Network Working Group E. Duros
Request for Comments: 3077 UDcast
Category: Standards Track W. Dabbous
INRIA Sophia-Antipolis
H. Izumiyama
N. Fujii
WIDE
Y. Zhang
HRL
March 2001
Network Working Group E. Duros
Request for Comments: 3077 UDcast
Category: Standards Track W. Dabbous
INRIA Sophia-Antipolis
H. Izumiyama
N. Fujii
WIDE
Y. Zhang
HRL
March 2001
A Link-Layer Tunneling Mechanism for Unidirectional Links
单向链路的链路层隧道机制
Status of this Memo
本备忘录的状况
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
本文件规定了互联网社区的互联网标准跟踪协议，并要求进行讨论和提出改进建议。有关本协议的标准化状态和状态，请参考当前版本的“互联网官方协议标准”（STD 1）。本备忘录的分发不受限制。
Copyright Notice
版权公告
Copyright (C) The Internet Society (2001). All Rights Reserved.
版权所有（C）互联网协会（2001年）。版权所有。
Abstract
摘要
This document describes a mechanism to emulate full bidirectional connectivity between all nodes that are directly connected by a unidirectional link. The "receiver" uses a link-layer tunneling mechanism to forward datagrams to "feeds" over a separate bidirectional IP (Internet Protocol) network. As it is implemented at the link-layer, protocols in addition to IP may also be supported by this mechanism.
本文档描述了一种模拟由单向链路直接连接的所有节点之间的完全双向连接的机制。“接收器”使用链路层隧道机制通过单独的双向IP（互联网协议）网络将数据报转发给“馈送”。由于它是在链路层实现的，因此除了IP之外，该机制还可以支持协议。
Internet routing and upper layer protocols assume that links are bidirectional, i.e., directly connected hosts can communicate with each other over the same link.
Internet路由和上层协议假定链路是双向的，即直接连接的主机可以通过同一链路相互通信。
This document describes a link-layer tunneling mechanism that allows a set of nodes (feeds and receivers, see Section 2 for terminology) which are directly connected by a unidirectional link to send datagrams as if they were all connected by a bidirectional link. We present a generic topology in section 3 with a tunneling mechanism
本文档描述了一种链路层隧道机制，该机制允许通过单向链路直接连接的一组节点（馈送和接收器，术语见第2节）发送数据报，就像它们都通过双向链路连接一样。我们在第3节中介绍了一种具有隧道机制的通用拓扑
that supports multiple feeds and receivers. Note, this mechanism is not designed for topologies where a pair of nodes are connected by 2 unidirectional links in opposite direction.
它支持多个馈送和接收器。注意，此机制不适用于一对节点由2个反向单向链路连接的拓扑。
The tunneling mechanism requires that all nodes have an additional interface to an IP interconnected infrastructure.
隧道机制要求所有节点都有一个到IP互连基础设施的附加接口。
The tunneling mechanism is implemented at the link-layer of the interface of every node connected to the unidirectional link. The aim is to hide from higher layers, i.e., the network layer and above, the unidirectional nature of the link. The tunneling mechanism also includes an automatic tunnel configuration protocol that allows nodes to come up/down at any time.
隧道机制在连接到单向链路的每个节点的接口的链路层实现。其目的是向更高的层（即网络层和更高的层）隐藏链路的单向性。隧道机制还包括一个自动隧道配置协议，允许节点随时上下移动。
Generic Routing Encapsulation [RFC2784] is suggested as the tunneling mechanism as it provides a means for carrying IP, ARP datagrams, and any other layer-3 protocol between nodes.
建议将通用路由封装[RFC2784]作为隧道机制，因为它提供了在节点之间承载IP、ARP数据报和任何其他第3层协议的方法。
The tunneling mechanism described in this document was discussed and agreed upon by the UDLR working group.
UDLR工作组讨论并商定了本文件中描述的隧道机制。
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this document, are to be interpreted as described in [RFC2119].
本文件中出现的关键词必须、不得、必需、应、不应、应、不应、建议、可和可选时，应按照[RFC2119]中的说明进行解释。
Unidirectional link (UDL): A one way transmission link, e.g., a broadcast satellite link.
单向链路（UDL）：单向传输链路，例如广播卫星链路。
Receiver: A router or a host that has receive-only connectivity to a UDL.
接收器：与UDL具有仅接收连接的路由器或主机。
Send-only feed: A router that has send-only connectivity to a UDL.
仅发送馈送：与UDL具有仅发送连接的路由器。
Receive capable feed: A router that has send-and-receive connectivity to a UDL.
支持接收的馈送：一个路由器，它与UDL具有发送和接收连接。
Feed: A send-only or a receive capable feed.
提要：仅发送或可接收的提要。
Node: A receiver or a feed.
节点：接收器或馈送。
Bidirectional interface: a typical communication interface that can send or receive packets, such as an Ethernet card, a modem, etc.
双向接口：可以发送或接收数据包的典型通信接口，如以太网卡、调制解调器等。
Feeds and receivers are connected via a unidirectional link. Send-only feeds can only send data over this unidirectional link, and receivers can only receive data from it. Receive capable feeds have both send and receive capabilities.
馈源和接收器通过单向链路连接。仅发送提要只能通过此单向链路发送数据，而接收方只能从中接收数据。支持接收的提要具有发送和接收功能。
This mechanism has been designed to work with any topology with any number of receivers and one or more feeds. However, it is expected that the number of feeds will be small. In particular, the special case of a single send-only feed and multiple receivers is among the topologies supported.
该机制设计用于任何具有任意数量接收器和一个或多个馈源的拓扑。然而，预计饲料的数量将很小。特别是，支持的拓扑中有一种特殊情况，即单个只发送提要和多个接收机。
A receiver has several interfaces, a receive-only interface and one or more additional bidirectional communication interfaces.
接收机具有多个接口、一个仅接收接口和一个或多个附加双向通信接口。
A feed has several interfaces, a send-only or a send-and-receive capable interface connected to the unidirectional link and one or more additional bidirectional communication interfaces. A feed MUST be a router.
feed具有多个接口，一个仅发送或可发送和接收的接口连接到单向链路，以及一个或多个额外的双向通信接口。提要必须是路由器。
Tunnels are constructed between the bidirectional interfaces of nodes, so these interfaces must be interconnected by an IP infrastructure. In this document we assume that that infrastructure is the Internet.
隧道是在节点的双向接口之间构建的，因此这些接口必须通过IP基础设施互连。在本文中，我们假设基础设施是互联网。
Figure 1 depicts a generic topology with several feeds and several receivers.
图1描述了具有多个提要和多个接收器的通用拓扑。
Unidirectional Link
单向链路
---->---------->------------------->------
| | | |
|f1u |f2u |r2u |r1u
-------- -------- -------- -------- ----------
|Feed 1| |Feed 2| |Recv 2| |Recv 1|---|subnet A|
-------- -------- -------- -------- ----------
|f1b |f2b |r2b |r1b |
| | | | |
----------------------------------------------------
| Internet |
----------------------------------------------------
Figure 1: Generic topology
---->---------->------------------->------
| | | |
|f1u |f2u |r2u |r1u
-------- -------- -------- -------- ----------
|Feed 1| |Feed 2| |Recv 2| |Recv 1|---|subnet A|
-------- -------- -------- -------- ----------
|f1b |f2b |r2b |r1b |
| | | | |
----------------------------------------------------
| Internet |
----------------------------------------------------
Figure 1: Generic topology
f1u (resp. f2u) is the IP address of the 'Feed 1' (resp. Feed 2) send-only interface.
f1u（resp.f2u）是“Feed 1”（resp.Feed 2）仅发送接口的IP地址。
f1b (resp. f2b) is the IP address of the 'Feed 1' (resp. Feed 2) bidirectional interface connected to the Internet.
f1b（resp.f2b）是连接到互联网的“Feed 1”（resp.Feed 2）双向接口的IP地址。
r1u (resp. r2u) is the IP address of the 'Receiver 1' (resp. Receiver 2) receive-only interface.
r1u（分别为r2u）是“接收器1”（分别为接收器2）仅接收接口的IP地址。
r1b (resp. r2b) is the IP address of the 'Receiver 1' (resp. Receiver 2) bidirectional interface connected to the Internet.
r1b（分别为r2b）是连接到互联网的“接收器1”（分别为接收器2）双向接口的IP地址。
Subnet A is a local area network connected to recv1.
