RFC 1001
Protocol standard for a NetBIOS service on a TCP/UDP transport: Concepts and methods
10. NetBIOS END-NODES End-nodes support NetBIOS service interfaces and contain applications. Three types of end-nodes are part of this standard: - Broadcast ("B") nodes - Point-to-point ("P") nodes - Mixed mode ("M") nodes An IP address may be associated with only one instance of one of the above types. Without having preloaded name-to-address tables, NetBIOS participants
are faced with the task of dynamically resolving references to one
another. This can be accomplished with broadcast or mediated point-
to-point communications.
B nodes use local network broadcasting to effect a rendezvous with
one or more recipients. P and M nodes use the NetBIOS Name Server
(NBNS) and the NetBIOS Datagram Distribution Server (NBDD) for this
same purpose.
End-nodes may be combined in various topologies. No matter how
combined, the operation of the B, P, and M nodes is not altered.
NOTE: It is recommended that the administration of a NetBIOS
scope avoid using both M and B nodes within the same scope.
A NetBIOS scope should contain only B nodes or only P and M
nodes.
10.1. BROADCAST (B) NODES
Broadcast (or "B") nodes communicate using a mix of UDP datagrams
(both broadcast and directed) and TCP connections. B nodes may
freely interoperate with one another within a broadcast area. A
broadcast area is a single MAC-bridged "B-LAN". (See Appendix A for
a discussion of using Internet Group Multicasting as a means to
extend a broadcast area beyond a single B-LAN.)
10.2. POINT-TO-POINT (P) NODES
Point-to-point (or "P") nodes communicate using only directed UDP
datagrams and TCP sessions. P nodes neither generate nor listen for
broadcast UDP packets. P nodes do, however, offer NetBIOS level
broadcast and multicast services using capabilities provided by the
NBNS and NBDD.
P nodes rely on NetBIOS name and datagram distribution servers.
These servers may be local or remote; P nodes operate the same in
either case.
10.3. MIXED MODE (M) NODES
Mixed mode nodes (or "M") nodes are P nodes which have been given
certain B node characteristics. M nodes use both broadcast and
unicast. Broadcast is used to improve response time using the
assumption that most resources reside on the local broadcast medium
rather than somewhere in an internet.
M nodes rely upon NBNS and NBDD servers. However, M nodes may
continue limited operation should these servers be temporarily
unavailable.
11. NetBIOS SUPPORT SERVERS Two types of support servers are part of this standard: - NetBIOS name server ("NBNS") nodes - Netbios datagram distribution ("NBDD") nodes NBNS and NBDD nodes are invisible to NetBIOS applications and are part of the underlying NetBIOS mechanism. NetBIOS name and datagram distribution servers are the focus of name and datagram activity for P and M nodes. Both the name (NBNS) and datagram distribution (NBDD) servers are permitted to shift part of their operation to the P or M end-node which is requesting a service. Since the assignment of responsibility is dynamic, and since P and M nodes must be prepared to operate should the NetBIOS server delegate control to the maximum extent, the system naturally accommodates improvements in NetBIOS server function. For example, as Internet Group Multicasting becomes more widespread, new NBDD implementations may elect to assume full responsibility for NetBIOS datagram distribution. Interoperability between different implementations is assured by imposing requirements on end-node implementations that they be able to accept the full range of legal responses from the NBNS or NBDD. 11.1. NetBIOS NAME SERVER (NBNS) NODES The NBNS is designed to allow considerable flexibility with its degree of responsibility for the accuracy and management of NetBIOS names. On one hand, the NBNS may elect not to accept full responsibility, leaving the NBNS essentially a "bulletin board" on which name/address information is freely posted (and removed) by P and M nodes without validation by the NBNS. Alternatively, the NBNS may elect to completely manage and validate names. The degree of responsibility that the NBNS assumes is asserted by the NBNS each time a name is claimed through a simple mechanism. Should the NBNS not assert full control, the NBNS returns enough information to the requesting node so that the node may challenge any putative holder of the name. This ability to shift responsibility for NetBIOS name management between the NBNS and the P and M nodes allows a network administrator (or vendor) to make a tradeoff between NBNS simplicity, security, and delay characteristics. A single NBNS may be implemented as a distributed entity, such as the Domain Name Service. However, this RFC does not attempt to define
the internal communications which would be used. 11.1.1. RELATIONSHIP OF THE NBNS TO THE DOMAIN NAME SYSTEM The NBNS design attempts to align itself with the Domain Name System in a number of ways. First, the NetBIOS names are encoded in a form acceptable to the domain name system. Second, a scope identifier is appended to each NetBIOS name. This identifier meets the restricted character set of the domain system and has a leading period. This makes the NetBIOS name, in conjunction with its scope identifier, a valid domain system name. Third, the negotiated responsibility mechanisms permit the NBNS to be used as a simple bulletin board on which are posted (name,address) pairs. This parallels the existing domain sytem query service. This RFC, however, requires the NBNS to provide services beyond those provided by the current domain name system. An attempt has been made to coalesce all the additional services which are required into a set of transactions which follow domain name system styles of interaction and packet formats. Among the areas in which the domain name service must be extended before it may be used as an NBNS are: - Dynamic addition of entries - Dynamic update of entry data - Support for multiple instance (group) entries - Support for entry time-to-live values and ability to accept refresh messages to restart the time-to-live period - New entry attributes 11.2. NetBIOS DATAGRAM DISTRIBUTION SERVER (NBDD) NODES The internet does not yet support broadcasting or multicasting. The NBDD extends NetBIOS datagram distribution service to this environment. The NBDD may elect to complete, partially complete, or totally refuse to service a node's request to distribute a NetBIOS datagram. An end-node may query an NBDD to determine whether the NBDD will deliver a datagram to a specific NetBIOS name. The design of NetBIOS-over-TCP lends itself to the use of Internet Group Multicast. For details see Appendix A.
