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Network Working Group W A Simpson
Internet Draft Daydreamer
expires in six months April 1993
SIP System Discovery
Status of this Memo
This memo is the product of the SIP Working Group of the Internet
Engineering Task Force (IETF). Comments on this memo should be
submitted to the sip@caldera.usc.edu mailing list.
Distribution of this memo is unlimited.
This document is an Internet Draft. Internet Drafts are working
documents of the Internet Engineering Task Force (IETF), its Areas,
and its Working Groups. Note that other groups may also distribute
working documents as Internet Drafts. Internet Drafts are draft
documents valid for a maximum of six months. Internet Drafts may be
updated, replaced, or obsoleted by other documents at any time. It
is not appropriate to use Internet Drafts as reference material or to
cite them other than as a ``working draft'' or ``work in progress.''
Please check the 1id-abstracts.txt listing contained in the
internet-drafts Shadow Directories on nic.ddn.mil, nnsc.nsf.net,
nic.nordu.net, ftp.nisc.sri.com, or munnari.oz.au to learn the
current status of any Internet Draft.
Abstract
This document specifies ICMP messages for the identification and
location of adjacent SIP systems. This is intended to replace ARP,
ICMP Router Advertisement, ICMP Redirect, and OSPF Hello in the SIP
environment.
[This is a rough first draft. Need assessment of needed fields,
much more text describing usage. Autoconfiguration will be in a
separate draft, since the issues here are already getting too big.]
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1. Criteria
Multicast support.
Nearly all of the respondents listed this as the first or
second desire stated. It is noted that not all media
supports multicast.
Reduced net traffic.
On one hand, a flood of hosts sending periodic
advertisements; on the other, 2 extra packets for every
address request.
Two solutions were proposed:
1) Sending the first packet to the all-systems multicast,
and receiving a redirect. This reduces the traffic from
3 to 2 packets.
2) Automatic router discovery. For those packets which are
clearly destined off net, the packet can be sent directly
to the next hop. Preference values were cited as useful.
Also, carrying media addresses within the router discovery
and redirect packets, so that a further query/response can be
avoided.
Low host overhead.
A host should only retain information for those systems with
with it is directly communicating.
Autoconfiguration.
In particular, automatic address discovery and automatic
address prefix changes.
Mobility support.
Partly a subset of the above, as related to dynamically
changing addresses while moving. In addition, the "hidden
transmitter" problem (you can hear another system, it can't
hear you, but there is a path through a third system which it
can hear, completing the circuit). This is not well
supported in any of the current protocols.
Black hole detection.
This was repeatedly cited as important. There is a basic
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tradeoff between frequent queries and resources used.
Explicit holding times were cited as useful.
Media independence.
There were many examples, such as point-to-point versus
broadcast versus LPDN. Media level redirects between logical
subnets on the same physical media. The difficulties with
carrying media addresses within packets, especially in the
presence of multi-media bridges. This is not well supported
in any of the current protocols.
Optimal route determination.
This is essentially a superset of next hop router discovery,
combined with resource reservation and possible policy
considerations, and the ability to redirect traffic under
changing conditions. The very things that have been causing
so much discussion of late. This is not well supported in
any of the current protocols.
Simplicity.
All of the above desires, and they want to keep it simple,
too.
Proposed Solution Space.
None of the current protocols are extensible in dimensions that fix
the desires above. While some have the ability to change in simple
terms, such as larger addresses, none were designed to add new kinds
of information to be carried in the same packet.
This proposal describes two replacement packets, not much different
from those already deployed. These familiar forms are re-packaged to
join common functions into the same packet to reduce traffic, and are
designed to be more extensible in the future.
In order to foster media independence, the packets are part of ICMP,
which allows the procotols to be used over broadcast, multicast,
partial-mesh, and point-to-point media. This is similar to the
positioning of ES-IS.
All of the advertisementmessages have expiration times.
Each message is composed of "optional" parts, designed to allow
flexibility and extensibility.
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One of the common parts is the media address, so that each message
contains enough information to return a reply directly to the sender,
without additional location traffic.
Another common part is a list of the routers which can be heard,
which allows routers to build a map of the paths between routers, and
routers to hosts. This solves the "hidden transmitter" problem, when
used together with the well-known link-state class of routing
protocols.
Examples of use:
Simple case -- J to K on the same fully-connected segment.
J sends the Where-Are-You (which contains its own media address)
to all-systems. K sends the I-Am-Here (which contains its own
media address) directly to J. At this point, they both know
that they can talk directly to each other, without regard to
subnet.