子网A是连接到recv1的局域网。
Note that nodes have IP addresses on their unidirectional and their bidirectional interfaces. The addresses on the unidirectional interfaces (f1u, f2u, r1u, r2u) will be drawn from the same IP network. In general the addresses on the bidirectional interfaces (f1b, f2b, r1b, r2b) will be drawn from different IP networks, and the Internet will route between them.
请注意，节点的单向和双向接口上都有IP地址。单向接口（f1u、f2u、r1u、r2u）上的地址将来自同一IP网络。一般来说，双向接口（f1b、f2b、r1b、r2b）上的地址将从不同的IP网络中提取，互联网将在它们之间路由。
Receive-only interfaces are "dumb" and send-only interfaces are "deaf". Thus a datagram passed to the link-layer driver of a receive-only interface is simply discarded. The link-layer of a send-only interface never receives anything.
仅接收接口为“哑”，仅发送接口为“聋”。因此，传递给仅接收接口的链路层驱动程序的数据报被简单地丢弃。仅发送接口的链接层从不接收任何内容。
The network layer has no knowledge of the underlying transmission technology except that it considers its access as bidirectional. Basically, for outgoing datagrams, the network layer selects the correct first hop on the connected network according to a routing table and passes the packet(s) to the appropriate link-layer driver.
网络层不了解底层传输技术，只是认为其访问是双向的。基本上，对于传出数据报，网络层根据路由表选择连接网络上正确的第一跳，并将数据包传递给适当的链路层驱动程序。
Referring to Figure 1, Recv 1 and Feed 1 belong to the same network. However, if Recv 1 initiates a 'ping f1u', it cannot get a response from Feed 1. The network layer of Recv 1 delivers the packet to the driver of the receive-only interface, which obviously cannot send it to the feed.
参考图1，Recv 1和Feed 1属于同一网络。但是，如果Recv 1启动“ping f1u”，则无法从提要1获得响应。Recv 1的网络层将数据包传送到仅接收接口的驱动程序，该接口显然无法将数据包发送到提要。
Many protocols in the Internet assume that links are bidirectional. In particular, routing protocols used by directly connected routers no longer behave properly in the presence of a unidirectional link.
因特网上的许多协议都假定链路是双向的。特别是，直接连接的路由器使用的路由协议在存在单向链路时不再正常工作。
The simplest solution is to emulate a broadcast capable link-layer network. This will allow the immediate deployment of existing higher level protocols without change. Though other network structures, such as NBMA, could also be emulated, a broadcast network is more generally useful. Though a layer 3 network could be emulated, a
最简单的解决方案是模拟支持广播的链路层网络。这将允许在不改变的情况下立即部署现有的更高级别协议。虽然也可以模拟其他网络结构，如NBMA，但广播网络通常更有用。虽然可以模拟第3层网络，但是
link-layer network allows the immediate use of any other network layer protocols, and most particularly allows the immediate use of ARP.
链路层网络允许立即使用任何其他网络层协议，尤其是允许立即使用ARP。
A link-layer tunneling mechanism which emulates bidirectional connectivity in the presence of a unidirectional link will be described in the next Section. We first consider the various communication scenarios which characterize a broadcast network in order to define what functionalities the link-layer tunneling mechanism has to perform in order to emulate a bidirectional broadcast link.
下一节将描述在存在单向链路的情况下模拟双向连接的链路层隧道机制。我们首先考虑描述广播网络的各种通信场景，以便定义链路层隧道机制必须执行哪些功能以模仿双向广播链路。
Here we enumerate the scenarios which would be feasible on a broadcast network, i.e., if feeds and receivers were connected by a bidirectional broadcast link:
这里我们列举了在广播网络上可行的场景，即，如果馈送和接收器通过双向广播链路连接：
Scenario 1: A receiver can send a packet to a feed (point-to-point communication between a receiver and a feed).
场景1：接收器可以向提要发送数据包（接收器和提要之间的点对点通信）。
Scenario 2: A receiver can send a broadcast/multicast packet on the link to all nodes (point-to-multipoint).
场景2：接收器可以在链路上向所有节点（点对多点）发送广播/多播数据包。
Scenario 3: A receiver can send a packet to another receiver (point-to-point communication between two receivers).
场景3：一个接收器可以向另一个接收器发送数据包（两个接收器之间的点对点通信）。
Scenario 4: A feed can send a packet to a send-only feed (point-to-point communication between two feeds).
场景4：提要可以将数据包发送到仅发送的提要（两个提要之间的点对点通信）。
Scenario 5: A feed can send a broadcast/multicast packet on the link to all nodes (point-to-multipoint).
场景5：提要可以在链路上将广播/多播数据包发送到所有节点（点对多点）。
Scenario 6: A feed can send a packet to a receiver or a receive capable feed (point-to-point).
场景6：提要可以将数据包发送给接收方或具有接收能力的提要（点对点）。
These scenarios are possible on a broadcast network. Scenario 6 is already feasible on the unidirectional link. The link-layer tunneling mechanism should therefore provide the functionality to support scenarios 1 to 5.
这些场景在广播网络上是可能的。场景6在单向链路上已经可行。因此，链路层隧道机制应提供支持场景1至5的功能。
Note that regular IP forwarding over such an emulated network (i.e., using the emulated network as a transit network) works correctly; the next hop address at the receiver will be the unidirectional link address of another router (a feed or a receiver) which will then relay the packet.
注意，在这样的模拟网络上的常规IP转发（即，使用模拟网络作为传输网络）工作正常；接收器处的下一跳地址将是另一个路由器（馈送或接收器）的单向链路地址，该路由器随后将中继数据包。
This link-layer tunneling mechanism operates underneath the network layer. Its aim is to emulate bidirectional link-layer connectivity. This is transparent to the network layer: the link appears and behaves to the network layer as if it was bidirectional.
这种链路层隧道机制在网络层下运行。其目的是模拟双向链路层连接。这对网络层是透明的：链接对网络层显示和行为就像它是双向的一样。
Figure 2 depicts a layered representation of the link-layer tunneling mechanism in the case of Scenario 1.
图2描述了场景1中链路层隧道机制的分层表示。
Send-only Feed Receiver
仅发送馈送接收器
decapsulation encapsulation
/-----***************----\ /-->---***************--\
| | | |
| | | |
--|---------------------- | | ---------------------|---
| | f1b | f1u | | | | x r1u | r1b | |
| | | ^ | | IP | | | | v |
| ^ | | | v | | | | | |
| | | | | | | | v | | |
|-|---------|-------|---| | | |----|------|--------|--|
| | | | | | ^ | | | | |
| | | | | | LL | | | | | |
| | | | | | | | | | | |
| | | O------/ \<------O | | |
|-|---------|-----------| |-----------|--------|--|
| | | | | | | |
| | | | PHY | | | |
| | | | | | v |
| | | | | | | | | |
--|-----------|---------- ----------|----------|---
| Bidir | Send-Only Recv-Only | Bidir |
^ Interf | Interf UDL Interf | Interf |
| \------------>------->------------/ |
\----------------------<------------------------<--------/
Bidirectional network
decapsulation encapsulation
/-----***************----\ /-->---***************--\
| | | |
| | | |
--|---------------------- | | ---------------------|---
| | f1b | f1u | | | | x r1u | r1b | |
| | | ^ | | IP | | | | v |
| ^ | | | v | | | | | |
| | | | | | | | v | | |
|-|---------|-------|---| | | |----|------|--------|--|
| | | | | | ^ | | | | |
| | | | | | LL | | | | | |
| | | | | | | | | | | |
| | | O------/ \<------O | | |
|-|---------|-----------| |-----------|--------|--|
| | | | | | | |
| | | | PHY | | | |
| | | | | | v |
| | | | | | | | | |
--|-----------|---------- ----------|----------|---
| Bidir | Send-Only Recv-Only | Bidir |
^ Interf | Interf UDL Interf | Interf |
| \------------>------->------------/ |
\----------------------<------------------------<--------/
Bidirectional network
x : IP layer at the receiver generates a datagram to be forwarded on the receive-only interface. O : Entry point where the link-layer tunneling mechanism is triggered.
接收方的x:IP层生成一个数据报，在仅接收接口上转发。O：触发链路层隧道机制的入口点。
Figure 2: Scenario 1 using the link-layer Tunneling Mechanism
图2：使用链路层隧道机制的场景1
On the receiver, a datagram is delivered to the link-layer of the unidirectional interface for transmission (see Figure 2). It is then encapsulated within a MAC header corresponding to the unidirectional link. This packet cannot be sent directly over the link, so it is then processed by the tunneling mechanism.