11.3. RELATIONSHIP OF NBNS AND NBDD NODES This RFC defines the NBNS and NBDD as distinct, separate entities. In the absence of NetBIOS name information, a NetBIOS datagram distribution server must send a copy to each end-node within a NetBIOS scope. An implementer may elect to construct NBNS and NBDD nodes which have a private protocol for the exchange of NetBIOS name information. Alternatively, an NBNS and NBDD may be implemented within the same device. NOTE: Implementations containing private NBNS-NBDD protocols or combined NBNS-NBDD functions must be clearly identified. 11.4. RELATIONSHIP OF NetBIOS SUPPORT SERVERS AND B NODES As defined in this RFC, neither NBNS nor NBDD nodes interact with B nodes. NetBIOS servers do not listen to broadcast traffic on any broadcast area to which they may be attached. Nor are the NetBIOS support servers even aware of B node activities or names claimed or used by B nodes. It may be possible to extend both the NBNS and NBDD so that they participate in B node activities and act as a bridge to P and M nodes. However, such extensions are beyond the scope of this specification. 12. TOPOLOGIES B, P, M, NBNS, and NBDD nodes may be combined in various ways to form useful NetBIOS environments. This section describes some of these combinations. There are three classes of operation: - Class 0: B nodes only. - Class 1: P nodes only. - Class 2: P and M nodes together. In the drawings which follow, any P node may be replaced by an M node. The effects of such replacement will be mentioned in conjunction with each example below. 12.1. LOCAL A NetBIOS scope is operating locally when all entities are within the same broadcast area.
12.1.1. B NODES ONLY Local operation with only B nodes is the most basic mode of operation. Name registration and discovery procedures use broadcast mechanisms. The NetBIOS scope is limited by the extent of the broadcast area. This configuration does not require NetBIOS support servers. ====+=========+=====BROADCAST AREA=====+==========+=========+==== | | | | | | | | | | +--+--+ +--+--+ +--+--+ +--+--+ +--+--+ | B | | B | | B | | B | | B | +-----+ +-----+ +-----+ +-----+ +-----+ 12.1.2. P NODES ONLY This configuration would typically be used when the network administrator desires to eliminate NetBIOS as a source of broadcast activity. ====+=========+==========+=B'CAST AREA=+==========+=========+==== | | | | | | | | | | | | +--+--+ +--+--+ +--+--+ +--+--+ +--+--+ +--+--+ | P | | P | |NBNS | | P | |NBDD | | P | +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ This configuration operates the same as if it were in an internet and is cited here only due to its convenience as a means to reduce the use of broadcast. Replacement of one or more of the P nodes with M nodes will not affect the operation of the other P and M nodes. P and M nodes will be able to interact with one another. Because M nodes use broadcast, overall broadcast activity will increase. 12.1.3. MIXED B AND P NODES B and P nodes do not interact with one another. Replacement of P nodes with M nodes will allow B's and M's to interact. NOTE: B nodes and M nodes may be intermixed only on a local broadcast area. B and M nodes should not be intermixed in an internet environment.
12.2. INTERNET 12.2.1. P NODES ONLY P nodes may be scattered at various locations in an internetwork. They require both an NBNS and an NBDD for NetBIOS name and datagram support, respectively. The NetBIOS scope is determined by the NetBIOS scope identifier (domain name) used by the various P (and M) nodes. An internet may contain numerous NetBIOS scopes. +-----+ | P | +--+--+ | +-----+ | |----+ P | | | +-----+ /-----+-----\ | +-----+ | | +------+ | +-----+ | P +------+ INTERNET +--+G'WAY |-+----+ P | +-----+ | | +------+ | +-----+ /-----+-----/ | / | | +-----+ / | |----+ P | +-----+ +--+--+ | +-----+ |NBNS + |NBDD | +-----+ +--+--+ Any P node may be replaced by an M node with no loss of function to any node. However, broadcast activity will be increased in the broadcast area to which the M node is attached.
12.2.2. MIXED M AND P NODES M and P nodes may be mixed. When locating NetBIOS names, M nodes will tend to find names held by other M nodes on the same common broadcast area in preference to names held by P nodes or M nodes elsewhere in the network. +-----+ | P | +--+--+ | | /-----+-----\ +-----+ | | +-----+ | P +------+ INTERNET +------+NBDD | +-----+ | | +-----+ /-----+-----/ / | / | +-----+ +--+--+ |NBNS + |G'WAY| +-----+ +--+--+ | | ====+=========+==========+=B'CAST AREA=+==========+=========+==== | | | | | | | | | | | | +--+--+ +--+--+ +--+--+ +--+--+ +--+--+ +--+--+ | M | | P | | M | | P | | M | | P | +-----+ +-----+ +--+--+ +-----+ +-----+ +-----+ NOTE: B and M nodes should not be intermixed in an internet environment. Doing so would allow undetected NetBIOS name conflicts to arise and cause unpredictable behavior. 13. GENERAL METHODS Overlying the specific protocols, described later, are a few general methods of interaction between entities. 13.1. REQUEST/RESPONSE INTERACTION STYLE Most interactions between entities consist of a request flowing in one direction and a subsequent response flowing in the opposite direction. In those situations where interactions occur on unreliable transports (i.e. UDP) or when a request is broadcast, there may not be a strict interlocking or one-to-one relationship between requests and responses.
In no case, however, is more than one response generated for a received request. While a response is pending the responding entity may send one or more wait acknowledgements. 13.1.1. RETRANSMISSION OF REQUESTS UDP is an unreliable delivery mechanism where packets can be lost, received out of transmit sequence, duplicated and delivery can be significantly delayed. Since the NetBIOS protocols make heavy use of UDP, they have compensated for its unreliability with extra mechanisms. Each NetBIOS packet contains all the necessary information to process it. None of the protocols use multiple UDP packets to convey a single request or response. If more information is required than will fit in a single UDP packet, for example, when a P-type node wants all the owners of a group name from a NetBIOS server, a TCP connection is used. Consequently, the NetBIOS protocols will not fail because of out of sequence delivery of UDP packets. To overcome the loss of a request or response packet, each request operation will retransmit the request if a response is not received within a specified time limit. Protocol operations sensitive to successive response packets, such as name conflict detection, are protected from duplicated packets because they ignore successive packets with the same NetBIOS information. Since no state on the responder's node is associated with a request, the responder just sends the appropriate response whenever a request packet arrives. Consequently, duplicate or delayed request packets have no impact. For all requests, if a response packet is delayed too long another request packet will be transmitted. A second response packet being sent in response to the second request packet is equivalent to a duplicate packet. Therefore, the protocols will ignore the second packet received. If the delivery of a response is delayed until after the request operation has been completed, successfully or not, the response packet is ignored. 13.1.2. REQUESTS WITHOUT RESPONSES: DEMANDS Some request types do not have matching responses. These requests are known as "demands". In general a "demand" is an imperative request; the receiving node is expected to obey. However, because demands are unconfirmed, they are used only in situations where, at most, limited damage would occur if the demand packet should be lost. Demand packets are not retransmitted.
