< draft-ietf-idmr-igmp-mrdisc-00.txt   draft-ietf-idmr-igmp-mrdisc-01.txt >
INTERNET DRAFT S. Biswas INTERNET DRAFT S. Biswas
IDMR Working Group B. Cain IDMR Working Group B. Cain
draft-ietf-idmr-igmp-mrdisc-00.txt March 1998 Nortel Networks
Expires September 1998 draft-ietf-idmr-igmp-mrdisc-01.txt February 1999
Expires August 1999
IGMP Multicast Router Discovery IGMP Multicast Router Discovery
<draft-ietf-idmr-igmp-mrdisc-00.txt> <draft-ietf-idmr-igmp-mrdisc-01.txt>
Status of this Memo STATUS OF THIS MEMO
This document is an Internet-Draft. Internet-Drafts are working This document is an Internet-Draft and is in full conformance with
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Abstract Abstract
Companies have been proposing "IGMP snooping" type schemes for Companies have been proposing "IGMP snooping" type schemes for
layer-2 bridging devices. A method for discovery multicast capable layer-2 bridging devices. A method for discovery multicast capable
routers is necessary for these schemes. An IGMP query message is routers is necessary for these schemes. An IGMP query message is
inadequate for discoverying multicast routers as one querier is inadequate for discoverying multicast routers as one querier is
elected. In order to "discover" multicast routers, we introduce elected. In order to "discover" multicast routers, we introduce
two new types of IGMP messages: Multicast Router Advertisement and two new types of IGMP messages: Multicast Router Advertisement and
Multicast Router Solicitation. These two messages can be used by Multicast Router Solicitation. These two messages can be used by
any device which listens to IGMP to discovery multicast routers. 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 1. Introduction
Multicast router discovery messages are useful for discovering Multicast router discovery messages are useful for discovering
multicast capable routers. This capability is useful in a layer-2 multicast capable routers. This capability is useful in a layer-2
bridging domain with "IGMP snooping" type of schemes. By listening bridging domain with "IGMP snooping" type of schemes. By listening
to multicast router discovery messages, layer-2 devices can to multicast router discovery messages, layer-2 devices can
determine where to send multicast source data and IGMP Host determine where to send multicast source data and IGMP Host
Membership Reports [RFC1112] [IGMPv2]. Multicast source data and Membership Reports [RFC1112] [IGMPv2]. Multicast source data and
IGMP Host Membership Reports must be received by all multicast IGMP Host Membership Reports must be received by all multicast
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from being used for other purposes. Extensible options have been from being used for other purposes. Extensible options have been
included in the advertisement message for future enhancements. included in the advertisement message for future enhancements.
The following are justifications for inventing another router The following are justifications for inventing another router
discovery protocol: discovery protocol:
1. Using ICMP router discovery is not an appropriate solution 1. Using ICMP router discovery is not an appropriate solution
for multicast router discovery because: 1.) It may confuse for multicast router discovery because: 1.) It may confuse
hosts listening to ICMP router advertisements; unicast and hosts listening to ICMP router advertisements; unicast and
multicast topologies may not be congruent. 2.) It is multicast topologies may not be congruent. 2.) It is
desirable to have advertisements sent to the all-multicast desirable to have advertisements sent to a special link-
routers group address. 3.) There is no way to tell from a local group address. 3.) There is no way to tell from a
ICMP router advertisementif a router is running a multicast ICMP router advertisement if a router is running a multicast
routing protocol. routing protocol.
2. By making multicast router discovery messages extensible 2. By making multicast router discovery messages extensible
and sending messages to the all-routers group, future and sending messages to a special address, future
enhancements can be made. enhancements can be made.
3. By inventing a generic IP layer message, multiple type of 3. By inventing a generic IP layer message, multiple type of
messages per link layer are not needed (i.e. including this messages per link layer are not needed (i.e. including this
functionality as part of IP is better than inventing N functionality as part of IP is better than inventing N
discovery protocols for N layer-2 technologies). 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 first use of these
messages is multicast specific.