在接收器上，数据报被传送到单向接口的链路层进行传输（见图2）。然后将其封装在对应于单向链路的MAC报头中。此数据包不能直接通过链路发送，因此它随后由隧道机制处理。
The packet is encapsulated within an IP header whose destination is the IP address of a feed bidirectional interface (f1b or f2b). This destination address is also called the tunnel end-point. The mechanism for a receiver to learn these addresses and to choose the feed is explained in Section 7. The type of encapsulation is described in Section 8.
包被封装在IP报头中，其目的地是馈送双向接口（f1b或f2b）的IP地址。此目标地址也称为隧道端点。接收器学习这些地址并选择提要的机制在第7节中进行了解释。第8节描述了封装的类型。
In all cases the packet is encapsulated, but the tunnel end-point (an IP address) depends on the encapsulated packet's destination MAC address. If the destination MAC address is:
在所有情况下，数据包都是封装的，但隧道端点（IP地址）取决于封装数据包的目标MAC地址。如果目标MAC地址为：
1) the MAC address of a feed interface connected to the unidirectional link (Scenario 1). The datagram is encapsulated, the destination address of the encapsulating datagram is the feed tunnel end-point (f1b referring to Figure 2).
1) 连接到单向链路的馈送接口的MAC地址（场景1）。数据报被封装，封装数据报的目标地址是馈送通道端点（f1b参考图2）。
2) a MAC broadcast/multicast address (Scenario 2). The datagram is encapsulated, the destination address of the encapsulating datagram is the default feed tunnel end-point. See Section 7.4 for further details on the default feed.
2) MAC广播/多播地址（场景2）。数据报被封装，封装数据报的目标地址是默认的馈送通道端点。有关默认提要的更多详细信息，请参见第7.4节。
3) a MAC address that belongs to the unidirectional network but is not a feed address (Scenario 3). The datagram is encapsulated, the destination address of the encapsulating datagram is the default feed tunnel end-point.
3) 属于单向网络但不是馈送地址的MAC地址（场景3）。数据报被封装，封装数据报的目标地址是默认的馈送通道端点。
The encapsulated datagram is passed to the network layer which forwards it according to its destination address. The destination address is a feed bidirectional interface which is reachable via the Internet. In this case, the encapsulated datagram is forwarded via the receiver bidirectional interface (r1b).
封装的数据报被传递到网络层，网络层根据其目标地址转发数据报。目标地址是一个可通过互联网访问的馈送双向接口。在这种情况下，封装的数据报经由接收器双向接口（r1b）转发。
A feed processes unidirectional link related packets in two different ways:
feed以两种不同的方式处理单向链路相关数据包：
- packets generated by a local application or packets routed as usual by the IP layer may have to be forwarded over the unidirectional link (Section 6.2.1)
- 本地应用程序生成的数据包或通常由IP层路由的数据包可能必须通过单向链路转发（第6.2.1节）
- encapsulated packets received from another receiver or feed need tunnel processing (Section 6.2.2).
- 从另一个接收器或馈源接收的封装数据包需要隧道处理（第6.2.2节）。
A feed cannot directly send a packet to a send-only feed over the unidirectional link (Scenario 4). In order to emulate this type of communication, feeds have to tunnel packets to send-only feeds. A feed MUST maintain a list of all other feed tunnel end-points. This list MUST indicate which are send-only feed tunnel end-points. This is configured manually at the feed by the local administrator, as described in Section 7.
提要不能通过单向链路将数据包直接发送到仅发送的提要（场景4）。为了模拟这种类型的通信，feed必须通过隧道包来只发送feed。进料必须保留所有其他进料通道端点的列表。此列表必须指明哪些是仅发送给料通道端点。这是由本地管理员在提要上手动配置的，如第7节所述。
When a datagram is delivered to the link-layer of the unidirectional interface of a feed for transmission, its treatment depends on the packet's destination MAC address. If the destination MAC address is:
当数据报被传送到馈送的单向接口的链路层进行传输时，其处理取决于数据包的目的地MAC地址。如果目标MAC地址为：
1) the MAC address of a receiver or a receive capable feed (Scenario 6). The packet is sent over the unidirectional link. This is classical "forwarding".
1) 接收器或可接收馈送的MAC地址（场景6）。数据包通过单向链路发送。这是经典的“转发”。
2) the MAC address of a send-only feed (Scenario 4). The packet is encapsulated and sent to the send-only feed tunnel end-point. The type of encapsulation is described in Section 8.
2) 仅发送源的MAC地址（场景4）。数据包被封装并发送到仅发送的馈送通道端点。第8节描述了封装的类型。
3) a broadcast/multicast destination (Scenario 5). The packet is sent over the unidirectional link. Concurrently, a copy of this packet is encapsulated and sent to every feed of the list of send-only feed tunnel end-points. Thus the broadcast/multicast will reach all receivers and all send-only feeds.
3) 广播/多播目的地（场景5）。数据包通过单向链路发送。同时，该包的副本被封装并发送到仅发送馈送隧道端点列表的每个馈送。因此，广播/多播将到达所有接收器和所有仅发送提要。
Feeds listen for incoming encapsulated datagrams on their tunnel end-points. Encapsulated packets will have been received on a bidirectional interface, and traversed their way up the IP stack. They will then enter a decapsulation process (See Figure 2).
提要在其隧道端点上侦听传入的封装数据报。封装的数据包将在双向接口上接收，并沿着IP堆栈向上遍历。然后，它们将进入脱封过程（见图2）。
Decapsulation reveals the original link-layer packet. Note that this has not been modified in any way by intermediate routers; in particular, the original MAC header will be intact.
解封装显示原始链路层数据包。请注意，中间路由器没有以任何方式对其进行修改；特别是，原始MAC报头将完好无损。
Further actions depend on the destination MAC address of the link-layer packet, which can be:
进一步的操作取决于链路层分组的目的地MAC地址，其可以是：
1) the MAC address of the feed interface connected to the unidirectional link, i.e., own MAC address (Scenarios 1 and 4). The packet is passed to the link-layer of the interface connected to the unidirectional link which can then deliver it up to higher layers. As a result, the datagram is processed as if it was coming from the unidirectional link, and being delivered locally. Scenarios 1 and 4 are now feasible, a receiver or a feed can send a packet to a feed.
1) 连接到单向链路的馈送接口的MAC地址，即自己的MAC地址（场景1和场景4）。数据包被传递到连接到单向链路的接口的链路层，然后单向链路可以将数据包传递到更高的层。因此，数据报的处理就像来自单向链路一样，并在本地传递。场景1和场景4现在是可行的，接收器或提要可以向提要发送数据包。
2) a receiver address (Scenario 3). The packet is passed to the link-layer of the interface connected to the unidirectional link. It is directly sent over the unidirectional link, to the indicated receiver. Note, the packet must not be delivered locally. Scenario 3 is now feasible, a receiver can send a packet to another receiver.
2) 接收方地址（场景3）。数据包被传递到连接到单向链路的接口的链路层。它直接通过单向链路发送到指定的接收器。注意，数据包不能在本地传递。场景3现在是可行的，一个接收器可以向另一个接收器发送数据包。
3) a broadcast/multicast address, this corresponds to Scenarios 2 and 5. We have to distinguish two cases, either (i) the encapsulated packet was sent from a receiver or (ii) from a feed (encapsulated broadcast/multicast packet sent to a send-only feed). These cases are distinguished by examining the source address of the encapsulating packet and comparing it with the configured list of feed IP addresses. The action then taken is:
3) 广播/多播地址，对应于场景2和场景5。我们必须区分两种情况：（i）封装的数据包是从接收器发送的，或者（ii）来自提要（封装的广播/多播数据包发送到仅发送的提要）。通过检查封装包的源地址并将其与配置的提要IP地址列表进行比较，可以区分这些情况。随后采取的行动是：
i) the feed was designated as a default feed by a receiver to forward the broadcast/multicast packet. The feed is then in charge of sending the multicast packet to all nodes. Delivery to all nodes is accomplished by executing all 3 of the following actions:
i) 接收器将该提要指定为转发广播/多播数据包的默认提要。然后，feed负责向所有节点发送多播数据包。通过执行以下所有3个操作来完成对所有节点的传递：
- The packet is encapsulated and sent to the list of send-only feed tunnel end-points. - Also, the packet is passed to the link-layer of the interface which forwards it directly over the unidirectional link (all receivers and receive capable feeds receive it). - Also, the link-layer delivers it locally to higher layers.
