Request for Comments: 2834 Silicon Graphics Inc.
Obsoletes: 1374 May 2000
Category: Standards Track
ARP and IP Broadcast over HIPPI-800
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.
Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
Abstract
This document specifies a method for resolving IP addresses to ANSI
High-Performance Parallel Interface (HIPPI) hardware addresses and
for emulating IP broadcast in a logical IP subnet (LIS) as a direct
extension of HARP. This memo defines a HARP that will interoperate
between HIPPI-800 and HIPPI-6400 (also known as Gigabyte System
Network, GSN). This document (when combined with RFC-2067 "IP over
HIPPI") obsoletes RFC-1374.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
3. Definitions . . . . . . . . . . . . . . . . . . . . . . . 3
3.1 Global Concepts . . . . . . . . . . . . . . . . . . . 3
3.2 Glossary . . . . . . . . . . . . . . . . . . . . . . 3
4. IP Subnetwork Configuration . . . . . . . . . . . . . . . 5
4.1 Background . . . . . . . . . . . . . . . . . . . . . 5
4.2 HIPPI LIS Requirements . . . . . . . . . . . . . . . 6
5. HIPPI Address Resolution Protocol - HARP . . . . . . . . 7
5.1 HARP Algorithm . . . . . . . . . . . . . . . . . . . 8
5.1.1 Selecting the authoritative HARP service . . . 8
5.1.2 HARP registration phase . . . . . . . . . . . . 9
5.1.3 HARP operational phase . . . . . . . . . . . . 10
5.2 HARP Client Operational Requirements . . . . . . . . . . 11
5.3 Receiving Unknown HARP Messages . . . . . . . . . . . 12
5.4 HARP Server Operational Requirements . . . . . . . . 12
5.5 HARP and Permanent ARP Table Entries . . . . . . . . 14
5.6 HARP Table Aging . . . . . . . . . . . . . . . . . . 14
6. HARP Message Encoding . . . . . . . . . . . . . . . . . . 15
6.1 HIPPI-LE Header of HARP Messages . . . . . . . . . . 15
6.1.1 IEEE 802.2 LLC . . . . . . . . . . . . . . . . 16
6.1.2 SNAP . . . . . . . . . . . . . . . . . . . . . 16
6.1.3 Diagram . . . . . . . . . . . . . . . . . . . . 17
6.2 HIPPI Hardware Address Formats and Requirements . . . 18
6.2.1 48-bit Universal LAN MAC Addresses . . . . . . 18
6.3 HARP and InHARP Message Formats . . . . . . . . . . . 19
6.3.1 Example Message encodings . . . . . . . . . . . 22
6.3.2 HARP_NAK message format . . . . . . . . . . . . 22
6.3.3 Combined HIPPI-LE and HARP message addresses . 22
7. Broadcast and Multicast . . . . . . . . . . . . . . . . . 23
7.1 Protocol for an IP Broadcast Emulation Server - PIBES 23
7.2 IP Broadcast Address . . . . . . . . . . . . . . . . 24
7.3 IP Multicast Address . . . . . . . . . . . . . . . . 24
7.4 A Note on Broadcast Emulation Performance . . . . . . 24
8. HARP for Scheduled Transfer Protocol . . . . . . . . . . 25
9. Discovery of One's Own Switch Address . . . . . . . . . . 25
10. Security Considerations . . . . . . . . . . . . . . . . . 26
11. Open Issues . . . . . . . . . . . . . . . . . . . . . . . 26
12. HARP Examples . . . . . . . . . . . . . . . . . . . . . . 26
12.1 Registration Phase of Client Y on Non-broadcast HW . 27
12.2 Registration Phase of Client Y on Broadcast Hardware 28
12.3 Operational Phase (phase II) . . . . . . . . . . . . 28
12.3.1 Standard successful HARP_Resolve example . . 29
12.3.2 Standard non-successful HARP_Resolve example 30
13. References . . . . . . . . . . . . . . . . . . . . . . . 31
14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . 32
15. Changes from RFC-1374 . . . . . . . . . . . . . . . . . . 32
16. Author's Address . . . . . . . . . . . . . . . . . . . . 33
17. Full Copyright Statement . . . . . . . . . . . . . . . . 34
1. Introduction
The ANSI High-Performance Parallel Interface (HIPPI) is a dual
simplex data channel. HIPPI can send and receive data
simultaneously at 800 or 1600 megabits per second. Between 1987 and
1997, the ANSI X3T11.1 HIPPI working group (now known as NCITS T11.1)
Standardized five documents that bear on the use of HIPPI as a
network interface. They cover the physical and electrical
specification (HIPPI-PH [1]), the framing of a stream of bytes
(HIPPI-FP [2]), encapsulation of IEEE 802.2 LLC (HIPPI-LE [3]), the
behavior of a physical layer switch (HIPPI-SC [4]) and the physical-
level and optical specification (HIPPI-Serial [5]). HIPPI-LE also
implies the encapsulation of Internet Protocol[5]. The reader should
be familiar with the ANSI HIPPI documents. Approved ANSI NCITS
standards are available from ANSI (http://www.ansi.org). The working
documents of the T11.1 working group may be obtained from the T11 web
page (http://www.t11.org/).
HIPPI switches can be used to connect a variety of computers and
peripheral equipment for many purposes, but the working group stopped
short of describing their use as Local Area Networks. RFC-2067 [15]
describes the encapsulation of IP over HIPPI-800. This memo takes up
where the working group and RFC-2067 [15] left off and defines
address resolution and LIS IP broadcast emulation for HIPPI-800
networks.