13.2. TRANSACTIONS Interactions between a pair of entities are grouped into "transactions". These transactions comprise one or more request/response pairs. 13.2.1. TRANSACTION ID Since multiple simultaneous transactions may be in progress between a pair of entities a "transaction id" is used. The originator of a transaction selects an ID unique to the originator. The transaction id is reflected back and forth in each interaction within the transaction. The transaction partners must match responses and requests by comparison of the transaction ID and the IP address of the transaction partner. If no matching request can be found the response must be discarded. A new transaction ID should be used for each transaction. A simple 16 bit transaction counter ought to be an adequate id generator. It is probably not necessary to search the space of outstanding transaction ID to filter duplicates: it is extremely unlikely that any transaction will have a lifetime that is more than a small fraction of the typical counter cycle period. Use of the IP addresses in conjunction with the transaction ID further reduces the possibility of damage should transaction IDs be prematurely re-used. 13.3. TCP AND UDP FOUNDATIONS This version of the NetBIOS-over-TCP protocols uses UDP for many interactions. In the future this RFC may be extended to permit such interactions to occur over TCP connections (perhaps to increase efficiency when multiple interactions occur within a short time or when NetBIOS datagram traffic reveals that an application is using NetBIOS datagrams to support connection- oriented service.) 14. REPRESENTATION OF NETBIOS NAMES NetBIOS names as seen across the client interface to NetBIOS are exactly 16 bytes long. Within the NetBIOS-over-TCP protocols, a longer representation is used. There are two levels of encoding. The first level maps a NetBIOS name into a domain system name. The second level maps the domain system name into the "compressed" representation required for interaction with the domain name system. Except in one packet, the second level representation is the only NetBIOS name representation used in NetBIOS-over-TCP packet formats. The exception is the RDATA field of a NODE STATUS RESPONSE packet.
14.1. FIRST LEVEL ENCODING The first level representation consists of two parts: - NetBIOS name - NetBIOS scope identifier The 16 byte NetBIOS name is mapped into a 32 byte wide field using a reversible, half-ASCII, biased encoding. Each half-octet of the NetBIOS name is encoded into one byte of the 32 byte field. The first half octet is encoded into the first byte, the second half- octet into the second byte, etc. Each 4-bit, half-octet of the NetBIOS name is treated as an 8-bit, right-adjusted, zero-filled binary number. This number is added to value of the ASCII character 'A' (hexidecimal 41). The resulting 8- bit number is stored in the appropriate byte. The following diagram demonstrates this procedure: 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |a b c d|w x y z| ORIGINAL BYTE +-+-+-+-+-+-+-+-+ | | +--------+ +--------+ | | SPLIT THE NIBBLES v v 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ |0 0 0 0 a b c d| |0 0 0 0 w x y z| +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ | | + + ADD 'A' | | 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ |0 1 0 0 0 0 0 1| |0 1 0 0 0 0 0 1| +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ This encoding results in a NetBIOS name being represented as a sequence of 32 ASCII, upper-case characters from the set {A,B,C...N,O,P}. The NetBIOS scope identifier is a valid domain name (without a leading dot). An ASCII dot (2E hexidecimal) and the scope identifier are appended to the encoded form of the NetBIOS name, the result forming a valid domain name.
For example, the NetBIOS name "The NetBIOS name" in the NetBIOS scope
"SCOPE.ID.COM" would be represented at level one by the ASCII
character string:
FEGHGFCAEOGFHEECEJEPFDCAHEGBGNGF.SCOPE.ID.COM
14.2. SECOND LEVEL ENCODING
The first level encoding must be reduced to second level encoding.
This is performed according to the rules defined in on page 31 of RFC
883[12] in the section on "Domain name representation and
compression". Also see the section titled "Name Formats" in the
Detailed Specifications[1].
15. NetBIOS NAME SERVICE
Before a name may be used, the name must be registered by a node.
Once acquired, the name must be defended against inconsistent
registration by other nodes. Before building a NetBIOS session or
sending a NetBIOS datagram, the one or more holders of the name must
be located.
The NetBIOS name service is the collection of procedures through
which nodes acquire, defend, and locate the holders of NetBIOS names.
The name service procedures are different depending whether the end-
node is of type B, P, or M.
15.1. OVERVIEW OF NetBIOS NAME SERVICE
15.1.1. NAME REGISTRATION (CLAIM)
Each NetBIOS node can own more than one name. Names are acquired
dynamically through the registration (name claim) procedures.
Every node has a permanent unique name. This name, like any other
name, must be explicitly registered by all end-node types.
A name can be unique (exclusive) or group (non-exclusive). A unique
name may be owned by a single node; a group name may be owned by any
number of nodes. A name ceases to exist when it is not owned by at
least one node. There is no intrinsic quality of a name which
determines its characteristics: these are established at the time of
registration.
Each node maintains state information for each name it has
registered. This information includes:
- Whether the name is a group or unique name
- Whether the name is "in conflict"
- Whether the name is in the process of being deleted
B nodes perform name registration by broadcasting claim requests, soliciting a defense from any node already holding the name. P nodes perform name registration through the agency of the NBNS. M nodes register names through an initial broadcast, like B nodes, then, in the absence of an objection, by following the same procedures as a P node. In other words, the broadcast action may terminate the attempt, but is not sufficient to confirm the registration. 15.1.2. NAME QUERY (DISCOVERY) Name query (also known as "resolution" or "discovery") is the procedure by which the IP address(es) associated with a NetBIOS name are discovered. Name query is required during the following operations: During session establishment, calling and called names must be specified. The calling name must exist on the node that posts the CALL. The called name must exist on a node that has previously posted a LISTEN. Either name may be a unique or group name. When a directed datagram is sent, a source and destination name must be specified. If the destination name is a group name, a datagram is sent to all the members of that group. Different end-node types perform name resolution using different techniques, but using the same packet formats: - B nodes solicit name information by broadcasting a request. - P nodes ask the NBNS. - M nodes broadcast a request. If that does not provide the desired information, an inquiry is sent to the NBNS. 15.1.3. NAME RELEASE NetBIOS names may be released explicitly or silently by an end- node. Silent release typically occurs when an end-node fails or is turned- off. Most of the mechanisms described below are present to detect silent name release. 15.1.3.1. EXPLICIT RELEASE B nodes explicitly release a name by broadcasting a notice. P nodes send a notification to their NBNS. M nodes both broadcast a notice and inform their supporting NBNS.
