RFCs in HTML Format


RFC 1841

            PPP Network Control Protocol for LAN Extension


Table of Contents

   1.0    Introduction ...........................................    3
      1.1   LAN Extension Interface Topology .....................    4
      1.2   LAN Extension Interface Architecture .................    5
      1.3   LAN Extension Interface Protocol .....................    6

   2.0    LAN Extension Interface Protocol Control Packets........    8
      2.1   Startup Options ......................................    8
      2.2   Remote Command Options ...............................   14
      2.3   Conditions for Sending PPP-LEX Packet ................   17

   3.0    Filter Protocol Type ...................................   18
      3.1   LEX_RCMD_REQUEST - Filter Protocol Type...............   19
      3.2   Response Packets - Filter Protocol Type...............   21

   4.0    Filter MAC Address .....................................   22
      4.1   LEX_RCMD_REQUEST - Filter MAC Address ................   23
      4.2   Response Packets - Filter MAC Address.................   25



Chapman, et al               Informational                      [Page 1]

RFC 1841 LAN Extension Interface Protocol September 1995 5.0 Set Priority ........................................... 27 5.1 LEX_RCMD_REQUEST - Set Priority ...................... 27 5.2 Response Packets - Set Priority ...................... 29 6.0 Disable LAN Extension Ethernet Interface ............... 30 6.1 LEX_RCMD_REQUEST - Disable LAN Extension Ethernet Interface ................................... 31 6.2 Response Packets - Disable LAN Extension Ethernet Interface ................................... 32 7.0 Enable LAN Extension Ethernet Interface ................ 33 7.1 LEX_RCMD_REQUEST - Enable LAN Extension Ethernet Interface ................................... 33 7.2 Response Packets - Enable LAN Extension Ethernet Interface ................................... 34 8.0 Reboot LAN Extension Interface Unit .................... 35 8.1 LEX_RCMD_REQUEST - Reboot LAN Extension Interface Unit ................................................. 35 8.2 Response Packets - Reboot LAN Extension Interface Unit ....................................... 36 9.0 Request Statistics ..................................... 37 9.1 LEX_RCMD_REQUEST - Request Statistics ................ 37 9.2 LEX_RCMD_ACK - Request Statistics .................... 39 9.3 LEX_RCMD_NAK/LEX_RCMD_REJ - Request Statistics ....... 44 10.0 Download Request ...................................... 45 10.1 LEX_RCMD_REQUEST - Download Request ................. 46 10.2 Response Packets - Download Request.................. 48 11.0 Download Data ......................................... 49 11.1 LEX_RCMD_REQUEST - Download Request ................. 49 11.2 Response Packets - Download Data .................... 51 12.0 Download Status ....................................... 52 12.1 LEX_RCMD_REQUEST - Download Status .................. 53 12.2 LEX_RCMD_ACK - Download Status ...................... 54 12.3 LEX_RCMD_NAK/LEX_RCMD_REJ - Download Status ......... 56 13.0 Inventory Request ..................................... 56 13.1 LEX_RCMD_REQUEST - Inventory Request ................ 57 13.2 LEX_RCMD_ACK - Inventory Request .................... 58 13.3 LEX_RCMD_NAK/LEX_RCMD_REJ - Inventory Request ....... 61 14.0 LAN Extension Interface Protocol Data Packets ......... 62 14.1 Frame Format ........................................ 62 14.2 Summary Field Descriptions........................... 63 Chapman, et al Informational [Page 2]
RFC 1841 LAN Extension Interface Protocol September 1995 NOTES ...................................................... 65 REFERENCES ................................................. 65 SECURITY CONSIDERATIONS .................................... 66 AUTHORS' ADDRESSES ......................................... 66 1.0 Introduction An increasing number of corporations allow their employees to telecommute to work due to local government regulations on traffic and air pollution. Additionally, many businesses are run out of internetworked home offices and small branch offices. With these changes in the workplace, more people and businesses require Internet access from small LANs. Today, routers serve the LAN-to-LAN traffic using high-speed WAN links such as leased lines, ISDN, or Frame Relay. This new breed of Internet users from home offices and small branch offices may have a different, less network-literate skill set than those connecting up to the Internet today. These new users need an alternative to the complex and hard-to-configure routers currently employed for connectivity. One such alternative is a LAN extension interface unit. A LAN extension interface unit is a hardware device installed at remote sites (such as a home office or small branch office) that connects a LAN across a WAN link to a router at a central site. The following sections introduce a LAN extension interface topology, architecture, and protocol. Chapman, et al Informational [Page 3]
