rfc1504.txt
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Once the data receiver opens a connection using the underlying transport, the data receiver sends an Open Request packet, or Open- Req, to the data sender. An Open-Req packet includes the following information: Send update information flags: The states of the four send update information (SUI) flags indicate whether the data sender should send various types of update information over the connection. Typically, the four SUI flags are set to 1. Version number: The version number field indicates the version of AURP used by the data receiver. The current version number of AURP is 1. Data field: The optional data field allows exterior routers with capabilities beyond those described in this document to notify other exterior routers about such options, by initiating option negotiation. An exterior router that has similar capabilities indicates that it accepts the options, completing option negotiation. An exterior router that lacks such options ignores the information in the data field. Open Response Packet When an exterior router receives an Open-Req, it becomes the data sender and responds with an Open Response packet, or Open-Rsp, as follows: If the exterior router accepts the connection, it returns information about its setup in the Open-Rsp. An Open-Rsp also contains an optional data field. This data field indicates whether the exterior router accepts the options in the data field of the Open-Req to which it is responding. If the exterior router cannot accept the connection-for example, because the Open-Req does not contain the correct version number-it returns an error in the Open-Rsp and closes the transport-layer connection. Figure 3-6 shows a connection-opening dialog between a data sender and a data receiver. <<Figure 3-6 Connection-opening dialog>>Oppenheimer [Page 23] RFC 1504 Appletalk Update-Based Routing Protocol August 1993 Routing Information Request Packet Under AURP, once two exterior routers establish a connection, the data receiver can request the data sender to send its routing information by sending it a Routing Information Request packet, or RI-Req. Routing Information Response Packets When the data sender receives an RI-Req, it reliably sends a sequence of Routing Information Response packets, or RI-Rsp, to the exterior router requesting the information. The RI-Rsp packets provide a list of exported networks on the data sender's local internet and the distance of each network from the data sender. The data sender must finish sending RI-Rsp packets to the exterior router requesting routing information before it can send any other sequenced data over the connection. Figure 3-7 shows a routing-information request/response dialog between a data sender and a data receiver. <<Figure 3-7 Routing-information request/response dialog>> Zone Information Request Packet The data receiver can obtain zone information for known networks on the data sender's local internet at any time, by sending it a Zone Information Request packet, or ZI-Req. A ZI-Req lists the numbers of networks for which the data receiver is requesting zone information. IMPORTANT: To prevent other exterior routers on a tunnel from sending endless streams of ZI-Req packets across the tunnel-causing what is referred to as a ZIP storm-an exterior router must not export information about a network until it has a complete zone list for that network. Zone Information Response Packets When the data sender receives a ZI-Req, it responds by sending unsequenced Zone Information Response packets, or ZI-Rsp, to the data receiver. Zone information is transaction data-thus, its reliable delivery is not guaranteed. Figure 3-8 shows a zone-information request/response dialog between a data sender and a data receiver. <<Figure 3-8 Zone-information request/response dialog>>Oppenheimer [Page 24] RFC 1504 Appletalk Update-Based Routing Protocol August 1993 Recovering Lost Zone Information A data receiver enters a network-to-zone list association in its routing table for each network for which it receives a ZI-Rsp packet. If a data receiver that requested zone information for a network does not receive a complete zone list for that network, it must retransmit ZI-Req packets, requesting zone information for that network, until it receives that network's complete zone information. To determine if any ZI-Rsp packets were lost, the data receiver periodically scans its routing table for networks for which the associated zone lists are incomplete-that is, for zone lists that do not include all zones associated with the networks. The data receiver sends a ZI-Req to each data sender from which it received incomplete zone information, listing the numbers of networks for which it has incomplete zone lists. The data sender responds to zone information requests by sending ZI-Rsp packets containing the requested information to the data receiver. Using AURP-Tr for Initial Information Exchange The following sections describe the use of AURP-Tr-the default transport-layer service for AURP-for initial information exchange. OPEN REQUEST PACKET: An exterior router sends an Open-Req packet to request that an AURP-Tr one-way connection with another exterior router be established specify the connection ID for that connection pass the AURP version number, SUI flags, and optional data to the other exterior router If the exterior router does not receive an Open-Rsp from the exterior router to which it sent an Open-Req, it must retransmit the Open-Req. OPEN RESPONSE PACKET: When using AURP-Tr, an exterior router sends an Open-Rsp to acknowledge that a one-way connection has been established reject a connection return information about its environment, as well as any optional data, to the exterior router from which it received an Open-ReqOppenheimer [Page 25] RFC 1504 Appletalk Update-Based Routing Protocol August 1993 If an exterior router receives an Open-Req on a one-way connection that is already open-that is, if