate the value of the third MTU in the extended community attribute Value field.

进一步地，本发明实施例提供的MTU的学习装置，还包括：MTU更新单元605；Further, the MTU learning device provided in the embodiment of the present invention further includes: anMTU updating unit 605;

相应地，比较单元603，还用于在BGP路由信息接收单元601当前接收的上游BGP邻居通告的BGP路由信息中的第一MTU与保存的第一MTU值不相等时，比较当前接收的所述BGP路由信息中的第一MTU与保存的第二MTU的大小确定两者中的较小值；Correspondingly, thecomparison unit 603 is further configured to compare the currently received first MTU in the BGP routing information of the upstream BGP neighbor advertisement received by the BGP routinginformation receiving unit 601 when the first MTU value is not equal to the stored first MTU value. The size of the first MTU in the BGP routing information and the size of the saved second MTU determines the smaller value of the two;

MTU更新单元605，用于当所述较小值与保存的第三MTU不相等时，使用所述较小值更新保存的第三MTU；AnMTU updating unit 605, configured to use the smaller value to update the saved third MTU when the smaller value is not equal to the saved third MTU;

路由通告单元604，还用于确定所述隧道中是否还存在下游BGP邻居，若存在，将更新后的第三MTU携带在到达该IPv6的BGP路由信息中并通告至所述下游BGP邻居。Theroute notification unit 604 is further configured to determine whether there are downstream BGP neighbors in the tunnel, and if so, carry the updated third MTU in the BGP routing information reaching the IPv6 and notify the downstream BGP neighbors.

进一步地，本发明实施例提供的MTU的学习装置中的MTU探测单元602，还用于在路由通告单元604将所述第三MTU携带在到达该IPv6网络的BGP路由信息中并通告至所述下游BGP邻居的步骤之后，周期地对到达该IPv6网络的BGP路由下一跳的第二MTU进行探测；Further, theMTU detection unit 602 in the MTU learning device provided by the embodiment of the present invention is also used to carry the third MTU in the BGP routing information reaching the IPv6 network in theroute notification unit 604 and notify it to the After the step of the downstream BGP neighbor, periodically detect the second MTU of the next hop of the BGP route arriving at the IPv6 network;

比较单元603，还用于在MTU探测单元602当前探测到的第二MTU与保存的第二MTU不相等时，比较当前探测到的第二MTU与保存的第一MTU，确定两者中的较小值；The comparingunit 603 is also used to compare the currently detected second MTU with the saved first MTU when the second MTU currently detected by theMTU detecting unit 602 is not equal to the saved second MTU, and determine the smaller one of the two. small value;

MTU更新单元605，还用于当所述较小值与保存的第三MTU不相等时，使用所述较小值更新保存的第三MTU的值；TheMTU update unit 605 is further configured to use the smaller value to update the saved value of the third MTU when the smaller value is not equal to the saved third MTU;

路由通告单元604，还用于确定隧道中是否还存在下游BGP邻居，若存在，将更新后的第三MTU携带在到达该IPv6的BGP路由信息中并通告至隧道中的下游BGP邻居。Theroute notification unit 604 is also used to determine whether there are downstream BGP neighbors in the tunnel, and if so, carry the updated third MTU in the BGP routing information reaching the IPv6 and notify the downstream BGP neighbors in the tunnel.

进一步地，当本发明实施例提供的MTU的学习装置位于连接该IPv6网络的运营商边界设备中时，还可以包括：Further, when the MTU learning device provided by the embodiment of the present invention is located in the operator's edge device connected to the IPv6 network, it may also include:

获取单元606，用于获取所述运营商边界设备中与到达IPv6网络的路由对应的出接口的MTU；An obtainingunit 606, configured to obtain the MTU of the outgoing interface corresponding to the route to the IPv6 network in the operator border device;

相应地，路由通告单元604，还用于确定所述隧道中是否还存在下游BGP邻居，若存在，将获取到所述出接口的MTU携带在到达该IPv6网络的BGP路由信息中并通告至所述下游BGP邻居。Correspondingly, theroute notification unit 604 is also used to determine whether there are downstream BGP neighbors in the tunnel, and if so, carry the obtained MTU of the outgoing interface in the BGP routing information to the IPv6 network and notify it to the Describe the downstream BGP neighbors.