15.1.3.2. NAME LIFETIME AND REFRESH Names held by an NBNS are given a lifetime during name registration. The NBNS will consider a name to have been silently released if the end-node fails to send a name refresh message to the NBNS before the lifetime expires. A refresh restarts the lifetime clock. NOTE: The implementor should be aware of the tradeoff between accuracy of the database and the internet overhead that the refresh mechanism introduces. The lifetime period should be tuned accordingly. For group names, each end-node must send refresh messages. A node that fails to do so will be considered to have silently released the name and dropped from the group. The lifetime period is established through a simple negotiation mechanism during name registration: In the name registration request, the end-node proposes a lifetime value or requests an infinite lifetime. The NBNS places an actual lifetime value into the name registration response. The NBNS is always allowed to respond with an infinite actual period. If the end node proposed an infinite lifetime, the NBNS may respond with any definite period. If the end node proposed a definite period, the NBNS may respond with any definite period greater than or equal to that proposed. This negotiation of refresh times gives the NBNS means to disable or enable refresh activity. The end-nodes may set a minimum refresh cycle period. NBNS implementations which are completely reliable may disable refresh. 15.1.3.3. NAME CHALLENGE To detect whether a node has silently released its claim to a name, it is necessary on occasion to challenge that node's current ownership. If the node defends the name then the node is allowed to continue possession. Otherwise it is assumed that the node has released the name. A name challenge may be issued by an NBNS or by a P or M node. A challenge may be directed towards any end-node type: B, P, or M. 15.1.3.4. GROUP NAME FADE-OUT NetBIOS groups may contain an arbitrarily large number of members. The time to challenge all members could be quite large. To avoid long delays when names are claimed through an NBNS, an
optimistic heuristic has been adopted. It is assumed that there will always be some node which will defend a group name. Consequently, it is recommended that the NBNS will immediately reject a claim request for a unique name when there already exists a group with the same name. The NBNS will never return an IP address (in response to a NAME REGISTRATION REQUEST) when a group name exists. An NBNS will consider a group to have faded out of existence when the last remaining member fails to send a timely refresh message or explicitly releases the name. 15.1.3.5. NAME CONFLICT Name conflict exists when a unique name has been claimed by more than one node on a NetBIOS network. B, M, and NBNS nodes may detect a name conflict. The detection mechanism used by B and M nodes is active only during name discovery. The NBNS may detect conflict at any time it verifies the consistency of its name database. B and M nodes detect conflict by examining the responses received in answer to a broadcast name query request. The first response is taken as authoritative. Any subsequent, inconsistent responses represent conflicts. Subsequent responses are inconsistent with the authoritative response when: The subsequent response has the same transaction ID as the NAME QUERY REQUEST. AND The subsequent response is not a duplicate of the authoritative response. AND EITHER: The group/unique characteristic of the authoritative response is "unique". OR The group/unique characteristic of the subsequent response is "unique". The period in which B and M nodes examine responses is limited by a conflict timer, CONFLICT_TIMER. The accuracy or duration of this timer is not crucial: the NetBIOS system will continue to operate even with persistent name conflicts. Conflict conditions are signaled by sending a NAME CONFLICT DEMAND to the node owning the offending name. Nothing is sent to the node which originated the authoritative response. Any end-node that receives NAME CONFLICT DEMAND is required to update its "local name table" to reflect that the name is in conflict. (The "local name table" on each node contains names that have been
successfully registered by that node.) Notice that only those nodes that receive the name conflict message place a conflict mark next to a name. Logically, a marked name does not exist on that node. This means that the node should not defend the name (for name claim purposes), should not respond to a name discovery requests for that name, nor should the node send name refresh messages for that name. Furthermore, it can no longer be used by that node for any session establishment or sending or receiving datagrams. Existing sessions are not affected at the time a name is marked as being in conflict. The only valid user function against a marked name is DELETE NAME. Any other user NetBIOS function returns immediately with an error code of "NAME CONFLICT". 15.1.4. ADAPTER STATUS An end-node or the NBNS may ask any other end-node for a collection of information about the NetBIOS status of that node. This status consists of, among other things, a list of the names which the node believes it owns. The returned status is filtered to contain only those names which have the same NetBIOS scope identifier as the requestor's name. When requesting node status, the requestor identifies the target node by NetBIOS name A name query transaction may be necessary to acquire the IP address for the name. Locally cached name information may be used in lieu of a query transaction. The requesting node sends a NODE STATUS REQUEST. In response, the receiving node sends a NODE STATUS RESPONSE containing its local name table and various statistics. The amount of status which may be returned is limited by the size of a UDP packet. However, this is sufficient for the typical NODE STATUS RESPONSE packet. 15.1.5. END-NODE NBNS INTERACTION There are certain characteristics of end-node to NBNS interactions which are in common and are independent of any particular transaction type. 15.1.5.1. UDP, TCP, AND TRUNCATION For all transactions between an end-node and an NBNS, either UDP or TCP may be used as a transport. If the NBNS receives a UDP based request, it will respond using UDP. If the amount of information exceeds what fits into a UDP packet, the response will contain a "truncation flag". In this situation, the end- node may open a TCP
connection to the NBNS, repeat the request, and receive a complete, untruncated response. 15.1.5.2. NBNS WACK While a name service request is in progress, the NBNS may issue a WAIT FOR ACKNOWLEDGEMENT RESPONSE (WACK) to assure the client end- node that the NBNS is still operational and is working on the request. 15.1.5.3. NBNS REDIRECTION The NBNS, because it follows Domain Name system styles of interaction, is permitted to redirect a client to another NBNS. 15.1.6. SECURED VERSUS NON-SECURED NBNS An NBNS may be implemented in either of two general ways: The NBNS may monitor, and participate in, name activity to ensure consistency. This would be a "secured" style NBNS. Alternatively, an NBNS may be implemented to be essentially a "bulletin board" on which name information is posted and responsibility for consistency is delegated to the end-nodes. This would be a "non-secured" style NBNS. 15.1.7. CONSISTENCY OF THE NBNS DATA BASE Even in a properly running NetBIOS scope the NBNS and its community of end-nodes may occasionally lose synchronization with respect to the true state of name registrations. This may occur should the NBNS fail and lose all or part of its database. More commonly, a P or M node may be turned-off (thus forgetting the names it has registered) and then be subsequently turned back on. Finally, errors may occur or an implementation may be incorrect. Various approaches have been incorporated into the NetBIOS-over- TCP protocols to minimize the impact of these problems. 1. The NBNS (or any other node) may "challenge" (using a NAME QUERY REQUEST) an end-node to verify that it actually owns a name. Such a challenge may occur at any time. Every end-node must be prepared to make a timely response. Failure to respond causes the NBNS to consider that the end-node has released the name in question.
