RFC2909 - The Multicast Address-Set Claim (MASC) Protocol

Network Working Group P. Radoslavov
Request for Comments: 2909 D. Estrin
Category: EXPerimental R. Govindan
USC/ISI
M. Handley
ACIRI
S. Kumar
USC/ISI
D. Thaler
Microsoft
September 2000
The Multicast Address-Set Claim (MASC) Protocol
Status of this Memo
This memo defines an Experimental Protocol for the Internet
community. It does not specify an Internet standard of any kind.
Discussion and suggestions for improvement are requested.
Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
Abstract
This document describes the Multicast Address-Set Claim (MASC)
protocol which can be used for inter-domain multicast address set
allocation. MASC is used by a node (typically a router) to claim and
allocate one or more address prefixes to that node"s domain. While a
domain does not necessarily need to allocate an address set for hosts
in that domain to be able to allocate group addresses, allocating an
address set to the domain does ensure that inter-domain group-
specific distribution trees will be locally-rooted, and that traffic
will be sent outside the domain only when and where external
receivers exist.
Table of Contents
1 IntrodUCtion .................................................. 4
1.1 Terminology ................................................. 4
1.2 Definitions ................................................. 4
2 Requirements for Inter-Domain Address Allocation .............. 5
3 Overall Architecture .......................................... 5
3.1 Claim-Collide vs. Query-Response Rationale .................. 6
4 MASC Topology ................................................. 6
4.1 Managed vs Locally-Allocated Space .......................... 8
4.2 Prefix Lifetime ............................................. 8
4.3 Active vs. Deprecated Prefixes .............................. 9
4.4 Multi-Parent Sibling-to-Sibling and Internal Peering ........ 9
4.5 Administratively-Scoped Address Allocation .................. 9
5 Protocol Details .............................................. 10
5.1 Claiming Space .............................................. 10
5.1.1 Claim Comparison Function ................................. 12
5.2 Renewing an Existing Claim .................................. 12
5.3 Expanding an Existing Prefix ................................ 12
5.4 Releasing Allocated Space ................................... 13
6 Constants ..................................................... 13
7 Message Formats ............................................... 14
7.1 Message Header Format ....................................... 14
7.2 OPEN Message Format ......................................... 15
7.3 UPDATE Message Format ....................................... 17
7.4 KEEPALIVE Message Format .................................... 21
7.5 NOTIFICATION Message Format ................................. 21
8 MASC Error Handling ........................................... 24
8.1 Message Header Error Handling ............................... 24
8.2 OPEN Message Error Handling ................................. 25
8.3 UPDATE Message Error Handling ............................... 26
8.4 Hold Timer Expired Error Handling ........................... 28
8.5 Finite State Machine Error Handling ......................... 28
8.6 NOTIFICATION Message Error Handling ......................... 28
8.7 Cease ....................................................... 29
8.8 Connection Collision Detection .............................. 29
9 MASC Version Negotiation ...................................... 30
10 MASC Finite State Machine .................................... 30
10.1 Open/Close MASC Connection FSM ............................. 31
11 UPDATE Message Processing .................................... 35
11.1 Accept/Reject an UPDATE .................................... 36
11.2 PREFIX_IN_USE Message Processing ........................... 38
11.2.1 PREFIX_IN_USE by PARENT .................................. 38
11.2.2 PREFIX_IN_USE by SIBLING ................................. 38
11.2.3 PREFIX_IN_USE by CHILD ................................... 38
11.2.4 PREFIX_IN_USE by INTERNAL_PEER ........................... 38
11.3 CLAIM_DENIED Message Processing ............................ 39
11.3.1 CLAIM_DENIED by CHILD or SIBLING ......................... 39
11.3.2 CLAIM_DENIED by INTERNAL_PEER ............................ 39
11.3.3 CLAIM_DENIED by PARENT ................................... 39
11.4 CLAIM_TO_EXPAND Message Processing ......................... 39
11.4.1 CLAIM_TO_EXPAND by PARENT ................................ 39
11.4.2 CLAIM_TO_EXPAND by SIBLING ............................... 40
11.4.3 CLAIM_TO_EXPAND by CHILD ................................. 40
11.4.4 CLAIM_TO_EXPAND by INTERNAL_PEER ......................... 40
11.5 NEW_CLAIM Message Processing ............................... 41
11.6 PREFIX_MANAGED Message Processing. ........................ 41
11.6.1 PREFIX_MANAGED by PARENT ................................. 41
11.6.2 PREFIX_MANAGED by CHILD or SIBLING ....................... 41
11.6.3 PREFIX_MANAGED by INTERNAL_PEER .......................... 41
11.7 WITHDRAW Message Processing ................................ 42
11.7.1 WITHDRAW by CHILD ........................................ 42
11.7.2 WITHDRAW by SIBLING ...................................... 42
11.7.3 WITHDRAW by INTERNAL ..................................... 42
11.7.4 WITHDRAW by PARENT ....................................... 43
11.8 UPDATE Message Ordering .................................... 43
11.8.1 Parent to Child .......................................... 43
11.8.2 Child to Parent .......................................... 44
11.8.3 Sibling to Sibling ....................................... 44
11.8.4 Internal to Internal ..................................... 44
12 Operational Considerations ................................... 45
12.1 Bootup Operations .......................................... 45
12.2 Leaf and Non-leaf MASC Domain Operation .................... 45
12.3 Clock Skew Workaround ...................................... 45
12.4 Clash Resolving Mechanism .................................. 46
12.5 Changing Network Providers ................................. 47
12.6 Debugging .................................................. 47
12.6.1 Prefix-to-Domain Lookup .................................. 47
12.6.2 Domain-to-Prefix Lookup .................................. 47
13 MASC Storage ................................................. 47
14 Security Considerations ...................................... 48
15 IANA Considerations .......................................... 48
16 Acknowledgments .............................................. 48
17 APPENDIX A: Sample Algorithms ................................ 49
17.1 Claim Size and Prefix Selection Algorithm .................. 49
17.1.1 Prefix Expansion ......................................... 49
17.1.2 Reducing Allocation Latency .............................. 50
17.1.3 Address Space Utilization ................................ 50
17.1.4 Prefix Selection After Increase of Demand ................ 50
17.1.5 Prefix Selection After Decrease of Demand ................ 51
17.1.6 Lifetime Extension Algorithm ............................. 51
18 APPENDIX B: Strawman Deployment .............................. 51
19 Authors" Addresses ........................................... 52
20 References ................................................... 54
21 Full Copyright Statement ..................................... 56
1. Introduction
This document describes MASC, a protocol for inter-domain multicast
address set allocation. The MASC protocol (a Layer-3 protocol in the
multicast address allocation architecture [MALLOC]) is used by a node
(typically a router) to claim and allocate one or more address
prefixes to that node"s domain. Each prefix has an associated
lifetime, and is chosen out of a larger prefix with a lifetime at
least as long, in a manner such that prefixes are aggregatable. At
any time, each MASC node (a Prefix Coordinator in [MALLOC]) will
typically advertise several prefixes with different lifetimes and
scopes, allowing Multicast Address Allocation Servers (MAAS"s) in
that domain or child MASC domains to choose appropriate addresses for
their clients.