While investigating possible solutions for HARP it became evident
that IP broadcast could easily be emulated for both HIPPI-800 and
HIPPI-6400 hardware types. This is useful since HIPPI switches are
not required to implement broadcast but many standard networking
protocols rely on broadcast. This memo therefore further addresses
the emulation of LIS IP broadcast as an extension of HARP.
2 Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [18].
3. Definitions
3.1 Global concepts used
In the following discussion, the terms "requester" and "target" are
used to identify the port initiating the address resolution request
and the port whose address it wishes to discover, respectively. If
not all switches in the LIS support broadcast then there will be a
HARP server providing the address resolution service and it will be
the source of the reply. If on the other hand all switches support
broadcast then the source address of a reply will be the target's
target address.
Values are decimal unless otherwise noted. Formatting follows IEEE
802.1A canonical bit order and and HIPPI-FP bit and byte order.
3.2 Glossary
Broadcast
A distribution mode which transmits a message to all ports.
Particularly also the port sending the message.
Classical/Conventional
Both terms are used to refer to networks such as Ethernet, FDDI, and
other 802 LAN types, as distinct from HIPPI-SC LANs.
Destination
The HIPPI port that receives data from a HIPPI Source.
HARP
HARP describes the whole set of HIPPI address resolution encodings
and algorithms defined in this memo. HARP is a combination and
adaptation of the Internet Address Resolution Protocol (ARP) RFC-826
[13] and Inverse ARP (InARP) [7] (see section 5). HARP also describes
the HIPPI specific version of ARP [10] (i.e. the protocol and the
HIPPI specific encoding).
HARP table
Each host has a HARP table which contains the IP to hardware address
mapping of IP members.
HIPPI-Serial
An implementation of HIPPI in serial fashion on coaxial cable or
optical fiber. (see [5])
HRAL
The HARP Request Address List. A list of ULAs to which HARP messages
are sent when resolving names to addresses (see section 4.2).
Hardware (HW) address
The hardware address of a port consisting of an I-Field and an
optional ULA (see section 6.2). Note: the term port as used in this
document refers to a HIPPI port and is roughly equivalent to the term
"interface" as commonly used in other IP documents.
Host
An entity, usually a computer system, that may have one or more HIPPI
ports and which may serve as a client or a HARP server.
Port
An entity consisting of one HIPPI Source/Destination dual simplex
pair that is connected by parallel or serial HIPPI to a HIPPI-SC
switch and that transmits and receives IP datagrams.
PIBES
The Protocol for Internet Broadcast Emulation Server (see section 7).
Switch Address
A value used as the address of a port on a HIPPI-SC network. It is
transmitted in the I-field. HIPPI-SC switches map Switch Addresses
to physical switch port numbers. The switch address is extended with
a mode byte to form an I-Field (see [4] and 6.2.2)
Source
The HIPPI port that generates data to send to a HIPPI Destination.
Universal LAN MAC Address (ULA)
A 48-bit globally unique address, administered by the IEEE, assigned
to each port on an Ethernet, FDDI, 802 network, or HIPPI-SC LAN.
4. IP Subnetwork Configuration
4.1 Background
ARP (address resolution protocol) as defined in [12] was meant to
work on the 'local' cable. This definition gives the ARP protocol a
local logical IP subnet (LIS) scope. In the LIS scenario, each
separate administrative entity configures its hosts and routers
within the LIS. Each LIS operates and communicates independently of
other LIS's on the same HIPPI network.
HARP has LIS scope only and serves all ports in the LIS.
Communication to ports located outside of the local LIS is usually
provided via an IP router. This router is a HIPPI port attached to
the HIPPI network that is configured as a member of one or more
LIS's. This configuration MAY result in a number of disjoint LIS's
operating over the same HIPPI network. Using this model, ports of
different IP subnets SHOULD communicate via an intermediate IP router
even though it may be possible to open a direct HIPPI connection
between the two IP members over the HIPPI network. This is a
consequence of using IP and choosing to have multiple LIS's on the
same HIPPI fabric.
By default, the HARP method detailed in section 5 and the classical
LIS routing model MUST be available to any IP member client in the
LIS.
4.2 HIPPI LIS Requirements
The requirement for IP members (hosts, routers) operating in a HIPPI
LIS configuration is:
o All members of the LIS SHALL have the same IP network/subnet
address and address mask [6].
The following list identifies the set of HIPPI-specific parameters
that MUST be implemented in each IP station connected to the HIPPI
network:
o HIPPI Hardware Address:
The HIPPI hardware address of an individual IP port MUST contain
the port's Switch Address (see section 9). The address SHOULD also
contain a non-zero ULA address. If there is no ULA then that field
MUST be zero.
o HARP Request Address List (HRAL):
The HRAL is an ordered list of two or more addresses identifying
the address resolution service(s). All HARP clients MUST be
configured identically, i.e. all ports MUST have the same
addresses(es) in the HRAL.
The HRAL MUST contain at least two HIPPI HW addresses identifying
the individual HARP service(s) that have authoritative
responsibility for resolving HARP requests of all IP members
located within the LIS.
By default the first address MUST be the reserved address for
broadcast, i.e. the address for "IP traffic conventionally
directed to the IEEE 802.1 broadcast address: 0xFE1" [4]. The ULA
for this HARP service entry SHALL be FF:FF:FF:FF:FF:FF.
It is REQUIRED that the second address be the address for
"Messages pertaining to (the) ... address resolution requests:
0xFE0" [4]. The ULA for this HARP server entry is
00:00:00:00:00:00.
