As per Relevance of the word designated, we have this rfc below:
Network Working Group L.
Request for Comments: 2642 Cabletron Systems
Category: Informational August 1999
Cabletron's VLS Protocol
Status of this
This memo provides information for the Internet community. It
not specify an Internet standard of any kind. Distribution of
memo is unlimited
Copyright
Copyright (C) The Internet Society (1999). All Rights Reserved
The Virtual LAN Link State Protocol (VLSP) is part of the
Message Protocol (ISMP) which provides interswitch
between switches running Cabletron's SecureFast VLAN (SFVLAN
product. VLSP is used to determine and maintain a fully
mesh topology graph of the switch fabric. Each switch maintains
identical database describing the topology. Call-originating
use the topology database to determine the path over which to route
call connection
VLSP provides support for equal-cost multipath routing,
recalculates routes quickly in the face of topological changes
utilizing a minimum of routing protocol traffic
Table of
1. Introduction............................................ 3
1.1 Acknowledgments..................................... 3
1.2 Data Conventions.................................... 3
1.3 ISMP Overview....................................... 4
2. VLS Protocol Overview................................... 5
2.1 Definitions of Commonly Used Terms.................. 6
2.2 Differences Between VLSP and OSPF................... 7
2.2.1 Operation at the Physical Layer............... 8
2.2.2 All Links Treated as Point-to-Point........... 8
2.2.3 Routing Path Information...................... 9
2.2.4 Configurable Parameters....................... 9
2.2.5 Features Not supported........................ 9
2.3 Functional Summary.................................. 10
2.4 Protocol Packets.................................... 11
Kane Informational [Page 1]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
2.5 Protocol Data Structures............................ 12
2.6 Basic Implementation Requirements................... 12
2.7 Organization of the Remainder of This Document...... 13
3. Interface Data Structure................................ 14
3.1 Interface States.................................... 16
3.2 Events Causing Interface State Changes.............. 18
3.3 Interface State Machine............................. 21
4. Neighbor Data Structure................................. 23
4.1 Neighbor States..................................... 25
4.2 Events Causing Neighbor State Changes............... 27
4.3 Neighbor State Machine.............................. 29
5. Area Data Structure..................................... 33
5.1 Adding and Deleting Link State Advertisements....... 34
5.2 Accessing Link State Advertisements................. 35
5.3 Best Path Lookup.................................... 35
6. Discovery Process....................................... 35
6.1 Neighbor Discovery.................................. 36
6.2 Bidirectional Communication......................... 37
6.3 Designated Switch................................... 38
6.3.1 Selecting the Designated Switch............... 39
6.4 Adjacencies......................................... 41
7. Synchronizing the Databases............................. 42
7.1 Link State Advertisements........................... 43
7.1.1 Determining
Link State Advertisement Is Newer............. 44
7.2 Database Exchange Process........................... 44
7.2.1 Database Description Packets.................. 44
7.2.2 Negotiating the Master/Slave Relationship..... 45
7.2.3 Exchanging Database Description Packets....... 46
7.3 Updating the Database............................... 48
7.4 An Example.......................................... 49
8. Maintaining the Databases............................... 51
8.1 Originating Link State Advertisements............... 52
8.1.1 Switch Link Advertisements.................... 52
8.1.2 Network Link Advertisements................... 55
8.2 Distributing Link State Advertisements.............. 56
8.2.1 Overview...................................... 57
8.2.2 Processing
Incoming Link State Update Packet............. 58
8.2.3 Forwarding Link State Advertisements.......... 60
8.2.4 Installing
State Advertisements in the Database.......... 62
8.2.5 Retransmitting Link State Advertisements...... 63
8.2.6 Acknowledging Link State Advertisements....... 64
8.3 Aging the Link State Database....................... 66
8.3.1 Premature Aging of Advertisements............. 66
9. Calculating the Best Paths.............................. 67
10. Protocol Packets........................................ 67
Kane Informational [Page 2]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
10.1 ISMP Packet Format................................. 68
10.1.1 Frame Header................................ 69
10.1.2 ISMP Packet Header.......................... 70
10.1.3 ISMP Message Body........................... 71
10.2 VLSP Packet Processing............................. 71
10.3 Network Layer Address Information.................. 72
10.4 VLSP Packet Header................................. 73
10.5 Options Field...................................... 75
10.6 Packet Formats..................................... 76
10.6.1 Hello Packets............................... 76
10.6.2 Database Description Packets................ 78
10.6.3 Link State Request Packets.................. 80
10.6.4 Link State Update Packets................... 82
10.6.5 Link State Acknowledgment Packets........... 83
11. Link State Advertisement Formats........................ 84
11.1 Link State Advertisement Headers................... 84
11.2 Switch Link Advertisements......................... 86
11.3 Network Link Advertisements........................ 89
12. Protocol Parameters..................................... 89
12.1 Architectural Constants............................ 90
12.2 Configurable Parameters............................ 91
13. End Notes............................................... 93
14. Security Considerations................................. 94
15. References.............................................. 94
16. Author's Address........................................ 94
17. Full Copyright Statement................................ 95
1.