- 数据包被封装并发送到仅发送馈送通道端点列表。-此外，数据包被传递到接口的链路层，该链路层直接通过单向链路转发数据包（所有接收器和具有接收能力的馈送都接收数据包）此外，链接层将其本地传送到更高的层。
Caution: a receiver which sends an encapsulated broadcast/multicast packet to a default feed will receive its own packet via the unidirectional link. Correct filtering as described in [RFC1112] must be applied.
警告：向默认提要发送封装的广播/多播数据包的接收器将通过单向链路接收自己的数据包。必须应用[RFC1112]中所述的正确过滤。
ii) the feed receives the packet and keeps it for local delivery. The packet is passed to the link-layer of the interface connected to the unidirectional link which delivers it to higher layers.
ii）提要接收数据包并将其保存以供本地交付。数据包被传递到连接到单向链路的接口的链路层，单向链路将数据包传递到更高层。
Scenario 2 is now feasible, a receiver can send a broadcast/multicast packet over the unidirectional link and it will be heard by all nodes.
场景2现在是可行的，接收器可以通过单向链路发送广播/多播数据包，所有节点都可以听到。
Receivers and feeds have to know the feed tunnel end-points in order to forward encapsulated datagrams (e.g., Scenarios 1 and 4).
接收器和馈送必须知道馈送通道端点，以便转发封装的数据报（例如，场景1和场景4）。
The number of feeds is expected to be relatively small (Section 3), so at every feed the list of all feeds is configured manually. This list should note which are send-only feeds, and which are receive capable feeds. The administrator sets up tunnels to all send-only feeds. A tunnel end-point is an IP address of a bidirectional link on a send-only feed.
feed的数量预计相对较少（第3节），因此在每个feed中，所有feed的列表都是手动配置的。此列表应注意哪些是仅发送提要，哪些是可接收提要。管理员为所有仅发送源设置通道。隧道端点是仅发送馈送上双向链路的IP地址。
For scalability reasons, manual configuration cannot be done at the receivers. Tunnels must be configured and maintained dynamically by receivers, both for scalability, and in order to cope with the following events:
出于可伸缩性的原因，无法在接收器上进行手动配置。接收器必须动态配置和维护隧道，以实现可伸缩性，并应对以下事件：
1) New feed detection. When a new feed comes up, every receiver must create a tunnel to enable bidirectional communication with it.
1) 新饲料检测。当一个新的feed出现时，每个接收器都必须创建一个隧道来实现与它的双向通信。
2) Loss of unidirectional link detection. When the unidirectional link is down, receivers must disable their tunnels. The tunneling mechanism emulates bidirectional connectivity between nodes. Therefore, if the unidirectional link is down, a feed should not receive datagrams from the receivers. Protocols that consider a link as operational if they receive datagrams from it (e.g., the RIP protocol [RFC2453]) require this behavior for correct operation.
2) 单向链路检测丢失。当单向链路断开时，接收器必须禁用其隧道。隧道机制模拟节点之间的双向连接。因此，如果单向链路断开，馈送不应接收来自接收器的数据报。如果一个链路从其接收数据报（例如RIP协议[RFC2453]），则需要考虑这种行为来进行正确的操作。
3) Loss of feed detection. When a feed is down, receivers must disable their corresponding tunnel. This prevents unnecessary datagrams from being tunneled which might overload the Internet. For instance, there is no need for receivers to forward a broadcast message through a tunnel whose end-point is down.
3) 饲料检测丢失。当馈源关闭时，接收器必须禁用相应的通道。这可以防止不必要的数据报被隧道传输，从而导致互联网过载。例如，接收器不需要通过端点向下的隧道转发广播消息。
The DTCP protocol provides a means for receivers to dynamically discover the presence of feeds and to maintain a list of operational tunnel end-points. Feeds periodically announce their tunnel end-point addresses over the unidirectional link. Receivers listen to these announcements and maintain a list of tunnel end-points.
DTCP协议为接收器提供了一种动态发现馈送存在并维护操作隧道端点列表的方法。提要通过单向链路定期宣布其隧道端点地址。接收者收听这些公告并保存隧道终点列表。
The DTCP protocol is a 'unidirectional protocol', messages are only sent from feeds to receivers.
DTCP协议是一种“单向协议”，消息仅从源发送到接收器。
The packet format is shown in Figure 3. Fields contain binary integers, in normal Internet order with the most significant bit first. Each tick mark represents one bit.
数据包格式如图3所示。字段包含二进制整数，按正常Internet顺序排列，最高位在前。每个记号代表一位。
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vers | Com | Interval | Sequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| res |F|IP Vers| Tunnel Type | Nb of FBIP | reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Feed BDL IP addr (FBIP1) (32/128 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ..... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Feed BDL IP addr (FBIPn) (32/128 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vers | Com | Interval | Sequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| res |F|IP Vers| Tunnel Type | Nb of FBIP | reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Feed BDL IP addr (FBIP1) (32/128 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ..... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Feed BDL IP addr (FBIPn) (32/128 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Packet Format
图3：数据包格式
Every datagram contains the following fields, note that constants are written in uppercase and are defined in Section 7.5:
每个数据报包含以下字段，请注意，常量以大写字母书写，并在第7.5节中定义：
Vers (4 bit unsigned integer): DTCP version number. MUST be DTCP_VERSION.
Vers（4位无符号整数）：DTCP版本号。必须是DTCP_版本。
Com (4 bit unsigned integer): Command field, possible values are 1 - JOIN A message announcing that the feed sending this message is up and running. 2 - LEAVE A message announcing that the feed sending this message is being shut down.
Com（4位无符号整数）：命令字段，可能的值为1-加入一条消息，宣布发送此消息的提要已启动并正在运行。2-留下一条消息，宣布发送此消息的源正在关闭。
Interval (8 bit unsigned integer): Interval in seconds between HELLO messages for the IP protocol in "IP Vers". Must be > 0. The recommended value is HELLO_INTERVAL. If this value is increased, the feed MUST continue to send HELLO messages at the old rate for at least the old HELLO_LEAVE period.
Interval（8位无符号整数）：IP协议的HELLO消息在“IP Vers”中的间隔（以秒为单位）。必须大于0。建议的值为HELLO_INTERVAL。如果此值增加，则提要必须至少在旧HELLO_休假期间继续以旧速率发送HELLO消息。
Sequence (16 bit unsigned integer): Random value initialized at boot time and incremented by 1 every time a value of the HELLO message is modified.
序列（16位无符号整数）：启动时初始化的随机值，每次修改HELLO消息的值时递增1。
res (3 bits): Reserved/unused field, MUST be zero.
res（3位）：保留/未使用字段，必须为零。
F (1 bit): bit indicating the type of feed: 0 = Send-only feed 1 = Receive-capable feed
F（1位）：表示馈送类型的位：0=仅发送馈送1=可接收馈送
IP Vers (4 bit unsigned integer): IP protocol version of the feed bidirectional IP addresses (FBIP): 4 = IP version 4 6 = IP version 6
IP版本（4位无符号整数）：馈送双向IP地址（FBIP）的IP协议版本：4=IP版本4 6=IP版本6
Tunnel Type (8 bit unsigned integer): tunneling protocol supported by the feed. This value is the IP protocol number defined in [RFC1700] [iana/protocol-numbers] and their legitimate descendents. Receivers MUST use this form of tunnel encapsulation when tunneling to the feed. 47 = GRE [RFC2784] (recommended) Other protocol types allowing link-layer encapsulation are permitted. Obtaining new values is documented in [RFC2780].
隧道类型（8位无符号整数）：提要支持的隧道协议。此值是[RFC1700][iana/协议编号]中定义的IP协议编号及其合法后代。当通过隧道传输到馈送时，接收器必须使用这种形式的隧道封装。47=GRE[RFC2784]（推荐）允许使用允许链路层封装的其他协议类型。获取新值记录在[RFC2780]中。
Nb of FBIP (8 bit unsigned integer): Number of bidirectional IP feed addresses which are enumerated in the HELLO message
FBIP的Nb（8位无符号整数）：在HELLO消息中枚举的双向IP馈送地址数
reserved (8 bits): Reserved/unused field, MUST be zero.