The set of prefixes ("address set") associated with a domain is
injected into an inter-domain routing protocol (e.g., BGP4+ [MBGP]),
where it can be used by an inter-domain multicast tree construction
protocol (e.g., BGMP [BGMP]) to construct inter-domain group-shared
trees.
Note that a domain does not need to allocate an address set for the
hosts in that domain to be able to allocate group addresses, nor does
allocating necessarily guarantee that hosts in other domains will not
use an address in the set (since, for example, hosts are not forced
to contact a MAAS before using a group address). Allocating an
address set to a domain does, however, ensure that inter-domain
group-specific multicast distribution trees for any group in the
address set will be locally-rooted, and that traffic will be sent
outside the given domain only when and where external receivers
exist.
1.1. 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 RFC2119 [RFC2119].
Constants used by this protocol are shown as [NAME_OF_CONSTANT], and
summarized in Section 6.
1.2. Definitions
This specification uses a number of terms that may not be familiar to
the reader. This section defines some of these and refers to other
documents for definitions of others.
MAAS (Multicast Address Allocation Server)
A host providing multicast address allocation services to end
users (e.g. via MADCAP [MADCAP]).
MASC server
A node running MASC.
Peer
Other MASC speakers a node directly communicates with.
Multicast
IP Multicast, as defined for IPv4 in [RFC1112] and for IPv6 in
[RFC2460].
Multicast Address
An IP multicast address or group address, as defined in [RFC1112]
and [RFC2373]. An identifier for a group of nodes.
2. Requirements for Inter-Domain Address Allocation
The key design requirements for the inter-domain address allocation
mechanism are:
o Efficient address space utilization when space is scare, which
naturally implies that address allocations be based on the actual
address usage patterns, and therefore that it be dynamic.
o Address aggregation, that implies that the address allocation
mechanism be hierarchical.
o Minimize flux in the allocated address sets (e.g. the address sets
should be reused when possible).
o Robustness, by using decentralized mechanisms.
The timeliness in oBTaining an address set is not a major design
constraint as this is taken care of at a lower level [MALLOC].
3. Overall Architecture
The Multicast Address Set Claim (MASC) protocol is used by MASC
domains to claim and allocate address sets for use by Multicast
Address Allocation Servers (MAASs) within each domain. Typically one
or more border routers of each domain that requires multicast address
space of its own would run MASC. Throughout this document, the term
"MASC domain" refers to a domain that has at least one node running
MASC; typically these domains will be Autonomous Systems (AS"s). A
MASC node (on behalf of its domain) chooses an address set to claim,
sends a claim to other MASC domains in the network, and waits while
listening for any colliding claims. If there is a collision, the
losing claimer gives up the colliding claim and claims a different
address set.
After a sufficiently long collision-free waiting period, the address
set chosen by a MASC node is considered allocated to that node"s
domain. Three things may then happen:
a) The allocated prefix can then be injected as a "multicast route"
into the inter-domain routing protocol (e.g., BGP4+ [MBGP]) as
"G-RIB" Network Layer Reachability Information (NLRI), where it
may be used by an inter-domain multicast routing protocol (e.g.,
BGMP [BGMP]) to construct group-shared trees. To reduce the size
and slow the growth of the G-RIB, MASC nodes may perform CIDR-like
aggregation [CIDR] of the multicast NLRI information. This
motivates the need for an algorithm to select prefixes for domains
in such a way as to ensure good aggregation in addition to
achieving good address space utilization.
b) The node"s domain may assign to itself a sub-prefix which can be
used by MAASs within the domain.
c) Sub-prefixes may be allocated to child domains, if any.
3.1. Claim-Collide vs. Query-Response Rationale
We choose a claim-collide mechanism instead of a query-response
mechanism for the following reasons. In a query-response mechanism,
replicas of the MASC node would be needed in parent MASC domains in
order to make their responses be robust to failures. This brings
about the associated problem of synchronization of the replicas and
possibly additional fragmentation of the address space. In addition,
even in this mechanism, address collisions would still need to be
handled. We believe the proposed claim-collide mechanism is simpler
and more robust than a query-response mechanism.
4. MASC Topology
The domain hierarchy used by MASC is congruent to the somewhat
hierarchical structure of the inter-domain topology, e.g., backbones
connected to regionals, regionals connected to metropolitan
providers, etc. As in BGP, MASC connections are locally configured.
A MASC domain that is a customer of other MASC domains will have one
or more of those provider domains as its parent. For example, a MASC
domain that is a regional provider will choose one (or more) of its
backbone provider domains as its parent(s). Children are configured
with their parent MASC domain, and parents are configured with their
children domains. At the top, a number of Top-Level Domains are
connected in a (sparse) mesh and share the global multicast address
space. To improve the robustness, a pair of children of the same
parent domain MAY be configured as siblings with regard to that
parent.
Figure 1 illustrates a sample topology. Double-line links denote
intra-domain TCP peering sessions, and single-line links denote
inter-domain TCP connections. T1 and T2 are Top-Level Domains (e.g.,
backbone providers), containing MASC speakers T1a and T2a,
respectively. P3 and P4 are regional domains, containing (P3a, P3b),
and (P4a, P4b) respectively. P3 has a single customer (or "child"),
C5, containing (C5a, C5b, C5c). P4 has three children, C5, C6, C7,
containing (C5a, C5b, C5c), (C6a, C6b), and (C7a) respectively.