(If UDP is being used as the underlying transport, the
challenge, like all other requests, must be retransmitted
some number of times in the absence of a response.)
2. The NBNS (or any other node) may request (using the NODE
STATUS REQUEST) that an end-node deliver its entire name
table.
This may occur at any time. Every end-node must be prepared
to make a timely response.
Failure to respond permits (but does not require) the NBNS
to consider that the end-node has failed and released all
names to which it had claims. (Like the challenge, on a UDP
transport, the request must be retransmitted in the absence
of a response.)
3. The NBNS may revoke a P or M node's use of a name by sending
either a NAME CONFLICT DEMAND or a NAME RELEASE REQUEST to
the node.
The receiving end-node may continue existing sessions which
use that name, but must otherwise cease using that name. If
the NBNS placed the name in conflict, the name may be re-
acquired only by deletion and subsequent reclamation. If
the NBNS requested that the name be released, the node may
attempt to re-acquire the name without first performing a
name release transaction.
4. The NBNS may impose a "time-to-live" on each name it
registers. The registering node is made aware of this time
value during the name registration procedure.
Simple or reliable NBNS's may impose an infinite time-to-
live.
5. If an end-node holds any names that have finite time-to-
live values, then that node must periodically send a status
report to the NBNS. Each name is reported using the NAME
REFRESH REQUEST packet.
These status reports restart the timers of both the NBNS and
the reporting node. However, the only timers which are
restarted are those associated with the name found in the
status report. Timers on other names are not affected.
The NBNS may consider that a node has released any name
which has not been refreshed within some multiple of name's
time-to-live.
A well-behaved NBNS, would, however, issue a challenge to-,
or request a list of names from-, the non-reporting end-
node before deleting its name(s). The absence of a
response, or of the name in a response, will confirm the
NBNS decision to delete a name.
6. The absence of reports may cause the NBNS to infer that the
end-node has failed. Similarly, receipt of information
widely divergent from what the NBNS believes about the node,
may cause the NBNS to consider that the end-node has been
restarted.
The NBNS may analyze the situation through challenges or
requests for a list of names.
7. A very cautious NBNS is free to poll nodes (by sending NAME
QUERY REQUEST or NODE STATUS REQUEST packets) to verify that
their name status is the same as that registered in the
NBNS.
NOTE: Such polling activity, if used at all by an
implementation, should be kept at a very low level or
enabled only during periods when the NBNS has some reason to
suspect that its information base is inaccurate.
8. P and M nodes can detect incorrect name information at
session establishment.
If incorrect information is found, NBNS is informed via a
NAME RELEASE REQUEST originated by the end-node which
detects the error.
15.1.8. NAME CACHING
An end-node may keep a local cache of NetBIOS name-to-IP address
translation entries.
All cache entries should be flushed on a periodic basis.
In addition, a node ought to flush any cache information associated
with an IP address if the node receives any information indicating
that there may be any possibility of trouble with the node at that IP
address. For example, if a NAME CONFLICT DEMAND is sent to a node,
all cached information about that node should be cleared within the
sending node.
15.2. NAME REGISTRATION TRANSACTIONS
15.2.1. NAME REGISTRATION BY B NODES
A name claim transaction initiated by a B node is broadcast
throughout the broadcast area. The NAME REGISTRATION REQUEST will be
heard by all B and M nodes in the area. Each node examines the claim
to see whether it it is consistent with the names it owns. If an
inconsistency exists, a NEGATIVE NAME REGISTRATION RESPONSE is
unicast to the requestor. The requesting node obtains ownership of
the name (or membership in the group) if, and only if, no NEGATIVE
NAME REGISTRATION RESPONSEs are received within the name claim
timeout, CONFLICT_TIMER. (See "Defined Constants and Variables" in
the Detailed Specification for the value of this timer.)
A B node proclaims its new ownership by broadcasting a NAME OVERWRITE
DEMAND.
B-NODE REGISTRATION PROCESS
<-----NAME NOT ON NETWORK------> <----NAME ALREADY EXISTS---->
REQ. NODE NODE REQ.NODE
HOLDING
NAME
(BROADCAST) REGISTER (BROADCAST) REGISTER
-------------------> <-------------------
REGISTER REGISTER
-------------------> <-------------------
REGISTER NEGATIVE RESPONSE
-------------------> ------------------------------>
OVERWRITE
-------------------> (NODE DOES NOT HAVE THE NAME)
(NODE HAS THE NAME)
The NAME REGISTRATION REQUEST, like any request, must be repeated if
no response is received within BCAST_REQ_RETRY_TIMEOUT. Transmission
of the request is attempted BCAST_REQ_RETRY_COUNT times.
15.2.2. NAME REGISTRATION BY P NODES
A name registration may proceed in various ways depending whether
the name being registered is new to the NBNS. If the name is known
to the NBNS, then challenges may be sent to the prior holder(s).
