- This note describes a resource location protocol for use in the ARPA
-
- Internet. It is most useful on networks employing technologies which
-
- support some method of broadcast addressing, however it may also be used
-
- on other types of networks. For maximum benefit, all hosts which
-
- provide significant resources or services to other hosts on the Internet
-
- should implement this protocol. Hosts failing to implement the Resource
-
- Location Protocol risk being ignored by other hosts which are attempting
-
- to locate resources on the Internet. This RFC specifies a draft
-
- standard for the ARPA Internet community.
-
- The Resource Location Protocol (RLP) utilizes the User Datagram Protocol
-
- (UDP) [1] which in turn calls on the Internet Protocol (IP) [3] to
-
- deliver its datagrams. See Appendix A and [6] for the appropriate port
-
- and protocol number assignments.
-
- Unless otherwise indicated, all numeric quantities in this document are
-
- decimal numbers.
-
- 1. Introduction
-
- From time to time, Internet hosts are faced with the problem of
-
- determining where on the Internet some particular network service or
-
- resource is being provided. For example, this situation will arise when
-
- a host needs to send a packet destined for some external network to a
-
- gateway on its directly connected network and does not know of any
-
- gateways. In another case, a host may need to translate a domain name
-
- to an Internet address and not know of any name servers which it can ask
-
- to perform the translation. In these situations a host may use the
-
- Resource Location Protocol to determine this information.
-
- In almost all cases the resource location problem is simply a matter of
-
- finding the IP address of some one (usually any) host, either on the
-
- directly connected network or elsewhere on the Internet, which
-
- understands a given protocol. Most frequently, the querying host itself
-
- understands the protocol in question. Typically (as in the case of
-
- locating a name server), the querying host subsequently intends to
-
- employ that protocol to communicate with the located host once its
-
- address is known (e.g. to request name to address translations). Less
-
- frequently, the querying host itself does not necessarily understand the
-
- protocol in question. Instead (as in the case of locating a gateway),
-
- it is simply attempting to find some other host which does (e.g. to
-
- determine an appropriate place to forward a packet which cannot be
-
- delivered locally).
-
-
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- Resource Location Protocol
-
- 2. Resource Naming
-
- Although the resource location problem can, in most cases, be reduced to
-
- the problem of finding a host which implements a given Internet based
-
- protocol, locating only a particular lowest level Internet protocol
-
- (i.e. one assigned a protocol number for transport using IP) is not
-
- completely sufficient. Many significant network services and resources
-
- are provided through higher level protocols which merely utilize the
-
- various lower level protocols for their own transport purposes (e.g. the
-
- FTP protocol [2] employs the TCP protocol [4] for its lower level
-
- transport). Conceptually, this protocol nesting may even be carried out
-
- to arbitrary levels.
-
- Consequently, the Resource Location Protocol names a resource by the
-
- protocol number assigned to its lowest level Internet transport protocol
-
- and by a variable length protocol/resource specific identifier. For
-
- example, the UDP based Echo Protocol can be named by its assigned
-
- protocol number (17) and its assigned 16-bit "well-known" port number
-
- (7). Alternatively, the Internet Control Message Protocol [5] (lacking
-
- any higher level client protocols) would be named simply by its assigned
-
- protocol number (1) and an empty protocol specific identifier. On the
-
- other hand, some as yet undefined resource protocol (provided via say
-
- TCP), might be named by the assigned protocol number (6), its 16-bit
-
- "well-known" TCP port number, and then some additional fixed or variable
-
- length identifier specific to that TCP port.
-
- In general, the components of the protocol/resource specific identifier
-
- are defined to be the "natural" quantities used to successively
-
- de-multiplex the protocol at each next highest protocol level. See
-
- section 5 for some sample assignments.
-
- 3. Protocol Summary
-
- The Resource Location Protocol is a simple request/reply procedure. The
-
- querying host constructs a list of resources which it would like to
-
- locate and sends a request message on the network. A request message
-
- may be sent either to a particular IP address and host or, on networks
-
- which provide broadcast address capability, to the IP address which
-
- refers to all hosts on that network (see [7]). For example, a host
-
- attempting to locate a domain name server might construct a request
-
- containing the resource name [17, 53] (referring to the Domain Name
-
- Server protocol provided at "well-known" UDP port 53) and then broadcast
-
- that request on its local network.