保留（8位）：保留/未使用字段，必须为零。
Feed BDL IP addr (32 or 128 bits). The bidirectional IP address feed is the IP address of a feed bidirectional interface (tunnel end-point) reachable via the Internet. A feed has 'Nb of FBIP' IP addresses which are operational tunnel end-points. They are enumerated in preferred order. FBIP1 being the most suitable tunnel end-point.
馈送BDL IP地址（32或128位）。双向IP地址馈送是可通过Internet访问的馈送双向接口（隧道端点）的IP地址。feed具有作为操作隧道端点的“Nb of FBIP”IP地址。它们是按优先顺序列举的。FBIP1是最合适的隧道端点。
The DTCP protocol runs on top of UDP. Packets are sent to the "DTCP announcement" multicast address over the unidirectional link on port HELLO_PORT with a TTL of 1. Due to existing deployments a feed SHOULD also support the use of the old DTCP announcement address, as described in Appendix B.
DTCP协议在UDP之上运行。数据包通过端口HELLO_端口上的单向链路发送到“DTCP公告”多播地址，TTL为1。由于现有部署，提要还应支持使用旧的DTCP公告地址，如附录B所述。
The source address of the HELLO packet is set to the IP address of the feed interface connected to the unidirectional link. In the rest of the document, this value is called FUIP (Feed Unidirectional IP address).
HELLO数据包的源地址设置为连接到单向链路的馈送接口的IP地址。在文档的其余部分中，该值称为FUIP（Feed单向IP地址）。
The process in charge of sending HELLO packets fills every field of the datagram according to the description given in Section 7.1.
根据第7.1节中给出的描述，负责发送HELLO数据包的过程填充数据报的每个字段。
As long as a feed is up and running, it periodically announces its presence to receivers. It MUST send HELLO packets containing a JOIN command every HELLO_INTERVAL over the unidirectional link.
只要feed启动并运行，它就会定期向接收者宣布它的存在。它必须在单向链路上每隔HELLO_间隔发送包含JOIN命令的HELLO数据包。
Referring to Figure 1 in Section 3, Feed 1 (resp. Feed 2) sends HELLO messages with the FBIP1 field set to f1b (resp. f2b).
参考第3节中的图1，Feed 1（resp.Feed 2）发送HELLO消息时，FBIP1字段设置为f1b（resp.f2b）。
When a feed is about to be shut down, or when routing over the unidirectional link is about to be intentionally interrupted, it is recommended that feeds:
当馈送即将关闭，或单向链路上的路由即将被有意中断时，建议馈送：
1) stop sending HELLO messages containing a JOIN command.
1) 停止发送包含JOIN命令的HELLO消息。
2) send a HELLO message containing a LEAVE command to inform receivers that the feed is no longer performing routing over the unidirectional link.
2) 发送包含LEAVE命令的HELLO消息，通知接收者提要不再通过单向链路执行路由。
Based on the reception of HELLO messages, receivers discover the presence of feeds, maintain a list of active feeds, and keep track of the tunnel end-points for those feeds.
基于对HELLO消息的接收，接收者发现feed的存在，维护活动feed的列表，并跟踪这些feed的隧道端点。
For each active feed, and each IP protocol supported, at least the following information will be kept:
对于每个活动提要和支持的每个IP协议，将至少保留以下信息：
FUIP - feed unidirectional link IP address FUMAC - MAC address corresponding to the above IP address (FBIP1,...,FBIPn) - list of tunnel end-points tunnel type - tunnel type supported by this feed Sequence - "Sequence" value from the last HELLO received from this feed timer - used to timeout this entry
FUIP-馈送单向链路IP地址FUMAC-与上述IP地址（FBIP1，…，FBIPn）对应的MAC地址-隧道端点列表-隧道类型-此馈送序列支持的隧道类型-从该馈送计时器接收到的最后一个HELLO的“序列”值-用于超时此条目
The FUMAC value for an active feed is needed for the operation of this protocol. However, the method of discovery of this value is not specified here.
本协议的操作需要有源馈电的FUMAC值。但是，此处未指定发现此值的方法。
Initially, the list of active feeds is empty.
最初，活动提要列表为空。
When a receiver is started, it MUST run a process which joins the "DTCP announcement" multicast group and listens to incoming packets on the HELLO_PORT port from the unidirectional link.
当接收器启动时，它必须运行一个进程，加入“DTCP公告”多播组并侦听来自单向链路的HELLO_端口上的传入数据包。
Upon the reception of a HELLO message, the process checks the version number of the protocol. If it is different from HELLO_VERSION, the packet is discarded and the process waits for the next incoming packet.
在接收到HELLO消息后，进程将检查协议的版本号。如果与HELLO_版本不同，则丢弃该数据包，进程等待下一个传入数据包。
After successfully checking the version number further action depends on the type of command:
成功检查版本号后，进一步的操作取决于命令的类型：
- JOIN:
- 加入：
The process verifies if the address FUIP already belongs to the list of active feeds.
该进程验证地址FUIP是否已属于活动源列表。
If it does not, a new entry, for feed FUIP, is created and added to the list of active feeds. The number of feed bidirectional IP addresses to read is deduced from the 'Nb of FBID' field. These tunnel end-points (FBIP1,...,FBIPn) can then be added to the new entry. The tunnel Type and Sequence values are also taken from the HELLO packet and recorded in the new entry. A timer set to HELLO_LEAVE is associated with this entry.
如果没有，将创建一个新条目，用于提要FUIP，并将其添加到活动提要列表中。要读取的馈送双向IP地址的数量是从“FBID的Nb”字段中推导出来的。然后可以将这些隧道端点（FBIP1，…，FBIPn）添加到新条目中。隧道类型和序列值也取自HELLO数据包，并记录在新条目中。设置为HELLO_LEAVE的计时器与此条目相关联。
If it does, the sequence number is compared to the sequence number contained in the previous HELLO packet sent by this feed. If they are equal, the timer associated with this entry is reset to HELLO_LEAVE. Otherwise all the information corresponding to FUIP is set to the values from the HELLO packet.
如果是，则将序列号与此提要发送的前一个HELLO数据包中包含的序列号进行比较。如果它们相等，则与此条目关联的计时器将重置为HELLO_LEAVE。否则，与FUIP对应的所有信息被设置为来自HELLO包的值。
Referring to Figure 1 in Section 3, both receivers (recv 1 and recv 2) have a list of active feeds containing two entries: Feed 1 with a FUIP of f1u and a list of tunnel end-points (f1b); and Feed 2 with a FUIP of f2u and a list of tunnel end-points (f2b).
参考第3节中的图1，两个接收器（recv 1和recv 2）都有一个有源馈源列表，其中包含两个条目：FUIP为f1u的馈源1和隧道端点列表（f1b）；并用f2u的FUIP和隧道端点列表（f2b）馈送2。
- LEAVE:
- 离开：
The process checks if there is an entry for FUIP in the list of active feeds. If there is, the timer is disabled and the entry is deleted from the list. The LEAVE message provides a means of quickly updating the list of active feeds.
该过程检查活动提要列表中是否有FUIP条目。如果有，计时器将被禁用，条目将从列表中删除。“离开”消息提供了一种快速更新活动提要列表的方法。
A timeout occurs for either of two reasons:
发生超时的原因有两种：
1) a feed went down without sending a LEAVE message. As JOIN messages are no longer sent from this feed, a timeout occurs at HELLO_LEAVE after the last JOIN message.
1) 一个订阅源没有发送留言就被关闭了。由于不再从此订阅源发送加入消息，在最后一条加入消息之后的HELLO_LEAVE处会发生超时。
2) the unidirectional link is down. Thus no more JOIN messages are received from any of the feeds, and they will each timeout independently. The timeout of each entry depends on its
2) 单向链路断开。因此，不再从任何提要接收更多的JOIN消息，它们将各自超时。每个条目的超时取决于其属性
individual HELLO_LEAVE value, and when the last JOIN message was sent by that feed, before the unidirectional link went down.
单个HELLO_LEAVE值，以及当该提要发送最后一条加入消息时，单向链接关闭之前。
In either case, bidirectional connectivity can no longer be ensured between the receiver and the feed (FUIP): either the feed is no longer routing datagrams over the unidirectional link, or the link is down. Thus the associated entry is removed from the list of active feeds, whatever the cause. As a result, the list only contains operational tunnel end-points.