T1a-----------T2a



P3a====P3b P4a====P4b
/ /
_______/ /
/ / ______
/ /
C5a====C5b C6a====C6b----------C7a
//
//
C5c
Figure 1: Example MASC Topology
All MASC communications use TCP. Each MASC node is connected to and
communicates directly with other MASC nodes. The local node acts in
exactly one of the following four roles with respect to each remote
note:
INTERNAL_PEER
The local and remote nodes are both in the same MASC domain. For
example, P4b is an INTERNAL_PEER of P4a.
CHILD
A customer relationship exists whereby the local node may obtain
address space from the remote node. For example, C6a is a CHILD
in its session with P4a.
PARENT
A provider relationship exists whereby the remote node may obtain
address space from the local node. For example, T2a is a PARENT
in its session with P4a. Whether space is actually requested is
up to the implementation and local policy configuration.
SIBLING
No customer-provider relationship exists. For example, T2a is a
SIBLING in its session with T1a (Top-Level Domain SIBLING
peering). Also, C6b is a SIBLING in its session with C7a with
regard to their common parent P4.
A node"s message will be propagated to its parent, all siblings with
the same parent, and its children. Since a domain need not have a
direct peering session with every sibling, a MASC domain must
propagate messages from a child domain to other children, can
propagate messages from a parent domain to other siblings, and, if a
Top-Level Domain, it must propagate messages from a sibling to other
siblings, otherwise may propagate messages from a sibling domain to
its parent and other siblings.
4.1. Managed vs Locally-Allocated Space
Each domain has a "Managed" Address Set, and a "Locally-Allocated"
Address Set. The "managed" space includes all address space which a
domain has successfully claimed via MASC. The "locally-allocated"
space, on the other hand, includes all address space which MAASs
inside the domain may use. Thus, the locally-allocated space is a
subset of the managed space, and refers to the portion which a domain
allocates for its own use.
For leaf domains (ones with no children), these two sets are
identical, since all claimed space is allocated for local use. A
parent domain, on the other hand, "manages" all address space which
it has claimed via MASC, while sub-prefixes can be allocated to
itself and to its children.
4.2. Prefix Lifetime
Each prefix has an associated lifetime. If a domain wants to use a
prefix longer than its lifetime, that domain must "renew" the prefix
BEFORE its lifetime expires (see Section 5.2). If the lifetime
cannot be extended, then the domain should either retry later to
extend, or should choose and claim another prefix.
After a prefix"s lifetime expires, MASC nodes in the domain that own
that prefix must stop using that prefix. The corresponding entry
from the G-RIB database must be removed, and all information
associated with the expired prefix may be deleted from the MASC
node"s local memory.
4.3. Active vs. Deprecated Prefixes
Each prefix advertised by a parent to its children can be either
"active" or "deprecated". A "deprecated" prefix is a prefix that the
parent wishes to discontinue to use after its lifetime expires. The
"active" prefixes only are candidates for size expansion or lifetime
extension. Usually, this information will be used by a child as a
hint to know which of the parent"s prefixes might have their lifetime
extended.
4.4. Multi-Parent Sibling-to-Sibling and Internal Peering
Two sibling nodes that have more than one common parent will create
and use between them a number of transport-level connections, one per
each common parent. The information associated with a parent will be
sent over the connection that corresponds to the same parent.
Internal peers do not need to open multiple connections between them;
a single connection is used for all information.
4.5. Administratively-Scoped Address Allocation
MASC can also be used for sub-allocating prefixes of addresses within
an administrative scope zone [SCOPE], but only if the scope is
"divisible" (as described in [MALLOC] and [MZAP]). A MASC node can
learn what scopes it resides within by listening to MZAP [MZAP]
messages.
A "Zone TLD" is a domain which has no parent domain within the scope
zone. Zone TLDs act as TLDs for the prefix associated with the
scope. Figure 2 gives an example, where a scope boundary around
domains P3 and C5 has been added to Figure 1. Domain P3 is a Zone
TLD, since its only parent (T1) is outside the boundary. Hence, P3
can claim space directly out of the prefix associated with the scope
itself. Domain C5, on the other hand, has a parent within the scope
(namely, P3), and hence is not a Zone TLD.
T1a-----------T2a

...................
. .
. P3a====P3b . P4a
. . /
. _______/
. / .
. / .
. C5a====C5b .
. // .
. // .
. C5c .
. .
. Admin Scope Zone .
....................
Figure 2: Scope Zone Example
It is assumed that the role of a node (as discussed in Section 4)
with respect to a given peering session is the same for every scope
in which both ends are contained. A peering session that crosses a
scope boundary (such as the session between C5b and P4a in Figure 2)
is ignored when propagating messages that pertain to the given scope.
That is, such messages are not sent across such sessions.
5. Protocol Details
5.1. Claiming Space
When a MASC node, on behalf of a MASC domain, needs more address
space, it decides locally the size and the value of the address
prefix(es) it will claim from one of its parents. For example, the
decision might be based on the knowledge this node has about its
parent"s address set, its siblings" claims and allocations, its own
address set, the claim messages from its siblings, and/or the demand
pattern of its children and the local domain. A sample algorithm is
given in Appendix A.
A MASC node which is not in a top-level domain can initiate a claim
toward a parent MASC domain if and only if it currently has an
established connection with at least one node in that parent domain.
After the prefix address and size are decided, the claim proceeds as
follows:
a) The claim is scheduled to be sent after a random delay in the
interval (0, [INITIATE_CLAIM_DELAY]). If a claim originated by a
node from the same MASC domain is received, and that claim
eliminates the need for the local claim, the local claim is
canceled and no further action is taken.
b) The claim is sent to one of the parents (if the domain is not a
top-level domain), all known siblings with the same parent, and
all internal peers. A Claim-Timer is then started at
[WAITING_PERIOD], and the MASC node starts listening for colliding
claims.
c) If a colliding claim is received while the Claim-Timer is running,
that claim is compared with the locally initiated claim using the
function described in Section 5.1.1. If the local claim is the
loser, a new prefix must be chosen to claim, and the loser claim"s
Claim-Timer must be canceled. The loser claim can be either
explicitly withdrawn, or can be left to expire without taking
further actions. If the winning claim was originated by a node
from the same MASC domain, no new claim will be initiated. If the
local claim is the winner, no actions need to be taken.
d) If the Claim-Timer expires, the claimed prefix becomes associated
with the claimer"s domain, i.e. it is considered allocated to that
domain and the following actions can be performed:
o Advertise the prefix to its parent, and to all siblings with
the same parent, by sending a PREFIX_IN_USE claim to them.
o Inject the prefix into the G-RIB of the inter-domain routing
protocol.
o Send a PREFIX_MANAGED message to all children and internal
peers, informing them that they may issue claims within the
managed space. A sub-prefix may then be claimed for local
usage (see Section 12.2).