Routed case -- J to K not on the same fully-connected segment.
If no resource reservation or policy routing is desired, J
simply sends its packets directly to the "best" router that it
has learned from the Advertisements. If there is a better
router for the first hop, that router sends the I-Am-Here to J,
but never-the-less forwards the packet.
In the presence of RR or PR, J sends the Where-Are-You to the
"best" router that it has learned from the Advertisements. That
router always returns the I-Am-Here (even if the correct hop is
itself), which contains the requested RR or PR status
information. J then sends its packets to the first hop
router as determined from the I-Am-Here.
General case -- J to K over disconnected partial mesh (radio/framerelay).
J sends the Where-Are-You (which contains its own media address,
and the addresses of its "heard" routers) to the all-systems
address. The routers use such messages to construct a map of
the current state of the topology. The routers now know who J
hears, and who hears J.
If the routing map doesn't contain a current whereabouts of K,
the Destination Unreachable message is returned by the "best"
router on J's "heard" list.
If the routing map contains the current whereabouts of K, the
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"best" router on K's "heard" list sends a copy of the
Where-Are-You to K, with a substitute list of routers which can
hear K. The list is ordered by the intersection of those
routers which can also hear J, minimizing the number of hops.
Of course, K may have heard J's Where-Are-You directly, in which
case it adds its own address to the front of the list of routers.
When K hears the J Where-Are-You, it sends the I-Am-Here to the
all-systems address. The "best" router on J's "heard" list
sends a copy of the I-Am-Here to J, with a substitute list of
routers which can hear J. The list is ordered by the
intersection of those routers which can also hear K.
At this point, the routing fabric knows which routers are heard
by J and K, and which routers can hear J and K. J and K know
whether they can hear each other directly. If not, they know
the "best" next hop router (which may not be the same in both
directions).
Unlike the fully-connected scenarios, this scheme requires that
the I-Am-Here is sent from time to time to keep the map updated.
However, only routers need store the information.
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2. Additional ICMP Packets
The Packet format and basic facilities are already defined for ICMP
[3], as modified for SIP [1].
Up-to-date values of the ICMP Type field are specified in the most
recent "Assigned Numbers" RFC [2]. This document concerns the
following values:
<TBD> System Solicitation
<TBD> System Advertisement
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2.1. System Solicitation
A summary of the System Solicitation message format is shown below.
The fields are transmitted from left to right.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ System Identifier +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extensions ...
+-+-+-+-+-+-+-+-+-+-+-+-+
Type
<TBD>
Code
0
Checksum
The ICMP Checksum.
System Identifier
The System Identifier field is eight octets in length, and contains
the identifier of the system which is sought.
Extensions
The Extensions field is variable in length and contains zero or more
Extensions. These Extensions are described in a later section.
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2.1.1. Description
The System Solicitation (Where-Are-You) message is used to determine
the presence and availability of the next hop. This message is also
used for resource reservation and policy route determination.
The message is sent on demand to the all-systems multicast, or to the
best first hop router, as indicated by the Advertisement. The
information is stored only by routers and the subject hosts.
[Need more text describing use for each case, and for resource
reservation and policy routing]
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2.2. System Advertisement
A summary of the System Advertisement message format is shown below.
The fields are transmitted from left to right.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number | LifeTime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ System Identifier +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Default Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask Size | | Area | Priority |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extensions ...
+-+-+-+-+-+-+-+-+-+-+-+-+
Type
<TBD>
Code
The Code field is one octet. Up-to-date values of the System
Advertisement Code field are specified in the most recent
"Assigned Numbers" RFC [2]. Current values are assigned as
follows:
0 RESERVED
1 Intermediate System
2 End System
3 Local Redirect
4 Remote Redirect
Checksum
The ICMP Checksum.
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Sequence Number
The Sequence Number field is two octets in length, and contains
the number of System Advertisements sent. This number MUST
include this advertisement.
LifeTime
The LifeTime field is two octets in length, and indicates the
seconds remaining before the entry is considered invalid.
System Identifier
The System Identifier field is eight octets in length, and
contains the primary identifier for this system. Other
identifiers are indicated with the Other Identifiers extension.
Default Metric
The Default Metric field is four octets in length, and indicates
the preference level for use of this system as a default router.
Lower values indicate greater preference.
End Systems MUST set this field to zero.
Mask Size
The Mask Size field is one octet in length, and indicates the
number of bits in the System Identifier which indicate the subnet
mask for the interface.
If the System Identifier does not indicate a valid local subnet,
the value is zero.
End Systems SHOULD have a Mask Size of 64.
