One document matched: draft-ietf-idmr-igmp-mrdisc-03.txt
Differences from draft-ietf-idmr-igmp-mrdisc-02.txt
IDMR Working Group S. Biswas
Internet Draft B. Cain
draft-ietf-idmr-igmp-mrdisc-03.txt B. Haberman
March 2000 Nortel Networks
September 2000
IGMP Multicast Router Discovery
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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 and may be updated, replaced, or obsoleted by other
documents at any time. It is inappropriate to use Internet- Drafts
as reference material or to cite them other than as "work in
progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Abstract
Companies have been proposing IGMP snooping schemes for layer-2
bridging devices. A method for discovering multicast capable routers
is necessary for these schemes. An IGMP query message is inadequate
for discovering multicast routers as one querier is elected. In
order to "discover" multicast routers, we introduce two new types of
IGMP messages: Multicast Router Advertisement and Multicast Router
Solicitation. These two messages can be used by any device which
listens to IGMP to discovery multicast routers. Multicast Router
Solicitation messages may be used by any network device (e.g. layer-2
switch) to solicit discovery messages from multicast routers.
1. Introduction
Multicast router discovery messages are useful for discovering
multicast capable routers. This capability is useful in a layer-2
bridging domain with "IGMP snooping" type of schemes. By listening
to multicast router discovery messages, layer-2 devices can determine
where to send multicast source data and IGMP Host Membership Reports
Biswas, Cain, Haberman 1
Internet Draft IGMP Multicast Router Discovery September 2000
[RFC1112] [IGMPv2]. Multicast source data and IGMP Host Membership
Reports must be received by all multicast routers on a segment.
Using IGMP Host Membership Queries to discover multicast routers is
not useful because of query suppression in IGMP.
Unlike ICMP router discovery messages [RFC1256], multicast router
discovery advertisements should not be listened to by hosts. Hosts
need not know the identity of multicast routers.
The use of the multicast router advertisement is not precluded from
being used for other purposes. Extensible options have been included
in the advertisement message for future enhancements.
The following are justifications for inventing another router
discovery protocol:
o Using ICMP router discovery is not an appropriate solution
for multicast router discovery because: 1.) It may confuse
hosts listening to ICMP router advertisements; unicast and
multicast topologies may not be congruent. 2.) There is
no way to tell from an ICMP router advertisement if a
router is running a multicast routing protocol.
o By making multicast router discovery messages extensible,
future enhancements can be made.
o By inventing a generic IP layer message, multiple types of
messages per link layer are not needed (i.e. including
this functionality as part of IP is better than inventing
N discovery protocols for N layer-2 technologies).
Although multicast router discovery messages could be sent as ICMP
messages, IGMP was chosen because IGMP snooping switches already
snoop IGMP messages and because the intended first use of these
protocol messages is multicast specific.
2. Protocol Overview
IGMP Multicast Router Discovery consists of three messages for
discovering multicast routers. The Multicast Router Advertisement is
sent by routers to advertise IP multicast forwarding enabled on an
interface. The Multicast Router Solicitation is used by routers to
solicit Multicast Router Advertisements. The Multicast Router
Termination message is sent when a router terminates its multicast
routing functions.
Multicast routers send Multicast Router Advertisements (hereafter
called advertisements) periodically on all interfaces on which
multicast forwarding is enabled.
Biswas, Cain, Haberman 2
Internet Draft IGMP Multicast Router Discovery September 2000
Multicast Router Advertisements are also sent in response to
Multicast Router Solicitations (hereafter called solicitations).
These are sent to solicit a response of Multicast Router
Advertisements from all multicast routers on a subnet. Solicitations
are sent to the IGMP-MRDISC multicast group.
Multicast Router Solicitations are sent whenever a router wishes to
discover multicast routers on a directly attached subnet.
Multicast Router Termination messages are sent when a router
terminates its multicast routing functions.
All IGMP Multicast Router Discovery messages are sent with an IP TLL
of 1 and contain the IP Router Alert Option [RFC2113] in their IP
header. All IGMP Multicast Router Discovery messages are sent with
to the All-Routers multicast group (224.0.0.2).