RFC 1841 LAN Extension Interface Protocol September 1995 1.1 LAN Extension Interface Topology Figure 1 shows the topology of LAN extension interfaces. The figure shows two LAN extension interface units connected via a WAN link to a central or "host router." Figure 1 LAN Extension Interface Topology ----------------------------------------- Router ----------------------------------------- Virtual Interface Virtual Interface 123.123.78.1 123.123.89.1 ......................................... Serial 0 Serial n ----------------------------------------- |<---- WAN Link ---->| ------------------ ------------------ | LAN Extension | | LAN Extension | | Interface Unit | | Interface Unit | ------------------ ------------------ | | ------------------ ------------------ | | ------------ ------------ | End node | | End node | ------------ ------------ 123.123.78.2 123.123.46.2 Each LAN extension interface unit maps to a virtual interface at the host router. The virtual interface mirrors the characteristics of the LAN extension interface unit. To the routing protocols, the virtual interface looks just like a local interface, but with the bandwidth of a serial line. The virtual interface keeps the state (up or down) of the LAN extension interface unit, and identifies each LAN extension interface unit by its MAC address. A LAN extension interface protocol transfers MAC frames from the LAN extension interface unit across the serial line to the host router. At the termination point in the router, the router routes the packets. This topology uses only one subnet per remote LAN rather than two, as is the case when routers exist on both ends of a WAN link. Figure 1 shows this subnetting structure. The IP addresses of the virtual interfaces on the router are in the same subnet as the IP addresses of the end nodes on the LAN of the LAN extension interface unit. The LAN extension interface unit itself has no IP address. Chapman, et al Informational [Page 4]
RFC 1841 LAN Extension Interface Protocol September 1995 LAN extension interface units resemble bridges, but with the following distinct differences: * LAN extension interface units always depend on a host router. They cannot operate standalone or even back-to-back with other LAN extension interface units. * LAN extension interface units need not employ any spanning tree algorithm. * (LAN extension interface units transfer MAC frames across a serial line (like bridges), but a router can either route or bridge the LAN extension interface data packets. 1.2 LAN Extension Interface Architecture Figure 2 shows the basic LAN extension interface architecture. Figure 2 LAN Extension Interface Architecture Router LAN Extension Interface ------------------- ------------------- | Network Layer | | MAC Layer | ------------------- ------------------- | | ------------------- ------------------- | |Virtual Interface| | Filters | | | ------------------- ------------------- | | | | | | ------------------- ------------- | | | PPP | | RCMD | | | | | | Handler | | | ------------------- ------------- | | | | | | ------------------- ------------------- | | |Serial Interface | | PPP | | | ------------------- ------------------- | | | | | | | ------------------- | | | | Serial Interface| | | | ------------------- | | | WAN Link | | | --------------------------------------- | | | | Outbound Inbound | --------------> <--------------- Chapman, et al Informational [Page 5]
RFC 1841 LAN Extension Interface Protocol September 1995 In the inbound direction (from the remote LAN, to the LAN extension interface unit, across the WAN link, to the host router), the LAN extension interface unit can filter received frames to optimize WAN utilization. The LAN extension interface unit can filter frames by protocol type or by MAC address. Frames that pass through the LAN extension interface filters go to the WAN protocol state machine. In Figure 2, this state machine is PPP. The LAN extension interface unit adds PPP encapsulation and forwards the packet to the router via the WAN serial link. Upon receiving the frame, the host router decapsulates the PPP header and passes the packet to the virtual interface. From there the virtual interface handles the packet like any packet received on a local interface -- by routing or bridging the packet to another interface, depending on configuration. In the outbound direction (from the host router, across the WAN link, to the LAN extension interface unit, to the LAN), the host router's virtual interface builds the full MAC header, before adding PPP encapsulation. The router then sends the packet across the WAN serial link to the LAN extension interface unit. The LAN extension interface unit strips the PPP header and forwards the packet directly onto the LAN. The host router has already determined that the packet needs to be forwarded to the LAN extension interface unit, hence there is no need for additional filtering or processing at that end. Embedded in the data stream is a control stream for configuring and managing the LAN extension interface unit from the host router. The virtual interface makes the remote LAN extension interface unit appear like a local router interface to the routing protocols. Configuration commands and statistics gathering commands are issued on the router to the virtual interface. The virtual interface formats the LAN extension interface remote commands into encoded messages and transfers them in-band with the data packets. The LAN extension interface unit decodes the remote commands and executes them. Responses are similarly formatted messages sent by the LAN extension interface unit to the host router. The remote command messages use a different encapsulation type than the data packets, as described later in this document in the "LAN Extension Interface Protocol Control Packets" and "LAN Extension Interface Protocol Data Packets" sections. 1.3 LAN Extension Interface Protocol To accommodate this LAN extension interface architecture, a new Network Control Protocol (NCP) for PPP exists. This NCP is called PPP-LEX. The basic functionality of PPP-LEX is to encapsulate LAN Chapman, et al Informational [Page 6]