1.1 Protocol Overview 1.1 Protocol Overview
IGMP Multicast Router Discovery consists of two messages for IGMP Multicast Router Discovery consists of two messages for
discovering multicast routers. The Multicast Router Advertisement discovering multicast routers. The Multicast Router Advertisement
is sent by routers to advertise IP multicast forwarding enabled is sent by routers to advertise IP multicast forwarding enabled
on an interface. The Multicast Router Solicitation is used by on an interface. The Multicast Router Solicitation is used by
routers to solicit Multicast Router Advertisements. routers to solicit Multicast Router Advertisements.
Multicast routers send Multicast Router Advertisements (hereafter Multicast routers send Multicast Router Advertisements (hereafter
called advertisements) periodically on all interfaces on which called advertisements) periodically on all interfaces on which
multicast forwarding is enabled. These messages are sent to the multicast forwarding is enabled. These messages are sent to the
All-Routers multicast group. IGMP-MRDISC multicast group.
Multicast Router Advertisements are also sent in response to Multicast Router Advertisements are also sent in response to
Multicast Router Solicitations (hereafter called solicitations). Multicast Router Solicitations (hereafter called solicitations).
These are sent to solicit a response of Multicast Router These are sent to solicit a response of Multicast Router
Advertisements from all multicast routers. Solicitations are sent Advertisements from all multicast routers on a subnet.
to the All-Routers multicast group. Solicitations are sent to the IGMP-MRDISC multicast group.
Multicast Router Solicitations are sent whenever a router wishes Multicast Router Solicitations are sent whenever a router wishes
to discover multicast routers on a directly attached subnet. to discover multicast routers on a directly attached subnet.
Solicitations are sent to the All-Routers multicast group.
All IGMP Multicast Router Discovery messages are sent with an All IGMP Multicast Router Discovery messages are sent with an
IP TLL of 1 and contain the IP Router Alert Option [RFC2113] in IP TLL of 1 and contain the IP Router Alert Option [RFC2113] in
their IP header. their IP header.
Other non-router networking devices (e.g. layer-2 switches) may
send Multicast Router Solicitations to solicit Multicast Router
Advertisements.
2. Multicast Router Advertisement 2. Multicast Router Advertisement
2.1 Overview 2.1 Overview
Multicast Router Advertisements are sent periodically on all router Multicast Router Advertisements are sent periodically on all router
interfaces on which multicast forwarding is enabled. They are also interfaces on which multicast forwarding is enabled. They are also
sent in response to Multicast Router Solicitations. sent in response to Multicast Router Solicitations.
Router advertisements are sent upon expiration of a periodic Router advertisements are sent upon expiration of a periodic
timer, when a router starts up, and when a router interface (that timer, when a router starts up, and when a router interface (that
has IP multicast forwarding enabled) initializes/restarts. has IP multicast forwarding enabled) initializes/restarts.
Advertisements are sent as IGMP messages to the All-Routers Advertisements are sent as IGMP messages to the IGMP-MRDISC
multicast address (224.0.0.2) and should be rate-limited. multicast address (224.0.0.x) and should be rate-limited.
Router advertisements may contain any number of options. Two Router advertisements may contain any number of options. Two
options are defined in this document and MUST be supported by any options are defined in this document and MUST be supported by any
implementation of IGMP multicast router discovery. These options implementation of IGMP multicast router discovery. These options
are described in Section 5. Additional options may be defined as are described in Section 5. Additional options may be defined as
needed by future work. needed by future work.
2.2 IP Header Fields 2.2 IP Header Fields
2.2.1 Source Address 2.2.1 Source Address
An IP address belonging to the interface from which this message is An IP address belonging to the interface from which this message is
sent. If multiple source addresses are configured on an interface, sent. If multiple source addresses are configured on an interface,
then the one chosen is implementation dependent. then the one chosen is implementation dependent.
2.2.1 Destination Address 2.2.1 Destination Address
Router Advertisements are sent to the All-Routers multicast Router Advertisements are sent to the IGMP-MRDISC multicast
address (224.0.0.2). address (224.0.0.x).