Other non-IP forwarding devices (e.g. layer-2 switches) may send
Multicast Router Solicitations to solicit Multicast Router
Advertisements.
3. Multicast Router Advertisement
3.1 Overview
Multicast Router Advertisements are sent periodically on all router
interfaces on which multicast forwarding is enabled. They are also
sent in response to Multicast Router Solicitations.
Router advertisements are sent upon expiration of a periodic timer,
when a router starts up, and when a router interface (that has IP
multicast forwarding enabled) initializes/restarts. Advertisements
are sent as IGMP messages to the All-Routers multicast address
(224.0.0.2) and should be rate-limited.
Router advertisements may contain any number of options. Two options
are defined in this document and MUST be supported by any
implementation of IGMP multicast router discovery. These options are
described in Section 5. Additional options may be defined as needed
by future work.
3.2 IP Header Fields
3.2.1 Source Address
An IP address belonging to the interface from which this message is
sent. If multiple source addresses are configured on an interface,
then the one chosen is implementation dependent.
Biswas, Cain, Haberman 3
Internet Draft IGMP Multicast Router Discovery September 2000
3.2.2 Destination Address
Router Advertisements are sent to the All-Routers multicast address
(224.0.0.2).
3.2.3 Time-to-Live
The Time-to-Live field MUST be 1.
3.2.4 Protocol
The protocol field is set to IGMP (2).
3.3 Multicast Router Advertisement Message Format
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 | Ad. Interval | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unused | Number of Options (N) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option [1] (TLV encoded) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option [...] (TLV encoded) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option [N] (TLV encoded) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3.3.1 Type Field
The type field is set to 0x24.
3.3.2 Advertisement Interval
This specifies the periodic time interval at which Multicast Router
Advertisements are sent in units of seconds. This value is set to
the configured MaxAdvertisementInterval variable.
3.3.3 Checksum
The checksum is the 16-bit one's complement of the one's complement
sum of the IGMP message, starting with the IGMP type. For computing
the checksum, the Checksum field is set to 0.
3.3.4 Number of Options (N)
The number of options contained in the router advertisement. If no
options are sent this field MUST be set to 0.
Biswas, Cain, Haberman 4
Internet Draft IGMP Multicast Router Discovery September 2000
3.3.5 Option[1..N]
Options are encoded as TLV in the following manner:
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 | Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
If the Number of Options field is not zero, a receiver MUST examine
all options. No strict ordering of options is enforced.
Type: Set to option type being advertised
Length: Length in bytes of Value field
Value: Option dependent value
3.4 Sending Multicast Router Advertisements
Router Advertisements are sent when the following events occur:
o When the periodic advertisement interval timer expires.
Note that it is not strictly periodic because the
advertisement interval is a random number between
MaxAdvertisementInterval and MinAdvertisementInterval.
(Default Value: 7-10 seconds).
o After waiting for a random delay less than
MaxInitialAdvertisementInterval when an interface first
comes up, is (re)initialized, or IGMP Multicast Router
Discovery is enabled. A router may send up to a maximum
of MaxInitialAdvertisements advertisements, waiting for a
random delay less than MaxInitialAdvertisementInterval
between each successive advertisement.
o This is to prevent an implosion of router advertisements.
An example of this occurring would be when many routers
are powered on at the same time. When a solicitation is
received, a router advertisement is sent in response with
a random delay less than MAX_RESPONSE_DELAY. If a
solicitation is received while an advertisement is pending
(because of a recent solicitation), that solicitation will
be ignored.
Whenever an advertisement is sent, the periodic advertisement
interval timer may be reset.
3.5 Receiving Multicast Router Advertisements
Biswas, Cain, Haberman 5
Internet Draft IGMP Multicast Router Discovery September 2000
Upon receiving a router advertisement, routers will validate the
message by the following criteria:
1. Verifying that the IGMP type is 0x24
2. Verifying the IGMP checksum
3. IP Destination Address = All-Routers multicast address
A router advertisement not meeting the validity requirements will be
silently discarded. Routers MUST process all options, discarding
options that are not recognized.