Area
The Area field is one octet in length, and indicates the area that
the system inhabits. A value of zero indicates that no area has
been assigned.
End Systems must set this field to zero.
Priority
The Priority field is one octet in length, and indicates the
priority for election to Designated Backup. A value of zero
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indicates that the system is not eligible.
End Systems must set this field to zero.
Extensions
The Extensions field is variable in length and contains zero or
more Extensions. These Extensions are described in a later
section.
2.2.1. Description
The System Advertisement (I-Am-Here) message is used to announce the
presence of an intermediate or end system, to indicate changes in the
topology, and to support system mobility.
It contains all of the information now in the old Router
Advertisement, ES Hello, IS Hello, OSPF Hello and RSPF Hello.
Intermediate Systems
The message is sent by each intermediate system periodically to
the all-systems multicast. The information is stored by all
systems.
The message is also sent in response to a System Solicitation.
End Systems
The message is sent in response to a System Solicitation. The
information is stored only by the affected systems.
Local Redirect
The message is sent in response to changes in the routing. The
information is stored only by the affected systems.
Remote Redirect
The message is sent to indicate movement of a system beyond the
local area. The information is stored only by the affected
systems.
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3. Extensions
Extensions allow variable amounts of information to be carried within
each Advertisement or Solicitation packet. Some extensions are
common to both packet types.
The end of the list of Extensions is indicated by the Payload Length
of the SIP packet.
A summary of the Extensions format is shown below. The fields are
transmitted from left to right.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Data ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
The Type field is one octet and indicates the type of Extension.
Up-to-date values of the Extension Type field are specified in the
most recent "Assigned Numbers" RFC [2]. Current values are
assigned as follows:
1 Media Access
2 Other Identifiers
3 System Heard
4 Routing Information
5 Service Information
Length
The Length field is one octet and indicates the length of the Data
field which has been used.
Each Extension ends on an octet boundary which is an integral
multiple of four octets. Any unused portion of the Data field is
padded with zeros.
length actual
0 through 2 4
3 through 6 8
7 through 10 12
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Data
The Data field is zero or more octets and contains the value or
other information for this Extension. The format and length of
the Data field is determined by the Type and Length fields.
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3.1. Media Access
A summary of the Media Access extension format is shown below. The
fields are transmitted from left to right.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Media Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
1
Length
>= 3
Media Type
The Media Type field is two octets in length. The value of this
field is the same as the Hardware Type used in ARP. Up-to-date
values of the Hardware Type field are specified in the most recent
"Assigned Numbers" RFC [2].
[Should we use the ifType from MIB-II instead?]
MAC Address
The MAC Address field is variable in length, and contains the media
address which is used to access this system.
The MAC Address is always specified in Canonical order.
The Media Access extension MUST be included in those messages sent from
an interface on a multi-access media.
It MUST NOT be included in a message sent from a point-to-point
interface, or in messages such as the Remote Redirect which pass through
intermediate systems.
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3.2. Other Identifiers
A summary of the Other Identifiers extension format is shown below. The
fields are transmitted from left to right.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | | Mask Size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preference |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ System Identifier +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
2
Length
14
System Identifier
The System Identifier field is eight octets in length, and contains
an identifier for this system. This may be another identifier for
the same interface that sent the message, or may identify another
interface on the same system which sent the message.
Preference
The Preference field is four octets in length, and indicates the
preference level for use of this system to forward packets to the
System Identifier. Lower values indicate greater preference.
End Systems MUST set this field to zero.
Mask Size
The Mask Size field is one octet in length, and indicates the number
of bits in the System Identifier which indicate the subnet mask for
the interface.
If the System Identifier does not indicate a valid local subnet, the
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value is zero.
End Systems SHOULD have a Mask Size of 64.
Every identifier for every interface is listed in each System
Advertisement message.
This supports multiple identifiers per interface, as well as multi-homed
systems.
This enables systems to determine the best next hop without sending a
Solicitation when the next hop is on another interface attached to the
same system.
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3.3. System Heard
A summary of the System Heard extension format is shown below. The
fields are transmitted from left to right.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Speed | Mask Size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number | LifeTime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ System Identifier +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Quality |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | MRU |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertisement Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
4
Length
30
Sequence Number
The Sequence Number field is two octets in length, and contains the
last heard sequence number from the system.
LifeTime
The LifeTime field is two octets in length, and indicates the seconds
remaining before the entry is considered invalid.
System Identifier
The System Identifier field is eight octets in length, and contains
the primary identifier for the system.