-
- Each receiving host examines the list of resources named in the request
-
- packet, determines which of the resources it provides, and returns a
-
- reply message to the querying host in confirmation. The receiving host
-
- determines whether or not it provides a resource by successive
-
- decomposition of the resource name until either the name is exhausted or
-
- it encounters a component which is not supported. In the previous
-
-
- Page 3
- Resource Location Protocol
-
- example, each host on the network receiving the broadcast request would
-
- examine the resource name by first consulting its tables to determine if
-
- it provided UDP service. If this was successful, it would then examine
-
- the UDP port component of the name and consult its UDP table to
-
- determine if it provided service on UDP port 53. At this point the name
-
- would be exhausted and if both checks were successful the host would
-
- return a reply message to the querying host indicating support for that
-
- resource.
-
- 3.1. Request Messages
-
- RLP provides two basic types of request messages which may be
-
- transmitted by a querying host. The first type requires any host
-
- receiving the request message to return a reply message only if it
-
- provides at least one of the resources named in the request list. The
-
- second type requires any host receiving the message to always return a
-
- reply message even if it provides none of the resources named in the
-
- request list.
-
- These two types of request messages are:
-
- <Who-Provides?>
-
This type requires any host receiving the message to return an
appropriate reply message which names all of the resources from the
request list which it provides. If the receiving host provides none
of the named resources, no reply may be returned.
- <Do-You-Provide?>
-
This type is identical to the <Who-Provides?> message but with the
extra requirement that a reply must always be returned. When a
receiving host provides none of the requested resources, it simply
returns an empty reply list. This empty reply list allows the
querying host to immediately detect that the confirming host
provides none of the named resources without having to timeout after
repeatedly retransmitting the request.
- The <Who-Provides?> request message is most typically used when
-
- broadcasting requests to an entire IP network. The <Do-You-Provide?>
-
- request message, on the other hand, is most typically used when
-
- confirming that a particular host does or does not provide one or more
-
- specific resources. It may not be broadcast (since such a request would
-
- flood the querying host with reply messages from all hosts on the
-
- network).
-
- In addition to the two basic types of request messages, an additional
-
- two variant types of request messages may also be transmitted by a
-
- querying host. These message types provide a "third-party" resource
-
- location capability. They differ from the basic message types by
-
-
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- Resource Location Protocol
-
- providing space for an additional qualifier with each listed resource to
-
- identify "third-party" hosts which the confirming host believes may
-
- provide the resource. As before, the first type requires any host
-
- receiving the request message to return a reply message only if it knows
-
- of some host which provides at least one of the resources named in the
-
- request list. The second type requires any host receiving the message
-
- to always return a reply message even if it knows of no hosts which
-
- provide any of the resources named in the request list.
-
- These two remaining types of request messages are:
-
- <Who-Anywhere-Provides?>
-
This message parallels the <Who-Provides?> message with the
"third-party" variant described above. The confirming host is
required to return at least its own IP address (if it provides the
named resource) as well as the IP addresses of any other hosts it
believes may provide the named resource. The confirming host
though, may never return an IP address for a resource which is the
same as an IP address listed with the resource name in the request
message. In this case it must treat the resource as if it was
unsupported at that IP address and omit it from any reply list.
- <Does-Anyone-Provide?>
-
This message parallels the <Do-You-Provide?> message again with the
"third-party" variant described above. As before, the confirming
host is required to return its own IP address as well as the IP
addresses of any other hosts it believes may provide the named
resource and is prohibited from returning the same IP address in the
reply resource specifier as was listed in the request resource
specifier. As in the <Do-You-Provide?> case and for the same
reason, this message also may not be broadcast.
- These variant request messages permit "smart" hosts to supply resource
-
- location information for networks without broadcast capability (provided
-
- that all hosts on the network always "know" the address of one or more
-
- such "smart" hosts). They also permit resource location information for
-
- services which are not provided anywhere on a directly connected network
-
- to be provided by "smart" gateways which have perhaps queried other
-
- networks to which they are attached or have somehow otherwise acquired
-
- the information.