This memo is being distributed to members of the Internet
in order to solicit reactions to the proposals contained herein
While the specification discussed here may not be directly
to the research problems of the Internet, it may be of interest
researchers and implementers
1.1
VLSP is derived from the OSPF link-state routing protocol
in [RFC2328], written by John Moy, formerly of Proteon, Inc.,
Westborough, Massachusetts. Much of the current memo has been
from [RFC2328]. Therefore, this author wishes to acknowledge
contribution Mr. Moy has (unknowingly) made to this document
1.2 Data
The methods used in this memo to describe and picture data adhere
the standards of Internet Protocol documentation [RFC1700].
particular
Kane Informational [Page 3]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
The convention in the documentation of Internet Protocols is
express numbers in decimal and to picture data in "big-endian
order. That is, fields are described left to right, with the
significant octet on the left and the least significant octet
the right. The order of transmission of the header and
described in this document is resolved to the octet level
Whenever a diagram shows a group of octets, the order
transmission of those octets is the normal order in which they
read in English
Whenever an octet represents a numeric quantity the left most
in the diagram is the high order or most significant bit.
is, the bit labeled 0 is the most significant bit
Similarly, whenever a multi-octet field represents a
quantity the left most bit of the whole field is the
significant bit. When a multi-octet quantity is transmitted
most significant octet is transmitted first
1.3 ISMP
The InterSwitch Message Protocol (ISMP) provides a consistent
of encapsulating and transmitting control messages exchanged
switches running Cabletron's SecureFast VLAN (SFVLAN) product,
described in [IDsfvlan]. ISMP provides the following services
o Topology services. Each switch maintains a distributed
of the switch fabric by exchanging the following
control messages with other switches
o Interswitch Keepalive messages are sent by each switch to
its existence to its neighboring switches and to establish
topology of the switch fabric. (Interswitch Keepalive
are exchanged in accordance with Cabletron's VlanHello protocol
described in [IDhello].)
o Interswitch Spanning Tree BPDU messages and Interswitch
Blocking messages are used to determine and maintain a loop-
flood path between all network switches in the fabric. This
path is used for all undirected interswitch messages -- that is
messages that are (potentially) sent to all switches in the
fabric
o Interswitch Link State messages (VLS protocol) are used
determine and maintain a fully connected mesh topology graph
the switch fabric. Call-originating switches use the
graph to determine the path over which to route a call connection
Kane Informational [Page 4]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
o Address resolution services. Interswitch Resolve messages
used to resolve a packet destination address when the
source and destination pair does not match a known connection
Interswitch New User messages are used to provide end-
address mobility between switches
o Tag-based flooding. A tag-based broadcast method is used
restrict the broadcast of unresolved packets to only those
within the fabric that belong to the same VLAN as the source
o Call tapping services. Interswitch Tap messages are used
monitor traffic moving between two end stations. Traffic can
monitored in one or both directions along the connection path
Note: Previous versions of VLSP treated all links as if they
broadcast (multi-access). Thus, if VLSP determines that a
switch is running an older version of the protocol software (
Section 6.1), it will change the interface type to broadcast
begin exchanging Hello packets with the single neighbor switch
2. VLS Protocol
VLSP is a dynamic routing protocol. It quickly detects
changes in the switch fabric (such as, switch interface failures)
calculates new loop-free routes after a period of convergence.
period of convergence is short and involves a minimum of
traffic
All switches in the fabric run the same algorithm and
identical databases describing the switch fabric topology.
database contains each switch's local state, including its
interfaces and reachable neighbors. Each switch distributes
local state throughout the switch fabric by flooding. From
topological database, each switch constructs a set of best path
(using itself as the root) that specify routes to all other
in the fabric
Kane Informational [Page 5]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
2.1 Definitions of Commonly Used
This section contains a collection of definitions for terms that
a specific meaning to the protocol and that are used throughout
text
Switch
A 10-octet value that uniquely identifies the switch within
switch fabric. The value consists of the 6-octet base MAC
of the switch, followed by 4 octets of zeroes
Network
The physical connection between two switches. A link
associated with a switch interface
There are two physical types of network links supported by VLSP
o Point-to-point links that join a single pair of switches.