RFC 1841 LAN Extension Interface Protocol September 1995 extension interface control and data packets. The IETF has assigned two new protocol types for these functions, as shown in Table 1. Table 1 IETF Protocol Types for PPP-LEX Protocol Type Function 0x8041 Encapsulates control packets 0x0041 Encapsulates data packets (MAC frames) PPP is a natural choice for a LAN extension interface protocol because it allows for negotiating a specific control protocol and options at connection time. This means that network administrators do not have to statically configure the router interface for remote interfaces. Rather, remote interfaces negotiate the link at connection time. The LAN extension interface protocol employs PPP link operation as described in RFC 1331, which reads as follows: In order to establish communications of a point-to-point link, each end of the PPP link must first send [Link Control Protocol] LCP packets to configure and test the data link. After the link has been established,the peer may be authenticated. Then PPP must send NCP packets to choose and configure one or more network layer protocols. Once each of the chosen network-layer protocols has been configured, datagrams from each network layer protocol can be sent over the link. The link will remain configured for communications until explicit LCP or NCP packets close the link down, or until some external event occurs (an inactivity timer expires or network administrator intervention). (References, [1]) Thus, the LAN extension interface unit and the host router exchange PPP-LCP packets at connection time to dynamically configure and test the WAN serial link. Once the link reaches an "opened" state, the LAN extension interface unit and host router exchange PPP-LEX NCP packets to configure the LAN extension interface protocol. Once it is configured, the NCP (PPP-LEX) reaches an "opened" state, and PPP carries the PPP-LEX control and data packets across the serial link. At this point, link traffic is a any combination of LCPs, PPP-LEX NCPs, PPP-LEX control packets, and PPP-LEX data packets. Note that the LAN extension interface protocol is not a bridging protocol. The only similarity to the PPP Bridging Control Protocol (References. [2]) is that the LAN extension interface protocol also encapsulates MAC frames. Chapman, et al Informational [Page 7]
RFC 1841 LAN Extension Interface Protocol September 1995 The following sections detail PPP-LEX control packets and data packets. 2.0 LAN Extension Interface Protocol Control Packets There are two types of PPP-LEX control packets, as follows: * Startup options packet * Remote command options packets The startup options packet is the first PPP-LEX NCP packet that the LAN extension interface unit sends to the host router after the LCP has reached an "opened" state. This required startup options packet configures the LAN extension interface protocol and puts the PPP-LEX NCP in an "opened" state. Remote command options are the PPP-LEX NCP packets that control the functioning and statistics gathering of the LAN extension interface protocol. 2.1 Startup Options The LAN extension interface unit sends a startup options packet to the host router to negotiate the following startup options: * MAC Type * MAC Address * LAN Extension The MAC Type startup option informs the host router of the type of media that the LAN extension interface unit is connected to. For example, the LAN extension interface unit may be connected to an Ethernet LAN or a Token Ring LAN. Currently, only Ethernet is supported. The MAC type tells the host router what type of traffic the LAN extension interface unit is prepared to receive. If the host router rejects the MAC type, the LAN extension interface unit sends the Configure-Request again. The MAC Address startup option sends the MAC address of the LAN extension interface unit to the host router to authenticate the LAN extension interface unit and bind it to the corresponding virtual interface at the host router. The host router also inserts the MAC address in outbound packets. The MAC address is represented in IEEE 802.3 canonical format. The LAN Extension startup option establishes the network layer protocol (NCP) as PPP-LEX and provides the host router with the LAN extension interface protocol version number. Chapman, et al Informational [Page 8]
RFC 1841 LAN Extension Interface Protocol September 1995 Each startup option is transmitted in a series of three fields: Option-Type, Option-Length, and Option-Data fields. The fields are concatenated in the startup options Configure-Request packet. Frame Format Figure 3 shows a summary of the frame format for the startup options packet. The LAN extension interface unit sends this startup options packet to the host router. The LAN extension interface unit transmits these fields from left to right. Figure 3 Startup Options Frame Format (Configure-Request) PPP Header <--------------------------------------------------------------> 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address | Control | Protocol Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (1 octet) (1) (2) LAN Extension Interface Protocol Header <--------------------------------------------------------------> 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Code | Identifier | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (1 octet) (1) (2) LAN Extension Interface Startup Options <--------------------------------------------------------------> 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option-Type | Option-Length | Option-Data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (1 octet) (1) Address This PPP-specified field is one octet and contains the binary sequence 11111111 (hexadecimal 0xFF), the All-Stations address. PPP does not assign individual station addresses. The All-Stations address must be recognized and received by all devices. For more information on this field, refer to "The Point-to-Point Protocol (PPP) for the Transmission of Multi-protocol Datagrams over Point- to-Point Links." (References, [1]) Chapman, et al Informational [Page 9]