If a router advertisement is not received for a particular neighbor
within NeighborDeadInterval time interval, then the neighbor is
considered to be unreachable.
3.6 Multicast Router Advertisement Configuration Variables
A router that implements multicast router discovery MUST allow for
the following variables to be configured by system management;
default values are specified so as to make it unnecessary to
configure any of these variables in many cases.
For each interface the following configurable variables are defined:
3.6.1 MaxAdvertisementInterval
The maximum time allowed between sending router advertisements from
the interface, in seconds. Must be no less than 2 seconds and no
greater than 180 seconds.
Default: 20 seconds.
3.6.2 MinAdvertisementInterval
The minimum time allowed between sending unsolicited router
advertisements from the interface, in seconds. Must be no less than 3
seconds and no greater than MaxAdvertisementInterval.
Default: 0.75 * MaxAdvertisementInterval
3.6.3 MaxInitialAdvertisementInterval
The first router advertisement out of an interface is sent after
waiting for a random interval less than this variable. This will
prevent a flood of router advertisements when many routers start up
at the same time.
Default: 2 seconds
Biswas, Cain, Haberman 6
Internet Draft IGMP Multicast Router Discovery September 2000
3.6.4 MaxInitialAdvertisements
The maximum number of router advertisements that will be sent on a
subnet after a router boots.
Default: 3
3.6.5 NeighborDeadInterval
The maximum time allowed before declaring that a neighbor can be
declared "dead". This variable is defined in seconds. In order for
all routers to have a consistent state, it is necessary for the
MaxAdvertisementInterval to be configured the same on all routers per
subnet.
Default: 3 * MaxAdvertisementInterval
4. Multicast Router Solicitation
4.1 Overview
Multicast Router Solicitations are used to solicit Multicast Router
Advertisements. These messages are used when a router (or other
device) wishes to discover multicast routers. Upon receiving a
solicitation on an interface with IP multicast forwarding enabled,
router will respond with an advertisement.
Router solicitations may be sent when a router starts up, when a
router interface (re)initializes, or when IGMP Multicast Router
Discovery is enabled. Solicitations are sent as IGMP messages to the
All-Routers multicast address (224.0.0.2) and should be rate-limited.
4.2 IP Header Fields
4.2.1 Source Address
An IP address belonging to the interface from which this message is
sent. If multiple source addresses are configured on an interface,
then the one chosen is implementation dependent.
If the solicitation is being sent from a device that does not have an
IP address (i.e. non-managed layer-2 switch), then the source address
should be set to all zeros.
4.2.2 Destination Address
Solicitation messages are sent to the All-Routers multicast address
(224.0.0.2).
4.2.3 Time-to-Live
Biswas, Cain, Haberman 7
Internet Draft IGMP Multicast Router Discovery September 2000
The time-to-live field MUST be 1.
4.2.4 Protocol
The protocol field is set to IGMP (2).
4.3 Multicast Router Solicitation Message Format
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 | Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4.3.1 Type Field
The type field is set to 0x25.
4.3.2 Reserved Field
Sent as 0; ignored on reception.
4.3.3 Checksum
The checksum is the 16-bit one's complement of the one's complement
sum of the IGMP message, starting with the IGMP type. For computing
the checksum, the Checksum field is set to 0.
4.4 Sending Multicast Router Solicitations
Router solicitations are sent when the following events occur:
1. After waiting for a random delay less than SOLICITATION_INTERVAL
when an interface first comes up, is (re)initialized, or IGMP
Multicast Router Discovery is enabled. A router may send up to
a maximum of MAX_SOLICITATIONS, waiting for a random delay less
than SOLICITATION_INTERVAL between each successive solicitation.
2. Optionally, for an implementation specific event. Solicitations
MUST be rate-limited; no more than MAX_SOLICITATIONS MUST be
sent in SOLICITATION_INTERVAL seconds.