在任何一种情况下，都无法再确保接收器和馈送（FUIP）之间的双向连接：馈送不再通过单向链路路由数据报，或者链路断开。因此，无论是什么原因，相关条目都将从活动提要列表中删除。因此，该列表仅包含运行隧道端点。
The HELLO protocol provides receivers with a list of feeds, and a list of usable tunnel end-points (FBIP1,..., FBIPn) for each feed. In the following Section, we describe how to integrate the HELLO protocol into the tunneling mechanism described in Sections 6.1 and 6.2.
HELLO协议为接收器提供了一个提要列表，以及每个提要的可用隧道端点列表（FBIP1，…，FBIPn）。在下一节中，我们将描述如何将HELLO协议集成到第6.1节和第6.2节中描述的隧道机制中。
This Section explains how the tunneling mechanism uses the list of active feeds to handle datagrams which are to be tunneled. Referring to Section 6.1, it shows how feed tunnel end-points are selected.
本节解释了隧道机制如何使用活动提要列表来处理要通过隧道传输的数据报。参考第6.1节，它说明了如何选择进料通道端点。
The choice of the default feed is made independently at each receiver. The choice is a matter of local policy, and this policy is out of scope for this document. However, as an example, the default feed may be the feed that has the lowest round trip time to the receiver.
默认馈源的选择在每个接收器上独立进行。选择取决于当地政策，本政策不在本文件范围内。然而，作为示例，默认馈送可以是到接收器的往返时间最低的馈送。
When a receiver sends a packet to a feed, it must choose a tunnel end-point from within the FBIP list. The 'preferred FBIP' is generally FBIP1 (Section 7.1). For various reasons, a receiver may decide to use a different FBIP, say FBIPi instead of FBIP1, as the tunnel end-point. For example, the receiver may have better connectivity to FBIPi. This decision is taken by the receiver administrator.
当接收器向提要发送数据包时，它必须从FBIP列表中选择隧道端点。“首选FBIP”通常为FBIP1（第7.1节）。出于各种原因，接收器可能决定使用不同的FBIP，例如FBIPi而不是FBIP1，作为隧道端点。例如，接收机可以具有到FBIPi的更好的连接。此决定由接收方管理员做出。
Here we show how the list of active feeds is involved when a receiver tunnels a link-layer packet. Section 6.1 listed the following cases, depending on whether the MAC destination address of the packet is:
在这里，我们展示了当接收器对链路层数据包进行隧道传输时，活动提要列表是如何涉及的。第6.1节列出了以下情况，具体取决于数据包的MAC目的地址是否为：
1) the MAC address of a feed interface connected to the unidirectional link: This is TRUE if the address matches a FUMAC address in the list of active feeds. The packet is tunneled to the preferred FBIP of the matching feed.
1) 连接到单向链路的馈送接口的MAC地址：如果地址与活动馈送列表中的FUMAC地址匹配，则为真。数据包通过隧道传输到匹配馈送的首选FBIP。
2) the broadcast address of the unidirectional link or a multicast address:
2) 单向链路的广播地址或多播地址：
This is determined by the MAC address format rules, and the list of active feeds is not involved. The packet is tunneled to the preferred FBIP of the default feed.
这由MAC地址格式规则决定，不涉及活动提要列表。数据包通过隧道传输到默认源的首选FBIP。
3) an address that belongs to the unidirectional network but is not a feed address: This is TRUE if the address is neither broadcast nor multicast, nor found in the list of active feeds. The packet is tunneled to the preferred FBIP of the default feed.
3) 属于单向网络但不是源地址的地址：如果该地址既不是广播地址，也不是多播地址，也没有在活动源列表中找到，则为真。数据包通过隧道传输到默认源的首选FBIP。
In all cases, the encapsulation type depends on the tunnel type required by the feed which is selected.
在所有情况下，封装类型取决于所选馈送所需的通道类型。
DTCP_VERSION is 1.
DTCP_版本为1。
HELLO_INTERVAL is 5 seconds.
你好，间隔5秒。
"DTCP announcement" multicast group is 224.0.0.36, assigned by IANA.
“DTCP公告”多播组为224.0.0.36，由IANA分配。
HELLO_PORT is 652. It is a reserved system port assigned by IANA, no other traffic must be allowed.
你好，港口是652。它是IANA分配的保留系统端口，不允许其他通信。
HELLO_LEAVE is 3*Interval, as advertised in a HELLO packet, i.e., 15 seconds if the default HELLO_INTERVAL was advertised.
HELLO_LEAVE是3*间隔，如HELLO数据包中所公布的，即，如果公布了默认的HELLO_间隔，则为15秒。
The tunneling mechanism operates at the link-layer and emulates bidirectional connectivity amongst receivers and feeds. We assume that hardware connected to the unidirectional link supports broadcast and unicast MAC addressing. That is, a feed can send a packet to a particular receiver using a unicast MAC destination address or to a set of receivers using a broadcast/multicast destination address. The hardware (or the driver) of the receiver can then filter the incoming packets sent over the unidirectional links without any assumption about the encapsulated data type.
隧道机制在链路层运行，模拟接收器和馈源之间的双向连接。我们假设连接到单向链路的硬件支持广播和单播MAC寻址。也就是说，提要可以使用单播MAC目的地地址向特定接收机发送分组，或者使用广播/多播目的地地址向一组接收机发送分组。然后，接收器的硬件（或驱动器）可以过滤通过单向链路发送的传入数据包，而无需对封装的数据类型进行任何假设。
In a similar way, a receiver should be capable of sending unicast and broadcast MAC packets via its tunnels. Link-layer packets are encapsulated. As a result, after decapsulating an incoming packet, the feed can perform link-layer filtering as if the data came directly from the unidirectional link (See Figure 2).
以类似的方式，接收器应该能够通过其隧道发送单播和广播MAC数据包。链路层数据包被封装。因此，在对传入数据包解除封装后，feed可以执行链路层过滤，就好像数据直接来自单向链路一样（见图2）。
Generic Routing Encapsulation (GRE) [RFC2784] suits our requirements because it specifies a protocol for encapsulating arbitrary packets, and allows use of IP as the delivery protocol.
通用路由封装（GRE）[RFC2784]适合我们的要求，因为它指定了封装任意数据包的协议，并允许使用IP作为传递协议。
The feed's local administrator decides what encapsulation it will demand that receivers use, and sets the tunnel type field in the HELLO message appropriately. The value 47 (decimal) indicates GRE. Other values can be used, but their interpretation must be agreed upon between feeds and receivers. Such usage is not defined here.
提要的本地管理员决定它将要求接收者使用什么封装，并在HELLO消息中适当地设置隧道类型字段。值47（十进制）表示GRE。可以使用其他值，但它们的解释必须在提要和接收者之间达成一致。这里没有定义这种用法。
A GRE packet is composed of a header in which a type field specifies the encapsulated protocol (ARP, IP, IPX, etc.). See [RFC2784] for details about the encapsulation. In our case, only support for the MAC addressing scheme of the unidirectional link MUST be implemented.
GRE数据包由标头组成，其中类型字段指定封装的协议（ARP、IP、IPX等）。有关封装的详细信息，请参见[RFC2784]。在我们的例子中，只能实现对单向链路的MAC寻址方案的支持。
A packet tunneled with a GRE encapsulation has the following format: the delivery header is an IP header whose destination is the tunnel end-point (FBIP), followed by a GRE header specifying the link-layer type of the unidirectional link. Figure 4 presents the entire encapsulated packet.
通过GRE封装进行隧道传输的数据包具有以下格式：传递头是目的地为隧道端点（FBIP）的IP头，后跟指定单向链路的链路层类型的GRE头。图4显示了整个封装包。
----------------------------------------
| IP delivery header |
| destination addr = FBIP |
| IP proto = GRE (47) |
----------------------------------------
| GRE Header |
| type = MAC type of the UDL |
----------------------------------------
| Payload packet |
| MAC packet |
----------------------------------------
----------------------------------------
| IP delivery header |
| destination addr = FBIP |
| IP proto = GRE (47) |
----------------------------------------
| GRE Header |
| type = MAC type of the UDL |
----------------------------------------
| Payload packet |
| MAC packet |
----------------------------------------
Figure 4: Encapsulated packet
图4：封装的数据包
Regardless of whether the link is unidirectional or bidirectional, if a feed sends a packet over a non-point-to-point type network, it requires the data link address of the destination. ARP [RFC826] is used on Ethernet networks for this purpose.