2.2.2 Time-to-Live 2.2.2 Time-to-Live
The Time-to-Live field MUST be 1. The Time-to-Live field MUST be 1.
2.2.3 Protocol 2.2.3 Protocol
The protocol field is set to IGMP (2). The protocol field is set to IGMP (2).
2.3 Multicast Router Advertisement Message Format 2.3 Multicast Router Advertisement Message Format
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2.3.4 Number of Options (N) 2.3.4 Number of Options (N)
The number of options contained in the router advertisement. If no The number of options contained in the router advertisement. If no
options are sent this field MUST be set to 0. options are sent this field MUST be set to 0.
2.3.5 Option[1..N] 2.3.5 Option[1..N]
Options are encoded as TLV in the following manner: Options are encoded as TLV in the following manner:
@
0 1 2 3 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 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 | | Type | Length | Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
If the Number of Options field is not zero, all options MUST be If the Number of Options field is not zero, all options MUST be
examined by a receiver. No strict ordering of options is enforced. examined by a receiver. No strict ordering of options is enforced.
Type: Set to option type being advertised Type: Set to option type being advertised
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1. When the a periodic advertisement interval timer expires. 1. When the a periodic advertisement interval timer expires.
Note that it is not strictly periodic because the Note that it is not strictly periodic because the
advertisement interval is a random number between advertisement interval is a random number between
MaxAdvertisementInterval and MinAdvertisementInterval. MaxAdvertisementInterval and MinAdvertisementInterval.
(Default Value: 7-10 seconds). (Default Value: 7-10 seconds).
2. After waiting for a random delay less than 2. After waiting for a random delay less than
MaxInitialAdvertisementInterval when an interface first MaxInitialAdvertisementInterval when an interface first
comes up, is (re)initialized, or IGMP Multicast Router comes up, is (re)initialized, or IGMP Multicast Router
Discovery is enabled. A router may send up to a maximum of Discovery is enabled. A router may send up to a maximum of
MaxInitialAdvertisements advertisements, waiting for a random MaxInitialAdvertisements advertisements, waiting for a
delay less than MaxInitialAdvertisementInterval between each random delay less than MaxInitialAdvertisementInterval
successive advertisement. between each successive advertisement.
This is to prevent an implosion of router advertisements. An This is to prevent an implosion of router advertisements. An
example of this occuring would be when many routers are example of this occuring would be when many routers are
powered on at the same time. powered on at the same time.
3. When a solicitation is received, a router advertisement is 3. When a solicitation is received, a router advertisement is
sent in response with a random delay less than sent in response with a random delay less than
MAX_RESPONSE_DELAY. If a solicitation is received while MAX_RESPONSE_DELAY. If a solicitation is received while
an advertisement is pending (because of a recent an advertisement is pending (because of a recent
solicitation), that solicitation will be ignored. solicitation), that solicitation will be ignored.
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Whenever an advertisement is sent, the periodic advertisement Whenever an advertisement is sent, the periodic advertisement
interval timer may be reset. interval timer may be reset.
2.5 Receiving Multicast Router Advertisements 2.5 Receiving Multicast Router Advertisements
Upon receiving a router advertisement, routers will validate the Upon receiving a router advertisement, routers will validate the
message by the following criteria: message by the following criteria:
1. Verifying that the IGMP type is 0x24 1. Verifying that the IGMP type is 0x24
2. Verifying the IGMP checksum 2. Verifying the IGMP checksum
3. IP Destination Address = All-Routers multicast address 3. IP Destination Address = IGMP-MRDISC multicast address
A router advertisement not meeting the validity requirements will A router advertisement not meeting the validity requirements will
be silently discarded. Routers MUST process all options, discarding be silently discarded. Routers MUST process all options, discarding
options that are not recognized. options that are not recognized.