4.5 Receiving Multicast Router Solicitations
Upon receiving a router solicitation, routers will validate the
message by:
1. Verifying that the IGMP type is 0x25
2. Verifying the IGMP checksum
Biswas, Cain, Haberman 8
Internet Draft IGMP Multicast Router Discovery September 2000
3. IP Destination Address = All-Routers multicast address
A router solicitation not meeting the validity requirements will be
silently discarded.
Solicitation message IP source addresses MUST NOT be used as part of
the validity check.
4.6 Multicast Router Solicitation Configuration Variables
There are no configurable variables with respect to router
solicitations.
5. Multicast Router Termination
5.1 Overview
The Multicast Router Termination message is used to expedite the
notification of a change in the status of a routers multicast
forwarding functions.
5.2 IP Header Fields
5.2.1 Source Address
An IP address belonging to the interface from which this message is
sent. If multiple source addresses are configured on an interface,
then the one chosen is implementation dependent.
5.2.2 Destination Address
Multicast Router Termination messages are sent to the All-Routers
multicast address (224.0.0.2).
5.2.3 Time-to-Live
The Time-to-Live field MUST be 1.
5.2.4 Protocol
The protocol field is set to IGMP (2).
5.3 Multicast Router Termination Message Format
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 | Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5.3.1 Type Field
Biswas, Cain, Haberman 9
Internet Draft IGMP Multicast Router Discovery September 2000
The type field is set to 0x26.
5.3.2 Reserved Field
Sent as 0; ignored on reception.
5.3.3 Checksum
The checksum is the 16-bit one's complement of the one's complement
sum of the IGMP message, starting with the IGMP type. For computing
the checksum, the Checksum field is set to 0.
5.4 Sending Multicast Router Termination Messages
Multicast Router Termination messages are sent for three reasons:
1. Multicast forwarding is disabled on the interface
2. The interface is administratively disabled
3. The router is gracefully shutdown
5.5 Receiving Multicast Router Termination Messages
Upon receiving a termination message, routers will validate the
message by the following criteria:
1. Verifying that the IGMP type is 0x26
2. Verifying the IGMP checksum
3. IP Destination Address = All-Routers multicast address
A termination message not meeting the validity requirements will be
silently discarded.
6. Multicast Router Discovery Protocol Constants
o MAX_RESPONSE_DELAY 2 seconds
o MAX_SOLICITATION_DELAY 1 second
o SOLICITATION_INTERVAL 3 seconds
o MAX_SOLICITATIONS 3 transmissions
7. Mandatory Advertisement Options
7.1 Overview of Options
Biswas, Cain, Haberman 10
Internet Draft IGMP Multicast Router Discovery September 2000
The following options MUST be supported by an implementation of IGMP
Multicast Router Discovery: Query Interval Advertisement Option and
Robustness Variable Advertisement Option. These options advertise
specific IGMP variables and are sent in an advertisement depending on
the version of IGMP enabled on an interface. Although no
requirements exist for multicast routers at this time, it is assumed
that all multicast routers support the IGMP protocol.
7.2 Query Interval Advertisement Option
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=1 | Length=2 | IGMP Query Interval |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
If a multicast router has any version of IGMP [RFC1112] enabled on an
interface on which IGMP Multicast Router Discovery is also enabled,
it MUST send all advertisements with the Query Interval Advertisement
Option. This option contains the IGMP "Query Interval" configured on
the interface on which advertisements are sent.
This option is sent regardless of whether the router is currently the
IGMP querier for the subnet. This option is sent regardless of what
version of IGMP the router is running.
IGMP Query Interval field is equal (in seconds) to the configured
IGMP "query interval" on the interface from which the advertisement
was sent.
7.3 Robustness Variable Advertisement Option
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=2 | Length=2 | Robustness Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
If a multicast router has IGMPv2 [IGMPv2] or IGMPv3 [IGMPv3] enabled
on an interface on which IGMP Multicast Router Discovery is also
enabled, it MUST send all advertisements with the Robustness Variable
Advertisement Option. This option contains the IGMP "Robustness
Variable" configured on the interface on which advertisements are
sent.