RFC 1841 LAN Extension Interface Protocol September 1995 Control This PPP-specified field is one octet and contains the binary sequence 00000011 (hexadecimal 0x03), the Unnumbered Information (UI) command with the P/F bit set to zero. For more information on this field, refer to "The Point-to-Point Protocol (PPP) for the Transmission of Multi-protocol Datagrams over Point-to Point Links." (References, [1]) Protocol-Type The Protocol-Type field is two octets and contains the IETF-assigned protocol type value. Valid LAN extension interface protocol type values are as follows: * 0x8041 (for control packets) * 0x0041 (for data packets) Because the startup options packet encapsulates LAN extension interface control data, the valid value for this field is 0x8041. Code The Code field is one octet and identifies the type of LCP packet that the LAN extension interface packet is sending. Valid values are as follows: * 0x01 - Configure-Request * 0x02 - Configure-Ack * 0x03 - Configure-Nak * 0x04 - Configure-Rej The LAN extension interface unit initiates the startup options packet; therefore, the valid value for this field is 1. Identifier The Identifier field is one octet and contains a randomly generated value. The value aids matching requests and replies. It is recommended that a non-zero value be used for the identifier. That is, zero could be used in the future for unsolicited messages from the LAN extension interface unit. Valid values are 0x01-0xFF. Chapman, et al Informational [Page 10]
RFC 1841 LAN Extension Interface Protocol September 1995 Length The Length field is two octets and indicates the length of the entire packet in octets, including the Code, Identifier, Length, and startup options fields. Option-Type The Option-Type field is one octet and identifies the startup option being negotiated. Valid values are as follows: * 0x01 - MAC Type * 0x03 - MAC Address * 0x05 - LAN Extension Option-Length The Option-Length field is one octet and specifies the length of the startup option fields, including the Option-Type, Option-Data, and Option-Length fields. Option-Data The Option-Data field contains the data relating to the value specified in the Option-Type field. That is, if the Option-Type field specifies MAC type (0x01), then the Option-Data field contains the MAC type (Ethernet, Token Ring, and so on). If the Option-Type field specifies MAC address (0x03), then the Option-Data field contains the actual MAC address. If the Option-Type field specifies LAN Extension (0x05), then the Option-Data field contains LAN extension interface software information. The following table defines the contents of the Option-Data field for each possible Option-Type field value: Option-Type Field Value Option-Data 0x01 (MAC Type) The most up-to-date value of the MAC type as specified in the most recent "Assigned Numbers" RFC. The current valid value from that RFC follows: * 0x01: IEEE 802.3/Ethernet with canonical addresses 0x03 (MAC Address) The burned-in MAC address in IEEE 802.3 canonical format. 0x05 (LAN Extension) The LAN extension interface protocol version number. 0x01 is the current protocol version supported. Chapman, et al Informational [Page 11]
RFC 1841 LAN Extension Interface Protocol September 1995 Example In the Configure-Request packet that it sends to the host router, the LAN extension interface unit concatenates the Option-Type, Option- Data, and Option-Length fields for each startup option, as shown in Figure 4. The LAN extension interface unit transmits these fields from left to right. Figure 4 Sample Startup Options Configure-Request Packet PPP Header <--------------------------------------------------------------> 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0xFF | 0x03 | 0x8041 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Address Control Protocol-Type LAN Extension Interface Protocol Header <--------------------------------------------------------------> 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x01 | 0x09 | 0x12 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Option-Type Identifier Length LAN Extension Interface Startup Options <------------------------------------------------ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x01 | 0x03 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Option-Type Option-Length ------------------------------> 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 0x01 | -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Option-Data Chapman, et al Informational [Page 12]
RFC 1841 LAN Extension Interface Protocol September 1995 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x03 | 0x08 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Option-Type Option-Length | 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 0A 0A 0A 0A 0B 0C | -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---------- Option-Data --------| 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x05 | 0x03 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Option-Type Option-Length 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 0x01 | -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Option-Data In Figure 4, the Address field always contains 0xFF, and the Control field always contains 0x03. The Protocol-Type field value is 0x8041 because the startup options packet is a LAN extension interface control packet. The Code field value is 0x01 because the LAN extension interface unit is sending an LCP Configure-Request packet to configure or negotiate PPP-LEX. The Identifier field contains a randomly generated number. The Length field gives the total length of the entire packet. The first startup option is the MAC Type startup option. The Option- Type value for MAC Type is 0x01. The Option-Length field value for the MAC type startup option is 3 octets. The Option-Data field value is 0x01 because, in this example, the LAN extension interface unit connects to an Ethernet LAN using 802.3 canonical addresses. The next startup option transmitted is the MAC Address. Its Option- Type field value is 0x03, its Option-Length field value is 8 octets, and its Option-Data field value is the actual MAC address. Lastly, the LAN Extension startup option is transmitted. Its Option- Type field value is 0x05, its Option-Length field value is 3 octets, and its Option-Data field value is the LAN extension interface protocol version number (0x01). Chapman, et al Informational [Page 13]