serial line is an example of a point-to-point network link
o Multi-access broadcast links that support the attachment
multiple switches, along with the capability to address
single message to all the attached switches. An
ethernet is an example of a multi-access broadcast
link
A single topology can contain both types of links. At startup
all links are assumed to be point-to-point. A link
determined to be multi-access when more than one
switch is discovered on the link
The port over which a switch accesses one of its links
Interfaces are identified by their interface ID, a 10-octet
consisting of the 6-octet base MAC address of the switch,
by the 4-octet local port number of the interface
Neighboring
Two switches attached to a common link
Kane Informational [Page 6]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
A relationship formed between selected neighboring switches
the purpose of exchanging routing information. Not every pair
neighboring switches become adjacent
Link state
Describes the local state of a switch or a link. Each link
advertisement is flooded throughout the switch fabric.
collected link state advertisements of all switches and links
the protocol's topological database
Designated
Each multi-access network link has a designated switch.
designated switch generates a link state advertisement for
link and has other special responsibilities in the running of
protocol
The use of a designated switch permits a reduction in the
of adjacencies required on multi-access links. This in
reduces the amount of routing protocol traffic and the size of
topological database
The designated switch is selected during the discovery process.
designated switch is not selected for a point-to-point
link
Backup designated
Each multi-access network link has a backup designated switch
The backup designated switch maintains adjacencies with the
switches on the link as the designated switch. This optimizes
failover time when the backup designated switch must take over
the (failed) designated switch
The backup designated switch is selected during the
process. A backup designated switch is not selected for a point
to-point network link
2.2 Differences Between VLSP and
The VLS protocol is derived from the OSPF link-state routing
described in [RFC2328].
Kane Informational [Page 7]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
2.2.1 Operation at the Physical
The primary differences between the VLS and OSPF protocols stem
the fact that OSPF runs over the IP layer, while VLSP runs at
physical MAC layer. This difference has the following repercussions
o VLSP does not support features (such as fragmentation) that
typically provided by network layer service providers
o Due to the unrelated nature of MAC address assignments,
provides no summarization of the address space (such as,
IP subnet information) or level 2 routing (such as
IS-IS Phase V DECnet). Thus, VLSP does not support
switches into areas. All switches exist in a single area.
a single domain exists within any switch fabric, there is no
for VLSP to provide interdomain reachability
o As mentioned in Section 10.1.1, ISMP uses a single well-
multicast address for all packets. However, parts of the
protocol (as derived from OSPF) are dependent on certain
layer addresses -- in particular, the AllSPFSwitches
AllDSwitches multicast addresses that drive the distribution
link state advertisements throughout the switch fabric. In
to facilitate the implementation of the protocol at the
MAC layer, network layer address information is encapsulated
the protocol packets (see Section 10.3). This information
unbundled and packets are then processed as if they had been
or received on that multicast address
2.2.2 All Links Treated as Point-to-
When the switch first comes on line, VLSP assumes all network
are point-to-point and no more than one neighboring switch will
discovered on any one port. Therefore, at startup, VLSP does
send its own Hello packets over its network ports, but instead
relies on the VlanHello protocol [IDhello] for the discovery of
neighbor switches. If a second neighbor is detected on a link,
link is then deemed multi-access and the interface type is changed
broadcast. At that point, VLSP exchanges its own Hello packets
the switches on the link in order to select a designated switch
designated backup switch for the link
This method eliminates unnecessary duplication of message traffic
processing, thereby increasing the overall efficiency of the
fabric
Kane Informational [Page 8]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
Note: Previous versions of VLSP treated all links as if they
broadcast (multi-access). Thus, if VLSP determines that a
switch is running an older version of the protocol software (
Section 6.1), it will change the interface type to broadcast
begin exchanging Hello packets with the single neighbor switch
2.2.3 Routing Path
Instead of providing the next hop to a destination, VLSP
and maintains complete end-to-end path information. On request,
list of individual port identifiers is generated describing
complete path from the source switch to the destination switch.
multiple equal-cost routes exist to a destination switch, up to
paths are calculated and returned
2.2.4 Configurable
OSPF supports (and requires) configurable parameters. In fact,
the default OSPF configuration requires that IP address
be specified. On the other hand, no configuration information
ever required for the VLS protocol. Switches are uniquely
by their base MAC addresses and ports are uniquely identified by
base MAC address of the switch and a port number
While a developer is free to implement configurable parameters
the VLS protocol, the current version of VLSP supports
path metrics only. Note that this has the following repercussions
o All switches are assigned a switch priority of 1. This forces
selection of the designated switch to be based solely on base
address
o Authentication is not supported
2.2.5 Features Not
In addition to those features mentioned in the previous sections,
following OSPF features are not supported by the current version
VLSP
o Periodic refresh of link state advertisements. (This
performance by eliminating unnecessary traffic between
switches.)
o Routing based on non-zero type of service (TOS).
