計算機專業外文翻譯--設計與實現由ipv4過渡到ipv6隧道-公路隧道(編輯修改稿)

　

【文章內容簡介】 he use Corresponding author. Tel.:+ 912332301327。 fax: +912332300831. Email addresses: (. Raste), (. Kulkarn i). 10848045/$ see front matter r 2020 Published by Elsevier Ltd. doi: 2 of IPv4overIPv6 tunnels (Wang et al., 2020) to carry IPv4 traf?c within an IPv6only work. Since the IPv4 globally routable address space available is being a scarce resource, it is assumed that users will deploy IPv6 to reduce the need and reliability on IPv4 within a portion of their works. Under this premise, supporting native IPv4 and native IPv6 simultaneously largely increases the plexity of work administration (address plan, routing infrastructure). It is proposed, in this case, to con?gure the work only for IPv6. When tunneling is deployed in a work, the nodes have both IPv4 and IPv6 addresses allocated. When an IPv4 application needs to establish munication with another IPv4 application on IPv6 node or another IPv4 only node, tunneling is employed. This allows either IPv6 nodes to municate with IPv4only nodes, or IPv4only applications to run on an IPv6 node without modi?cation. Thus IPv4 packets are hidden in the IPv6 packets on an IPv6 domain (Bound et al., 2020). This simpli?es work management: only the IPv6 routing plan is managed inside the work. 2. Con?guration of IPv4 stack As long as munications can take place in native IPv6, no tunneling mechanism is required. The host can detect the need of a tunnel by different methods: when a query to the DNS resolver results in an IPv4 destination address, when an application opens an IPv4 socket, or when an IPv4 packet is sent to the kernel and no interface is ready to forward that packet (Bound et al., 2020). When the ?rst IPv4 packet needs to be sent, the client obtains the IPv6 address of a TEP (Af?? and Tountain, 1999). This information is used to con?gure the 4over6 interface. The important step in tunnel con?guration is creation of a virtual interface for the tunnel and creation of a route entry in the IPv4 routing table of the node. This enables the IPv4 application to divert the IPv4 packets to the tunnel code written in the kernel. Net ?lter hooks can be used to detect the need to install such a tunnel on the node. 3. Net?lter hooks The need for virtual interface creation can be detected by using ?lter (Net?lter homopage。 Chakeres) hooks. Net?lter can be used by our implementation to identify many of the events that trigger the routing action. Net?lter consists of a number of hooks at various points inside the Linux protocol stack. It allows userde?ned kernel modules to register callback functions to these hooks. When a packet traverses a hook, the packet ?ows through the user de?ned callback method inside the kernel module. There are ?ve hooks de?ned in the ?lter architecture, as shown in Fig. 1 At the top of the ?gure there are two hooks, NF_IP_LOCAL_IN and NF_IP_LOCAL_OUT. These hooks are for all packets to and from local processes. At the bottom of the ?gure there are two hooks, NF_IP_PRE_ROUTING and NF_IP_POST_ROUTING. These are for all packets from and to other hosts on the work. There is also a hook for packets that are forwarded by the current host, NF_IP_FORWARD. As an example of how packets traverse these hooks, suppose a packet is created by a local process for a remote process. It ?rst traverses the NF_IP_LOCAL_OUT hook. Next, a routing decision is performed to see if the packet is bound for the local host or another host on the work. The packet is found to be destined for a remote host, and the packet is passed through the 3 Fig. 1. Net?lter hooks. NF_IP_POST_ROUTING hook and then onto a work interface. The call back function registered returns one of the ?ve values NF_ACCEPT (accept the packet and continue the chain), NF_DROP (drop the packet), NF_QUEUE (queue the packet to user space) or NF_STOLEN (packet stolen from work stack). 4. Virtual interface From the kernel’s point of view, a work interface is a software object that can process outgoing packets, and the actual transmission mechanism remains hidden inside the interface driver. Even though most interfaces are associated to physical devices (or, for the loopback interface, to a softwareonly data loop), it is possible to design work interface drivers that rely on other interfaces to perform actual packet transmission. The idea of a ‘‘virtual’’ interface can be useful to implement specialpurpose processing on data packets while avoiding hacking with the work subsystem of the kernel. This idea can be used in tunneling of packets inside another protocol. Thus creating a tunnel implies creating a virtual interface in the kernel and maintaining the information for encapsulation in its private data structure. 5. Design The