RFC 1841 LAN Extension Interface Protocol September 1995 The host router responds to this LCP Configure-Request packet with an LCP Configure-Ack packet, Configure-Nak packet, or Configure-Rej packet. For more information on these packets, refer to "The Point- to-Point Protocol (PPP) for the Transmission of Multi-protocol Datagrams over Point-to-Point Links" RFC. (References, [1]) 2.2 Remote Command Options Once the host router responds to the startup options Configure- Request packet with a Configure-Ack packet, the PPP-LEX NCP is in an "opened" state, and the LAN extension interface unit and the host router freely exchange PPP-LEX data packets and remote command options packets. The host router initiates PPP-LEX remote command options packets to control the configuration of the LAN extension interface unit and to gather statistics. There are 11 types of remote command options that the host router can send in a LEX_RCMD_REQUEST packet to the LAN extension interface unit. The LAN extension interface unit responds to a LEX_RCMD_REQUEST packet with a LEX_RCMD_ACK, LEX_RCMD_NAK, or LEX_RCMD_REJ packet. Frame Format Figure 5 shows a summary of the frame format for a remote command options packet. These fields are transmitted from left to right. Figure 5 Remote Command Options Frame Format PPP Header <--------------------------------------------------------------> 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address | Control | Protocol Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (1 octet) (1) (2) LAN Extension Interface Protocol Header <--------------------------------------------------------------> 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Code | Identifier | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (1 octet) (1) (2) Chapman, et al Informational [Page 14]
RFC 1841 LAN Extension Interface Protocol September 1995 LAN Extension Interface Remote Command Options <-------------------------------- 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option-Type | Option-Flags | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (1 octet) (1) ----------------------------------------------> 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Option-Length | Option-Data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (2) Address This PPP-specified field is a single octet and contains the binary sequence 11111111 (hexadecimal 0xFF), the All-Stations address. PPP does not assign individual station addresses. The All-Stations address must be recognized and received by all devices. For more information on this field, refer to "The Point-to-Point Protocol (PPP) for the Transmission of Multi-protocol Datagrams over Point- to-Point Links." (References, [1]) Control This PPP-specified field is a single octet and contains the binary sequence 00000011 (hexadecimal 0x03), the Unnumbered Information (UI) command with the P/F bit set to zero. For more information on this field, refer to "The Point-to-Point Protocol (PPP) for the Transmission of Multi-protocol Datagrams over Point-to Point Links." (References, [1]) Note: Hereafter the Address and Control fields will be represented together as a 2-octet field containing "0xFF03". Protocol-Type The Protocol-Type field is two octets and contains the IETF-assigned protocol type value. Valid LAN extension interface protocol type values follow: * 0x8041 (for control packets) * 0x0041 (for data packets) Chapman, et al Informational [Page 15]
RFC 1841 LAN Extension Interface Protocol September 1995 Because the remote command options packet encapsulates LAN extension interface control data, the valid value for this field is 0x8041. Code The Code field is one octet and identifies the type of PPP-LEX packet. Valid values are as follows: * 0x40 - LEX_RCMD_REQUEST packet * 0x41 - LEX_RCMD_ ACK packet * 0x42 - LEX_RCMD_NAK packet * 0x43 - LEX_RCMD_REJ packet The host router sends the LEX_RCMD_REQUEST packet, and the LAN extension interface unit sends the LEX_RCMD_ACK, LEX_RCMD_NAK, and LEX_RCMD_REJ packets. Identifier The Identifier field is one octet and contains a randomly generated value. The value aids matching requests and replies. It is recommended that a non-zero value be used for the identifier. That is, zero could be used in the future for unsolicited messages from the LAN extension interface unit. Valid values are 0x01-0xFF. Length The Length field is two octets and indicates the length in octets of the entire packet, including the Code, Identifier, Length, and remote command options fields. Option-Type The Option-Type field is one octet and identifies the remote command option being transmitted. Valid values are as follows: * 0x01 - Filter Protocol Type * 0x02 - Filter MAC Address * 0x03 - Set Priority * 0x04 - Disable LAN Extension Ethernet Interface * 0x05 - Enable LAN Extension Ethernet Interface * 0x06 - Reboot LAN Extension Interface Unit * 0x07 - Request Statistics * 0x08 - Download Request * 0x09 - Download Data * 0x0A - Download Status * 0x0B- Inventory Request Chapman, et al Informational [Page 16]