15.2.2.1. NEW NAME, OR NEW GROUP MEMBER
The diagram, below, shows the sequence of events when an end-node
registers a name which is new to the NBNS. (The diagram omits WACKs,
NBNS redirections, and retransmission of requests.)
This same interaction will occur if the name being registered is a
group name and the group already exists. The NBNS will add the
registrant to the set of group members.
P-NODE REGISTRATION PROCESS
(server has no previous information about the name)
P-NODE NBNS
REGISTER
--------------------------------->
POSITIVE RESPONSE
<---------------------------------
The interaction is rather simple: the end-node sends a NAME
REGISTRATION REQUEST, the NBNS responds with a POSITIVE NAME
REGISTRATION RESPONSE.
15.2.2.2. EXISTING NAME AND OWNER IS STILL ACTIVE
The following diagram shows interactions when an attempt is made to
register a unique name, the NBNS is aware of an existing owner, and
that existing owner is still active.
There are two sides to the diagram. The left side shows how a non-
secured NBNS would handle the matter. Secured NBNS activity is shown
on the right.
P-NODE REGISTRATION PROCESS
(server HAS a previous owner that IS active)
<------NON-SECURED STYLE-------> <---------SECURED STYLE------->
REQ. NODE NBNS NODE NBNS REQ.NODE
HOLDING
NAME
REGISTER REGISTER
-------------------> <-------------------
QUERY
END-NODE CHALLENGE <------------
<------------------- QUERY
<------------
QUERY
----------------------------->
POSITIVE RESP
QUERY ------------>
-----------------------------> NEGATIVE RESPONSE
----------------->
POSITIVE RESPONSE
<----------------------------
A non-secured NBNS will answer the NAME REGISTRATION REQUEST with a END-NODE CHALLENGE REGISTRATION RESPONSE. This response asks the end-node to issue a challenge transaction against the node indicated in the response. In this case, the prior node will defend against the challenge and the registering end-node will simply drop the registration attempt without further interaction with the NBNS. A secured NBNS will refrain from answering the NAME REGISTRATION REQUEST until the NBNS has itself challenged the prior holder(s) of the name. In this case, the NBNS finds that that the name is still being defended and consequently returns a NEGATIVE NAME REGISTRATION RESPONSE to the registrant. Due to the potential time for the secured NBNS to make the challenge(s), it is likely that a WACK will be sent by the NBNS to the registrant. Although not shown in the diagram, a non-secured NBNS will send a NEGATIVE NAME REGISTRATION RESPONSE to a request to register a unique name when there already exists a group of the same name. A secured NBNS may elect to poll (or challenge) the group members to determine whether any active members remain. This may impose a heavy load on the network. It is recommended that group names be allowed to fade- out through the name refresh mechanism. 15.2.2.3. EXISTING NAME AND OWNER IS INACTIVE The following diagram shows interactions when an attempt is made to register a unique name, the NBNS is aware of an existing owner, and that existing owner is no longer active. A non-secured NBNS will answer the NAME REGISTRATION REQUEST with a END-NODE CHALLENGE REGISTRATION RESPONSE. This response asks the end-node to issue a challenge transaction against the node indicated in the response. In this case, the prior node will not defend against the challenge. The registrant will inform the NBNS through a NAME OVERWRITE REQUEST. The NBNS will replace the prior name information in its database with the information in the overwrite request. A secured NBNS will refrain from answering the NAME REGISTRATION REQUEST until the NBNS has itself challenged the prior holder(s) of the name. In this case, the NBNS finds that that the name is not being defended and consequently returns a POSITIVE NAME REGISTRATION RESPONSE to the registrant.
P-NODE REGISTRATION PROCESS
(server HAS a previous owner that is NOT active)
<------NON-SECURED STYLE-----> <----------SECURED STYLE-------->
REQ. NODE NBNS NODE NBNS REQ.NODE
HOLDING
NAME
REGISTER REGISTER
-------------------> <-------------------
QUERY
END-NODE CHALLENGE <------------
<------------------- QUERY
<------------
NAME QUERY REQUEST POSITIVE RESPONSE
----------------------------> ------------------>
QUERY
---------------------------->
OVERWRITE
------------------->
POSITIVE RESPONSE
<------------------
Due to the potential time for the secured NBNS to make the
challenge(s), it is likely that a WACK will be sent by the NBNS to
the registrant.
A secured NBNS will immediately send a NEGATIVE NAME REGISTRATION
RESPONSE in answer to any NAME OVERWRITE REQUESTS it may receive.
15.2.3. NAME REGISTRATION BY M NODES
An M node begin a name claim operation as if the node were a B node:
it broadcasts a NAME REGISTRATION REQUEST and listens for NEGATIVE
NAME REGISTRATION RESPONSEs. Any NEGATIVE NAME REGISTRATION RESPONSE
prevents the M node from obtaining the name and terminates the claim
operation.
If, however, the M node does not receive any NEGATIVE NAME
REGISTRATION RESPONSE, the M node must continue the claim procedure
as if the M node were a P node.
Only if both name claims were successful does the M node acquire the
name.
The following diagram illustrates M node name registration:
M-NODE REGISTRATION PROCESS
<---NAME NOT IN BROADCAST AREA--> <--NAME IS IN BROADCAST AREA-->
REQ. NODE NODE REQ.NODE
HOLDING
NAME
(BROADCAST) REGISTER (BROADCAST) REGISTER
-------------------> <-------------------
REGISTER REGISTER
-------------------> <-------------------
REGISTER NEGATIVE RESPONSE
-------------------> ------------------------------->
! (NODE DOES NOT HAVE THE NAME)
INITIATE !
A P-NODE !
REGISTRATION !
V
15.3. NAME QUERY TRANSACTIONS
Name query transactions are initiated by end-nodes to obtain the IP
address(es) and other attributes associated with a NetBIOS name.
15.3.1. QUERY BY B NODES
The following diagram shows how B nodes go about discovering who owns
a name.
The left half of the diagram illustrates what happens if there are no
holders of the name. In that case no responses are received in
answer to the broadcast NAME QUERY REQUEST(s).
The right half shows a POSITIVE NAME QUERY RESPONSE unicast by a name
holder in answer to the broadcast request. A name holder will make
this response to every NAME QUERY REQUEST that it hears. And each
holder acts this way. Thus, the node sending the request may receive
many responses, some duplicates, and from many nodes.