Each MASC node receives all claims from its siblings and children. A
received claim must be evaluated against all claims saved in the
local cache using the function described in Section 5.1.1. The
output of the function will define the further processing of that
claim (see Section 11).
5.1.1. Claim Comparison Function
Each claim message includes:
o a "type", being one of: PREFIX_IN_USE, CLAIM_DENIED,
CLAIM_TO_EXPAND, or NEW_CLAIM (PREFIX_MANAGED and WITHDRAW are
not considered as claims that have to be compared)
o timestamp when the claim was initiated
o the claimed prefix and lifetime
o MASC Identifier of the node that originated the claim
When two claims are compared, first the type is compared based on the
following precedence:
PREFIX_IN_USE > CLAIM_DENIED > CLAIM_TO_EXPAND > NEW_CLAIM
If the type is the same, then the timestamps are used to compare the
claims. In practice, two claims will have the same type if the type
is either NEW_CLAIM (ordinary collision) or PREFIX_IN_USE (signal for
a clash). When the timestamps are compared, the claim with the
smallest, i.e. earliest timestamp wins. If the timestamps are the
same, then the claim with the smallest Origin Node Identifier wins.
5.2. Renewing an Existing Claim
The procedure for extending the lifetime of prefixes already in use
is the same as claiming new space (see Section 5.1), except that the
claim type must be CLAIM_TO_EXPAND, while the Address and the Mask of
the claim (see Section 7.3) must be the same as the already allocated
prefix. If the Claim-Timer expires and there is no collision, the
desired lifetime is assumed.
5.3. Expanding an Existing Prefix
The procedure for extending the lifetime of prefixes already in use
is the same as claiming new space (see Section 5.1), except that the
claim type must be CLAIM_TO_EXPAND, while the Address and the Mask of
the claim (see Section 7.3) must be set to the desired values. If
the Claim-Timer expires and there is no collision, the desired larger
prefix is associated with the local domain.
5.4. Releasing Allocated Space
If the lifetime of a prefix allocated to the local domain expires and
the domain does not need to reuse it, all resources associated with
this prefix are deleted and no further actions are taken. If the
lifetime of the prefix has not expired, and if no subranges of that
prefix have being allocated for local usage or by some of the
children domains, the space may be released by sending a withdraw
message to the parent domain, all known siblings with the same
parent, and all internal peers.
6. Constants
MASC uses the following constants:
[PORT_NUMBER]
2587. The TCP port number used to listen for incoming MASC
connections, as assigned by IANA.
[WAITING_PERIOD]
The amount of time (in seconds) that must pass between a NEW_CLAIM
(or CLAIM_TO_EXPAND), and a PREFIX_IN_USE for the same prefix.
This must be long enough to reasonably span any single inter-
domain network partition. Default: 172800 seconds (i.e. 48
hours).
[INITIATE_CLAIM_DELAY]
The amount of time (in seconds) a MASC node must wait before
initiating a new claim or a claim for space expansion. This must
be a random value in the interval (0, [INITIATE_CLAIM_DELAY]).
Default value for [INITIATE_CLAIM_DELAY]: 600 seconds (i.e. 10
minutes).
[TLD_ID]
The Parent Domain Identifier used by a Top-Level Domain (which has
no parent). Must be 0.
[HOLDTIME]
The amount of time (in seconds) that must pass without any
messages received from a remote node before considering the
connection is down. Default: 240 seconds (i.e. 4 minutes).
7. Message Formats
This section describes message formats used by MASC.
Messages are sent over a reliable transport protocol connection. A
message is processed only after it is entirely received. The maximum
message size is 4096 octets. All implementations are required to
support this maximum message size.
7.1. Message Header Format
Each message has a fixed-size (4-octets) header. There may or may
not be a data portion following the header, depending on the message
type. The layout of these fields is shown below:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Length Type Reserved
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Length:
This 2-octet unsigned integer indicates the total length of the
message, including the header, in octets. Thus, e.g., it allows
one to locate in the transport-level stream the start of the next
message. The value of the Length field must always be at least 4
and no greater than 4096, and may be further constrained,
depending on the message type. No "padding" of extra data after
the message is allowed, so the Length field must have the smallest
value required given the rest of the message.
Type:
This 1-octet unsigned integer indicates the type code of the
message. The following type codes are defined:
1 - OPEN
2 - UPDATE
3 - NOTIFICATION
4 - KEEPALIVE
Reserved:
This 1-octet field is reserved. MUST be set to zero by the sender,
and MUST be ignored by the receiver.
7.2. OPEN Message Format
After a transport protocol connection is established, the first
message sent by each side is an OPEN message. If the OPEN message is
acceptable, a KEEPALIVE message confirming the OPEN is sent back.
Once the OPEN is confirmed, UPDATE, KEEPALIVE, and NOTIFICATION
messages may be exchanged.
The minimum length of the OPEN message is 20 octets (including
message header). In addition to the fixed-size MASC header, the OPEN
message contains the following fields:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Version R AddrFam Rol Hold Time
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Sender Domain Identifier (variable length)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Sender MASC Node Identifier (variable length)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Parent"s Domain Identifier (variable length)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

+ (Optional Parameters)

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Version:
This 1-octet unsigned integer indicates the protocol version
number of the message. The current MASC version number is 1.
R bit:
This 1-bit field is reserved. MUST be set to zero by the sender,
and MUST be ignored by the receiver.
AddrFam:
This 5-bit field is the IANA-assigned address family number of the
encoded prefix [IANA]. These include (among others):
Number Description
------ -----------
1 IP (IP version 4)
2 IPv6 (IP version 6)
My Role (Rol):
This 2-bit field indicates the proposed relationship of the
sending system to the receiving system:
00 = INTERNAL_PEER (sent from one internal peer to another)
01 = CHILD (sent from a child to its parent)
10 = SIBLING (sent from one sibling to another)
11 = PARENT (sent from a parent to its child)
Hold Time:
This 2-octet unsigned integer indicates the number of seconds that
the sender proposes for the value of the Hold Timer. Upon receipt
of an OPEN message, a MASC speaker MUST calculate the value of the
Hold Timer by using the smaller of its configured Hold Time for
that peer and the Hold Time received in the OPEN message. The
Hold Time MUST be either zero or at least three seconds. An
implementation may reject connections on the basis of the Hold
Time. The calculated value indicates the maximum number of
seconds that may elapse between the receipt of successive
KEEPALIVE and/or UPDATE messages by the sender. RECOMMENDED value
is [HOLDTIME] seconds.