Therefore, the HRAL entries are sorted in the following order:
1st ** : broadcast address (0x07000FE1 FF:FF:FF:FF:FF:FF),
2nd ** : official HARP server address (0x07000FE0 00:00:00:00:00:00),
3rd & on: any additional HARP server addresses will be sorted in
decreasing order of the 12bit destination switch
address portion of their I-Field (see section 6.2).
** REQUIRED
Within the restrictions mentioned above and in Section 6.2.2, local
administration choose address(es) for the additional HARP services
which they will put into the HRAL.
An example of such a list:
1st entry: 0x07000FE1 FF:FF:FF:FF:FF:FF
2nd entry: 0x07000FE0 00:00:00:00:00:00
3rd entry: 0x07000001 <Alternate-HARP-server-ula>
...
Manual configuration of the addresses and address lists presented in
this section is implementation dependent and beyond the scope of this
memo.
5. HIPPI Address Resolution Protocol - HARP
Address resolution within the HIPPI LIS SHALL make use of the HIPPI
Address Resolution Protocol (HARP) and the Inverse HIPPI Address
Resolution Protocol (InHARP). HARP provides the same functionality as
the Internet Address Resolution Protocol (ARP). HARP is based on ARP
which is defined in RFC-826 [13]. Knowing the Internet address,
conventional networks use ARP to discover another port's hardware
address. HARP presented in this section further specifies the
combination of the original protocol definitions to form a coherent
address resolution service that is independent of the hardware's
broadcast capability.
InHARP is based on the original Inverse ARP (InARP) protocol
presented in [7]. Knowing its hardware address, InARP is used to
discover the other party's Internet address.
This memo further REQUIRES the PIBES (see section 7 below) extension
to the HARP protocol, guaranteeing broadcast service to upper layer
protocols like IP.
Internet addresses are assigned independent of ULAs and switch
addresses. Before using HARP, each port MUST know its IP and its
hardware addresses. The ULA is optional but is RECOMMENDED if
bridging to conventional networks is desired.
5.1 HARP Algorithm
This section defines the behavior and requirements for HARP
implementations on both broadcast and non-broadcast capable HIPPI-SC
networks. HARP creates a table in each port which maps the IP address
of each port to a hardware address, so that when an application
requests a connection to a remote port by its IP address, the
hardware address can be determined, a correct HIPPI-LE header can be
built, and a connection to the port can be established using the
correct Switch Address in the I-field.
HARP is a two phase protocol. The first phase is the registration
phase and the second phase is the operational phase. In the
registration phase the port detects if it is connected to broadcast
hardware or not. The InHARP protocol is used in the registration
phase. In case of non-broadcast capable hardware, the InHARP
Protocol will register and establish a table entry with the server.
The operational phase works much like conventional ARP with the
exception of the message format.
5.1.1 Selecting the authoritative HARP service
Within the HIPPI LIS, there SHALL be an authoritative HARP service.
At each point in time there is only one authoritative HARP service.
To select the authoritative HARP service, each port needs to
determine if it is connected to a broadcast network.
The port SHALL send an InHARP_REQUEST to the first address in its
HRAL (0x07000FE1 FF:FF:FF:FF:FF:FF). If the port sees its own
InHARP_REQUEST, then it is connected to a broadcast capable network.
In this case, the rest of the HRAL is ignored and the authoritative
HARP service is the broadcast entry.
If the port is connected to a non-broadcast capable network, then the
port SHALL send the InHARP_REQUEST to all of the remaining entries in
the HRAL. Every address which sends an InHARP_REPLY is considered to
be a responsive HARP server. The authoritative HARP service SHALL be
the HARP server which appears first in the HRAL.
The sequence of the HRAL is only important for deciding which address
will be the authoritative one. On a non-broadcast network, the port
is REQUIRED to keep "registered" with all HARP server addresses in
the HRAL (NOTE: not the broadcast address since it is not a HARP
server address). If for instance the authoritative HARP service is
non-responsive, then the port will consider the next address in the
HRAL as a candidate for the authoritative address and send an
InHARP_REQUEST.
The authoritative HARP server SHOULD be considered non-responsive
when it has failed to reply to: (1) one or more registration requests
by the client (see section 5.1.2 and 5.2), (2) any two HARP_REQUESTs
in the last 120 seconds or (3) if an external agent has detected
failure of the authoritative HARP server. The details of such an
external agent and its interaction with the HARP client are beyond
the scope of this document. Should an authoritative HARP server
become non-responsive, then the registration process SHOULD be
restarted. Alternative methods for choosing an authoritative HARP
service are not prohibited.
5.1.2 HARP registration phase
HARP clients SHALL initiate the registration phase by sending an
InHARP_REQUEST message using the addresses in the HRAL in order. The
client SHALL terminate the registration phase and transition into the
operational phase, either when it receives its own InHARP_REQUEST or
when it receives an InHARP_REPLY from at least one of the HARP
servers and when it has determined the authoritative HARP service as
described in section 5.1.1.
When ports are initiated they send an InHARP_REQUEST to the
authoritative address as described in section 5.1.2. The first
address to be tried will be the broadcast address "0x07000FE1
FF:FF:FF:FF:FF:FF". There are two outcomes:
1. The port sees its own InHARP_REQUEST: then the port is connected
to a broadcast capable network. The first address becomes and
remains the authoritative address for the HARP service.
2. The port does not receive its InHARP_REQUEST: then the port is
connected to a non-broadcast capable network.