o Use of external routing information for destinations outside
switch fabric
Kane Informational [Page 9]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
2.3 Functional
There are essentially four operational stages of the VLS protocol
o Discovery Process The discovery process involves two steps
o Neighboring switches are detected by the VlanHello
[IDhello] which then notifies VLSP of the neighbor
o If more than one neighbor switch is detected on a single port
the link is determined to be multi-access. VLSP then sends
own Hello packets over the link in order to discover the
set of neighbors on the link and select a designated switch
designated backup switch for the link. Note that
selection process is unnecessary on point-to-point links
The discovery process is described in more detail in Section 6.
o Synchronizing the
Adjacencies are used to simplify and speed up the process
synchronizing the topological database (also known as the
state database) maintained by each switch in the fabric.
switch is only required to synchronize its database with
neighbors to which it is adjacent. This reduces the amount
routing protocol traffic across the fabric, particularly
multi-access links with multiple switches
The process of synchronizing the databases is described in
detail in Section 7.
o Maintaining the
Each switch advertises its state (also known as its link state
any time its link state changes. Link state advertisements
distributed throughout the switch fabric using a reliable
algorithm that ensures that all switches in the fabric
notified of any link state changes
The process of maintaining the databases is described in
detail in Section 8.
Kane Informational [Page 10]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
o Calculating the Best
The link state database consists of the collection of link
advertisements received from each switch. Each switch uses
link state database to calculate a set of best paths, using
as root, to all other switches in the fabric
The process of recalculating the set of best paths is described
more detail in Section 9.
2.4 Protocol
In addition to the frame header and the ISMP packet header
in Section 10.1, all VLS protocol packets share a common
header, described in Section 10.4.
The VLSP packet types are listed below in Table 1. Their formats
described in Section 10.6.
Type Packet Name Protocol
1 Hello Select DS and Backup
2 Database Description Summarize database
3 Link State Request Database
4 Link State Update Database
5 Link State Ack Flooding
Table 1: VLSP Packet
The Hello packets are used to select the designated switch and
backup designated switch on multi-access links. The
Description and Link State Request packets are used to
adjacencies. Link State Update and Link State Acknowledgment
are used to update the topological database
Each Link State Update packet carries a set of link
advertisements. A single Link State Update packet may contain
link state advertisements of several switches. There are
different types of link state advertisement, as shown below in
2.
Kane Informational [Page 11]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
LS Advertisement Advertisement
Type
1 Switch link Originated by all switches.
advertisements advertisement describes the
states of the switch's interfaces
2 Network link Originated by the designated switch
advertisements This advertisement contains the
of switches connected to the
link
Table 2: VLSP Link State
2.5 Protocol Data
The VLS protocol is described in this specification in terms of
operation on various protocol data structures. Table 3 lists
primary VLSP data structures, along with the section in which
are described in detail
Structure Name
Interface Data Structure Section 3
Neighbor Data Structure Section 4
Area Data Structure Section 5
Table 3: VLSP Data
2.6 Basic Implementation
An implementation of the VLS protocol requires the following
of system support
Two types of timer are required. The first type, known as a one
shot timer, expires once and triggers an event. The second type
known as an interval timer, expires at preset intervals.
timers are used to trigger events at periodic intervals.
granularity of both types of timers is one second
Interval timers should be implemented in such a way as to
drift. In some switch implementations, packet processing
affect timer execution. For example, on a multi-access link
multiple switches, regular broadcasts can lead to
synchronization of routing packets unless the interval timers
been implemented to avoid drift. If it is not possible
Kane Informational [Page 12]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
implement drift-free timers, small random amounts of time
be added to or subtracted from the timer interval at each firing
List manipulation
Much of the functionality of VLSP is described here in terms
its operation on lists of link state advertisements.
particular advertisement may be on many such lists.
of VLSP must be able to manipulate these lists, adding
deleting constituent advertisements as necessary
Tasking
Certain procedures described in this specification invoke
procedures. At times, these other procedures should be
in-line -- that is, before the current procedure has finished
This is indicated in the text by instructions to "execute"
procedure. At other times, the other procedures are to
executed only when the current procedure has finished. This
indicated by instructions to "schedule" a task. Implementation
VLSP must provide these two types of tasking support
2.7 Organization of the Remainder of This
The remainder of this document is organized as follows
o Section 3 through Section 5 describe the primary data
used by the protocol. Note that this specification is
in terms of these data structures in order to make
more precise. Implementations of the protocol must support
functionality described, but need not use the exact
structures that appear in this specification
o Section 6 through Section 9 describe the four operational
of the protocol: the discovery process, synchronizing
databases, maintaining the databases, and calculating the set
best paths
o Section 10 describes the processing of VLSP packets and
detailed descriptions of their formats
o Section 11 presents detailed descriptions of link
advertisements
o Section 12 summarizes the protocol parameters
Kane Informational [Page 13]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
3. Interface Data
The port over which a switch accesses a network link is known as
link interface. Each switch maintains a separate interface
structure for each network link
The following data items are associated with each interface
The type of network to which the interface is attached -- point
to-point or broadcast (multi-access). This data item
initialized to point-to-point when the interface
operational. If a second neighbor is detected on the link
the first neighbor has been discovered, the link interface type
changed to broadcast. The type remains as broadcast until
interface is declared down, at which time the type reverts
point-to-point
Note: Previous versions of VLSP treated all links as if they
multi-access. Thus, if VLSP determines that a neighbor switch
running an older version of the protocol software (see Section 6.1),
it will change the interface type to broadcast
The functional level of the interface. The state of the
is included in all switch link advertisements generated by
switch, and is also used to determine whether full adjacencies
allowed on the interface. See Section 3.1 for a
description of interface states
Interface
A 10-octet value that uniquely identifies the interface.