RFC 1841 LAN Extension Interface Protocol September 1995 Each remote command option is discussed in detail in its own section later in this document. Option-Flags This field is one octet and further specifies the remote command option, containing specific actions that must be followed. Option-Length The Option-Length field is two octets and specifies the length in octets of the remote command option fields, including the Option- Type, Option-Flags, Option-Length, and Option-Data fields. Option-Data Option-Data field contains data relating to the remote command option specified in the Option-Type field. 2.3 Conditions for Sending PPP-LEX Packet This section describes the general conditions under which PPP-LEX packet types are sent. For specific information by remote command, refer to the appropriate remote command section later in this document. LEX RCMD_REQUEST Packet The host router sends LEX_RCMD_REQUEST packets to the LAN extension interface unit to initiate a remote command request. Until the host router receives a LEX_RCMD_ACK, LEX_RCMD_NAK, or LEX_RCMD_REJ packet from the LAN extension interface unit, the host router continues to send the LEX_RCMD_REQUEST packet a default number of times, at which point the host router times out. LEX_RCMD_ACK Packet The LAN extension interface unit responds to a LEX_RCMD_REQUEST packet with a LEX_RCMD_ACK packet when it correctly receives the request and is able to perform the request. LEX RCMD_NAK Packet The LAN extension interface unit responds to a LEX_RCMD_REQUEST packet with a LEX_RCMD_NAK packet when the LAN extension interface unit recognizes all the elements of the remote command option, but some elements are not acceptable. Upon receipt of a LEX_RCMD_NAK packet, the host router immediately stops sending the request. Chapman, et al Informational [Page 17]
RFC 1841 LAN Extension Interface Protocol September 1995
RFC 1841 LAN Extension Interface Protocol September 1995 LAN Extension Interface Remote Command Option <-------------------------------- 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option-Type | Option-Flags | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (1) (1) -----------------------------------------------> 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Option-Length | Option-Data | -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (2) Where the Option-Data field contains the following fields: 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Status (16 bits) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Summary Field Descriptions For a complete descriptions of the fields in the PPP Header, the LAN Extension Interface Protocol Header, and the LAN Extension Interface Remote Command Option, refer to the "Remote Command Options" section earlier in this document. Table 22 provides a summary of these fields when sending a status information to the host router. Table 22 Field Values for LEX_RCMD_ACK Packet - Download Status Field Value Address/Control 0xFF03 (Broadcast address/Unnumbered information) Protocol-Type 0x8041 (Control packet) Code 0x41 (LEX_RCMD_ACK packet) Identifier The same value as that sent by the LEX_RCMD_REQUEST packet Length 14 octets Option-Type 0x0A (Download Status) Option-Flags None Option-Length 6 octets Option-Data Status information. See the following "Option-Data Field Descriptions" section for details. Chapman, et al Informational [Page 55]
RFC 1841 LAN Extension Interface Protocol September 1995 Option-Data Field Descriptions The Option-Data field uses the Status field to send the download status to the host router. The Status field reports the following status information: * 1 - Acknowledgment that no errors occurred * 3 - Sequence error occurred * 6 - Flash write error occurred * 7 - Checksum error 12.3 LEX RCMD_NAK/LEX RCMD_REJ - Download Status Refer to the "Conditions for Sending PPP-LEX Packets" section earlier in this document for information on when the LAN extension interface unit sends a Download Status LEX_RCMD_NAK packet and Download Status LEX_RCMD_REJ packet. The frame format for these two response packets mirror the frame format of the Download Status LEX_RCMD_REQUEST packet. Table 23 summarizes the field values of the Download Status LEX_RCMD_NAK and LEX_RCMD_REJ packets. Table 23 Field Values for LEX_RCMD_NAK/LEX_RCMD_REJ Packets - Download Status Field Value Address/Control 0xFF03 (Broadcast address/Unnumbered information) Protocol-Type 0x8041 (Control packet) Code Valid values: * 0x42 (LEX_RCMD_NAK packet) * 0x43 (LEX_RCMD_REJ packet) Identifier The same value as that sent by the LEX_RCMD_REQUEST packet Length 12 octets Option-Type 0x0A (Download Status) Option-Flags None Option-Length 4 octets Option-Data None 13.0 Inventory Request The host router sends a LEX_RCMD_REQUEST packet with an Option-Type of 0x0B to the LAN extension interface unit to request inventory information. The host router may use this remote command option to accomplish the following: Chapman, et al Informational [Page 56]
RFC 1841 LAN Extension Interface Protocol September 1995 * Distinguish between different versions of the LAN extension interface unit for determining their capabilities * Determine whether a new version of Flash code should be downloaded 13.1 LEX RCMD_REQUEST - Inventory Request Figure 18 shows the frame format for a LEX_RCMD_REQUEST packet with an Inventory Request remote command option. The host router transmits the fields from left to right. Figure 18 LEX_RCMD_REQUEST Packet Frame Format - Inventory Request PPP Header <--------------------------------------------------------------> 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0xFF03 | Protocol-Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (2 octets) (2) LAN Extension Interface Protocol Header <--------------------------------------------------------------> 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Code | Identifier | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (1) (1) (2) LAN Extension Interface Remote Command Option <--------------------------------------------------------------> 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option-Type | Option-Flags | Option-Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (1) (1) (2) Summary Field Descriptions For a complete description of the fields in the PPP Header, the LAN Extension Interface Protocol Header, and the LAN Extension Interface Remote Command Option, refer to the "Remote Command Options" section earlier in this document. Table 24 provides a summary of these fields when sending a LEX_RCMD_REQUEST packet that requests inventory information. Chapman, et al Informational [Page 57]