-
- The restriction against returning the same IP address in a reply as was
-
- specified in the request provides a primitive mechanism for excluding
-
- certain known addresses from consideration in a reply (see section 5,
-
- example 3). It may also be used to override the receiving host's
-
- preference for its own IP address in "third-party" replies when this is
-
- required.
-
-
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- Resource Location Protocol
-
- 3.2. Reply Messages
-
- Each of the types of request messages has an associated type of reply
-
- message. The basic reply message type is returned in response to both
-
- <Who-Provides?> and <Do-You-Provide?> request messages and supplies
-
- information about the resources provided by the confirming host. The
-
- other reply message type is the "third-party" variant returned in
-
- response to both <Who-Anywhere-Provides?> and <Does-Anyone-Provide?>
-
- request messages and supplies information about resources provided by
-
- hosts known to the confirming host.
-
- These two types of reply messages are:
-
- <I-Provide>
-
This reply message contains a list of exactly those resources from
the request list which the confirming host provides. These
resources must occur in the reply list in precisely the same order
as they were listed in the request message.
- <They-Provide>
-
This reply message similarly contains a list of exactly those
resources from the request list (appropriately qualified with IP
addresses) which the confirming host provides or believes another
host provides. These resources again must occur in the reply list
in precisely the same order as they were listed in the request
message.
- Neither type of reply message may be broadcast.
-
- A querying host which receives a <They-Provide> reply message from a
-
- confirming host on behalf of a third host is not required to
-
- unquestioningly rely on the indirectly provided information. This
-
- information should usually be regarded simply as a hint. In most cases,
-
- the querying host should transmit a specific <Do-You-Provide?> request
-
- to the third host and confirm that the resource is indeed provided at
-
- that IP address before proceeding.
-
- 4. Message Formats
-
- RLP messages are encapsulated in UDP packets to take advantage of the
-
- multiplexing capability provided by the UDP source and destination ports
-
- and the extra reliability provided by the UDP checksum. Request
-
- messages are sent from a convenient source port on the querying host to
-
- the assigned RLP destination port of a receiving host. Reply messages
-
- are returned from the assigned RLP source port of the confirming host to
-
- the appropriate destination port of the querying host as determined by
-
- the source port in the request message.
-
- The format of the various RLP messages is described in the following
-
- diagrams. All numeric quantities which occupy more than one octet are
-
-
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- Resource Location Protocol
-
- stored in the messages from the high order octet to the low order octet
-
- as per the usual Internet protocol standard. All packet diagrams
-
- indicate the octets of the message from left to right and then top to
-
- bottom as they occur in the data portion of the encapsulating UDP
-
- packet.
-
- Each RLP packet has the general format
-
+--------+--------+--------+--------+
| | | |
| Type | Flags | Message-ID |
| | | |
+--------+--------+--------+--------+
| -
| Resource-List -
| -
+--------+--------+--------+---\\---+
- +
- Resource-List |
- |
+--------+--------+--------+---\\---+
- where
-
- <Type>
-
is a single octet which identifies the message type. The currently
defined types are:
0 <Who-Provides?>
1 <Do-You-Provide?>
2 <Who-Anywhere-Provides?>
3 <Does-Anyone-Provide?>
4 <I-Provide>
5 <They-Provide>
6-255 Reserved.
-
- Page 7
- Resource Location Protocol
-
- <Flags>
-
is a single octet specifying possible modifications to the standard
interpretation of <Type>. Bits in this field are numbered from left
to right (from most significant to least significant) beginning with
bit 1. The currently defined flag bits are:
Bit 1 <Local-Only>. Requires that any reply message generated in
response to a request message with this flag bit set may
only name IP addresses which are on the same IP network as
the sender of the request message. This flag also requires
that multi-homed hosts answering broadcast <Who-Provides?>
requests use the appropriate local network IP source
address in the returned reply. This bit must be zero in
reply messages.
Bits 2-8 Reserved. Must be zero.