value consists of the 6-octet base MAC address of the
switch, followed by the 4-octet local port number of
interface
Area
A 4-octet value identifying the area. Since VLSP does not
multiple areas, the value here is always zero
Kane Informational [Page 14]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
The interval, in seconds, at which the switch sends VLSP
packets over the interface. This parameter is not used on point
to-point links
The length of time, in seconds, that neighboring switches
wait before declaring the local switch dNeighboring
A list of the neighboring switches attached to this network link
This list is created during the discovery process. Adjacencies
formed to one or more of these neighbors. The set of
neighbors can be determined by examining the states of
neighboring switches as shown in their link state advertisements
Designated
The designated switch selected for the multi-access network link
(A designated switch is not selected for a point-to-point link.)
This data item is initialized to zero when the switch comes on
line, indicating that no designated switch has been chosen for
link
Backup designated
The backup designated switch selected for the multi-access
link. (A backup designated switch is not selected for a point
to-point link.) This data item is initialized to zero when
switch comes on-line, indicating that no backup designated
has been chosen for the link
Interface output cost(s
The cost of sending a packet over the interface. The link cost
expressed in the link state metric and must be greater than zero
The number of seconds between link state
retransmissions, for adjacencies belonging to this interface.
value is also used to time the retransmission of
Description and Link State Request packets
Kane Informational [Page 15]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
3.1 Interface
This section describes the various states of a switch interface.
states are listed in order of progressing functionality. For example
the inoperative state is listed first, followed by a list of
intermediate states through which the interface passes
attaining the final, fully functional state. The specification
use of this ordering by references such as "those interfaces in
greater than X".
Figure 1 represents the interface state machine, showing
progression of interface state changes. The arrows on the
represent the events causing each state change. These events
described in Section 3.2. The interface state machine is
in detail in Section 3.3.
This is the initial state of the interface. In this state,
interface is unusable, and no protocol traffic is sent or
on the interface. In this state, interface parameters are set
their initial values, all interface timers are disabled, and
adjacencies are associated with the interface
Kane Informational [Page 16]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
+-------+
| any | Interface +----------+ Unloop Ind +----------+
| state | -----------> | Down | <----------- | Loopback |
+-------+ Down +----------+ +----------+
| ^
| Interface Up |
+-------+ [pt-to-pt] | |
| Point |<------------type? Loop Ind |
| to | | |
| Point | | [broadcast] |
+-------+ V +-------+
+-----------+ | any |
| Waiting | | state |
+-----------+ +-------+
|
Backup Seen |
| Wait
|
|
+----------+ Neighbor V Neighbor +----------+
| DS | <------------> [ ] <------------> | DS Other |
+----------+ Change ^ Change +----------+
|
|
Neighbor Change |
|
+----------+
| Backup |
+----------+
Figure 1: Interface State
In this state, the switch interface is looped back, either
hardware or in software. The interface is unavailable for
data traffic
Point-to-
In this state, the interface is operational and is connected to
physical point-to-point link. On entering this state, the
attempts to form an adjacency with the neighboring switch
Kane Informational [Page 17]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
In this state, the switch is attempting to identify the
designated switch for the link by monitoring the Hello packets
receives. The switch does not attempt to select a
switch or a backup designated switch until it changes out of
state, thereby preventing unnecessary changes of the
switch and its backup
DS
In this state, the interface is operational and is connected to
multi-access broadcast link on which other switches have
selected as the designated switch and the backup
switch. On entering this state, the switch attempts to
adjacencies with both the designated switch and the
designated switch
In this state, the switch itself is the backup designated
on the attached multi-access broadcast link. It will be
to designated switch if the current designated switch fails.
switch establishes adjacencies with all other switches attached
the link. (See Section 6.3 for more information on the
performed by the backup designated switch.)