In the second case, the port SHALL choose the next address in the
HRAL as a candidate for a authoritative address and send an
InHARP_REQUEST to that address: (0x07000FE0 00:00:00:00:00:00).
o If the port receives its own message, then the port itself is the
HARP server and the port is REQUIRED to provide broadcast services
using the PIBES (see section 7).
o If the port receives an InHARP_REPLY, then it is a HARP client and
not a HARP server.
In both cases, the current candidate address becomes the
authoritative HARP service address.
If the client determines it is connected to a non-broadcast capable
network then the client SHALL continue to retry each non-broadcast
HARP server address in the HRAL at least once every 5 seconds until
one of these two termination criteria are met for each address.
InHARP is an application of the InARP protocol for a purpose not
originally intended. The purpose is to accomplish registration of
port IP address mappings with a HARP server if one exists or detect
hardware broadcast capability.
If the HIPPI-SC LAN supports broadcast, then the client will see its
own InHARP_REQUEST message and SHALL complete the registration phase.
The client SHOULD further note that it is connected to a broadcast
capable network and use this information for aging the HARP server
entry and for IP broadcast emulation as specified in sections 5.4 and
5.6 respectively.
If the client doesn't see its own InHARP_REQUEST, then it SHALL await
an InHARP_REPLY before completing the registration phase. This will
also provide the client with the protocol address by which the HARP
server is addressable. This will be the case when the client happens
to be connected to a non-broadcast capable HIPPI-SC network.
5.1.3 HARP operational phase
Once a HARP client has completed its registration phase it enters the
operational phase. In this phase of the protocol, the HARP client
SHALL gain and refresh its own HARP table which contains the IP to HW
address mapping of IP members by sending HARP_REQUESTS to the
authoritative address in the HRAL and receiving HARP_REPLYs. The
client is fully operational during the operational phase.
In the operational phase, the client's behavior for requesting HARP
resolution is the same for broadcast or non-broadcast networks.
The target of an address resolution request updates its address
mapping tables with any new information it can find in the request.
If it is the target port it SHALL formulate and send a reply message.
A port is the target of an address resolution request if at least ONE
of the following statements is true of the request:
1. The port's IP address is in the target protocol address field
(ar$tpa) of the HARP message.
2. The port's ULA (if non-zero), is in the ULA part of the Target
Hardware Address field (ar$tha) of the message.
3. The port's switch address is in the Target Switch Address field of
Target Hardware Address field (ar$tha) of the message (see section
6.2.2).
4. The port is a HARP server.
NOTE: It is RECOMMENDED that all HARP servers run on a ports which
each have a non-zero ULA.
5.2 HARP Client Operational Requirements
The HARP client is responsible for contacting the HARP server(s) to
have its own HARP information registered and to gain and refresh its
own HARP entry/information about other IP members. This means, as
noted above, that HARP clients MUST be configured with the hardware
address of the HARP server(s) in the HRAL.
HARP clients MUST:
1. When an interface is enabled (e.g. "ifconfig <interface> up" with
an IP address) or assigned the first or an additional IP address
(i.e. an IP alias), the client SHALL initiate the registration
phase.
2. In the operational phase the client MUST respond to HARP_REQUEST
and InHARP_REQUEST messages if it is the target port. If an
interface has multiple IP addresses (e.g., IP aliases) then the
client MUST cycle through all the IP addresses and generate an
InHARP_REPLY for each such address. In that case an InHARP_REQUEST
will have multiple replies. (Refer to Section 7, "Protocol
Operation" in RFC-1293 [7].)
3. React to address resolution reply messages appropriately to build
or refresh its own client HARP table entries. All solicited and
unsolicited HARP_REPLYs from the authoritative HARP server SHALL
be used to update and refresh its own client HARP table entries.
Explanation: This allows the HARP server to update the clients
when one of server's mappings change, similar to what is
accomplished on Ethernet with gratuitous ARP.
4. Generate and transmit InHARP_REQUEST messages as needed and
process InHARP_REPLY messages appropriately (see section 5.1.2 and
5.6). All InHARP_REPLY messages SHALL be used by the client to
build or refresh its HARP table entries. (Refer to Section 7,
"Protocol Operation" in [7].)
If the registration phase showed that the hardware does not support
broadcast, then the client MUST refresh its own entry for the HARP
server, created during the registration phase, at least once every 15
minutes. This can be accomplished either through the exchange of a
HARP request/reply with the HARP server or by repeating step 1. To
decrease the redundant network traffic, this timeout SHOULD be reset
after each HARP_REQUEST/HARP_REPLY exchange.
Explanation: The HARP_REQUEST shows the HARP server that the client
is still alive. Receiving a HARP_REPLY indicates to the client that
the server must have seen the HARP_REQUEST.
If the registration phase shows that the underlying network supports
broadcast, then periodic InHARP_REQUEST/InHARP_REPLY operations of
step 4 are NOT REQUIRED.
5.3 Receiving Unknown HARP Messages
If a HARP client receives a HARP message with an operation code
(ar$op) that it does not support, it MUST gracefully discard the
message and continue normal operation. A HARP client is NOT REQUIRED
to return any message to the sender of the undefined message.
5.4 HARP Server Operational Requirements
A HARP server MUST accept HIPPI connections from other HIPPI ports.
The HARP server expects an InHARP_REQUEST as the first message from
the client. A server examines the IP source address, the hardware
source address of the InHARP_REQUEST and adds or updates its HARP
table entry <IP address(es), switch address, ULA> as well as the
time stamp.