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Quality
The Quality field is four octets in length, and contains an
indication of the signal quality received from this system. Higher
values indicate greater quality.
Speed
The Speed field is one octet in length, and indicates the speed of
the link. Higher values indicate greater speed. The speed value is
related to the log2 of the speed in bits per second.
Unfortunately, there are several series which don't quite match. Is
there a standard assignment out there?
0 link is down
8 1,200 or less
9 2,400
4,800
9,600
10 14,400
19,200
12 28,800
38,400
14 57,600
64,000
17 128,000
18 153,600
19 256,000
22 1,544,000 T1
23 2,048,000 E1
24 4,000,000 Token Ring
6,312,000 T2
25 10,000,000 Ethernet
26 16,000,000 Token Ring
28 44,736,000 T3
30 155,520,000 STS-3/STM-1
32 622,080,000 STS-12/STM-4
34 2,488,320,000 STS-48/STM-16
Mask Size
The Mask Size field is one octet in length, and indicates the number
of bits in the System Identifier which indicate the subnet mask for
the interface.
If the System Identifier does not indicate a valid local subnet, the
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value is zero.
End Systems SHOULD have a Mask Size of 64.
Advertisement Count
The Advertisement Count field is four octets in length, and indicates
the number of advertisements that have been heard from the identified
system.
Error Count
The Error Count field is four octets in length, and indicates the
number of errors which have been detected on the link with the
identified system.
The System Heard extension MUST be included in every System
Advertisement.
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3.4. Routing Information
A summary of the Routing Information extension format is shown below.
The fields are transmitted from left to right.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Designated Backup +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
5
Length
14
Designated Backup
The Designated Backup field is eight octets in length, and contains
the identifier of the designated backup for this area.
This extension is included in the Intermediate System Advertisement of
the Designated Router, to assert its status as the Designated Router,
and indicate the Designated Backup.
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3.5. Service Information
A summary of the Service Information extension format is shown below.
The fields are transmitted from left to right.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | QoS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preference |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
6
Length
6
QoS
The Quality of Service field is two octets in length, and indicates a
service for which transit will be accepted.
Preference
The Preference field is four octets in length, and indicates the
preference level for use of this network to forward packets of the
indicated service. Lower values indicate greater preference.
This extension is included in the Intermediate System Advertisement to
indicate that it will accept transit traffic. If this extension is not
included, the system will treat the link as a stub network.
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4. Abstraction Algorithm
An Area is defined to be a collection of subnets which are aggregated
as the same next hop.
The areas are learned from the Advertisements, which contain the
necessary subnet information. The subnets are assigned by hand.
When the subnet mask shortens by at least one bit, a new level of
area is created. The area is defined by an area index (assigned by
the designated router of the affected area), and the count of bits
common to the subnet. This can be expressed as a pair of 8-bit
numbers.
Discovery of stub areas (probably the most common type) is easy and
automatic. Discovery of aggregate areas is made by routers one hop
out from the area. This is communicated through its Advertisements,
which are heard by the routers bordering the area.
This algorithm results in a few, fairly large areas. There can never
be more than 64 levels of area, and it is more likely to be 5 to 10
because of natural assignment boundaries. The numbering space also
places a limit on the number of routers bordering an area to 255, but
that is highly unlikely.
Fragmentation of areas simply results in automatic generation of
internal areas, and has no effect on area levels farther out.
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Security Considerations
Security issues are not discussed in this memo.
References
[1]
[2]
Acknowledgments
Chair's Address
The working group can be contacted via the current chairs:
Author's Address
Questions about this memo can also be directed to:
William Allen Simpson
Daydreamer
Computer Systems Consulting Services
P O Box 6205
East Lansing, MI 48826-6205
EMail: Bill.Simpson@um.cc.umich.edu
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Table of Contents
1. Criteria .............................................. 1
2. Additional ICMP Packets ............................... 5
2.1 System Solicitation ............................. 6
2.1.1 Description ..................................... 6
2.2 System Advertisement ............................ 8
2.2.1 Description ..................................... 10
3. Extensions ............................................ 11
3.1 Media Access .................................... 13
3.2 Other Identifiers ............................... 14
3.3 System Heard .................................... 16
3.4 Routing Information ............................. 19
3.5 Service Information ............................. 20
4. Abstraction Algorithm ................................. 21
SECURITY CONSIDERATIONS ...................................... 22
REFERENCES ................................................... 22
ACKNOWLEDGEMENTS ............................................. 22
CHAIR'S ADDRESS .............................................. 22
AUTHOR'S ADDRESS ............................................. 22