In this state, this switch itself is the designated switch on
attached multi-access broadcast link. The switch
adjacencies with all other switches attached to the link.
switch is responsible for originating network link
for the link, containing link information for all
attached to the link, including the designated switch itself
(See Section 6.3 for more information on the functions
by the designated switch.)
3.2 Events Causing Interface State
The state of an interface changes due to an interface event.
section describes these events
Interface events are shown as arrows in Figure 1, the
representation of the interface state machine. For more
on the interface state machine, see Section 3.3.
Kane Informational [Page 18]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
Interface
This event is generated by the VlanHello protocol [IDhello]
it discovers a neighbor switch on the interface. The interface
now operational. This event causes the interface to change out
the Down state. The state it enters is determined by
interface type. If the interface type is broadcast (multi
access), this event also causes the switch to begin
periodic Hello packets out over the interface
Wait
This event is generated when the one-shot Wait timer expires
triggering the end of the required waiting period before
switch can begin the process of selecting a designated switch
a backup designated switch on a multi-access link
Backup
This event is generated when the switch has detected the
or non-existence of a backup designated switch for the link,
determined in one of the following two ways
o A Hello packet has been received from a neighbor that claims
be the backup designated switch
o A Hello packet has been received from a neighbor that claims
be the designated switch. In addition, the packet
that there is no backup
In either case, the interface must have bidirectional
with its neighbor -- that is, the local switch must be listed in
neighbor's Hello packet
This event signals the end of the Waiting state
Neighbor
This event is generated when there has been one of the
changes in the set of bidirectional neighbors associated with
interface. (See Section 4.1 for information on neighbor states.)
o Bidirectional communication has been established with
neighbor -- the state of the neighbor has changed to 2-Way
higher
o Bidirectional communication with a neighbor has been lost --
the state of the neighbor has changed to Init or lower
Kane Informational [Page 19]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
o A bidirectional neighbor has just declared itself to be
the designated switch or the backup designated switch,
detected by examination of that neighbor's Hello packets
o A bidirectional neighbor is no longer declaring itself to
either the designated switch or the backup designated switch
as detected by examination of that neighbor's Hello packets
o The advertised switch priority of a bidirectional neighbor
changed, as detected by examination of that neighbor's
packets
When this event occurs, the designated switch and the
designated switch must be reselected
Loop
This event is generated when an interface enters the
state. This event can be generated by either the
management service or by the lower-level protocols
Unloop
This event is generated when an interface leaves the
state. This event can be generated by either the
management service or by the lower-level protocols
Interface
This event is generated under the following two circumstances
o The VlanHello [IDhello] protocol has determined that
interface is no longer functional
o The neighbor state machine has detected a second
switch on a link presumed to be of type point-to-point.
addition to generating the Interface Down event,
neighbor state machine changes the interface type
broadcast
In both instances, this event forces the interface state to Down
However, when the event is generated by the neighbor
machine, it is immediately followed by an Interface Up event
(See Section 4.3.)
Kane Informational [Page 20]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
3.3 Interface State
This section presents a detailed description of the interface
machine
Interface states (see Section 3.1) change as the result of
events (see Section 3.2). However, the effect of each event
vary, depending on the current state of the interface. For
reason, the state machine described in this section is
according to the current interface state and the occurring event
For each state/event pair, the new interface state is listed,
with a description of the required processing
Note that when the state of an interface changes, it may be
to originate a new switch link advertisement. See Section 8.1
more information
Some of the processing described here includes generating events
the neighbor state machine. For example, when an interface
inoperative, all neighbor connections associated with the
must be destroyed. For more information on the neighbor
machine, see Section 4.3.
State(s):
Event: Interface
New state: Depends on action
Action
If the interface is a point-to-point link, set the interface
to Point-to-Point. Otherwise, start the Hello interval timer
enabling the periodic sending of Hello packets over the interface
If the switch is not eligible to become the designated switch
change the interface state to DS Other. Otherwise, set
interface state to Waiting and start the one-shot wait timer
Create a new neighbor data structure for the neighbor switch
initialize all neighbor parameters and set the stateof
neighbor to Down
State(s):
Event: Backup
New state: Depends on action
Action
Select the designated switch and backup designated switch for
attached link, as described in Section 6.3.1. As a result of
selection, set the new state of the interface to either DS Other
Backup or DS
Kane Informational [Page 21]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
State(s):
Event: Wait
New state: Depends on action
Action
Select the designated switch and backup designated switch for
attached link, as described in Section 6.3.1. As a result of
selection, set the new state of the interface to either DS Other
Backup or DS
State(s): DS Other, Backup or
Event: Neighbor
New state: Depends on action
Action
Reselect the designated switch and backup designated switch
the attached link, as described in Section 6.3.1. As a result
this selection, set the new state of the interface to either
Other, Backup or DS
State(s): Any
Event: Interface
New state:
Action
Reset all variables in the interface data structure and
all timers. In addition, destroy all neighbor
associated with the interface by generating the KillNbr event
all neighbors listed in the interface data structure
State(s): Any
Event: Loop
New state:
Action
Reset all variables in the interface data structure and
all timers. In addition, destroy all neighbor
associated with the interface by generating the KillNbr event
all neighbors listed in the interface data structure
State(s):
Event: Unloop
New state:
Action
No action is necessary beyond changing the interface state to
because the interface was reset on entering the Loopback state
Kane Informational [Page 22]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
4. Neighbor Data
Each switch conducts a conversation with its neighboring switches
each conversation is described by a neighbor data structure.