本发明实施例提供的MTU的学习装置，在具体实施时，可以通过设计下述功能模块实现：BGP模块、路由表管理模块、MTU自动探测模块，其中：The learning device of the MTU that the embodiment of the present invention provides can be realized by designing the following functional modules during specific implementation: BGP module, routing table management module, MTU automatic detection module, wherein:

BGP模块用于通告BGP路由信息，优选和计算最优路由，更新路由对应的MTU的值以及向路由表安装更新路由表项。The BGP module is used to advertise BGP routing information, optimize and calculate the optimal route, update the value of the MTU corresponding to the route, and install and update the routing table entry to the routing table.

路由表管理模块用于管理路由表项，如确定路由对应的下一跳、出接口，以及出接口MTU的值，同时也负责向BGP模块通告路由更新的信息。The routing table management module is used to manage routing table items, such as determining the corresponding next hop, outgoing interface, and the value of the outgoing interface MTU, and is also responsible for notifying the BGP module of routing update information.

MTU自动探测模块用于自动探测到达某个地址的传输MTU值，并向BGP模块通告达到某个地址的MTU值。The MTU auto-detection module is used to automatically detect the transmission MTU value to a certain address, and notify the BGP module of the MTU value to a certain address.

为了实现利用上述学习到的MTU进行数据转发，在该装置中，还可以设置数据转发模块，用于利用学习到的MTU执行数据报文的分片和转发。In order to implement data forwarding by using the learned MTU, in the device, a data forwarding module may also be set for performing fragmentation and forwarding of data packets by using the learned MTU.

上述功能模块的划分和实现方式仅是一个具体实例，本发明实施例提供的MTU的学习装置并不限于上述的具体实现方式。The division and implementation of the above functional modules is only a specific example, and the apparatus for learning the MTU provided in the embodiment of the present invention is not limited to the above specific implementation.

本发明实施例还提供了一种路由设备，该路由设备包含本发明实施例提供的上述MTU学习装置。An embodiment of the present invention also provides a routing device, which includes the above-mentioned MTU learning apparatus provided by the embodiment of the present invention.

较佳地，本发明实施例提供的上述路由设备，在实际组网时，可以作为6PE应用场景中的运营商边界设备或者自治系统边界路由器。Preferably, the above-mentioned routing device provided by the embodiment of the present invention can be used as an operator border device or an autonomous system border router in a 6PE application scenario during actual networking.