RFC 1841 LAN Extension Interface Protocol September 1995 Table 24 Field Values for LEX_RCMD_REQUEST Packet-Inventory Request Field Value Address/Control 0xFF03 (Broadcast address/Unnumbered information) Protocol-Type 0x8041 (Control packet) Code 0x40 (LEX_RCMD_REQUEST packet) Identifier Valid values: 0x01-0xFF Length 12 octets Option-Type 0x0B (Inventory Request) Option-Flags None Option-Length 4 octets Option-Data None 13.2 LEX RCMD_ACK - Inventory Request When it correctly receives the Inventory Request remote command option and retrieves the inventory information, the LAN extension interface unit responds with an acknowledgment. This acknowledgment contains the requested inventory information in the Option-Data field. Figure 19 shows the frame format for the Inventory Request LEX_RCMD_ACK packet. Figure 19 LEX_RCMD_ACK Packet Frame Format - Inventory Request PPP Header <--------------------------------------------------------------> 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0xFF03 | Protocol-Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (2 octets) (2) LAN Extension Interface Protocol Header <--------------------------------------------------------------> 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Code | Identifier | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (1) (1) (2) Chapman, et al Informational [Page 58]
RFC 1841 LAN Extension Interface Protocol September 1995 LAN Extension Interface Remote Command Option <-------------------------------- 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option-Type | Option-Flags | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (1) (1) -----------------------------------------------> 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Option-Length | Option-Data | -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (2) Where the Option-Data field contains the following fields: (32 bits) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flash Size | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Serial Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | HW Version | PROM Major Ver| PROM Minor Ver|Flash Major Ver| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Flash Minor Ver| FLAGS | RAM Major Ver | RAM Minor Ver | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Mac Address (6 octets) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Summary Field Descriptions For a complete description of the fields in the PPP Header, the LAN Extension Interface Protocol Header, and the LAN Extension Interface Remote Command Option, refer to the "Remote Command Options" section earlier in this document. Table 25 provides a summary of these fields when acknowledging a LEX_RCMD_REQUEST packet that requests inventory information. Table 25 Field Values for LEX_RCMD_ACK Packet - Inventory Request Field Value Address/Control 0xFF03 (Broadcast address/Unnumbered information) Protocol-Type 0x8041 (Control packet) Code 0x41 (LEX_RCMD_ACK packet) Chapman, et al Informational [Page 59]
RFC 1841 LAN Extension Interface Protocol September 1995 Identifier The same value as that sent by LEX_RCMD_REQUEST packet Length 34 octets Option-Type 0x0B (Inventory Request) Option-Flags None Option-Length 26 octets Option-Data Inventory data. See the following "Option-Data Field Descriptions" section for details. Option-Data Field Descriptions The Option-Data field of the LEX_RCMD_ACK packet uses the following fields to send inventory data to the host router about the LAN extension interface unit. * Flash Size This field contains the LAN extension interface unit's Flash size in bytes. * Serial Number This field provides the LAN extension interface unit's serial number. This is an unassigned, 32-bit number. * HW Version This field contains the version number of the LAN extension interface hardware unit. * PROM Major Ver This field contains part of the version number of the PROM image. "Major" indicates which major software release this revision belongs to. For example, if the PROM version number is 1.2, then the major version number is 1. * PROM Minor Ver This field contains part of the version number of the PROM image. "Minor" indicates which minor software release this revision belongs to. For example, if the PROM version number is 1.2, then the minor version number is 2. Chapman, et al Informational [Page 60]
RFC 1841 LAN Extension Interface Protocol September 1995 * Flash Major Ver This field contains the "major" version number of the Flash image. For example, if the Flash image version number is 1.2, then the major version number is 1. * Flash Minor Ver This field contains the "minor" version number of the Flash image. For example, if the Flash image version number is 1.2, then the minor version number is 2. * FLAGS FLAGS report the boot status of the LAN extension interface unit. The flags are as follows: - 0x01 - Running PROM image - 0x02 - Running Flash image - 0x04 - PROM image passed checksum - 0x08 - Flash image passed checksum * RAM Major Ver This field contains the "major" version number of the running image in RAM. For example, if the RAM image version number is 1.2, then the major version number is 1. * RAM Minor Ver This field contains the "minor" version number of the running image in RAM. For example, if the RAM image version number is 1.2, then the minor version number is 2. * MAC Address The MAC Address is the LAN extension interface unit's burned-in MAC address in canonical format. This field is six octets. 13.3 LEX RCMD_NAK/LEX RCMD_REJ - Inventory Request Refer to the "Conditions for Sending PPP-LEX Packets" section earlier in this document for information on when the LAN extension interface unit sends an Inventory Request LEX_RCMD_NAK packet and Inventory Request LEX_RCMD_REJ packet. The frame format of these two response packets mirrors that of the request. Table 26 summarizes the field values for such Inventory Chapman, et al Informational [Page 61]