Sender Domain Identifier:
A globally unique identifier. Its length is determined based on
the Address Family, and should be treated as an unsigned integer
(e.g. a 4-octet integer for IPv4, or a 16-octet integer for IPv6),
but must be at least 4 octets long. It should be set to the
Autonomous System number of the sender, but the network unicast
prefix address is also acceptable.
Sender MASC Node Identifier:
This field"s length and format are same as the Sender Domain
Identifier field, and indicates the MASC Node Identifier of the
sender. A given MASC speaker sets the value of its MASC Node
Identifier to a globally-unique value assigned to that MASC
speaker (e.g., an IPv4 or IPv6 address). The value of the MASC
Node Identifier is determined on startup and is the same for every
MASC session opened.
Parent"s Domain Identifier:
This field"s length and format are same as the Sender Domain
Identifier field, and is set to the Domain Identifier of the
sender"s parent (e.g. the parent"s Autonomous System number, or
network prefix address), or is set to [TLD_ID] if the sender is a
TLD. Used only when Rol is INTERNAL_PEER or SIBLING, otherwise is
ignored. This field is used to determine the common parents
between siblings, to associate each sibling-to-sibling connection
with a particular parent, and to discover TLD-related
configuration problems among internal peers. If a non-TLD node
does not know yet the Domain ID of any of its parents, it can use
its own Domain ID in the OPEN messages to its internal peers.
Optional Parameters:
This field may contain a list of optional parameters, where each
parameter is encoded as a <Parameter Length, Parameter Type,
Parameter Value> triplet. The combined length of all optional
parameters can be derived from the Length field in the message
header.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
Parm. Length Parm. Type Parameter Value (variable)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
Parameter Length is a one octet field that contains the length of
the Parameter Value field in octets. Parameter Type is a one
octet field that unambiguously identifies individual parameters.
Parameter Value is a variable length field that is interpreted
according to the value of the Parameter Type field. Unrecognized
optional parameters MUST be silently ignored.
This document does not define any optional parameters.
7.3. UPDATE Message Format
UPDATE messages are used to transfer Claim/Collision/PrefixManaged
information between MASC speakers. The UPDATE message always
includes the fixed-size MASC header, and one or more attributes as
described below. The minimum length of the UPDATE message is 40
octets (including the message header).
Each attribute is of the form:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Length Type Reserved
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Data ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
All attributes are 4-octets aligned.
Length:
The Length is the length of the entire attribute, including the
length, type, and data fields. If other attributes are nested
within the data field, the length includes the size of all such
nested attributes.
Type:
This 1-octet unsigned integer indicates the type code of the
attribute. The following type codes are defined:
0 = PREFIX_IN_USE (prefix is being used by the origin)
1 = CLAIM_DENIED (the claim is refused (probably by the
origin"s parent domain))
2 = CLAIM_TO_EXPAND (origin is trying to expand the size of
an existing prefix)
3 = NEW_CLAIM (origin is trying to claim a new prefix)
4 = PREFIX_MANAGED (parent is informing child of space
available)
5 = WITHDRAW (origin is withdrawing a previous claim)
Types 128-255 are reserved for "optional" attributes. If a
required attribute is unrecognized, a NOTIFICATION with UPDATE
Error Code and Unrecognized Required Attribute subcode will be
sent. Unrecognized optional attributes are simply ignored.
Reserved:
This 1-octet field is reserved. MUST be set to zero by the
sender, and MUST be ignored by the receiver.
Types 0-3 are collectively called "CLAIMs". The message format below
describes the encoding of a CLAIM, PREFIX_MANAGED and WITHDRAW.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved1 D AddrFam Rol Reserved2
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Claim Timestamp
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Claim Lifetime
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Claim Holdtime
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Origin Domain Identifier (variable length)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Origin Node Identifier (variable length)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Address (variable length)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Mask (variable length)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

+ (Optional Parameters)

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved1:
This 1-octet field is reserved. MUST be set to zero by the
sender, and MUST be ignored by the receiver.
D-bit:
DEPRECATED_PREFIX bit. If set, indicates that the advertised
address prefix is Deprecated, otherwise the prefix is Active (see
Section 4.3).
AddrFam:
This 5-bit field is the IANA-assigned address family number of the
encoded prefix [IANA].
Rol:
This 2-bit field indicates the relationship/role of the Origin of
the message to the node sending that message:
00 = INTERNAL (originated by the sender"s domain)
01 = CHILD (originated by a child of the sender"s domain)
10 = SIBLING (originated by a sibling of the sender"s domain)
11 = PARENT (originated by a parent of the sender"s domain)
Reserved2:
This 2-octet field is reserved. MUST be set to zero by the
sender, and MUST be ignored by the receiver.
Claim Timestamp:
The timestamp of the claim when it was originated. The timestamp
is expressed in number of seconds since midnight (0 hour), January
1, 1970, Greenwich.
Claim Lifetime:
The time in seconds between the Claim Timestamp, and the time at
which the prefix will become free.
Claim Holdtime:
The time in seconds between the Claim Timestamp, and the time at
which the claim should be deleted from the local cache. For
PREFIX_IN_USE and PREFIX_MANAGED claims it should be equal to
Claim Lifetime; for CLAIM_TO_EXPAND, NEW_CLAIM, and CLAIM_DENIED
it should be equal to [WAITING_PERIOD].
Origin Domain Identifier:
The domain identifier of the claim originator. Its length and
format definition are same as the Sender Domain Identifier (see
Section 7.2).
Origin Node Identifier:
The MASC Node ID of the claim originator. Its length and format
definition are same as the Sender MASC Node Identifier (see
Section 7.2).
Address:
The address associated with the given prefix to be encoded. The
length is determined based on the Address Family (e.g. 4 octets
for IPv4, 16 for IPv6)
Mask:
The mask associated with the given prefix. The length is the same
as the Address field and is determined based on the Address
Family. The field contains the full bitmask.
