📄 rfc2097.txt
字号:
Network Working Group G. Pall
Request for Comments: 2097 Microsoft Corp.
Category: Standards Track January 1997
The PPP NetBIOS Frames Control Protocol (NBFCP)
Status of this Memo
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.
Abstract
The Point-to-Point Protocol (PPP) [1] provides a standard method for
transporting multi-protocol datagrams over point-to-point links. PPP
defines an extensible Link Control Protocol, and proposes a family of
Network Control Protocols for establishing and configuring different
network-layer protocols.
The NBF protocol [3] was originally called the NetBEUI protocol. This
document defines the Network Control Protocol for establishing and
configuring the NBF protocol over PPP.
The NBFCP protocol is only applicable for an end system to connect to
a peer system or the LAN that peer system is connected to. It is not
applicable for connecting two LANs together due to NetBIOS name
limitations and NetBIOS name defense mechanisms.
Table of Contents
1. Introduction .......................................... 2
1.1 Specification of Requirements ................... 2
1.2 Terminology ..................................... 3
2. A PPP Network Control Protocol for NBF ................ 3
2.1 Sending NBF Datagrams ........................... 4
2.2 Bridging NBF Datagrams........................... 5
2.3 NetBIOS Name Defense............................. 5
3. NBFCP Configuration Options ........................... 6
3.1 Name-Projection.................................. 6
3.2 Peer-Information................................. 8
3.3 Multicast-Filtering.............................. 10
3.4 IEEE-MAC-Address-Required........................ 11
SECURITY CONSIDERATIONS ...................................... 12
REFERENCES ................................................... 12
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RFC 2097 NBFCP January 1997
ACKNOWLEDGEMENTS ............................................. 13
CHAIR'S ADDRESS .............................................. 13
AUTHOR'S ADDRESS ............................................. 13
1. Introduction
PPP has three main components:
1. A method for encapsulating multi-protocol datagrams.
2. A Link Control Protocol (LCP) for establishing, configuring,
and testing the data-link connection.
3. A family of Network Control Protocols for establishing and
configuring different network-layer protocols.
In order to establish communications over a point-to-point link, each
end of the PPP link must first send LCP packets to configure and test
the data link. After the link has been established and optional
facilities have been negotiated as needed by the LCP, PPP must send
NBFCP packets to choose and configure the NBF network-layer protocol.
Once NBFCP has reached the Opened state, NBF datagrams can be sent
over the link.
The link will remain configured for communications until explicit LCP
or NBFCP packets close the link down, or until some external event
occurs (an inactivity timer expires or network administrator
intervention).
1.1. Specification of Requirements
In this document, several words are used to signify the requirements
of the specification. These words are often capitalized.
MUST This word, or the adjective "required", means that the
definition is an absolute requirement of the specification.
MUST NOT This phrase means that the definition is an absolute
prohibition of the specification.
SHOULD This word, or the adjective "recommended", means that there
may exist valid reasons in particular circumstances to
ignore this item, but the full implications should be
understood and carefully weighed before choosing a
different course.
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RFC 2097 NBFCP January 1997
MAY This word, or the adjective "optional", means that this
item is one of an allowed set of alternatives. An
implementation which does not include this option MUST be
prepared to interoperate with another implementation which
does include the option.
1.2. Terminology
This document frequently uses the following terms:
peer The other end of the point-to-point link.
silently discard
This means the implementation discards the packet without
further processing. The implementation SHOULD provide the
capability of logging the error, including the contents of
the silently discarded packet, and SHOULD record the event
in a statistics counter.
end-system
A user's machine. It only sends packets to servers and
other end-systems. It doesn't pass any packets through
itself.
router Allows packets to pass through, usually from one ethernet
segment to another. Sometimes these are called
"intermediate-systems".
bridge Allows packets to pass through with the data field
unmodified. Usually from one ethernet segment to another
or from one ethernet segment to a token-ring segment.
gateway Allows packets to be sent from one network protocol to
the same or different network protocol. For example,
NetBIOS packets from an NBF network to a TCP/IP network
which has implemented RFC 1001 and RFC 1002.
local access only server A server which does not pass any packets
through itself to other servers.
2. A PPP Network Control Protocol for NBF
The NBF Control Protocol (NBFCP) is responsible for configuring,
enabling, and disabling the NBF protocol modules on both ends of the
point-to-point link. NBFCP uses the same packet exchange mechanism
as the Link Control Protocol. NBFCP packets MUST NOT be exchanged
until PPP has reached the Network-Layer Protocol phase. NBFCP
packets received before this phase is reached should be silently
Pall Standards Track [Page 3]
RFC 2097 NBFCP January 1997
discarded.
The NBF Control Protocol is exactly the same as the Link Control
Protocol [1] with the following exceptions:
Frame Modifications
The packet may utilize any modifications to the basic frame format
which have been negotiated during the Link Establishment phase.
Data Link Layer Protocol Field
Exactly one NBFCP packet is encapsulated in the Information field
of a PPP Data Link Layer frame where the Protocol field indicates
type hex 803f (NBF Control Protocol).
Code field
Only Codes 1 through 7 (Configure-Request, Configure-Ack,
Configure-Nak, Configure-Reject, Terminate-Request, Terminate-Ack
and Code-Reject) are used. Other Codes should be treated as
unrecognized and should result in Code-Rejects.