conversation is associated with a switch interface, and is
by the neighboring switch ID
Note that if two switches have multiple attached links in common
multiple conversations ensue, each described by a unique
data structure. Each separate conversation is treated as a
neighbor
The neighbor data structure contains all information relevant to
adjacency formed between the two neighbors. Remember, however,
not all neighbors become adjacent. An adjacency can be thought of
a highly developed conversation between two switches
The functional level of the neighbor conversation. See
4.1 for a complete description of neighbor states
Inactivity
A one-shot timer used to determine when to declare the
down if no Hello packet is received from this (multi-access
neighbor. The length of the timer is SwitchDeadInterval seconds
as contained in the neighbor's Hello packet. This timer is
used on point-to-point links
Master/slave
A flag indicating whether the local switch is to act as the
or the slave in the database exchange process (see Section 7.2).
The master/slave relationship is negotiated when the
changes to the ExStart state
Sequence
A 4-octet number identifying individual Database
packets. When the neighbor state ExStart is entered and
database exchange process is started, the sequence number is
to a value not previously seen by the neighboring switch. (
possible scheme is to use the switch's time of day counter.)
sequence number is then incremented by the master with each
Database Description packet sent. See Section 7.2 for
information on the database exchange process
Kane Informational [Page 23]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
Neighbor
The switch ID of the neighboring switch, as discovered by
VlanHello protocol [IDhello] or contained in the neighbor's
packets
Neighbor
The switch priority of the neighboring switch, as contained in
neighbor's Hello packets. Switch priorities are used
selecting the designated switch for the attached multi-
link. Priority is not used on point-to-point links
Interface
A 10-octet value that uniquely identifies the interface over
this conversation is being held. This value consists of the 6-
octet base MAC address of the neighbor switch, followed by the 4-
octet local port number of the interface
Neighbor's designated
The switch ID identifying the neighbor's idea of the
switch, as contained in the neighbor's Hello packets. This
is used in the local selection of the designated switch. It
not used on point-to-point links
Neighbor's backup designated
The switch ID identifying the neighbor's idea of the
designated switch, as contained in the neighbor's Hello packets
This value is used in the local selection of the backup
switch. It is not used on point-to-point links
Link state retransmission
The list of link state advertisements that have been
over but not acknowledged on this adjacency. The local
retransmits these link state advertisements at periodic
until they are acknowledged or until the adjacency is destroyed
(For more information on retransmitting link state advertisements
see Section 8.2.5.)
Kane Informational [Page 24]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
Database summary
The set of link state advertisement headers that summarize
local link state database. When the conversation changes to
Exchange state, this list is sent to the neighbor via
Description packets. (For more information on the
of databases, see Section 7.)
Link state request
The list of link state advertisements that must be received
order to synchronize with the neighbor switch's link
database. This list is created as Database Description
are received, and is then sent to the neighbor in Link
Request packets. (For more information on the synchronization
databases, see Section 7.)
4.1 Neighbor
This section describes the various states of a conversation with
neighbor switch. The states are listed in order of
functionality. For example, the inoperative state is listed first
followed by a list of the intermediate states through which
conversation passes before attaining the final, fully
state. The specification makes use of this ordering by
such as "those neighbors/adjacencies in state greater than X".
Figure 2 represents the neighbor state machine. The arrows on
graph represent the events causing each state change. These
are described in Section 4.2. The neighbor state machine
described in detail in Section 4.3.
This is the initial state of a neighbor conversation
In this state, the neighbor has been discovered, but
communication has not yet been established. All neighbors in
state or higher are listed in the VLS Hello packets sent by
local switch over the associated (multi-access) interface
Kane Informational [Page 25]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
+----------+ KillNbr, LLDown, +-----------+
| Down | <--------------------- | any state |
+----------+ or Inactivity Timer +-----------+
|
Hello |
Rcvd |
|
+-----< [pt-to-pt?]