Optional Parameters:
This field may contain a list of optional parameters, where each
parameter is encoded using same format as the optional parameters
of an OPEN message (see Section 7.2). Unrecognized optional
parameters MUST be silently ignored. This document does not
define any optional parameters.
7.4. KEEPALIVE Message Format
MASC does not use any transport protocol-based keep-alive mechanism
to determine if peers are reachable. Instead, KEEPALIVE messages are
exchanged between peers often enough as not to cause the Hold Timer
to expire. A reasonable maximum time between the last KEEPALIVE or
UPDATE message sent, and the time at which a KEEPALIVE message is
sent, would be one third of the Hold Time interval. KEEPALIVE
messages MUST NOT be sent more frequently than one per second. An
implementation MAY adjust the rate at which it sends KEEPALIVE
messages as a function of the Hold Time interval.
If the negotiated Hold Time interval is zero, then periodic KEEPALIVE
messages MUST NOT be sent.
A KEEPALIVE message consists of only a message header, and has a
length of 4 octets.
7.5. NOTIFICATION Message Format
A NOTIFICATION message is sent when an error condition is detected.
Depending on the error condition, the MASC connection might or must
be closed immediately after sending the message. If the sender of
the NOTIFICATION decides that the connection is to be closed, it will
indicate this by zeroing the O-bit in the NOTIFICATION message (see
below).
In addition to the fixed-size MASC header, the NOTIFICATION message
contains the following fields:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
O Error code Error subcode Data
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
O-bit:
Open-bit. If zero, it indicates that the sender will close the
connection. If "1", it indicates that the sender has chosen to
keep the connection open.
Error Code:
This 7-bit unsigned integer indicates the type of NOTIFICATION.
The following Error Codes have been defined:
Error Code Symbolic Name Reference
1 Message Header Error Section 8.1
2 OPEN Message Error Section 8.2
3 UPDATE Message Error Section 8.3
4 Hold Timer Expired Section 8.4
5 Finite State Machine Error Section 8.5
6 NOTIFICATION Message Error Section 8.6
7 Cease Section 8.7
Error subcode:
This 1-octet unsigned integer provides more specific information
about the nature of the reported error. Each Error Code may have
one or more Error Subcodes associated with it. If no appropriate
Error Subcode is defined, then a zero (Unspecific) value is used
for the Error Subcode field, and the O-bit must be zero (i.e. the
connection will be closed). The notation used in the error
description below is: MC = Must Close connection = O-bit is zero;
CC = Can Close connection = O-bit might be zero.
Message Header Error subcodes:
0 - Unspecific (MC)
1 - Bad Message Length (MC)
2 - Bad Message Type (CC)
OPEN Message Error subcodes:
0 - Unspecific (MC)
1 - Unsupported Version Number (MC)
2 - Bad Peer Domain ID (MC)
3 - Bad Peer MASC Node ID (MC)
6 - Unacceptable Hold Time (MC)
7 - Invalid Parent Configuration (MC)
8 - Inconsistent Role (MC)
9 - Bad Parent Domain ID (MC)
10 - No Common Parent (MC)
13 - Unrecognized Address Family (MC)
UPDATE Message Error subcodes:
0 - Unspecific (MC)
1 - Malformed Attribute List (MC)
2 - Unrecognized Required Attribute (CC)
5 - Attribute Length Error (MC)
10 - Invalid Address field (CC)
11 - Invalid Mask field (CC)
12 - Non-Contiguous Mask (CC)
13 - Unrecognized Address Family (MC)
14 - Claim Type Error (CC)
15 - Origin Domain ID Error (CC)
16 - Origin Node ID Error (CC)
17 - Claim Lifetime Too Short (CC)
18 - Claim Lifetime Too Long (CC)
19 - Claim Timestamp Too Old (CC)
20 - Claim Timestamp Too New (CC)
21 - Claim Prefix Size Too Small (CC)
22 - Claim Prefix Size Too Large (CC)
23 - Illegal Origin Role Error (CC)
24 - No Appropriate Parent Prefix (CC)
25 - No Appropriate Child Prefix (CC)
26 - No Appropriate Internal Prefix (CC)
27 - No Appropriate Sibling Prefix (CC)
28 - Claim Holdtime Too Short (CC)
29 - Claim Holdtime Too Long (CC)
Hold Timer Expired subcodes (the O-bit is always zero):
0 - Unspecific (MC)
Finite State Machine Error subcodes:
0 - Unspecific (MC)
1 - Open/Close MASC Connection FSM Error (MC)
2 - Unexpected Message Type FSM Error (MC)
Cease subcodes (the O-bit is always zero):
0 - Unspecific (MC)
NOTIFICATION subcodes (the O-bit is always zero):
0 - Unspecific (MC)
Data:
This variable-length field is used to diagnose the reason for the
NOTIFICATION. The contents of the Data field depend upon the
Error Code and Error Subcode. See Section 8 for more details.
Note that the length of the Data field can be determined from the
message Length field by the formula:
Message Length = 6 + Data Length
The minimum length of the NOTIFICATION message is 6 octets
(including message header).
8. MASC Error Handling
This section describes actions to be taken when errors are detected
while processing MASC messages. MASC Error Handling is similar to
that of BGP [BGP].
When any of the conditions described here are detected, a
NOTIFICATION message with the indicated Error Code, Error Subcode,
and Data fields is sent. In addition, the MASC connection might be
closed. If no Error Subcode is specified, then a zero (Unspecific)
must be used.
The phrase "the MASC connection is closed" means that the transport
protocol connection has been closed and that all resources for that
MASC connection have been deallocated.
Unless specified explicitly, the Data field of the NOTIFICATION
message is empty.
8.1. Message Header Error Handling
All errors detected while processing the Message Header are indicated
by sending the NOTIFICATION message with Error Code Message Header
Error. The Error Subcode elaborates on the specific nature of the
error. The Data field contains the erroneous Message (including the
message header).
If the Length field of the message header is less than 4 or greater
than 4096, or if the length of an OPEN message is less than the
minimum length of the OPEN message, or if the length of an UPDATE
message is less than the minimum length of the UPDATE message, or if
the length of a KEEPALIVE message is not equal to 4, then the Error
Subcode is set to Bad Message Length.
If the Type field of the message header is not recognized, then the
Error Subcode is set to Bad Message Type.