本发明实施例提供的最大传输单元的学习方法、装置及路由设备，对于IPv4网络中形成的IPv6报文传输隧道中的每个运行BGP的路由设备，执行下述操作即：接收上游BGP邻居通告的到达IPv6网络的BGP路由信息；该BGP路由信息携带有该上游BGP邻居确定出的到达IPv6网络的路由的第一MTU；对接收的BGP路由信息携带的到达该IPv6网络的BGP路由下一跳对应的第二MTU进行探测；比较第一MTU与探测到的第二MTU的大小，将两者中较小值作为确定出的到达IPv6网络的BGP路由的第三MTU并保存；如果还存在下游BGP邻居，则将第三MTU携带在到达该IPv6网络的BGP路由信息中并通告至下游BGP邻居，直至该隧道中的每个运行BGP的路由设备都学习到了到达该IPv6网络的BGP路由对应的MTU。本发明实施例在支持BGP协议的运营商边界设备和自治系统边界路由之间通过BGP路由传递MTU的值，使得传输IPv6报文的隧道的终点即连接另一IPv6网络的运营商边界设备可以计算出到达目的IPv6网络的路由中各跳的MTU的最小值，并将其作为发送IPv6报文是否需要进行分片的依据，经过上述过程之后，在该隧道的终点收到发往该IPv6网络的IPv6报文时，将该报文的大小与自身保存的MTU的大小进行比较，决定是否需要分片，如果进行分片，分片后的报文的长度是到达该IPv6网络的路由中各跳MTU的最小值，因此，对于通过IPv4网络实现IPv6网络的互联互通的应用场景尤其是跨多个IPv4自治域实现IPv6网络的互联互通的应用场景来说，不论IPv4网络中传输IPv6报文的隧道需要跨越多少中间设备(例如P设备)或边界设备，任何中间设备或者边界设备，都不会因为IPv6报文长度的大小超出了该路由设备出接口的MTU的大小而丢弃该IPv6报文，从而避免了现有6PE技术出现的IPv6报文的传输受阻的情况，并且在该隧道的终点对收到的IPv6报文进行分片操作后，该隧道中其他路由设备也不会再执行报文的分片操作，提高了IPv6报文在隧道中转发效率。The MTU learning method, device and routing device provided by the embodiments of the present invention, for each routing device running BGP in the IPv6 message transmission tunnel formed in the IPv4 network, perform the following operations: receive the upstream BGP neighbor notification The BGP routing information to reach the IPv6 network; the BGP routing information carries the first MTU of the route to the IPv6 network determined by the upstream BGP neighbor; the next hop of the BGP route to the IPv6 network carried by the received BGP routing information The corresponding second MTU is detected; compare the size of the first MTU and the detected second MTU, and save the smaller value of the two as the third MTU of the determined BGP route to the IPv6 network; if there is still a downstream The BGP neighbor carries the third MTU in the BGP routing information reaching the IPv6 network and notifies it to the downstream BGP neighbor until each routing device running BGP in the tunnel has learned the BGP routing corresponding to the IPv6 network. MTU. In the embodiment of the present invention, the value of the MTU is transmitted through the BGP route between the operator's border device supporting the BGP protocol and the autonomous system border route, so that the end point of the tunnel that transmits the IPv6 message, that is, the operator's border device connected to another IPv6 network, can calculate The minimum value of the MTU of each hop in the route to the destination IPv6 network, and use it as the basis for whether fragmentation is required to send IPv6 packets. After the above process, the end of the tunnel receives the IPv6 network For an IPv6 message, compare the size of the message with the size of the MTU saved by itself to determine whether fragmentation is required. If fragmentation is performed, the length of the fragmented message is the length of each hop in the route to the IPv6 network. The minimum value of the MTU. Therefore, for the application scenario of realizing the interconnection and intercommunication of the IPv6 network through the IPv4 network, especially the application scenario of realizing the interconnection and intercommunication of the IPv6 network across multiple IPv4 autonomous How many intermediate devices (such as P devices) or border devices need to be crossed, any intermediate device or border device will not discard the IPv6 packet because the size of the IPv6 packet length exceeds the MTU size of the outgoing interface of the routing device, thereby It avoids the situation that the transmission of IPv6 packets that occurs in the existing 6PE technology is blocked, and after the end point of the tunnel fragments the received IPv6 packets, other routing devices in the tunnel will no longer execute the fragmentation of the packets. Fragmentation operation improves the forwarding efficiency of IPv6 packets in the tunnel.

显然，本领域的技术人员可以对本发明进行各种改动和变型而不脱离本发明的精神和范围。这样，倘若本发明的这些修改和变型属于本发明权利要求及其等同技术的范围之内，则本发明也意图包含这些改动和变型在内。Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and equivalent technologies thereof, the present invention also intends to include these modifications and variations.