- <Message-ID>
-
is a two octet (16-bit) value which identifies the request message.
It is used simply to aid in matching requests with replies. The
sending host should initialize this field to some convenient value
when constructing a request message. The receiving host must return
this same value in the <Message-ID> field of any reply message
generated in response to that request.
- <Resource-List>
-
is the list of resources being queried or for which location
information is being supplied. This list is a sequence of octets
beginning at the octet following the <Message-ID> and extending
through the end of the UDP packet. The format of this field is
explained more fully in the following section. The size of this
list is implicitly specified by the length of the encapsulating UDP
datagram.
- 4.1. Resource Lists
-
- A <Resource-List> consists of zero or more resource specifiers. Each
-
- resource specifier is simply a sequence of octets. All resource
-
- specifiers have a common resource name initial format
-
+--------+--------+--------+---\\---+
| | | |
|Protocol|IDLength| Resource-ID |
| | | |
+--------+--------+--------+---\\---+
- where
-
-
- Page 8
- Resource Location Protocol
-
- <Protocol>
-
is the protocol number assigned to the lowest level Internet
protocol utilized for accessing the resource.
- <IDLength>
-
is the length of the resource identifier associated with this
<Protocol>. This length may be a fixed or variable value depending
on the particular resource. It is included so that specifiers which
refer to resources which a host may not provide can be skipped over
without needing to know the specific structure of the particular
resource identifier. If the <Protocol> has no associated natural
identifier, this length is 0.
- <Resource-ID>
-
is the qualifying identifier used to further refine the resource
being queried. If the <IDLength> field was 0, then this field is
empty and occupies no space in the resource specifier.
- In addition, resource specifiers in all <Who-Anywhere-Provides?>,
-
- <Does-Anyone-Provide?> and <They-Provide> messages also contain an
-
- additional qualifier following the <Protocol-ID>. This qualifier has
-
- the format
-
+--------+--------+--------+--------+---//---+
| | |
|IPLength| IP-Address-List |
| | |
+--------+--------+--------+--------+---//---+
- where
-
-
- Page 9
- Resource Location Protocol
-
- <IPLength>
-
is the number of IP addresses containing in the following
<IP-Address-List> (the <IP-Address-List> field thus occupies the
last 4*<IPLength> octets in its resource specifier). In request
messages, this is the maximum number of qualifying addresses which
may be included in the corresponding reply resource specifier.
Although not particularly useful, it may be 0 and in that case
provides no space for qualifying the resource name with IP addresses
in the returned specifier. In reply messages, this is the number of
qualifying addresses known to provide the resource. It may not
exceed the number specified in the corresponding request specifier.
This field may not be 0 in a reply message unless it was supplied as
0 in the request message and the confirming host would have returned
one or more IP addresses had any space been provided.
- <IP-Address-List>
-
is a list of four-octet IP addresses used to qualify the resource
specifier with respect to those particular addresses. In reply
messages, these are the IP addresses of the confirming host (when
appropriate) and the addresses of any other hosts known to provide
that resource (subject to the list length limitations). In request
messages, these are the IP addresses of hosts for which resource
information may not be returned. In such messages, these addresses
should normally be initialized to some "harmless" value (such as the
address of the querying host) unless it is intended to specifically
exclude the supplied addresses from consideration in any reply
messages.
- The receiving host determines if it provides any of the resources named
-
- in the request list by successively decomposing each resource name. The
-
- first level of decomposition is the Internet protocol number which can
-
- presumably be looked up in a table to determine if that protocol is
-
- supported on the host. Subsequent decompositions are based on previous
-
- components until one of three events occur:
-
- 1. the current component identifies some aspect of the previous
-
components which the host does not support,
- 2. the resource name from the request list is exhausted, or
-
- 3. the resource name from the request list is not exhausted but
-
the host does not expect any further components in the name
given the previous components
- In case 1, the receiving host has determined that it does not provide
-
- the named resource. The resource specifier may not be included in any
-
- reply message returned.