8.2. OPEN Message Error Handling
All errors detected while processing the OPEN message are indicated
by sending the NOTIFICATION message with Error Code OPEN Message
Error. The Error Subcode elaborates on the specific nature of the
error. The Data field contains the erroneous OPEN Message (excluding
the Message Header), unless stated otherwise.
If the version number contained in the Version field of the received
OPEN message is not supported, then the Error Subcode is set to
Unsupported Version Number. The Data field is a 1-octet unsigned
integer, which indicates the largest locally supported version number
less than the version the remote MASC node bid (as indicated in the
received OPEN message).
If the Sender Domain Identifier field of the OPEN message is
unacceptable, then the Error Subcode is set to Bad Peer Domain ID.
The determination of acceptable Domain IDs is outside the scope of
this protocol.
If the Sender MASC Node Identifier field of the OPEN message is
unacceptable, then the Error Subcode is set to Bad Peer MASC Node ID.
The determination of acceptable Node IDs is outside the scope of this
protocol.
If the Hold Time field of the OPEN message is unacceptable, then the
Error Subcode MUST be set to Unacceptable Hold Time. An
implementation MUST reject Hold Time values of one or two seconds.
An implementation MAY reject any proposed Hold Time. An
implementation which accepts a Hold Time MUST use the negotiated
value for the Hold Time.
If the remote system"s proposed Role is INTERNAL_PEER, and either
(but not both) the local system or the remote system"s Parent Domain
ID is [TLD_ID], then the Error Subcode is set to Invalid Parent
Configuration. The Data field must be filled with all the local
system"s Parent Domain IDs.
If the remote system"s proposed Role conflicts with its expected role
(based on the local system"s configured Role), then the Error Subcode
is set to Inconsistent Role. The Data field is 1-octet long, and
contains the local system"s configured Role.
If the remote system"s Parent Domain ID is unacceptable, then the
Error Subcode is set to Bad Parent Domain ID, and the Data field is
filled with the erroneous Parent Domain ID. The determination of
acceptable Parent Domain ID is outside the scope of this protocol.
If the remote system is supposed to be a sibling, but it does not
have a common parent with the local system (based on the Parent
Domain ID information in the OPEN message), the Error Subcode is set
to No Common Parent, and the Data field is filled with all Parent
Domain IDs of the local MASC domain.
If the Address Family is unrecognized, then the Error Subcode is set
to Unrecognized Address Family.
8.3. UPDATE Message Error Handling
All errors detected while processing the UPDATE message are indicated
by sending the NOTIFICATION message with Error Code UPDATE Message
Error. The error subcode elaborates on the specific nature of the
error. The Data field contains the erroneous UPDATE Message
(including the attribute header, but excluding the Message Header),
unless stated otherwise.
If any recognized attribute has an Attribute Length that conflicts
with the expected length (based on the attribute type code), then the
Error Subcode is set to Attribute Length Error.
If any of the mandatory well-known attributes are not recognized,
then the Error Subcode is set to Unrecognized Required Attribute.
If the Address field includes an invalid address (except 0), then the
Error Subcode is set to Invalid Address.
If the Mask field includes an invalid mask (for example, starting
with 0), then the Error Subcode is set to Invalid Mask.
If the Mask field includes a non-contiguous bitmask, and that MASC
server does not support, or is not configured to use non-contiguous
masks, then the Error Subcode is set to Non-Contiguous Mask.
If the Address Family is unrecognized, then the Error Subcode is set
to Unrecognized Address Family.
If the Origin Role/Claim Type combination is not one of the
following, then the Error Subcode is set to Claim Type Error.
Origin Claim
Role Type
ICS PREFIX_IN_USE (0)
I P CLAIM_DENIED (1)
ICS CLAIM_TO_EXPAND (2)
ICS NEW_CLAIM (3)
I P PREFIX_MANAGED (4)
ICSP WITHDRAW (5)
If there is a reason to believe that the Origin Domain ID is invalid,
then the Error Subcode is set to Origin Domain ID Error. The same
applies for Origin Node ID (the corresponding error is Origin Node ID
Error).
If a node (usually a parent receiving a claim from a child) decides
that the Claim Lifetime is too short (for example, less than 172800,
i.e. 48 hours), it MAY send an UPDATE Message Error with subcode
Claim Lifetime Too Short.
If a node (usually a parent receiving a claim from a child) decides
that the Claim Lifetime is too long (for example, more than
15,768,000, i.e. half year), then it MAY send an UPDATE Message Error
with subcode Claim Lifetime Too Long. Note that usually a parent
MASC node should send first CLAIM_DENIED collision messages with
Claim Lifetime field filled with the longest acceptable lifetime. If
the child refuses to claim with shorter lifetime, then Claim Lifetime
Too Long should be sent.
If a node (usually a parent receiving a claim from a child) decides
that the Claim Timestamp is too small, i.e. too old (for example, if
a node is self-confident that its clock is quite accurate), then it
MUST send an UPDATE Message Error with subcode Claim Timestamp Too
Old. Claim Timestamp Too New is defined similarly.
If a node (usually a parent receiving a claim from a child) decides
that the prefix size implied by the Mask field is too small (for
example, smaller than 16 addresses), then it MAY send an UPDATE
Message Error with subcode Claim Prefix Size Too Small.
If a node (usually a parent receiving a claim from a child) decides
that the prefix size implied by the Mask field is too large, then it
MAY send an UPDATE Message Error with subcode Claim Prefix Size Too
Large. Note that usually a parent MASC node should send first
CLAIM_DENIED collision messages for some subrange of the child"s
large claimed address range. If the child refuses to shrink the
claim size, then Claim Prefix Size Too Large should be sent.
If the received UPDATE message"s computed Updated Origin Role is
illegal (see Table 1 in Section 11.1), then the Error Subcode is set
to Illegal Origin Role Error.
If the received UPDATE message needs to be associated with a parent"s
prefix, but the association is not successful, then the Error Subcode
is set to No Appropriate Parent Prefix. The No Appropriate Child
Prefix, No Appropriate Internal Prefix, and No Appropriate Sibling
Prefix Error Subcodes are defined similarly.
If a node decides that the Claim Holdtime is too short (for example,
just few seconds), it MAY send an UPDATE Message Error with subcode
Claim Holdtime Too Short.
If a node decides that the Claim Holdtime is too long (for example,
more than 15,768,000, i.e. half year), then it SHOULD send an UPDATE
Message Error with subcode Claim Holdtime Too Long.