Claims (12)

Translated fromChinese

1.一种最大传输单元MTU的学习方法，其特征在于，包括：1. A learning method of maximum transmission unit MTU, is characterized in that, comprises:对于IPv4网络中形成的IPv6报文传输隧道中的每个运行边界网关协议BGP的路由设备执行下述操作：For each routing device running Border Gateway Protocol BGP in the IPv6 packet transmission tunnel formed in the IPv4 network, perform the following operations:接收IPv6报文传输隧道中上游边界网关协议BGP邻居通告的到达IPv6网络的BGP路由信息；所述BGP路由信息中携带有所述上游BGP邻居确定出的到达IPv6网络的路由的第一MTU；Receiving the BGP routing information to reach the IPv6 network notified by the upstream Border Gateway Protocol BGP neighbor in the IPv6 message transmission tunnel; the BGP routing information carries the first MTU of the route to the IPv6 network determined by the upstream BGP neighbor;对接收的所述BGP路由信息携带的到达该IPv6网络的BGP路由下一跳对应的第二MTU进行探测；Detecting the second MTU corresponding to the next hop of the BGP route to the IPv6 network carried by the received BGP routing information;比较所述第一MTU与探测到的第二MTU的大小，将两者中的较小值作为确定出的到达IPv6网络的BGP路由的第三MTU并保存；Comparing the size of the first MTU and the detected second MTU, using the smaller value of the two as the third MTU of the BGP route determined to reach the IPv6 network and saving;确定所述隧道中是否还存在下游BGP邻居，若存在，将所述第三MTU携带在到达该IPv6网络的BGP路由信息中并通告至所述下游BGP邻居；若不存在，则结束MTU的学习过程。Determine whether there is still a downstream BGP neighbor in the tunnel, if it exists, carry the third MTU in the BGP routing information arriving at the IPv6 network and notify it to the downstream BGP neighbor; if not, end the learning of the MTU process.2.如权利要求1所述的方法，其特征在于，在到达IPv6网络的BGP路由信息中携带第一MTU或者第三MTU，通过下述方式实现：2. The method according to claim 1, characterized in that, carrying the first MTU or the third MTU in the BGP routing information arriving at the IPv6 network is realized in the following manner:自定义BGP路由信息中的扩展团体属性，将自定义的扩展团体属性的类型字段设置为MTU；将第一MTU或第三MTU的值封装在所述扩展团体属性的Value字段中。Customize the extended community attribute in the BGP routing information, set the type field of the customized extended community attribute to MTU; encapsulate the value of the first MTU or the third MTU in the Value field of the extended community attribute.3.如权利要求1所述的方法，其特征在于，所述上游BGP邻居为连接该IPv6网络的运营商边界设备时，所述第一MTU为所述运营商边界设备获取的所述运营商边界设备中与到达IPv6网络的路由对应的出接口的MTU。3. The method according to claim 1, wherein when the upstream BGP neighbor is an operator border device connected to the IPv6 network, the first MTU is the operator border device obtained by the operator border device MTU of the outbound interface corresponding to the route to the IPv6 network on the border device.4.如权利要求1-3任一项所述的方法，其特征在于，还包括：4. The method according to any one of claims 1-3, further comprising:保存所述第一MTU值与所述探测到的第二MTU的值。Save the first MTU value and the detected second MTU value.5.如权利要求4所述的方法，其特征在于，在当前接收的上游BGP邻居通告的BGP路由信息中的第一MTU与保存的第一MTU值不相等时，还包括：5. The method according to claim 4, wherein when the first MTU in the BGP routing information of the currently received upstream BGP neighbor advertisement is not equal to the first MTU value preserved, it also includes:比较当前接收的所述BGP路由信息中的第一MTU与保存的第二MTU的大小确定两者中的较小值，并当所述较小值与保存的第三MTU不相等时，使用所述较小值更新保存的第三MTU，确定所述隧道中是否还存在下游BGP邻居，若存在，将更新后的第三MTU携带在到达该IPv6的BGP路由信息中并通告至所述下游BGP邻居。Comparing the size of the first MTU in the currently received BGP routing information with the size of the saved second MTU to determine the smaller value of the two, and when the smaller value is not equal to the saved third MTU, use the saved Update the saved third MTU with the smaller value, determine whether there is still a downstream BGP neighbor in the tunnel, and if so, carry the updated third MTU in the BGP routing information reaching the IPv6 and notify it to the downstream BGP Neighbor.6.