RFC 1841 LAN Extension Interface Protocol September 1995 Request LEX_RCMD_NAK/LEX_RCMD_REJ packets. Table 26 Field Values for LEX_RCMD_NAK/LEX_RCMD_REJ Packets - Inventory Request Field Value Address/Control 0xFF03 (Broadcast address/Unnumbered information) Protocol-Type 0x8041 (Control packet) Code Valid values: * 0x42 (LEX_RCMD_NAK packet) * 0x43 (LEX_RCMD_REJ packet) Identifier The same value as that sent by the LEX_RCMD_REQUEST packet Length 12 octets Option-Type 0x0B (Inventory Request) Option-Flags None Option-Length 4 octets Option-Data None 14.0 LAN Extension Interface Protocol Data Packets When the PPP-LEX NCP is in an "opened" state, the LAN extension interface unit and the host router also exchange PPP-LEX data packets (as well as control packets). There is only one type of PPP-LEX data packet. This data packet is a subset of the PPP-BCP packet format. The format subsetting is such that a PPP-BCP implementation will successfully process a LAN extension interface protocol packet. The differences are as follows: * LAN ID field will not be present. * LAN FCS field will never be present (that is, the F flag will always be off [=0]). * LAN ID flag (I) will always be off. * Pad field for the serial link will never be present, and the count field will be 0. For detailed information on PPP-BCP packets, refer to the "PPP Bridging Control Protocol (BCP)" RFC. (References, [2]) 14.1 Frame Format Figure 20 shows the frame format for a PPP-LEX data packet. The MAC frame is transferred except for the FCS field. The LAN extension interface unit computes the FCS for packets transferred to the LAN and strips the FCS for packets destined for the host router. Chapman, et al Informational [Page 62]
RFC 1841 LAN Extension Interface Protocol September 1995 Figure 20 PPP-LEX Data Packet Frame Format (8 bits) (8 bits) (8 bits) (8 bits) +-+-+-+-+-+-+-+-+ | HDLC FLAG | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0xFF | 0x03 | 0x0041 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | F|I|Z|0| Pad | Mac Type | Destination MAC Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Destination MAC Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source MAC Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source MAC Address | Length/Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LLC Data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | (Serial) HDLC CRC | HDLC FLAG | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 14.2 Summary Field Descriptions HDLC FLAG HDLC Frame delimiter. 0xFF This Address field contains the broadcast address. 0x03 This Control field contains unnumbered information. 0x0041 This field contains the IETF-assigned protocol type value for a PPP-LEX data packet. In this case this field will always contain 0x0041. Flags The flags F, I, Z, 0 have the following meanings: Chapman, et al Informational [Page 63]
RFC 1841 LAN Extension Interface Protocol September 1995 * F: Set bit F if the LAN FCS field is present. Because PPP-LEX data packets do not contain the LAN FCS field, this bit should not be set (field=0). * I: Set bit I if the LAN ID field is present. Because PPP-LEX data packets do not contain the field, this bit should not be set (field=0). * Z: Set bit Z if IEEE 802.3 Pad must be zero filled to minimum size. * 0: Reserved, must be zero. Pad Any PPP frame may have padding inserted in the Optional Data Link Layer Padding field. The value tells the receiving system how many pad octets to strip off. The LAN extension interface protocol does not support the Optional Data Link Layer Padding field, so the value of this field should be zero. MAC Type This field contains the most up-to-date value of the MAC type as specified in the most recent "Assigned Numbers" RFC. The current value is as follows: * 1: IEEE 802.3/Ethernet with canonical addresses Destination MAC Address This field is 6 octets and contains the MAC address of the destination system as defined by IEEE. The MAC Type field defines the bit ordering. Source MAC Address This field is 6 octets and contains the MAC address of the destination system as defined by IEEE. The MAC Type field defines the bit ordering. Length/Type This field is any Ethernet protocol type (See RFC 1700 in the references "Assigned Numbers"). For IEEE 802.3 frames, this is a length field. Chapman, et al Informational [Page 64]
RFC 1841 LAN Extension Interface Protocol September 1995 LLC Data This field is the remainder of the MAC frame which is (or would be if it were present) protected by the LAN FCS. (Serial) HDLC CRC This is a 16 bit Cyclic Redundancy Check field. For complete information on the above fields and their relationship to PPP-BCP packets, refer to the "PPP Bridging Control Protocol (BCP)" RFC. (References, [2]) Notes 1. The LAN extension interface protocol does allow the segmentation of individual LAN packets across the serial link. Each LAN packet must be transmitted across the serial link as one PPP-LEX encapsulation. 2. MAC addresses in PPP-LEX packets should be in canonical format. References [1] Simpson, W., "The Point-To-Point Protocol (PPP) for the Transmission of Multi-protocol Datagrams over Point-To-Point Links", RFC 1331, Daydreamer, May 1992. [2] Baker, F., and R. Bowen, "PPP Bridging Control Protocol (BCP)", RFC 1638, ACC, IBM, June 1994. [3] Lloyd, B., and W. Simpson, "PPP Authentication Protocols", RFC 1334, Lloyd & Associates, Daydreamer, October 1992. [4] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC 1700, USC/Information Sciences Institute, October 1994. [5] Reynolds, J., and J. Postel, "Standard for the transmission of IP datagrams over IEEE 802 networks", RFC 1042, USC/Information Sciences Institute, February 1988. Chapman, et al Informational [Page 65]
RFC 1841 LAN Extension Interface Protocol September 1995



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