A HARP server SHALL reply to HARP_REQUESTs and InHARP_REQUESTs based
on the information which it has in its HARP table. The HARP server
SHALL reply with a HARP_REPLY or a InHARP_REPLY, if it has the
requested information in its tables; otherwise it SHALL reply with a
HARP_NAK. The HARP server replies SHALL contain the hardware type and
corresponding format of the request (see also section 6).
The following table shows all possible source address combinations on
an incoming message and the actions to be taken. "linked" indicates
that an existing "IP entry" is linked to a "hardware entry". It is
possible to have an existing "IP entry" and to have an existing
"hardware entry" but neither is linked to the other.
+---+----------+----------+------------+---------------------+
| # | IP entry | HW entry | misc | Action |
+---+----------+----------+------------+---------------------+
| 1 | exists | exists | linked | * |
| 2 | exists | exists | not linked | *, a, b, e, f |
| 3 | exists | new | not linked | *, a, b, d, e, f |
| 4 | new | exists | not linked | *, c, e, f |
| 5 | new | new | not linked | *, c, d, e, f |
+---+----------+----------+------------+---------------------+
Actions:
*: update timeout value
a: break the existing IP -> hardware (HW) - old link
b: delete HW(old) -> IP link and decrement HW(old) refcount, if
refcount = 0, delete HW(old)
c: create new IP entry
d: create new HW entry
e: add new IP -> HW link to IP entry
f: add new HW -> IP link to HW entry
Examples of when this could happen (Numbers match lines in above
table):
1: supplemental message
Just update timer.
2: move an IP alias to an existing interface
If the IP source address of the InHARP_REQUEST duplicates a table
entry IP address (e.g. IPa <-> HWa) and the InHARP_REQUEST
hardware source address matches a hardware address entry (e.g. HWb
<-> IPb), but they are not linked together, then:
- HWa entry needs to have its reference to the current IPa
address removed.
- HWb needs to have a new reference to IPa added
- IPa needs to be linked to HWb
3: move IP address to a new interface
If the InHARP_REQUEST requester's IP source address duplicates a
table entry IP address and the InHARP_REQUEST hardware source
address does not match the table entry hardware address, then a
new HW entry SHALL be created. The requestor's IP address SHALL be
moved from the original HW entry to the new one (see above).
4: add IP alias to table
If the InHARP_REQUEST requester's hardware source address
duplicates a hardware source address entry, but there is no IP
entry matching the received IP address, then the IP address SHALL
be added to the hardware entries previous IP address(es). (E.g.
adding an IP alias).
5: fresh entry, add it
Standard case, create both entries and link them.
A server MUST update the HARP table entry's timeout for each
HARP_REQUEST. Explanation: if the client is sending HARP requests to
the server, then the server SHOULD note that the client is still
"alive" by updating the timeout on the client's HARP table entry.
A HARP server SHOULD use the PIBES (see section 7) to send out
HARP_REPLYs to all hardware addresses in its table when the HARP
server table changes mappings. This feature decreases the time of
stale entries in the clients.
If there are multiple addresses in the HRAL, then a server needs to
act as a client to the other servers.
5.5 HARP and Permanent ARP Table Entries
An IP station MUST have a mechanism (e.g. manual configuration) for
determining what permanent entries it has. The details of the
mechanism are beyond the scope of this memo. The permanent entries
allow interoperability with legacy HIPPI adapters which do not yet
implement dynamic HARP and use a table-based static ARP. Permanent
entries are not aged.
The HARP server SHOULD use the static entries to resolve incoming
HARP_REQUESTs from the clients. This feature eliminates the need for
maintaining a static HARP table on the client ports.
5.6 HARP Table Aging
HARP table aging MUST be supported since IP addresses, especially IP
aliases and also interfaces (with their ULA), are likely to move.
When so doing the mapping in the clients own HARP table/cache becomes
invalid and stale.
o When a client's HARP table entry ages beyond 15 minutes, a HARP
client MUST invalidate the table entry.
o When a server's HARP table entry ages beyond 20 minutes, the HARP
server MUST delete the table entry.
NOTE: the client SHOULD revalidate a HARP table entry before it ages,
thus restarting the aging time when the table entry is successfully
revalidated. The client MAY continue sending traffic to the port
referred to by this entry while revalidation is in progress, as long
as the table entry has not aged. The client MUST revalidate an aged
entry prior to transmitting any non-address-resolution traffic to the
port referred to by this entry.
The client revalidates the entry by querying the HARP server with a
HARP_REQUEST. If a valid reply is received (e.g. HARP_REPLY), the
entry is updated. If the address resolution service cannot resolve
the entry (e.g. HARP_NAK, "host not found"), the associated table
entry is removed. If the address resolution service is not available
(i.e. "server failure") the client MUST attempt to revalidate the
entry by transmitting an InHARP_REQUEST to the hardware address of
the entry in question and updating the entry on receipt of an
InHARP_REPLY. If the InHARP_REQUEST attempt fails to return an
InHARP_REPLY, the associated table entry is removed.
6. HARP Message Encoding
The HARP Message is encapsulated over HIPPI-FP and HIPPI-LE headers.
The HARP FP header values are to be set as defined in RFC-2067 "IP
over HIPPI" [15]. The following sections detail the HIPPI-LE field
contents and HARP message structure and contents. In a broadcast
capable network the client MAY also support Type 1 and 6, Ethernet
and IEEE 802 ARP packet formats.
6.1 HIPPI-LE Header of HARP Messages
The HIPPI message format for Internet datagrams shall conform to the
HIPPI-FP [2] and HIPPI-LE [3] standards. The length of a HIPPI
message, including trailing fill, shall be a multiple of eight bytes
as required by HIPPI-LE. The HIPPI-LE header fields of HARP and
InHARP requests and replies SHALL be:
FC (3 bits) SHALL contain zero.