如权利要求4所述的方法，其特征在于，将所述第三MTU携带在到达该IPv6网络的BGP路由信息中并通告至所述下游BGP邻居的步骤之后，还包括：6. The method according to claim 4, characterized in that, after the step of carrying the third MTU in the BGP routing information arriving at the IPv6 network and announcing it to the downstream BGP neighbor, further comprising:周期地对到达该IPv6网络的BGP路由下一跳的第二MTU进行探测，并在当前探测到的第二MTU与保存的第二MTU不相等时，比较当前探测到的第二MTU与保存的第一MTU确定两者中的较小值；并当所述较小值与保存的第三MTU不相等时，使用所述较小值更新保存的第三MTU的值，确定所述隧道中是否还存在下游BGP邻居，若存在，将更新后的第三MTU携带在到达该IPv6的BGP路由信息中并通告至隧道中的下游BGP邻居。Periodically detect the second MTU of the next hop of the BGP route reaching the IPv6 network, and compare the currently detected second MTU with the saved second MTU when the currently detected second MTU is not equal to the saved second MTU The first MTU determines the smaller value of the two; and when the smaller value is not equal to the saved third MTU, use the smaller value to update the value of the saved third MTU to determine whether in the tunnel There is also a downstream BGP neighbor. If there is, the updated third MTU is carried in the BGP routing information reaching the IPv6 and notified to the downstream BGP neighbor in the tunnel.7.一种最大传输单元MTU的学习装置，其特征在于，包括：7. A learning device for maximum transmission unit MTU, characterized in that it comprises:BGP路由信息接收单元，用于接收IPv6报文传输隧道中上游边界网关协议BGP邻居通告的到达IPv6网络的BGP路由信息；所述BGP路由信息中携带有所述上游BGP邻居确定出的到达IPv6网络的路由的第一MTU；The BGP routing information receiving unit is configured to receive the BGP routing information to reach the IPv6 network notified by the upstream Border Gateway Protocol BGP neighbor in the IPv6 message transmission tunnel; the BGP routing information carries the reachable IPv6 network determined by the upstream BGP neighbor The first MTU of the route;MTU探测单元，用于对接收的所述BGP路由信息携带的到达该IPv6网络的BGP路由下一跳对应的第二MTU进行探测；The MTU detection unit is used to detect the second MTU corresponding to the next hop of the BGP route carried by the received BGP routing information to reach the IPv6 network;比较单元，用于将比较所述第一MTU与探测到的第二MTU的大小，将两者中较小值作为确定出的到达IPv6网络的BGP路由的第三MTU并保存；The comparison unit is used to compare the size of the first MTU and the detected second MTU, and save the smaller value as the determined third MTU of the BGP route to the IPv6 network;路由通告单元，用于确定所述隧道中是否还存在下游BGP邻居，若存在，将所述第三MTU携带在到达该IPv6网络的BGP路由信息中并通告至所述下游BGP邻居。A route notification unit, configured to determine whether there are downstream BGP neighbors in the tunnel, and if so, carry the third MTU in the BGP routing information to the IPv6 network and notify the downstream BGP neighbors.8.如权利要求7所述的装置，其特征在于，所述路由通告单元，进一步用于自定义BGP路由信息中的扩展团体属性，将自定义的扩展团体属性的类型字段设置为MTU；将第三MTU的值封装在所述扩展团体属性的Value字段中。8. The device according to claim 7, wherein the route notification unit is further used to customize the extended community attribute in the BGP routing information, and the type field of the self-defined extended community attribute is set to MTU; The value of the third MTU is encapsulated in the Value field of the extended community attribute.9.