If any other error is encountered when processing attributes, then
the Error Subcode is set to Malformed Attribute List, and the erratic
attribute is included in the data field.
8.4. Hold Timer Expired Error Handling
If a system does not receive successive KEEPALIVE and/or UPDATE
and/or NOTIFICATION messages within the period specified in the Hold
Time field of the OPEN message, then the NOTIFICATION message with
Hold Timer Expired Error Code must be sent and the MASC connection
closed.
8.5. Finite State Machine Error Handling
Any error detected by the MASC Finite State Machine (e.g., receipt of
an unexpected event) is indicated by sending the NOTIFICATION message
with Error Code Finite State Machine Error. The Error Subcode
elaborates on the specific nature of the error.
8.6. NOTIFICATION Message Error Handling
If a node sends a NOTIFICATION message, and there is an error in that
message, and the O-bit of that message is not zero, a NOTIFICATION
with O-bit zeroed, Error Code of NOTIFICATION Error, and subcode
Unspecific must be sent. In addition, the Data field must include
the erratic NOTIFICATION message. However, if the erratic
NOTIFICATION message had the O-bit zeroed, then any error, such as an
unrecognized Error Code or Error Subcode, should be noticed, logged
locally, and brought to the attention of the administrator of the
remote node. The means to do this, however, lies outside the scope
of this document.
8.7. Cease
In absence of any fatal errors (that are indicated in this section),
a MASC node may choose at any given time to close its MASC connection
by sending the NOTIFICATION message with Error Code Cease. However,
the Cease NOTIFICATION message must not be used when a fatal error
indicated by this section does exist.
8.8. Connection Collision Detection
If a pair of MASC speakers try simultaneously to establish a TCP
connection to each other, then two parallel connections between this
pair of speakers might well be formed. We refer to this situation as
connection collision. Clearly, one of these connections must be
closed. Note that if the nodes were siblings, and each of those
connections was associated with a different parent, then we do not
consider this situation as collision (see Section 4.4).
Based on the value of the MASC Node Identifier a convention is
established for detecting which MASC connection is to be preserved
when a connection collision does occur. The convention is to compare
the MASC Node Identifiers of the remote nodes involved in the
collision and to retain only the connection initiated by the MASC
speaker with the higher-valued MASC Node Identifier.
Upon receipt of an OPEN message, the local system must examine all of
its connections that are in the OpenConfirm state. A MASC speaker
may also examine connections in an OpenSent state if it knows the
MASC Node Identifier of the remote node by means outside of the
protocol. If among these connections there is a connection to a
remote MASC speaker whose MASC Node Identifier equals the one in the
OPEN message, and, in case of a sibling-to-sibling connection, the
Parent Domain ID of that connection equals the one in the OPEN
message, then the local system performs the following connection
collision resolution procedure:
1. The MASC Node Identifier of the local system is compared to the
MASC Node Identifier of the remote system (as specified in the
OPEN message). Comparing MASC Node Identifiers is done by
treating them as unsigned integers (e.g. 4-octets long for IPv4
and 16-octets long for IPv6).
2. If the value of the local MASC Node Identifier is less than the
remote one, the local system closes MASC connection that already
exists (the one that is already in the OpenConfirm state), and
accepts the MASC connection initiated by the remote system.
3. Otherwise, the local system closes the newly created MASC
connection (the one associated with the newly received OPEN
message), and continues to use the existing one (the one that is
already in the OpenConfirm state).
A connection collision with an existing MASC connection that is in
the Established state causes unconditional closing of the newly
created connection. Note that a connection collision cannot be
detected with connections that are in Idle, or Connect, or Active
states (see Section 10).
Closing the MASC connection (that results from the collision
resolution procedure) is accomplished by sending the NOTIFICATION
message with the Error Code Cease.
9. MASC Version Negotiation
MASC speakers may negotiate the version of the protocol by making
multiple attempts to open a MASC connection, starting with the
highest version number each supports. If an open attempt fails with
an Error Code OPEN Message Error, and an Error Subcode Unsupported
Version Number, then the MASC speaker has available the version
number it tried, the version number the remote node tried, the
version number passed by the remote node in the NOTIFICATION message,
and the version numbers that it supports. If the two MASC speakers
do support one or more common versions, then this will allow them to
rapidly determine the highest common version. In order to support
MASC version negotiation, future versions of MASC must retain the
format of the OPEN and NOTIFICATION messages.
10. MASC Finite State Machine
This section specifies MASC operation in terms of a Finite State
Machine (FSM). The FSM and the operations are peer peering session.
Following is a brief summary and overview of MASC operations by state
as determined by this FSM.
Initially the peering session is in the Idle state.
10.1. Open/Close MASC Connection FSM
Idle state:
In this state MASC refuses all incoming MASC connections from the
peer. No resources are allocated to the remote node. In response
to the Start event (initiated by either system or operator) the
local system initializes all MASC resources, starts the
ConnectRetry timer, initiates a transport connection to the remote
node, while listening for a connection that may be initiated by
the remote MASC node, and changes its state to Connect. The exact
value of the ConnectRetry timer is a local matter, but should be
sufficiently large to allow TCP initialization.
If a MASC speaker detects an error, it shuts down the connection
and changes its state to Idle. Getting out of the Idle state
requires generation of the Start event. If such an event is
generated automatically, then persistent MASC errors may result in
persistent flapping of the speaker. To avoid such a condition it
is recommended that Start events should not be generated
immediately for a node that was previously transitioned to Idle
due to an error. For a node that was previously transitioned to
Idle due to an error, the time between consecutive generation of
Start events, if such events are generated automatically, shall
exponentially increase. The value of the initial timer shall be 60
seconds. The time shall be doubled for each consecutive retry, but
shall not be longer than 24 hours.
Any other event received in the Idle state is ignored.
Connect state:
In this state MASC is waiting for the transport protocol
connection to be completed.
If the transport protocol connection succeeds, the local system
clears the ConnectRetry timer, completes initialization, sends an
OPEN message to the remote node, and changes its state to
OpenSent. If the transport protocol connect fails (e.g.,
retransmission timeout), the local system restarts the
ConnectRetry timer, continues to listen for a connection that may
be initiated by the remote MASC node, and changes its state to
Active state.
In response to the ConnectRetry timer expired event, the local
system restarts