Double-wide SHOULD be set according to HIPPI-LE [3]. This memo does
NOT address the implications on HARP when this bit is set to 1
indicating the possibility of a port being able to accept 64-bit
HIPPI connections.
Message_Type SHALL contain 0 to indicate a data message. HARP
messages are identified using the Ethertype and the message type in
the ar$op field of the HARP message.
Destination_Switch_Address, SHALL be the Switch Address of the
destination port.
Destination_IEEE_Address SHALL be the ULA of the destination port, if
known, otherwise zero.
Destination_Address_Type SHALL be 2, a 12-bit logical address. The
behavior with type = 1, source routing, is NOT defined in this
specification.
Source_Switch_Address in requests SHALL be the sender's Switch
Address.
Source_IEEE_Address SHALL be the sender's ULA if known, otherwise
zero.
Source_Address_Type SHALL be 2, a 12-bit logical address. The
behavior with type = 1, source routing, is NOT defined in this
specification.
6.1.1 IEEE 802.2 LLC
The IEEE 802.2 LLC Header SHALL begin in the first byte of the
HIPPI-FP D2_Area.
The LLC value for SSAP-DSAP-CTL SHALL be 0xAA-AA-03 (3 bytes)
indicating the presence of a SNAP header.
6.1.2 SNAP
The OUI value for Organization Code SHALL be 0x00-00-00 (3 bytes)
indicating that the following two-bytes is an Ethertype.
The Ethertype value SHALL be set as defined in Assigned Numbers [16]:
InHARP = InARP = HARP = ARP = 2054 = 0x0806.
The total size of the LLC/SNAP header is fixed at 8-bytes.
6.1.3 HIPPI-LE header Diagram
HIPPI-LE header for HARP/InHARP PDUs:
31 28 23 21 15 10 7 2 0
+-----+---------+-+-+-----------+---------+-----+---------+-----+
0 | 04 = IP ULP |1|0| 000 | 03 | 0 |
+---------------+-+-+---------------------+---------------+-----+
1 | n + 8 |
+-----+-+-------+-----------------------+-----------------------+
2 |[LA] |W|M_Type | 000 | Dest. Switch Addr |
+-----+-+-------+-----------------------+-----------------------+
3 | D_A_T | S_A_T | 000 | Source Switch Addr |
+-------+-------+---------------+-------+-----------------------+
4 | 00 00 | |
+-------------------------------+ |
5 | Destination ULA |
+-------------------------------+-------------------------------+
6 | [LA] | |
+-------------------------------+ |
7 | Source ULA |
+===============+===============+===============+===============+
8 | AA | AA | 03 | 00 |
+---------------+---------------+---------------+---------------+
9 | 00 | 00 | Ethertype (2054) |
+---------------+---------------+-------------------------------+
10 |Message byte 0 |Message byte 1 |Message byte 2 | . . . |
+---------------+---------------+---------------+--- |
| . . . |
+ ------------+---------------+---------------+---------------+
| . . . | byte (n-2) | byte (n-1) | FILL |
+---------------+---------------+---------------+---------------+
N-1| FILL | FILL | FILL | FILL |
+---------------+---------------+---------------+---------------+
HIPPI Message Format
Words 0-1: HIPPI-FP Header
Words 2-7: D1_Area (HIPPI-LE Header)
Words 8-9: D2_Area (IEEE 802.2 LLC/SNAP)
Words 10-(N-1): D2_Area (HARP message)
(n+8) is the nb of bytes in the HARP message, incl. LLC/SNAP.
+====+ denotes the boundary between D1_Area and D2_Area.
[LA] fields are zero unless used otherwise locally.
Abbreviations:
"W" = Double_Wide field SHALL be 0
"M_Type" = Message_Type field SHALL be set according to
HIPPI-LE
"D_A_T" = Destination_Address_Type SHALL be 2
"S_A_T" = Source_Address_Type SHALL be 2
[FILL] bytes complete the HIPPI message to an even
number of 32 bit words. The number of fill bytes
is not counted in the data length.
6.2 HIPPI Hardware Address Formats and Requirements
For HIPPI-800, the Hardware Address is a 10-byte unit that SHALL
contain the Switch Address AND the ULA. The format of a hardware
address is:
31 23 15 7 0
+---------------+---------------+-------+-------+---------------+
| Mode Byte | 00 | 0 | X | XX |
+---------------+---------------+-------+-------+---------------+
| ULA byte 0 | ULA byte 1 | ULA byte 2 | ULA byte 3 |
+---------------+---------------+---------------+---------------+
| ULA byte 4 | ULA byte 5 |
+---------------+---------------+
Where "XXX" is the 12 bit HIPPI logical address defined in HIPPI-SC
[4]. Details on ULA see next section.
Two switch addresses are considered to be the same when they have the
same 12 bit destination HIPPI logical address.
NOTE: In the case of HIPPI-6400, the hardware address is ONLY the 6-
byte ULA. Therefore the length of the hardware address clearly
defines which version of HIPPI is being used.
6.2.1 48-bit Universal LAN MAC Addresses
IEEE Standard 802.1A [11] specifies the Universal LAN MAC Address
format. The globally unique part of the 48-bit space is administered
by the IEEE. Each port on a HIPPI-SC LAN SHOULD be assigned a ULA.
Multiple ULAs may be used if a port contains more than one IEEE 802.2
LLC protocol entity.