B-NODE DISCOVERY PROCESS
<------NAME NOT ON NETWORK------> <---NAME PRESENT ON NETWORK-->
REQ. NODE NODE REQ.NODE
HOLDING
NAME
(BROADCAST) QUERY (BROADCAST) QUERY
----------------------> <---------------------
NAME QUERY REQUEST NAME QUERY REQUEST
----------------------> <---------------------
QUERY POSITIVE RESPONSE
----------------------> ------------------------------>
Name query is generally, but not necessarily, a prelude to NetBIOS
session establishment or NetBIOS datagram transmission. However,
name query may be used for other purposes.
A B node may elect to build a group membership list for subsequent
use (e.g. for session establishment) by collecting and saving the
responses.
15.3.2. QUERY BY P NODES
An NBNS answers queries from a P node with a list of IP address and
other information for each owner of the name. If there are multiple
owners (i.e. if the name is a group name), the NBNS loads as many
answers into the response as will fit into a UDP packet. A
truncation flag indicates whether any additional owner information
remains. All the information may be obtained by repeating the query
over a TCP connection.
The NBNS is not required to impose any order on its answer list.
The following diagram shows what happens if the NBNS has no
information about the name:
P-NODE DISCOVERY PROCESS
(server has no information about the name)
P-NODE NBNS
NAME QUERY REQUEST
--------------------------------->
NEGATIVE RESPONSE
<---------------------------------
The next diagram illustrates interaction between the end-node and the
NBNS when the NBNS does have information about the name. This
diagram shows, in addition, the retransmission of the request by the
end-node in the absence of a timely response. Also shown are WACKs
(or temporary, intermediate responses) sent by the NBNS to the end-
node:
P-NODE QUERY PROCESS
(server HAS information about the name)
P-NODE NBNS
NAME QUERY REQUEST
/---------------------------------------->
/
! (OPTIONAL) WACK
! <- - - - - - - - - - - - - - - - - - - -
! !
!timer !
! ! (optional timer restart)
! !
\ V QUERY
\--------------------------------------->
.
.
.
QUERY
/---------------------------------------->
/
! (OPTIONAL) WACK
! <- - - - - - - - - - - - - - - - - - - -
! !
!timer !
! ! (optional timer restart)
! !
\ V QUERY
\--------------------------------------->
.
.
POSITIVE RESPONSE
<-----------------------------------------
The following diagram illustrates NBNS redirection. Upon receipt of
a NAME QUERY REQUEST, the NBNS redirects the client to another NBNS.
The client repeats the request to the new NBNS and obtains a
response. The diagram shows that response as a POSITIVE NAME QUERY
RESPONSE. However any legal NBNS response may occur in actual
operation.
NBNS REDIRECTION
P-NODE NBNS
NAME QUERY REQUEST
--------------------------------->
REDIRECT NAME QUERY RESPONSE
<---------------------------------
(START FROM THE
VERY BEGINNING
USING THE ADDRESS
OF THE NEWLY
SUPPLIED NBNS.)
NEW
P-NODE NBNS
NAME QUERY REQUEST
--------------------------------->
POSITIVE NAME QUERY RESPONSE
<---------------------------------
The next diagram shows how a P or M node tells the NBNS that the NBNS
has provided incorrect information. This procedure may begin after a
DATAGRAM ERROR packet has been received or a session set-up attempt
has discovered that the NetBIOS name does not exist at the
destination, the IP address of which was obtained from the NBNS
during a prior name query transaction. The NBNS, in this case a
secure NBNS, issues queries to verify whether the information is, in
fact, incorrect. The NBNS closes the transaction by sending either a
POSITIVE or NEGATIVE NAME RELEASE RESPONSE, depending on the results
of the verification.
CORRECTING NBNS INFORMATION BASE
P-NODE NBNS
NAME RELEASE REQUEST
--------------------------------->
QUERY
---------------->
QUERY
---------------->
(NAME TAKEN OFF THE DATABASE
IF NBNS FINDS IT TO BE
INCORRECT)
POSITIVE/NEGATIVE RESPONSE
<---------------------------------
15.3.3. QUERY BY M NODES M node name query follows the B node pattern. In the absence of adequate results, the M node then continues by performing a P node type query. This is shown in the following diagram: M-NODE DISCOVERY PROCESS <---NAME NOT ON BROADCAST AREA--> <--NAME IS ON BROADCAST AREA-> REQ. NODE NODE REQ.NODE HOLDING NAME (BROADCAST) QUERY (BROADCAST) QUERY ---------------------> <---------------------- NAME QUERY REQUEST NAME QUERY REQUEST ---------------------> <---------------------- QUERY POSITIVE RESPONSE ---------------------> -------------------------------> ! INITIATE ! A P-NODE ! DISCOVERY ! PROCESS ! V 15.3.4. ACQUIRE GROUP MEMBERSHIP LIST The entire membership of a group may be acquired by sending a NAME QUERY REQUEST to the NBNS. The NBNS will respond with a POSITIVE NAME QUERY RESPONSE or a NEGATIVE NAME QUERY RESPONSE. A negative response completes the procedure and indicates that there are no members in the group. If the positive response has the truncation bit clear, then the response contains the entire list of group members. If the truncation bit is set, then this entire procedure must be repeated, but using TCP as a foundation rather than UDP.
15.4. NAME RELEASE TRANSACTIONS 15.4.1. RELEASE BY B NODES A NAME RELEASE DEMAND contains the following information: - NetBIOS name - The scope of the NetBIOS name - Name type: unique or group - IP address of the releasing node - Transaction ID REQUESTING OTHER B-NODE B-NODES NAME RELEASE DEMAND ----------------------------------> 15.4.2. RELEASE BY P NODES A NAME RELEASE REQUEST contains the following information: - NetBIOS name - The scope of the NetBIOS name - Name type: unique or group - IP address of the releasing node - Transaction ID A NAME RELEASE RESPONSE contains the following information: - NetBIOS name - The scope of the NetBIOS name - Name type: unique or group - IP address of the releasing node - Transaction ID - Result: - Yes: name was released - No: name was not released, a reason code is provided REQUESTING P-NODE NBNS NAME RELEASE REQUEST ----------------------------------> NAME RELEASE RESPONSE <--------------------------------- 15.4.3. RELEASE BY M NODES The name release procedure of the M node is a combination of the P and B node name release procedures. The M node first performs the P
release procedure. If the P procedure fails then the release
procedure does not continue, it fails. If and only if the P
procedure succeeds then the M node broadcasts the NAME RELEASE DEMAND
to the broadcast area, the B procedure.