无论链路是单向的还是双向的，如果提要通过非点对点类型的网络发送数据包，它都需要目的地的数据链路地址。ARP[RFC826]用于以太网网络。
The link-layer mechanism emulates a bidirectional network in the presence of an unidirectional link. However, there are asymmetric delays between every (feed, receiver) pair. The backchannel between a receiver and a feed has varying delays because packets go through the Internet. Furthermore, a typical example of a unidirectional link is a GEO satellite link whose delay is about 250 milliseconds.
链路层机制模拟存在单向链路的双向网络。然而，每个（馈源、接收器）对之间都存在不对称延迟。由于数据包通过互联网，接收器和馈送之间的反向通道具有不同的延迟。此外，单向链路的典型示例是延迟约为250毫秒的GEO卫星链路。
Because of long round trip delays, reactive address resolution methods such as ARP [RFC826] may not work well. For example, a feed may have to forward packets at high data rates to a receiver whose hardware address is unknown. The stream of packets is passed to the link-layer driver of the feed send-only interface. When the first packet arrives, the link-layer realizes it does not have the corresponding hardware address of the next hop, and sends an ARP request. While the link-layer is waiting for the response (at least 250 ms for the GEO satellite case), IP packets are buffered by the feed. If it runs out of space before the ARP response arrives, IP packets will be dropped.
由于长的往返延迟，像ARP[RFC826]这样的反应式地址解析方法可能无法很好地工作。例如，提要可能必须以高数据速率将数据包转发给硬件地址未知的接收器。数据包流被传递到feed-send-only接口的链路层驱动程序。当第一个数据包到达时，链路层意识到它没有下一跳的相应硬件地址，并发送ARP请求。当链路层等待响应时（对于GEO卫星情况，至少250 ms），IP数据包由馈送缓冲。如果在ARP响应到达之前空间不足，IP数据包将被丢弃。
This problem of address resolution protocols is not addressed in this document. An ad-hoc solution is possible when the MAC address is configurable, which is possible in some satellite receiver cards. A simple transformation (maybe null) of the IP address can then be used as the MAC address. In this case, senders do not need to "resolve" an IP address to a MAC address, they just need to perform the simple transformation.
本文档未解决地址解析协议的这个问题。当MAC地址是可配置的时，一个特别的解决方案是可能的，这在一些卫星接收器卡中是可能的。然后，IP地址的简单转换（可能为空）可以用作MAC地址。在这种情况下，发送者不需要将IP地址“解析”为MAC地址，他们只需要执行简单的转换。
The link-layer tunneling mechanism hides from the network and higher layers the fact that feeds and receivers are connected by a unidirectional link. Communication is bidirectional, but asymmetric in bandwidths and delays.
链路层隧道机制向网络和更高层隐藏了馈源和接收器通过单向链路连接的事实。通信是双向的，但在带宽和延迟方面是不对称的。
In order to incorporate unidirectional links in the Internet, feeds and receivers might have to run routing protocols in some topologies. These protocols will work fine because the tunneling mechanism results in bidirectional connectivity between all feeds and receivers. Thus routing messages can be exchanged as on any bidirectional network.
为了将单向链路合并到Internet中，提要和接收器可能必须在某些拓扑中运行路由协议。这些协议可以很好地工作，因为隧道机制会导致所有提要和接收机之间的双向连接。因此，可以像在任何双向网络上一样交换路由消息。
The tunneling mechanism allows any IP traffic, not just routing protocol messages, to be forwarded between receivers and feeds. Receivers can route datagrams on the Internet using the most suitable feed or receiver as a next hop. Administrators may want to set the metrics used by their routing protocols in order to reflect in routing tables the asymmetric characteristics of the link, and thus direct traffic over appropriate paths.
隧道机制允许任何IP通信，而不仅仅是路由协议消息，在接收器和提要之间转发。接收器可以使用最合适的馈源或接收器作为下一跳在互联网上路由数据报。管理员可能希望设置其路由协议使用的度量，以便在路由表中反映链路的不对称特性，从而通过适当的路径引导流量。
Feeds and receivers may implement multicast routing and therefore dynamic multicast routing can be performed over the unidirectional link. However issues related to multicast routing (e.g., protocol configuration) are not addressed in this document.
馈源和接收器可以实现多播路由，因此可以在单向链路上执行动态多播路由。但是，与多播路由相关的问题（例如，协议配置）未在本文档中讨论。
The DTCP protocol does not generate a lot of traffic whatever the number of nodes. The problem with a large number of nodes is not related to this protocol but to more general issues such as the maximum number of nodes which can be connected to any link. This is out of scope of this document.
DTCP协议不会产生大量的通信量，无论节点的数量如何。大量节点的问题与此协议无关，而是与更一般的问题有关，例如可以连接到任何链路的最大节点数。这超出了本文档的范围。
IANA has reserved the address 224.0.0.36 for the "DTCP announcement" multicast address as defined in Section 7.
IANA已为第7节中定义的“DTCP公告”多播地址保留了地址224.0.0.36。
IANA has reserved the udp port 652 for the HELLO_PORT as defined in Section 7.
IANA为第7节中定义的HELLO_端口保留了udp端口652。
Many unidirectional link technologies are characterised by the ease with which the link contents can be received. If sensitive or valuable information is being sent, then link-layer security mechanisms are an appropriate measure. For the UDLR protocol itself, the feed tunnel end-point addresses, sent in HELLO messages, may be considered sensitive. In such cases link-layer security mechanisms may be used.
许多单向链接技术的特点是易于接收链接内容。如果发送敏感或有价值的信息，则链路层安全机制是一种适当的措施。对于UDLR协议本身，在HELLO消息中发送的馈送通道端点地址可能被认为是敏感的。在这种情况下，可以使用链路层安全机制。
Security in a network using the link-layer tunneling mechanism should be relatively similar to security in a normal IPv4 network. However, as the link-layer tunneling mechanism requires the use of tunnels, it introduces a potential for unauthorised access to the service. In particular, ARP and IP spoofing are potential threats because nodes may not be authorised to tunnel packets. This can be countered by authenticating all tunnels. The authenticating mechanism is not specified in this document, it can take place either in the delivery IP protocol (e.g., AH[RFC2402]) or in an authentication protocol integrated with the tunneling mechanism.
使用链路层隧道机制的网络中的安全性应该与正常IPv4网络中的安全性相对类似。但是，由于链路层隧道机制需要使用隧道，因此可能会导致未经授权访问服务。特别是，ARP和IP欺骗是潜在的威胁，因为节点可能未被授权对数据包进行隧道传输。这可以通过验证所有隧道来应对。本文件中未规定认证机制，认证机制可以在交付IP协议（例如，AH[RFC2402]）或与隧道机制集成的认证协议中发生。
At a higher level, receivers may not be authorised to provide routing information even though they are connected to the unidirectional link. In order to prevent unauthorised receivers from providing fake routing information, routing protocols running on top of the link-layer tunneling mechanism MUST use authentication mechanisms when available.
在更高级别上，即使接收器连接到单向链路，也可能无权提供路由信息。为了防止未经授权的接收者提供虚假的路由信息，在链路层隧道机制之上运行的路由协议必须在可用时使用身份验证机制。
We would like to thank Tim Gleeson (Cisco Japan) for his valuable editing and technical input during the finalization phase of the document.
我们要感谢Tim Gleeson（思科日本公司）在文件定稿阶段提供的宝贵编辑和技术投入。
We would like to thank Patrick Cipiere (UDcast) for his valuable input concerning the design of the encapsulation mechanism.
我们要感谢Patrick Cipiere（UDcast）对封装机制设计的宝贵意见。
We would like also to thank for their participation: Akihiro Tosaka (IMD), Akira Kato (Tokyo Univ.), Hitoshi Asaeda (IBM/ITS), Hiromi Komatsu (JSAT), Hiroyuki Kusumoto (Keio Univ.), Kazuhiro Hara (Sony), Kenji Fujisawa (Sony), Mikiyo Nishida (Keio Univ.), Noritoshi Demizu (Sony CSL), Jun Murai (Keio Univ.), Jun Takei (JSAT) and Harri Hakulinen (Nokia).