The format of the HIPPI hardware address within its HARP message
follows IEEE 802.1A canonical bit order and HIPPI-FP bit and byte
order. For example the requester's ULA part of the HIPPI hardware
address would decompose to:
31 23 15 7 0
+---------------+---------------+---------------+---------------+
|ULA byte 0 |L|G| ULA byte 1 | ULA byte 2 | ULA byte 3 |
+---------------+---------------+---------------+---------------+
| ULA byte 4 | ULA byte 5 |
+---------------+---------------+
Universal LAN MAC Address Format
L (U/L bit) = 1 for Locally administered addresses,
0 for Universal.
G (I/G bit) = 1 for Group addresses,
0 for Individual.
The use of ULAs is OPTIONAL, but RECOMMENDED. The use of ULAs is
REQUIRED if a port wishes to interoperate with a conventional
network.
ULAs may also be used by bridging devices that replace HIPPI hardware
headers with the MAC headers of other LANs.
6.3 HARP and InHARP Message Formats
The HARP protocols use the HIPARP hardware type (ar$hrd) [16],
protocol type (ar$pro), and operation code (ar$op) data formats as
the ARP, and InARP protocols [15,7]. In addition, HARP makes use of
an additional operation code for ARP_NAK introduced with [12]. The
remainder of the HARP/InHARP message format is different than the
ARP/InARP message format defined in [15,7,10] and it is also
different from the format defined in the first "IP and ARP on HIPPI"
RFC-1374 [14].
HARP messages SHALL be transmitted with the HIPARP hardware type code
of 28 (decimal). Furthermore, HARP messages SHALL be accepted if
received with hardware type codes of either 28, 1 or 6 (decimal).
The HARP message has several fields that have the following format
and values:
Data sizes and field meaning:
ar$hrd 16 bits Hardware type
ar$pro 16 bits Protocol type of the protocol fields below
ar$op 16 bits Operation code (request, reply, or NAK)
ar$pln 8 bits byte length of each protocol address
ar$rhl 8 bits requester's HIPPI hardware address length (q)
ar$thl 8 bits target's HIPPI hardware address length (x)
ar$rpa 32 bits requester's protocol address
ar$tpa 32 bits target's protocol address
ar$rha qbytes requester's HIPPI Hardware address
ar$tha xbytes target's HIPPI Hardware address
Where :
ar$hrd - SHALL contain 28. (HIPARP)
ar$pro - SHALL contain the IP protocol code 2048 (decimal).
ar$op - SHALL contain the operational value (decimal):
1 for HARP_REQUESTs
2 for HARP_REPLYs
8 for InHARP_REQUESTs
9 for InHARP_REPLYs
10 for HARP_NAK
ar$pln - SHALL contain 4.
ar$rln - SHALL contain 10 IF this is a HIPPI-800 HW address
ELSE, for HIPPI-6400, it SHALL contain 6.
ar$thl - SHALL contain 10 IF this is a HIPPI-800 HW address
ELSE, for HIPPI-6400, it SHALL contain 6.
ar$rha - in requests and NAKs it SHALL contain the requester's
HW address. In replies it SHALL contain the target
port's HW address.
ar$rpa - in requests and NAKs it SHALL contain the requester's IP
address if known, otherwise zero.
In other replies it SHALL contain the target
port's IP address.
ar$tha - in requests and NAKs it SHALL contain the target's
HW address if known, otherwise zero.
In other replies it SHALL contain the requester's
HW addressA.
ar$tpa - in requests and NAKs it SHALL contain the
target's IP address if known, otherwise zero.
In other replies it SHALL contain the requester's
IP address.
The format of the six bytes of the ULA SHALL be the same as required
in the HIPPI-LE header (see section 6.2), except for the alignment of
the ULAs with respect to the 32-bit HIPPI word, which is different
between ARP and HIPPI-LE. No bit reversal is necessary as is
required with FDDI.
31 28 23 21 15 10 7 2 0
+-----+---------+-+-+-----------+---------+-----+---------+-----+
0 | 04 |1|0| 000 | 03 | 0 |
+---------------+-+-+---------------------+---------------+-----+
1 | 45 |
+-----+-+-------+-----------------------+-----------------------+
2 |[LA] |W|MsgT= 0| 000 | Dest. Switch Addr |
+-----+-+-------+-----------------------+-----------------------+
3 | 2 | 2 | 000 | Source Switch Addr |
+---------------+---------------+-------+-----------------------+
4 | 00 00 | |
+-------------------------------+ |
5 | Destination ULA |
+-------------------------------+-------------------------------+
6 | [LA] | |
+-------------------------------+ |
7 | Source ULA |
+===============+===============+===============+===============+
8 | AA | AA | 03 | 00 |
+---------------+---------------+---------------+---------------+
9 | 00 | 00 | Ethertype (2054) |
+---------------+---------------+-------------------------------+
10 | hrd (28) | pro (2048) |
+---------------+---------------+---------------+---------------+
11 | op (ar$op) | pln (6) | rhl (q) |
+---------------+---------------+---------------+---------------+
12 | thl = (x) | Requester IP Address upper (24 bits) |
+---------------------------------------------------------------+
13 | Req. IP lower | Target IP Address upper (24 bits) |
+---------------+-----------------------------------------------+
14 | Tgt. IP lower | Requester HIPPI Hardware Address bytes 0 - 2 |
+---------------+-----------------------------------------------+
15 | Requester HIPPI Hardware Address bytes 3 - 6 |
+-----------------------------------------------+---------------+
16 | Requester HW Address bytes 7 - q | Tgt HW byte 0 |
+---------------+---------------+---------------+---------------+