If a router advertisement is not received for a particular neighbor If a router advertisement is not received for a particular neighbor
within NeighborDeadInterval time interval, then the neigbor is within NeighborDeadInterval time interval, then the neigbor is
considered to be unreachable. considered to be unreachable.
2.6 Multicast Router Advertisement Configuration Variables 2.6 Multicast Router Advertisement Configuration Variables
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the following variables to be configured by system management; the following variables to be configured by system management;
default values are specified so as to make it unnecessary to default values are specified so as to make it unnecessary to
configure any of these variables in many cases. configure any of these variables in many cases.
For each interface the following configurable variables are For each interface the following configurable variables are
defined: defined:
2.6.1 MaxAdvertisementInterval 2.6.1 MaxAdvertisementInterval
The maximum time allowed between sending router advertisements from The maximum time allowed between sending router advertisements from
the interface, in seconds. Must be no less than 4 seconds and no the interface, in seconds. Must be no less than 2 seconds and no
greater than 1800 seconds. greater than 180 seconds.
Default: 600 seconds. Default: 20 seconds.
2.6.2 MinAdvertisementInterval 2.6.2 MinAdvertisementInterval
The minimum time allowed between sending unsolicited router The minimum time allowed between sending unsolicited router
advertisements from the interface, in seconds. Must be no less advertisements from the interface, in seconds. Must be no less
than 3 seconds and no greater than MaxAdvertisementInterval. than 3 seconds and no greater than MaxAdvertisementInterval.
Default: 0.75 * MaxAdvertisementInterval Default: 0.75 * MaxAdvertisementInterval
Note: The default value will cause an the periodic interval to be
set to a period of 450-600 seconds.
2.6.3 MaxInitialAdvertisementInterval 2.6.3 MaxInitialAdvertisementInterval
The first router advertisement out of an interface is sent after The first router advertisement out of an interface is sent after
waiting for a random interval less than this variable. This will waiting for a random interval less than this variable. This will
prevent a flood of router advertisements when many routers start up prevent a flood of router advertisements when many routers start up
at the same time. at the same time.
Default: 10 seconds Default: 2 seconds
2.6.4 MaxInitialAdvertisement 2.6.4 MaxInitialAdvertisements
The maximum number of router advertisements that will be sent The maximum number of router advertisements that will be sent
per event sending event. on a subnet after a router boots.
Default: 3 Default: 3
2.6.5 NeighborDeadInterval 2.6.5 NeighborDeadInterval
The maximum time allowed before declaring that a neighbor can The maximum time allowed before declaring that a neighbor can
can be declared "dead". This variable is defined in seconds. can be declared "dead". This variable is defined in seconds.
In order for all routers to have a consistent state, it is In order for all routers to have a consistent state, it is
necessary for the MaxAdvertisementInterval to be configured the necessary for the MaxAdvertisementInterval to be configured the
same on all routers per subnet. same on all routers per subnet.
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Multicast Router Solitications are used to solicit Multicast Router Multicast Router Solitications are used to solicit Multicast Router
Advertisements. These messages are used when a router (or other Advertisements. These messages are used when a router (or other
device) wishes to discover multicast routers. Upon receiving a device) wishes to discover multicast routers. Upon receiving a
solicitation on an interface with IP multicast forwarding enabled, solicitation on an interface with IP multicast forwarding enabled,
router will respond with an advertisement. router will respond with an advertisement.
Router solicitations may be sent when a router starts up, when Router solicitations may be sent when a router starts up, when
a router interface (re)initializes, or when IGMP Multicast Router a router interface (re)initializes, or when IGMP Multicast Router
Discovery is enabled. Solicitations are sent as IGMP messages to Discovery is enabled. Solicitations are sent as IGMP messages to
the All-Routers multicast address (224.0.0.2) and should be the IGMP-MRDISC multicast address (224.0.0.x) and should be
rate-limited. rate-limited.
3.2 IP Header Fields 3.2 IP Header Fields
3.2.1 Source Address 3.2.1 Source Address
An IP address belonging to the interface from which this message is An IP address belonging to the interface from which this message is
sent. If multiple source addresses are configured on an interface, sent. If multiple source addresses are configured on an interface,
then the one chosen is implementation dependent. then the one chosen is implementation dependent.