NOTE: An M node typically performs a B-style operation and then a
P-style operation. In this case, however, the P-style
operation comes first.
The following diagram illustrates the M node name release procedure:
<-----P procedure fails-------> <-------P procedure succeeds--->
REQUESTING NBNS REQUESTING NBNS
M-NODE M-NODE
NAME RELEASE REQUEST NAME RELEASE REQUEST
--------------------------> ------------------------>
NEGATIVE RELEASE RESPONSE POSITIVE RELEASE RESPONSE
<-------------------------- <-------------------------
OTHER
M-NODES
NAME RELEASE DEMAND
------------------------>
15.5. NAME MAINTENANCE TRANSACTIONS
15.5.1. NAME REFRESH
Name refresh transactions are used to handle the following
situations:
a) An NBNS node needs to detect if a P or M node has "silently"
gone down, so that names held by that node can be purged
from the data base.
b) If the NBNS goes down, it needs to be able to reconstruct
the data base when it comes back up.
c) If the network should be partitioned, the NBNS needs to be
able to able to update its data base when the network
reconnects.
Each P or M node is responsible for sending periodic NAME REFRESH
REQUESTs for each name that it has registered. Each refresh packet
contains a single name that has been successfully registered by that
node. The interval between such packets is negotiated between the
end node and the NBNS server at the time that the name is initially
claimed. At name claim time, an end node will suggest a refresh
timeout value. The NBNS node can modify this value in the reply
packet. A NBNS node can also choose to tell the end node to not send
any refresh packet by using the "infinite" timeout value in the
response packet. The timeout value returned by the NBNS is the
actual refresh timeout that the end node must use.
When a node sends a NAME REFRESH REQUEST, it must be prepared to
receive a negative response. This would happen, for example, if the
the NBNS discovers that the the name had already been assigned to
some other node. If such a response is received, the end node should
mark the name as being in conflict. Such an entry should be treated
in the same way as if name conflict had been detected against the
name. The following diagram illustrates name refresh:
<-----Successful Refresh-----> <-----Unsuccessful Refresh---->
REFRESHING NBNS REFRESHING NBNS
NODE NODE
NAME REFRESH REQUEST NAME REFRESH REQUEST
------------------------> ----------------------->
POSITIVE RESPONSE NEGATIVE RESPONSE
<------------------------ <-----------------------
!
!
V
MARK NAME IN
CONFLICT
15.5.2. NAME CHALLENGE
Name challenge is done by sending a NAME QUERY REQUEST to an end node
of any type. If a POSITIVE NAME QUERY RESPONSE is returned, then
that node still owns the name. If a NEGATIVE NAME QUERY RESPONSE is
received or if no response is received, it can be assumed that the
end node no longer owns the name.
Name challenge can be performed either by the NBNS node, or by an end
node. When an end-node sends a name claim packet, the NBNS node may
do the challenge operation. The NBNS node can choose, however, to
require the end node do the challenge. In that case, the NBNS will
send an END-NODE CHALLENGE RESPONSE packet to the end node, which
should then proceed to challenge the putative owner.
Note that the name challenge procedure sends a normal NAME QUERY
REQUEST packet to the end node. It does not require a special
packet. The only new packet introduced is the END-NODE CHALLENGE
RESPONSE which is sent by an NBNS node when the NBNS wants the end- node to perform the challenge operation. 15.5.3. CLEAR NAME CONFLICT It is possible during a refresh request from a M or P node for a NBNS to detects a name in conflict. The response to the NAME REFRESH REQUEST must be a NEGATIVE NAME REGISTRATION RESPONSE. Optionally, in addition, the NBNS may send a NAME CONFLICT DEMAND or a NAME RELEASE REQUEST to the refreshing node. The NAME CONFLICT DEMAND forces the node to place the name in the conflict state. The node will eventually inform it's user of the conflict. The NAME RELEASE REQUEST will force the node to flush the name from its local name table completely. This forces the node to flush the name in conflict. This does not cause termination of existing sessions using this name. The following diagram shows an NBNS detecting and correcting a conflict: REFRESHING NODE NBNS NAME REFRESH REQUEST -----------------------------------------> NEGATIVE NAME REGISTRATION RESPONSE <----------------------------------------- NAME CONFLICT DEMAND <----------------------------------------- OR NAME RELEASE REQUEST <----------------------------------------- POSITIVE/NEGATIVE RELEASE REQUEST -----------------------------------------> 15.6. ADAPTER STATUS TRANSACTIONS Adapter status is obtained from a node as follows: 1. Perform a name discovery operation to obtain the IP addresses of a set of end-nodes. 2. Repeat until all end-nodes from the set have been used: a. Select one end-node from the set. b. Send a NODE STATUS REQUEST to that end-node using UDP.
c. Await a NODE STATUS RESPONSE. (If a timely response is
not forthcoming, repeat step "b" UCAST_REQ_RETRY_COUNT
times. After the last retry, go to step "a".)
d. If the truncation bit is not set in the response, the
response contains the entire node status. Return the
status to the user and terminate this procedure.
e. If the truncation bit is set in the response, then not
all status was returned because it would not fit into
the response packet. The responder will set the
truncation bit if the IP datagram length would exceed
MAX_DATAGRAM_LENGTH. Return the status to the user and
terminate this procedure.
3. Return error to user, no status obtained.
The repetition of step 2, above, through all nodes of the set, is
optional.
Following is an example transaction of a successful Adapter Status
operation:
REQUESTING NODE NAME OWNER
NAME QUERY REQUEST
----------------------------------------->
POSITIVE NAME QUERY RESPONSE
<-----------------------------------------
NODE STATUS REQUEST
----------------------------------------->
NODE STATUS RESPONSE
<-----------------------------------------
(page 48 continued on part 3)