17 | Target HIPPI Hardware Address bytes 1 - 4 |
+---------------------------------------------------------------+
18 | Target HIPPI Hardware Address bytes 5 - 8 |
+---------------+---------------+---------------+---------------+
19 |Tgt HW byte 9-x| FILL | FILL | FILL |
+---------------+---------------+---------------+---------------+
HARP - InHARP Message
6.3.1 Example Message encodings:
HARP_REQUEST message
HARP ar$op = 1 (HARP_REQUEST)
HARP ar$rpa = IPy HARP ar$tpa = IPa
HARP ar$rha = SWy ULAy HARP ar$tha = 0 **
** is what we would like to find out
HARP_REPLY message format
HARP ar$op = 2 (HARP_REPLY)
HARP ar$rpa = IPa HARP ar$tpa = IPy
HARP ar$rha = SWa ULAa * HARP ar$tha = SWy ULAy
* answer we were looking for
InHARP_REQUEST message format
HARP ar$op = 8 (InHARP_REQUEST)
HARP ar$rpa = IPy HARP ar$tpa = 0 **
HARP ar$rha = SWy ULAy HARP ar$tha = SWa ULAa
** is what we would like to find out
InHARP_REPLY message format
HARP ar$op = 9 (InHARP_REPLY)
HARP ar$rpa = IPs * HARP ar$tpa = IPy
HARP ar$rha = SWa ULAa HARP ar$tha = SWy ULAy
* answer we were looking for
6.3.2 HARP_NAK message format
The HARP_NAK message format is the same as the received HARP_REQUEST
message format with the operation code set to HARP_NAK; i.e. the
HARP_REQUEST message data is copied byte for byte for transmission
with the HARP_REQUEST operation code changed to the HARP_NAK value.
HARP makes use of an additional operation code for HARP_NAK. Hence,
HARP_NAK MUST be implemented.
6.3.3 Combined HIPPI-LE and HARP message addresses
The combined HIPPI-LE/HARP message contains ten addresses, two for
the destination and two for the source of the message, three for the
requester and three for the target:
Destination Switch Address (HIPPI-LE)
Destination ULA (HIPPI_LE)
Source Switch Address (HIPPI-LE)
Source ULA (HIPPI-LE)
Requester IP Address (HARP)
Requester ULA (HARP)
Requester Switch Address (HARP)
Target IP Address (HARP)
Target ULA (HARP)
Target Switch Address (HARP)
Examples:
The following relations are true for a HARP_REQUEST and
InHARP_REQUESTs.
LIS without broadcast - Dest SW Addr = HARP server SW Addr
(with HARP server) Dest ULA = HARP server ULA
Source SW Addr = Requester's SW Addr
Source ULA = Requester's ULA
7 Broadcast and Multicast
HIPPI-SC does not require switches to support broadcast. Broadcast
support has therefore been absent from many HIPPI networks.
During its registration phase, every port, including HARP server(s),
discover if the underlying medium is capable of broadcast (see
section 5.1.2). Should this not be the case, then the HARP server(s)
MUST emulate broadcast through an IP broadcast emulation server.
A HIPPI IP broadcast server (PIBES) is an extension to the HARP
server and only makes sense when the LIS does not inherently support
broadcast. The PIBES allows common upper layer networking protocols
(RIP, TCP, UDP, etc.) to access IP LIS broadcast.
7.1 Protocol for an IP Broadcast Emulation Server - PIBES
To emulate broadcast within an LIS, a PIBES SHALL use the currently
valid HARP table of the HARP server as a list of addresses called the
target list. The broadcast server SHALL validate that all incoming
messages have a source address which corresponds to an address in the
target list. Only messages addressed to the IP LIS broadcast
addresses, multicast address or 255.255.255.255 are considered valid
messages for broadcasting. Invalid messages MUST be dropped. All
valid incoming messages shall be forwarded to all addresses in the
target list.
It is RECOMMENDED that the broadcast server run on the same port as
the HARP server since this memo does not define the protocol for
exchanging the valid HARP table. The default address to use for the
broadcast address is the operational HARP server address.
7.2 IP Broadcast Address
This memo only defines IP broadcast. It is independent of the
underlying hardware addressing and broadcast capabilities. Any port
can differentiate between IP traffic directed to itself and a
broadcast message sent to it by looking at the IP address. All IP
broadcast messages SHALL use the IP LIS broadcast address or.
It is RECOMMENDED that the PIBES run on the same port as the HARP
server. In that case, the PIBES SHALL use the same address as the
HARP server.
7.3 IP Multicast Address
HIPPI does not directly support multicast address, therefore there
are no mappings available from IP multicast addresses to HIPPI
multicast services. Current IP multicast implementations (i.e. MBONE
and IP tunneling, see [9]) will continue to operate over HIPPI-based
logical IP subnets if all IP multicast packets are sent using the
same algorithm as if the packet were being sent to 255.255.255.255.
7.4 A Note on Broadcast Emulation Performance
It is obvious that a broadcast emulation service (as defined in
section 7.1) has an inherent performance limit. In an LIS with n
ports, the upper bound on the bandwidth that such a service can
broadcast is:
(total bandwidth)/(n+1)
since each message must first enter the broadcast server, accounting
for the additional 1, and then be sent to all n ports. The broadcast
server could forward the message destined to the port on which it
runs internally, thus reducing (n+1) to (n) in a first optimization.
This service is adequate for the standard networking protocols such
as RIP, OSPF, NIS, etc. since they usually use a small fraction of