-
- In case 2, the receiving host has determined that it does indeed provide
-
- the named resource (note: this may occur even if the receiving host
-
-
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- Resource Location Protocol
-
- would have expected the resource name to contain more components than
-
- were actually present). The resource specifier must be included (modulo
-
- IP address prohibitions) in any reply message returned.
-
- In case 3, the receiving host has determined that it does not completely
-
- provide the named resource since name components remain which it does
-
- not understand (this might occur with specializations of or extensions
-
- to a known protocol which are not universally recognized). The resource
-
- specifier may not be included in any reply message returned.
-
- 5. Sample Usage
-
- The following scenarios illustrate some typical uses of RLP. In all
-
- cases the indicated messages are encapsulated in a UDP datagram with the
-
- appropriate source and destination port numbers, message length, and
-
- checksum. This datagram is further encapsulated in an IP datagram with
-
- the appropriate source address of the sending host and destination
-
- address (either broadcast or individual) for the receiving host.
-
- All numeric protocol examples are as specified in the appropriate
-
- protocol description documents listed in the references.
-
- 1. Suppose a freshly rebooted host H wishes to find some gateway
-
on its directly connected network to which it can send its
first external packet. It then broadcasts the request
<Who-Provides?> <Flags>=<Local-Only> <Message-ID>=12345
<Resource-List>={[GGP], [EGP]}
encoded as the 8 octet message
+-----+-----+-----+-----+-----+-----+-----+-----+
| 0 | 128 | 12345 | 3 | 0 | 8 | 0 |
+-----+-----+-----+-----+-----+-----+-----+-----+
on its local network.
- Gateway G1 (which understands EGP) receives the request and
returns the reply
<I-Provide> <Flags>=none <Message-ID>=12345
<Resource-List>={[EGP]}
encoded as the 6 octet message
+-----+-----+-----+-----+-----+-----+
| 4 | 0 | 12345 | 8 | 0 |
+-----+-----+-----+-----+-----+-----+
to host H which then remembers that gateway G1 may be used
-
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- Resource Location Protocol
-
to route traffic to the rest of the Internet.
- At the same time, gateway G2 (which understands both GGP
and EGP) might also receive the request and return the reply
<I-Provide> <Flags>=none <Message-ID>=12345
<Resource-List>={[GGP], [EGP]}
encoded as the 8 octet message
+-----+-----+-----+-----+-----+-----+-----+-----+
| 4 | 0 | 12345 | 3 | 0 | 8 | 0 |
+-----+-----+-----+-----+-----+-----+-----+-----+
to host H which might then also add gateway G2 to its list
if it chooses.
- 2. Assume instead that host H is a stand-alone system which has
-
just encountered some fatal software error and wishes to locate
a crash dump server to save its state before reloading.
Suppose that the crash dump protocol on the host's local
network is implemented using the Trivial File Transfer Protocol
(TFTP) [8]. Furthermore, suppose that the special file name
"CRASH-DUMP" is used to indicate crash dump processing (e.g.
the server might locally generate a unique file name to hold
each dump that it receives from a host). Then host H might
broadcast the request
<Who-Provides?> <Flags>=none <Message-ID>=54321
<Resource-List>={[UDP, TFTP, WRQ, "CRASH-DUMP"]}
encoded as the 21 octet message
+-----+-----+-----+-----+-----+-----+-----+-----+
| 0 | 0 | 54321 | 17 | 15 | 69 |
+-----+-----+-----+-----+-----+-----+-----+-----+
| 2 | 'C' 'R' 'A' 'S' 'H' '-' |
+-----+-----+-----+-----+-----+-----+-----+-----+
| 'D' 'U' 'M' 'P' 0 |
+-----+-----+-----+-----+-----+
to its local network (note that the file name component is
explicitly terminated by a null so as not to exclude future
further specialization of the crash dump protocol).
- Host C (which supports this specialization of the TFTP
protocol) receives the request and returns the reply
<I-Provide> <Flags>=none <Message-ID>=54321
<Resource-List>={[UDP, TFTP, WRQ, "CRASH-DUMP"]}
-
- Page 12
- Resource Location Protocol
-
encoded as the 21 octet message
+-----+-----+-----+-----+-----+-----+-----+-----+
| 4 | 0 | 54321 | 17 | 15 | 69 |
+-----+-----+-----+-----+-----+-----+-----+-----+
| 2 | 'C' 'R' 'A' 'S' 'H' '-' |
+-----+-----+-----+-----+-----+-----+-----+-----+
| 'D' 'U' 'M' 'P' 0 |
+-----+-----+-----+-----+-----+
to host H which may then proceed to send its crash dump to
host C and reload.