| yes |
| |
|
| +----------+ 1-Way +----------+
| | Init | <-------- | >= 2-way |
| +----------+ +----------+
| |
| 2-Way |
| Rcvd | +-------+ AdjOK? +------------+
| +----------------> | 2-Way | <------- | >= ExStart |
| | (no adjacency) +-------+ no +------------+
| |
|
| +---------+ Seq Number Mismatch +-------------+
+----> | ExStart | <--------------------- | >= Exchange |
+---------+ or BadLSReq +-------------+
|
Negotiation |
Done |
+----------+
| Exchange |
+----------+
|
Exchange | +--------+
Done +----------------------> | Full |
| (request list empty) +--------+
| ^
V |
+---------+ Loading Done |
| Loading | ----------------------->
+---------+
Figure 2: Neighbor State
Kane Informational [Page 26]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
2-
In this state, communication between the two switches
bidirectional. This is the most advanced state short of
to establish an adjacency. On a multi-access link, the
switch and the backup designated switch are selected from the
of neighbors in state 2-Way or greater
This state indicates that the two switches have begun to
an adjacency by determining which switch is the master, as well
the initial sequence number for Database Descriptor packets
Neighbor conversations in this state or greater are
adjacencies
In this state, the switches are exchanging Database
packets. (See Section 7.2 for a complete description of
process.) All adjacencies in the Exchange state or greater
used by the distribution procedure (see Section 8.2), and
capable of transmitting and receiving all types of VLSP
packets
In this state, the local switch is sending Link State
packets to the neighbor asking for the more recent
that were discovered in the Exchange state
In this state, the two switches are fully adjacent.
adjacencies will now appear in switch link and network
advertisements generated for the link
4.2 Events Causing Neighbor State
The state of a neighbor conversation changes due to neighbor events
This section describes these events
Neighbor events are shown as arrows in Figure 2, the
representation of the neighbor state machine. For more
on the neighbor state machine, see Section 4.3.
Kane Informational [Page 27]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
Hello
This event is generated when a Hello packet has been received
a neighbor
2-Way
This event is generated when the local switch sees its own
ID listed in the neighbor's Hello packet, indicating
bidirectional communication has been established between the
switches
Negotiation
This event is generated when the master/slave relationship
been successfully negotiated and initial packet sequence
have been exchanged. This event signals the start of the
exchange process (see Section 7.2).
Exchange
This event is generated when the database exchange process
complete and both switches have successfully transmitted a
sequence of Database Description packets. (For more
on the database exchange process, see Section 7.2.)
This event is generated when a Link State Request has
received for a link state advertisement that is not contained
the database. This event indicates an error in
synchronization process
Loading
This event is generated when all Link State Updates have
received for all out-of-date portions of the database. (
Section 7.3.)
AdjOK
This event is generated when a decision must be made as to
an adjacency will be established or maintained with the neighbor
This event will initiate some adjacencies and destroy others
Kane Informational [Page 28]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
Seq Number
This event is generated when a Database Description packet
been received with any of the following conditions
o The packet contains an unexpected sequence number
o The packet (unexpectedly) has the Init bit set
o The packet has a different Options field than
previously seen
These conditions all indicate that an error has occurred
the establishment of the adjacency
1-
This event is generated when bidirectional communication with
neighbor has been lost. That is, a Hello packet has been
from the neighbor in which the local switch is not listed
This event is generated when further communication with
neighbor is impossible
Inactivity
This event is generated when the inactivity timer has expired
indicating that no Hello packets have been received from
neighbor in SwitchDeadInterval seconds. This timer is used
on broadcast (multi-access) links
This event is generated by the lower-level switch
protocols and indicates that the neighbor is now unreachable
4.3 Neighbor State
This section presents a detailed description of the neighbor
machine
Neighbor states (see Section 4.1) change as the result of
events (see Section 4.2). However, the effect of each event
vary, depending on the current state of the conversation with
neighbor. For this reason, the state machine described in
section is organized according to the current neighbor state and
occurring event. For each state/event pair, the new neighbor
is listed, along with a description of the required processing
Kane Informational [Page 29]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
Note that when the neighbor state changes as a result of an
Neighbor Change event (see Section 3.2), it may be necessary to
the designated switch selection algorithm. In addition, if
interface associated with the neighbor conversation is in the
state (that is, the local switch is the designated switch),
in the neighbor state may cause a new network link advertisement
be originated (see Section 8.1).
When the neighbor state machine must invoke the interface
machine, it is invoked as a scheduled task. This
processing, by ensuring that neither state machine
recursively
State(s):
Event: Hello
New state: Depends on the interface
Action
If the interface type of the associated link is point-to-point
change the neighbor state to ExStart. Otherwise, change
neighbor state to Init and start the inactivity timer for
neighbor. If the timer expires before another Hello packet
received, the neighbor switch is declared dead
State(s): Init or
Event: Hello
New state: No state
Action
If the interface type of the associated link is point-to-point
determine whether this notification is for a different
than the one previously seen. If so, generate an 