我们还要感谢他们的参与：Tosaka明博（IMD）、加藤明博（东京大学）、浅田仁（IBM/ITS）、小松广美（JSAT）、Kusumoto广幸（庆应大学）、Hara Kazuhiro Hara（索尼）、藤泽健二（索尼）、西田美纪子（庆应大学）、北藤俊二（索尼CSL）、村村俊（庆应大学）、武井俊（庆应大学）和哈里哈库宁（诺基亚）。
Appendix A: Conformance and interoperability
附录A：一致性和互操作性
This document describes a mechanism to emulate bidirectional connectivity between nodes that are directly connected by a unidirectional link. Applicability over a variety of equipment and environments is ensured by allowing a choice of several key system parameters.
本文档描述了一种模拟由单向链路直接连接的节点之间的双向连接的机制。通过允许选择几个关键系统参数，可确保对各种设备和环境的适用性。
Thus in order to ensure interoperability of equipment it is not enough to simply claim conformance with the mechanism defined here. A usage profile for a particular environment will require the definition of several parameters:
因此，为了确保设备的互操作性，仅仅声称符合此处定义的机制是不够的。特定环境的使用配置文件需要定义几个参数：
- the MAC format used - the tunneling mechanism to be used (GRE is recommended) - the "tunnel type" indication if GRE is not used
- 使用的MAC格式-要使用的隧道机制（建议使用GRE）-如果未使用GRE，“隧道类型”指示
For example, a system might claim to implement "the link-layer tunneling mechanism for unidirectional links, using IEEE 802 LLC, and GRE encapsulation for the tunnels."
例如，一个系统可能声称实现“单向链路的链路层隧道机制，使用IEEE 802 LLC和隧道的GRE封装。”
Appendix B: DTCP announcement address transition plan
附录B：DTCP公告地址过渡计划
Some older receivers listen for DTCP announcements on the 224.0.1.124 multicast address (the "old DTCP announcement" address). In order to support such legacy receivers, feeds SHOULD be configurable to send all announcements simultaneously to both the "DTCP announcement" address, and the "old DTCP announcement" address. The default setting is to send announcements to just the "DTCP announcement" address.
一些较旧的接收器在224.0.1.124多播地址（“旧DTCP公告”地址）上侦听DTCP公告。为了支持此类遗留接收器，提要应可配置为同时向“DTCP公告”地址和“旧DTCP公告”地址发送所有公告。默认设置是只向“DTCP公告”地址发送公告。
In order to encourage the transition plan, the "old" feeds MUST be updated to send DTCP announcements as defined in this section. The number of "old" feeds originally deployed is relatively small and therefore the update should be fairly easy. "New" receivers only support "new" feeds, i.e., they listen to DTCP announcements on the "DTCP announcement" address.
为了鼓励过渡计划，必须更新“旧”提要以发送本节中定义的DTCP公告。最初部署的“旧”提要数量相对较少，因此更新应该相当容易。“新”接收器仅支持“新”源，即，他们收听“DTCP公告”地址上的DTCP公告。
References
工具书类
[RFC826] Plummer, D., "An Ethernet Address Resolution Protocol", STD 37, RFC 826, November 1982.
[RFC826]Plummer，D.，“以太网地址解析协议”，STD 37，RFC 826，1982年11月。
[RFC1112] Deering, S., "Host Extensions for IP Multicasting", STD 5, RFC 1112, August 1989
[RFC1112]Deering，S.，“IP多播的主机扩展”，STD 5，RFC11121989年8月
[RFC1700] Reynolds, J. and J. Postel, "ASSIGNED NUMBERS", STD 2, RFC 1700, October 1994.
[RFC1700]Reynolds，J.和J.Postel，“分配的数字”，标准2，RFC 1700，1994年10月。
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2119]Bradner，S.，“RFC中用于表示需求水平的关键词”，BCP 14，RFC 2119，1997年3月。
[RFC2402] Kent, S. and R. Atkinson, "IP Authentication Header", RFC 2402, November 1998.
[RFC2402]Kent，S.和R.Atkinson，“IP认证头”，RFC 2402，1998年11月。
[RFC2453] Malkin, G., "RIP Version 2", STD 56, RFC 2453, November 1998.
[RFC2453]Malkin，G.，“RIP版本2”，STD 56，RFC 2453，1998年11月。
[RFC2780] Bradner, S. and V. Paxson, "IANA Allocation Guidelines For Values In the Internet Protocol and Related Headers", BCP 37, RFC 2780, March 2000.
[RFC2780]Bradner，S.和V.Paxson，“互联网协议和相关报头中值的IANA分配指南”，BCP 37，RFC 2780，2000年3月。
[RFC2784] Farinacci, D., Hanks, S., Meyer, D. and P. Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, March 2000.
[RFC2784]Farinaci，D.，Hanks，S.，Meyer，D.和P.Traina，“通用路由封装（GRE）”，RFC 2784，2000年3月。
Authors' Addresses
作者地址
Emmanuel Duros UDcast 1681, route des Dolines Les Taissounieres - BP 355 06906 Sophia-Antipolis Cedex France
Emmanuel Duros UDcast 1681，法国索菲亚-安提波利斯-塞德克斯索菲娅-安提波利斯公路-英国石油公司355 06906号
Phone : +33 4 93 00 16 60
Fax : +33 4 93 00 16 61
EMail : Emmanuel.Duros@UDcast.com
Phone : +33 4 93 00 16 60
Fax : +33 4 93 00 16 61
EMail : Emmanuel.Duros@UDcast.com
Walid Dabbous INRIA Sophia Antipolis 2004, Route des Lucioles BP 93 06902 Sophia Antipolis France
Walid Dabbous INRIA Sophia Antipolis 2004，Lucioles路线BP 93 06902 Sophia Antipolis法国
Phone : +33 4 92 38 77 18
Fax : +33 4 92 38 79 78
EMail : Walid.Dabbous@inria.fr
Phone : +33 4 92 38 77 18
Fax : +33 4 92 38 79 78
EMail : Walid.Dabbous@inria.fr
Hidetaka Izumiyama JSAT Corporation Toranomon 17 Mori Bldg.5F 1-26-5 Toranomon, Minato-ku Tokyo 105 Japan
Hidetaka Izumiyama JSAT Corporation Toranomon 17 Mori Bldg.5楼Toranomon，Minato ku东京105
Phone : +81-3-5511-7568
Fax : +81-3-5512-7181
EMail : izu@jsat.net
Phone : +81-3-5511-7568
Fax : +81-3-5512-7181
EMail : izu@jsat.net
Noboru Fujii Sony Corporation 2-10-14 Osaki, Shinagawa-ku Tokyo 141 Japan
日本东京市新川区大阪2-10-14号藤井信介索尼公司141
Phone : +81-3-3495-3092
Fax : +81-3-3495-3527
EMail : fujii@dct.sony.co.jp
Phone : +81-3-3495-3092
Fax : +81-3-3495-3527
EMail : fujii@dct.sony.co.jp
Yongguang Zhang HRL RL-96, 3011 Malibu Canyon Road Malibu, CA 90265, USA
张永光HRL RL-96，美国加利福尼亚州马里布市马里布峡谷路3011号，邮编90265
Phone : 310-317-5147 Fax : 310-317-5695 EMail : ygz@hrl.com
电话：310-317-5147传真：310-317-5695电子邮件：ygz@hrl.com
Full Copyright Statement
完整版权声明
Copyright (C) The Internet Society (2001). All Rights Reserved.
版权所有（C）互联网协会（2001年）。版权所有。
This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English.
本文件及其译本可复制并提供给他人，对其进行评论或解释或协助其实施的衍生作品可全部或部分编制、复制、出版和分发，不受任何限制，前提是上述版权声明和本段包含在所有此类副本和衍生作品中。但是，不得以任何方式修改本文件本身，例如删除版权通知或对互联网协会或其他互联网组织的引用，除非出于制定互联网标准的需要，在这种情况下，必须遵循互联网标准过程中定义的版权程序，或根据需要将其翻译成英语以外的其他语言。
The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns.
上述授予的有限许可是永久性的，互联网协会或其继承人或受让人不会撤销。
This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
本文件和其中包含的信息是按“原样”提供的，互联网协会和互联网工程任务组否认所有明示或暗示的保证，包括但不限于任何保证，即使用本文中的信息不会侵犯任何权利，或对适销性或特定用途适用性的任何默示保证。
Acknowledgement
确认
Funding for the RFC Editor function is currently provided by the Internet Society.
RFC编辑功能的资金目前由互联网协会提供。