如权利要求7或8所述的装置，其特征在于，还包括：MTU更新单元；9. The device according to claim 7 or 8, further comprising: an MTU update unit;所述比较单元，还用于在BGP路由信息接收单元当前接收的上游BGP邻居通告的BGP路由信息中的第一MTU与保存的第一MTU值不相等时，比较当前接收的所述BGP路由信息中的第一MTU与保存的第二MTU的大小确定两者中的较小值；The comparison unit is further configured to compare the currently received BGP routing information when the first MTU in the BGP routing information currently received by the upstream BGP neighbor advertisement received by the BGP routing information receiving unit is not equal to the saved first MTU value The size of the first MTU and the saved second MTU in determine the smaller value of the two;所述MTU更新单元，用于当所述较小值与保存的第三MTU不相等时，使用所述较小值更新保存的第三MTU；The MTU update unit is configured to use the smaller value to update the saved third MTU when the smaller value is not equal to the saved third MTU;所述路由通告单元，还用于确定所述隧道中是否还存在下游BGP邻居，若存在，将更新后的第三MTU携带在到达该IPv6的BGP路由信息中并通告至所述下游BGP邻居。The route notification unit is also used to determine whether there are downstream BGP neighbors in the tunnel, and if so, carry the updated third MTU in the BGP routing information reaching the IPv6 and notify the downstream BGP neighbors.10.如权利要求7或8所述的装置，其特征在于，还包括：MTU更新单元；10. The device according to claim 7 or 8, further comprising: an MTU update unit;所述MTU探测单元，还用于在路由通告单元将所述第三MTU携带在到达该IPv6网络的BGP路由信息中并通告至所述下游BGP邻居的步骤之后，周期地对到达该IPv6网络的BGP路由下一跳的第二MTU进行探测；The MTU detecting unit is further configured to periodically check the routing information arriving at the IPv6 network after the route advertising unit carries the third MTU in the BGP routing information arriving at the IPv6 network and notifies it to the downstream BGP neighbor. The second MTU of the next hop of the BGP route is detected;所述比较单元，还用于在所述MTU探测单元当前探测到的第二MTU与保存的第二MTU不相等时，比较当前探测到的第二MTU与保存的第一MTU确定两者中的较小值；The comparison unit is further configured to compare the currently detected second MTU with the saved first MTU to determine the difference between the second MTU currently detected by the MTU detection unit and the saved second MTU when the second MTU currently detected by the MTU detection unit is not equal to the saved second MTU. smaller value;所述MTU更新单元，用于当所述较小值与保存的第三MTU不相等时，使用所述较小值更新保存的第三MTU的值；The MTU updating unit is configured to use the smaller value to update the saved third MTU value when the smaller value is not equal to the saved third MTU;所述路由通告单元，还用于确定所述隧道中是否还存在下游BGP邻居，若存在，将更新后的第三MTU携带在到达该IPv6的BGP路由信息中并通告至隧道中的下游BGP邻居。The route notification unit is also used to determine whether there are downstream BGP neighbors in the tunnel, and if so, carry the updated third MTU in the BGP routing information reaching the IPv6 and notify the downstream BGP neighbors in the tunnel .11.如权利要求7所述的装置，其特征在于，当所述装置位于连接该IPv6网络的运营商边界设备中时，还包括：11. The device according to claim 7, further comprising:获取单元，用于获取所述运营商边界设备中与到达IPv6网络的路由对应的出接口的MTU；An acquisition unit, configured to acquire the MTU of the outbound interface corresponding to the route to the IPv6 network in the operator border device;所述路由通告单元，还用于确定所述隧道中是否还存在下游BGP邻居，若存在，将获取到所述出接口的MTU携带在到达该IPv6网络的BGP路由信息中并通告至所述下游BGP邻居。The route notification unit is also used to determine whether there are downstream BGP neighbors in the tunnel, and if so, carry the obtained MTU of the outgoing interface in the BGP routing information to the IPv6 network and notify the downstream BGP neighbors.12.一种路由设备，其特征在于，包括如权利要求7～11任一项所述的最大传输单元MTU的学习装置。12. A routing device, characterized by comprising the learning device of the maximum transmission unit (MTU) according to any one of claims 7-11.

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