Timeouts
NBFCP packets MUST NOT be exchanged until PPP has reached the
Network-Layer Protocol phase. An implementation should be
prepared to wait for Authentication and Link Quality Determination
to finish before timing out waiting for a Configure-Ack or other
response. It is suggested that an implementation give up only
after user intervention or a configurable amount of time. Also,
because NetBIOS name defense takes time (typically a minimum of
3 seconds if names are added in parallel), it is suggested that
if Name-Projection is negotiated, the timeouts are increased to 10
seconds.
Configuration Option Types
NBFCP has a distinct set of Configuration Options.
2.1. Sending NBF Datagrams
Before any NBF packets may be communicated, PPP must reach the
Network-Layer Protocol phase, and the NBF Control Protocol must reach
the Opened state.
Unless otherwise negotiated, exactly one NBF packet is encapsulated
in the Information field of a PPP Data Link Layer frame where the
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RFC 2097 NBFCP January 1997
Protocol field indicates type hex 003f (NBF datagram).
Since NBF datagrams for PPP do not contain a datagram length field,
the encapsulated NBF packet MUST NOT contain any extra octet padding
except when Self-Defining-Padding is negotiated.
The maximum length of an NBF datagram transmitted over a PPP link is
the same as the maximum length of the Information field of a PPP data
link layer frame. Since there is no standard method for fragmenting
and reassembling NBF datagrams, PPP links supporting NBF MUST allow
at least 576 octets in the information field of a data link layer
frame. It is recommended that an implementation allow 1500 octets in
the information field unless the IEEE-MAC-Address-Required boolean
option is negotiated (see below).
2.2 Bridging NBF Datagrams
There exist at least four different MAC header implementations for
NBF packets: 802.3 Ethernet, 802.5 Token-Ring, DIX Ethernet, and
FDDI. Because NBF is not a routable protocol, some PPP
implementations may require IEEE MAC addresses to properly route or
bridge NBF packets. Some PPP implementations may require the entire
MAC media header in order to properly route or bridge NBF packets.
Other smarter implementations may only require the IEEE MAC addreses,
and still other implementations (such as NetBIOS gateways) may not
require any MAC address fields. NBFCP implementations which require
IEEE Addresses should negotiate the NBFCP IEEE-MAC-Address-Required
boolean configuartion option so that the MAC header can be provided
in the NBF packet.
If IEEE-MAC-Address-Required boolean configuration option is
negotiated, all NBF datagrams MUST be sent with the specified 12
octet IEEE MAC address header. Since negotiation of this option
occurs after the LCP phase, NBF packets MAY exceed the negotiated PPP
MRU size. A PPP implementation which negotiates this option MUST
allow reception of PPP NBF packets 12 octets larger than the
negotiated MRU size.
2.3 NetBIOS Name Defense
In order to guarantee uniqueness of NetBIOS Names on the network,
NBFCP requires that end-system implementations MUST negotiate the
Name-Projection configuration option.
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RFC 2097 NBFCP January 1997
3. NBFCP Configuration Options
NBFCP Configuration Options allow modifications to the standard
characteristics of the network-layer protocol to be negotiated. If a
Configuration Option is not included in a Configure-Request packet,
the default value for that Configuration Option is assumed.
NBFCP uses the same Configuration Option format defined for LCP [1],
with a separate set of Options.
Up-to-date values of the NBFCP Option Type field are specified in the
most recent "Assigned Numbers" RFC [2]. Current values are assigned
as follows:
1 Name-Projection
2 Peer-Information
3 Multicast-Filtering
4 IEEE-MAC-Address-Required
3.1. Name-Projection
Description
This Configuration Option provides a method for the peer to
provide the NetBIOS names registered on its network. The sender
of the Configure-Request states which NetBIOS names should be
added by the remote peer. More than one Name-Projection option
MAY appear in a single Configure-Request.
Implementations which do not attempt to add any NetBIOS names MUST
Configure-Reject the Name-Projection Configuration Option.
If the Name-Projection Configuration Option is not offered by the
remote peer, but is required by the local peer, the local peer
should Configure-Nak the request and indicate that it wishes the
remote peer to add zero NetBIOS names because it is the only known
acceptable value. The remote peer may then terminate NBFCP,
attempt to add zero NetBIOS names, or attempt add one or more
NetBIOS names.
When the receiving peer cannot add all the requested names, it
MUST Configure-Nak with the complete list of names requested.
Those names which could be added should have the Added field set
to zero. Those names which could not be added should have the
Added field set to an appropriate non-zero return code. The
sender of this Configuration Option SHOULD then resend the
Configure-Request with the successfully added names.
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RFC 2097 NBFCP January 1997
The implementation may choose to fail configuration if the
complete list of NetBIOS names is not accepted. By failing, the
implementation should terminate NBFCP by sending a Terminate-
Request packet.
Because adding NetBIOS names can take time (usually 3 seconds) and
because PPP may default the restart timer to 3 seconds, the
restart timer SHOULD default to 10 seconds when configuring
NetBIOS names.
A summary of the Name-Projection Configuration Option format is shown
below. The fields are transmitted from left to right.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | 1st NetBIOS-Name
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1st NetBIOS-Name (cont.)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1st NetBIOS-Name (cont.)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1st NetBIOS-Name (cont.)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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