- Host D (which provides TFTP service but not the crash dump
specialization), however, might receive the request and
determine that it provides no support for the resource
(since the resource name contains components following the
UDP port number which it does not understand). It would
therefore return no reply to host H.
- 3. Finally, suppose host M wishes to locate some domain name
-
translation server (either UDP or TCP based) anywhere on the
Internet. Furthermore, suppose that host M is on a IP network
which does not provide broadcast address capabilities and that
host R is a "known" resource location server for that network.
First, since host M prefers to find a domain name server on its
own locally connected network if possible, it sends the request
<Does-Anyone-Provide?> <Flags>=<Local-Only>
<Message-ID>=12321 <Resource-List>=
{[TCP, <DOMAIN-NAME-SERVER-PORT>] {M},
[UDP, <DOMAIN-NAME-SERVER-PORT>] {M}}
encoded as the 22 octet message
+-----+-----+-----+-----+
| 3 | 128 | 12321 |
+-----+-----+-----+-----+-----+-----+-----+-----+-----+
| 6 | 2 | 53 | 1 | M |
+-----+-----+-----+-----+-----+-----+-----+-----+-----+
| 17 | 2 | 53 | 1 | M |
+-----+-----+-----+-----+-----+-----+-----+-----+-----+
to host R.
Host R receives the request and consults its tables for any
hosts known to support either variety of domain name service.
It finds entries indicating that both hosts S and T provide UDP
-
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- Resource Location Protocol
-
based domain name service but that neither host is on the same
IP network as host H. It must then send the negative
confirmation reply
<They-Provide> <Flags>=none <Message-ID>=12321
<Resource-List>={}
encoded as the 4 octet message
+-----+-----+-----+-----+
| 5 | 0 | 12321 |
+-----+-----+-----+-----+
back to host M.
Host M, receiving this reply, might now abandon any hope of
finding a server on its own network, reformat its request to
permit any host address, and resend
<Does-Anyone-Provide?> <Flags>=none <Message-ID>=12322
<Resource-List>=
{[TCP, <DOMAIN-NAME-SERVER-PORT>] {M},
[UDP, <DOMAIN-NAME-SERVER-PORT>] {M}}
encoded as the 22 octet message
+-----+-----+-----+-----+
| 3 | 0 | 12322 |
+-----+-----+-----+-----+-----+-----+-----+-----+-----+
| 6 | 2 | 53 | 1 | M |
+-----+-----+-----+-----+-----+-----+-----+-----+-----+
| 17 | 2 | 53 | 1 | M |
+-----+-----+-----+-----+-----+-----+-----+-----+-----+
again to host R.
Host R receives this new request and is no longer constrained
to return only local addresses. However, since only space for
a single qualifying IP address was provided in each request
resource specifier, it may not immediately return both
addresses. Instead, it is forced to return only the first
address and replies
<They-Provide> <Flags>=none <Message-ID>=12322
<Resource-List>={[UDP, <DOMAIN-NAME-SERVER-PORT>] {S}}
encoded as the 13 octet message
-
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- Resource Location Protocol
-
+-----+-----+-----+-----+-----+-----+-----+-----+
| 5 | 0 | 12322 | 17 | 2 | 53 |
+-----+-----+-----+-----+-----+-----+-----+-----+
| 1 | S |
+-----+-----+-----+-----+-----+
to Host M.