If the solicitation is being sent from a device which does not have
an IP address (i.e. non-managed layer-2 switch), then the source
address should be set to all zeros.
3.2.2 Destination Address 3.2.2 Destination Address
Solicitation messages are sent to the All-Routers multicast Solicitation messages are sent to the IGMP-MRDISC multicast
address (224.0.0.2). address (224.0.0.x).
3.2.3 Time-to-Live 3.2.3 Time-to-Live
The time-to-live field MUST be 1. The time-to-live field MUST be 1.
3.2.4 Protocol 3.2.4 Protocol
The protocol field is set to IGMP (2). The protocol field is set to IGMP (2).
3.3 Multicast Router Solicitation Message Format 3.3 Multicast Router Solicitation Message Format
0 1 2 3 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 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 | | Type | Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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MAX_SOLICITATIONS MUST be sent in SOLICITATION_INTERVAL MAX_SOLICITATIONS MUST be sent in SOLICITATION_INTERVAL
seconds. seconds.
3.5 Receiving Multicast Router Solicitations 3.5 Receiving Multicast Router Solicitations
Upon receiving a router solicitation, routers will validate the Upon receiving a router solicitation, routers will validate the
message by: message by:
1. Verifying that the IGMP type is 0x25 1. Verifying that the IGMP type is 0x25
2. Verifying the IGMP checksum 2. Verifying the IGMP checksum
3. IP Destination Address = All-Routers multicast address 3. IP Destination Address = IGMP-MRDISC multicast address
A router solicitation not meeting the validity requirements will be A router solicitation not meeting the validity requirements will be
silently discarded. silently discarded.
Solicitation message IP source addresses MUST NOT be used as part
of the validity check.
3.6 Multicast Router Solicitation Configuration Variables 3.6 Multicast Router Solicitation Configuration Variables
There are no configurable variables with respect to router There are no configurable variables with respect to router
solicitations. solicitations.
4. Multicast Router Discovery Protocol Constants 4. Multicast Router Discovery Protocol Constants
MAX_INITIAL_ADVERT_INTERVAL 10 seconds
MAX_INITIAL_ADVERTISEMENTS 3 transmissions
MAX_RESPONSE_DELAY 2 seconds MAX_RESPONSE_DELAY 2 seconds
MAX_SOLICITATION_DELAY 1 second MAX_SOLICITATION_DELAY 1 second
SOLICITATION_INTERVAL 3 seconds SOLICITATION_INTERVAL 3 seconds
MAX_SOLICITATIONS 3 transmissions MAX_SOLICITATIONS 3 transmissions
5. Mandatory Advertisement Options 5. Mandatory Advertisement Options
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[IGMPv3] Cain, B., Deering, S., Thyagarajan, A., "Internet Group [IGMPv3] Cain, B., Deering, S., Thyagarajan, A., "Internet Group
Management Protocol, Version 3", Internet-Draft, November Management Protocol, Version 3", Internet-Draft, November
1997. 1997.
[RFC2113] Katz, D., "IP Router Alert Option," RFC 2113, April 1996. [RFC2113] Katz, D., "IP Router Alert Option," RFC 2113, April 1996.
8. Authors' Addresses 8. Authors' Addresses
Shantam Biswas Shantam Biswas
Bay Networks Nortel Networks
600 Technology Park Drive 600 Technology Park Drive
Billerica, MA 01821 Billerica, MA 01821
EMail: sbiswas@baynetworks.com EMail: sbiswas@baynetworks.com
Phone: 1-978-916-8048 Phone: 1-978-916-8048
Brad Cain Brad Cain
Bay Networks Nortel Networks
3 Federal Street 3 Federal Street
Billerica, MA 01821 Billerica, MA 01821
EMail: bcain@baynetworks.com EMail: bcain@baynetworks.com
Phone: 1-978-916-1316 Phone: 1-978-916-1316
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