it receives an Open-Req with the same connection ID as an open one-way connection-an Open-Rsp sent previously may have been lost. The exterior router receiving the duplicate Open-Req should send a duplicate Open-Rsp to the sending exterior router, unless it has already received some other packet on the connection-such as an RI-Req-indicating the existence of a fully established connection. ROUTING INFORMATION RESPONSE PACKETS: When responding to a request for routing information using AURP-Tr, an exterior router sends a sequence of RI-Rsp packets to the exterior router requesting the information. However, an exterior router's complete list of network numbers often fits in a single RI-Rsp packet. Each RI-Rsp packet contains the following information: Connection ID: The connection ID identifies the specific one-way connection to which a packet belongs. Sequence number: The sequence number identifies an individual packet on a connection. Packets on a connection are numbered starting with the number 1. The data sender sending routing information must wait for the data receiver to acknowledge that it has received each RI-Rsp packet in the sequence-by sending an RI-Ack packet-before sending the next RI- Rsp packet. Each RI-Rsp contains a flag that indicates whether it is the last packet in the sequence. In the last RI-Rsp in the sequence, this flag is set to 1. If the data sender receives no acknowledgment of an RI-Rsp from the data receiver within a specified period of time, it must retransmit the RI-Rsp. ROUTING INFORMATION RESPONSE PACKETS: When an exterior router receives an RI-Rsp, it verifies the packet's connection ID and sequence number. The connection ID must be the same as that in the Open-Req. The sequence number must be either the last sequence number received, indicating that the previous acknowledgment was lost or delayed, and that this is a duplicate RI-Rsp the next number in the sequence, indicating that this RI-Rsp contains new routing information If the connection ID or sequence number is invalid, the data receiver discards the packet. Figure 3-9 shows a dialog between a data sender and a data receiver in which the data receiver requests routing information, the data sender responds by sending its routing information, and the data receiver acknowledges the data sender's response. If the data sender receives no acknowledgment, it sendsOppenheimer [Page 26] RFC 1504 Appletalk Update-Based Routing Protocol August 1993 duplicate RI-Rsp packets until the data receiver responds with an acknowledgment. <<Figure 3-9 Routing-information request/response/acknowledgment dialog>> Once the data receiver has verified the information in the RI-Rsp, it responds with a Routing Information Acknowledgment packet, or RI-Ack, which contains the following information: Connection ID: The connection ID is the same as that in the RI-Rsp packet. Sequence number: The sequence number is the same as that in the RI- Rsp packet. Send zone information flag: The state of the send zone information (SZI) flag in an RI-Ack packet indicates whether the RI-Ack packet doubles as a ZI-Req packet. If the SZI flag is set to 1, the data receiver sends the zone information associated with the networks about which it sent routing information in the previous RI-Rsp. Figure 3-10 shows a data receiver sending zone information to a data sender in response to a ZI-Req and in response to an RI-Ack, which optimizes the data flow. When the data sender receives an RI-Ack, it verifies that the RI-Ack corresponds to the outstanding RI-Rsp-that is, both packets have the same connection ID and sequence number. Once the data sender has verified the information in the RI-Ack, it responds by sending the next RI-Rsp in the sequence, if any. <<Figure 3-10 Nonoptimized and optimized flows of zone information>> ZONE INFORMATION RESPONSE PACKETS: If the data sender receives an RI-Ack with its SZI flag set to 1, it responds by sending ZI-Rsp packets that contain the zone information associated with the networks about which it sent routing information in the RI-Rsp being acknowledged-just as it would if it received a ZI-Req for those networks. The data sender sends RI-Rsp and ZI-Rsp packets as independent data streams. It sends RI-Rsp packets as sequenced data and ZI-Rsp packets as transaction data. If the data sender receives an RI-Ack with its SZI flag set to 1, it sends an unsequenced series of ZI-Rsp packets that contain the following information: Connection ID: The connection ID is the same as that in theOppenheimer [Page 27] RFC 1504 Appletalk Update-Based Routing Protocol August 1993 associated RI-Req. Network number and zone list tuples: The exterior router sends the zone information associated with each network number in the corresponding RI-Rsp. Reobtaining Routing Information An exterior router can reobtain another exterior router's complete routing information at any time, by sending an RI-Req packet. An exterior router might need to reobtain complete routing information for a one-way connection on which it is the data receiver under the following circumstances: During the initial routing-information exchange, the exterior router set the SUI flags in the Open-Req to disable updates. The exterior router can subsequently poll the other exterior router on the connection by sending an RI-Req to that exterior router to determine whether any of its routing information has changed. The exterior router set the SUI flags to request updates, but suspects that the routing information for the other exterior router on the connection is incorrect or obsolete. The exterior router should send an RI-Req to the other exterior router to obtain its complete, updated routing information. Whenever an exterior router receives an RI-Req from an exterior router requesting updated routing information, it responds by sending RI-Rsp packets, just as it does when it first receives an RI-Req. The data sender also ⌨️ 快捷键说明
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