Host M receives the reply and (being the suspicious sort)
decides to confirm it with host S. It then sends
<Do-You-Provide?> <Flags>=none <Message-ID>=12323
<Resource-List>={[UDP, <DOMAIN-NAME-SERVER-PORT>]}
encoded as the 8 octet message
+-----+-----+-----+-----+-----+-----+-----+-----+
| 1 | 0 | 12323 | 17 | 2 | 53 |
+-----+-----+-----+-----+-----+-----+-----+-----+
to host S and receives back from host S the reply
<I-Provide> <Flags>=none <Message-ID>=12323
<Resource-List>={}
encoded as the 4 octet message
+-----+-----+-----+-----+
| 4 | 0 | 12323 |
+-----+-----+-----+-----+
denying any support for UDP based domain name service.
In desperation host M again queries host R, this time excluding
host S from consideration, and sends the request
<Does-Anyone-Provide?> <Flags>=none <Message-ID>=12324
<Resource-List>=
{[TCP, <DOMAIN-NAME-SERVER-PORT>] {S},
[UDP, <DOMAIN-NAME-SERVER-PORT>] {S}}
encoded as the 22 octet message
+-----+-----+-----+-----+
| 3 | 0 | 12324 |
+-----+-----+-----+-----+-----+-----+-----+-----+-----+
| 6 | 2 | 53 | 1 | S |
+-----+-----+-----+-----+-----+-----+-----+-----+-----+
| 17 | 2 | 53 | 1 | S |
+-----+-----+-----+-----+-----+-----+-----+-----+-----+
-
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- Resource Location Protocol
-
and this time receives the reply
<They-Provide> <Flags>=none <Message-ID>=12324
<Resource-List>={[UDP, <DOMAIN-NAME-SERVER-PORT>] {T}}
encoded as the 13 octet message
+-----+-----+-----+-----+-----+-----+-----+-----+
| 5 | 0 | 12324 | 17 | 2 | 53 |
+-----+-----+-----+-----+-----+-----+-----+-----+
| 1 | T |
+-----+-----+-----+-----+-----+
from host R which of course host M again insists on confirming
by sending the request
<Do-You-Provide?> <Flags>=none <Message-ID>=12325
<Resource-List>=
{[UDP, <DOMAIN-NAME-SERVER-PORT>]}
encoded as the 8 octet message
+-----+-----+-----+-----+-----+-----+-----+-----+
| 1 | 0 | 12325 | 17 | 2 | 53 |
+-----+-----+-----+-----+-----+-----+-----+-----+
to host T and finally receives confirmation from host T with
the reply
<I-Provide> <Flags>=none <Message-ID>=12325
<Resource-List>={[UDP, <DOMAIN-NAME-SERVER-PORT>]}
encoded as the 8 octet message
+-----+-----+-----+-----+-----+-----+-----+-----+
| 4 | 0 | 12325 | 17 | 2 | 53 |
+-----+-----+-----+-----+-----+-----+-----+-----+
that it indeed provides domain name translation service at UDP
port 53.
- A. Assigned Numbers
-
- The "well-known" UDP port number for the Resource Location Protocol is
-
- 39 (47 octal).
-
-
- Page 16
- Resource Location Protocol
-
REFERENCES
- [1] Postel, J.
-
User Datagram Protocol.
RFC 768, USC/Information Sciences Institute, August, 1980.
- [2] Postel, J.
-
File Transfer Protocol.
RFC 765, USC/Information Sciences Institute, June, 1980.
- [3] Postel, J.
-
Internet Protocol - DARPA Internet Program Protocol Specification.
RFC 791, USC/Information Sciences Institute, September, 1981.
- [4] Postel, J.
-
Transmission Control Protocol- DARPA Internet Program Protocol
Specification.
RFC 793, USC/Information Sciences Institute, September, 1981.
- [5] Postel, J.
-
Internet Control Message Protocol - DARPA Internet Program
Protocol Specification.
RFC 792, USC/Information Sciences Institute, September, 1981.
- [6] Reynolds, J., and J. Postel.
-
Assigned Numbers.
RFC 870, USC/Information Sciences Institute, October, 1983.
- [7] Gurwitz, R., and R. Hinden.
-
IP - Local Area Network Addressing Issues.
IEN 212, Bolt Beranek and Newman, September, 1982.
- [8] Sollins, K.
-
The TFTP Protocol (revision 2).
RFC 783, MIT/Laboratory for Computer Science, June, 1981.
-