This option is sent regardless of whether the router is currently the
IGMP querier for the subnet. This option may be omitted if IGMPv1 is
enabled on the interface.
Robustness Variable is an integer that MUST not be zero [IGMPv2] and
is equal to the IGMPv2 robustness variable.
Biswas, Cain, Haberman 11
Internet Draft IGMP Multicast Router Discovery September 2000
8. IPv6 Support
The Multicast Router Discovery function for IPv6 is accomplished
using the Neighbor Discovery Protocol for IPv6 [RFC2461] (hereafter
called NDP). Specifically, the Router Advertisement message contains
new fields to support the discovery of multicast routers. For this
reason, the timing mechanisms defined for NDP will be used instead of
those defined in this document for IPv4 support.
8.1 Router Advertisement Message
The Router Advertisement message contains two new fields to support
the multicast router discovery mechanism. The modified message
format is:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cur Hop Limit |M|O|H|D|E|Rsrvd| Router Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reachable Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Retrans Timer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-
The two new fields are the 'D' and 'E' bits. All other fields retain
their definitions and functions as described in Section 4.2 of the
NDP specification [RFC2461].
8.1.1 Discovery (D) bit
The 'D' bit is used by a router to indicate support for the Multicast
Router Discovery protocol. A value of '1' indicates that the router
supports the discovery protocol. A value of '0' indicates no
support. This allows for backwards compatibility of the Router
Advertisement message.
8.1.2 Enabled (E) bit
The 'E' bit indicates whether multicast routing is enabled on the
router's interface. A value of '1' indicates that multicast
forwarding is enabled on the router's interface. A value of '0'
indicates that multicast forwarding is disabled.
When the state of multicast forwarding changes on an interface, a
router must stop its Router Advertisement timer, transmit a Router
Biswas, Cain, Haberman 12
Internet Draft IGMP Multicast Router Discovery September 2000
Advertisement with the 'E' bit set to the value associated with the
new multicast forwarding state, and restart its Router Advertisement
timer.
8.2 Router Solicitations
An NDP Router Solicitation message can be sent to solicit a Router
Advertisement message in order to determine the multicast forwarding
state of a router. The periodic transmission of solicitation
messages is outlined in RFC 2461.
9. Acknowledgements
ICMP Router Discovery [RFC1256] was used as a general model for IGMP
Multicast Router Discovery.
10. References
[RFC1256] Deering, S., "ICMP Router Discovery Messages", RFC 1256,
September 1991.
[RFC1112] Deering, S., "Host Extensions for IP Multicasting",
RFC 1112, August 1989.
[IGMPv2] Fenner, W., "Internet Group Management Protocol,
Version 2", Internet-Draft, November 1997.
[IGMPv3] Cain, B., Deering, S., Thyagarajan, A., "Internet Group
Management Protocol, Version 3", Internet-Draft, November
1997.
[RFC2113] Katz, D., "IP Router Alert Option," RFC 2113, April 1996.
[RFC2461] Narten, T., Nordmark, E., and Simpson, W., "Neighbor
Discovery IP Version 6 (IPv6)", RFC 2461, December 1998.
10. Authors' Addresses
Shantam Biswas
Nortel Networks
600 Technology Park Drive
Billerica, MA 01821
Email: sbiswas@baynetworks.com
Phone: 1-978-916-8048
Brad Cain
Nortel Networks
600 Technology Park Drive
Billerica, MA 01821
Email: bcain@baynetworks.com
Phone: 1-978-916-1316
Biswas, Cain, Haberman 13
Internet Draft IGMP Multicast Router Discovery September 2000
Brian Haberman
Nortel Networks
4309 Emperor Blvd
Suite 200
Durham, NC 27703
Email: haberman@nortelnetworks.com
Phone: 1-919-992-4439
Biswas, Cain, Haberman 14
| PAFTECH AB 2003-2026 | 2026-04-23 11:26:36 |