📄 rfc2642.txt
字号:
Much of the functionality of VLSP is described here in terms of
its operation on lists of link state advertisements. Any
particular advertisement may be on many such lists. Implementation
of VLSP must be able to manipulate these lists, adding and
deleting constituent advertisements as necessary.
Tasking support
Certain procedures described in this specification invoke other
procedures. At times, these other procedures should be executed
in-line -- that is, before the current procedure has finished.
This is indicated in the text by instructions to "execute" a
procedure. At other times, the other procedures are to be
executed only when the current procedure has finished. This is
indicated by instructions to "schedule" a task. Implementation of
VLSP must provide these two types of tasking support.
2.7 Organization of the Remainder of This Document
The remainder of this document is organized as follows:
o Section 3 through Section 5 describe the primary data structures
used by the protocol. Note that this specification is presented
in terms of these data structures in order to make explanations
more precise. Implementations of the protocol must support the
functionality described, but need not use the exact data
structures that appear in this specification.
o Section 6 through Section 9 describe the four operational stages
of the protocol: the discovery process, synchronizing the
databases, maintaining the databases, and calculating the set of
best paths.
o Section 10 describes the processing of VLSP packets and presents
detailed descriptions of their formats.
o Section 11 presents detailed descriptions of link state
advertisements.
o Section 12 summarizes the protocol parameters.
Kane Informational [Page 13]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
3. Interface Data Structure
The port over which a switch accesses a network link is known as the
link interface. Each switch maintains a separate interface data
structure for each network link.
The following data items are associated with each interface:
Type
The type of network to which the interface is attached -- point-
to-point or broadcast (multi-access). This data item is
initialized to point-to-point when the interface becomes
operational. If a second neighbor is detected on the link after
the first neighbor has been discovered, the link interface type is
changed to broadcast. The type remains as broadcast until the
interface is declared down, at which time the type reverts to
point-to-point.
Note: Previous versions of VLSP treated all links as if they were
multi-access. Thus, if VLSP determines that a neighbor switch is
running an older version of the protocol software (see Section 6.1),
it will change the interface type to broadcast.
State
The functional level of the interface. The state of the interface
is included in all switch link advertisements generated by the
switch, and is also used to determine whether full adjacencies are
allowed on the interface. See Section 3.1 for a complete
description of interface states.
Interface identifier
A 10-octet value that uniquely identifies the interface. 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.
Area ID
A 4-octet value identifying the area. Since VLSP does not support
multiple areas, the value here is always zero.
Kane Informational [Page 14]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
HelloInterval
The interval, in seconds, at which the switch sends VLSP Hello
packets over the interface. This parameter is not used on point-
to-point links.
SwitchDeadInterval
The length of time, in seconds, that neighboring switches will
wait before declaring the local switch dNeighboring switches
A list of the neighboring switches attached to this network link.
This list is created during the discovery process. Adjacencies are
formed to one or more of these neighbors. The set of adjacent
neighbors can be determined by examining the states of the
neighboring switches as shown in their link state advertisements.
Designated switch
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 the
link.
Backup designated switch
The backup designated switch selected for the multi-access network
link. (A backup 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 backup designated switch
has been chosen for the link.
Interface output cost(s)
The cost of sending a packet over the interface. The link cost is
expressed in the link state metric and must be greater than zero.
RxmtInterval
The number of seconds between link state advertisement
retransmissions, for adjacencies belonging to this interface. This
value is also used to time the retransmission of Database
Description and Link State Request packets.
Kane Informational [Page 15]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
3.1 Interface States
This section describes the various states of a switch interface. The
states are listed in order of progressing functionality. For example,
the inoperative state is listed first, followed by a list of the
intermediate states through which the interface passes before
attaining the final, fully functional state. The specification makes
use of this ordering by references such as "those interfaces in state
greater than X".
Figure 1 represents the interface state machine, showing the
progression of interface state changes. The arrows on the graph
represent the events causing each state change. These events are
described in Section 3.2. The interface state machine is described
in detail in Section 3.3.
Down
This is the initial state of the interface. In this state, the
interface is unusable, and no protocol traffic is sent or received
on the interface. In this state, interface parameters are set to
their initial values, all interface timers are disabled, and no
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 Timer
|
|
+----------+ Neighbor V Neighbor +----------+
| DS | <------------> [ ] <------------> | DS Other |
+----------+ Change ^ Change +----------+
|
|
Neighbor Change |
|
V
+----------+
| Backup |
+----------+
Figure 1: Interface State Machine
Loopback
In this state, the switch interface is looped back, either in
hardware or in software. The interface is unavailable for regular
data traffic.
Point-to-Point
In this state, the interface is operational and is connected to a
physical point-to-point link. On entering this state, the switch
attempts to form an adjacency with the neighboring switch.
Kane Informational [Page 17]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
Waiting
In this state, the switch is attempting to identify the backup
designated switch for the link by monitoring the Hello packets it
receives. The switch does not attempt to select a designated
switch or a backup designated switch until it changes out of this
state, thereby preventing unnecessary changes of the designated
switch and its backup.
DS Other
In this state, the interface is operational and is connected to a
multi-access broadcast link on which other switches have been
selected as the designated switch and the backup designated
switch. On entering this state, the switch attempts to form
adjacencies with both the designated switch and the backup
designated switch.
Backup
In this state, the switch itself is the backup designated switch
on the attached multi-access broadcast link. It will be promoted
to designated switch if the current designated switch fails. The
switch establishes adjacencies with all other switches attached to
the link. (See Section 6.3 for more information on the functions
performed by the backup designated switch.)
DS
In this state, this switch itself is the designated switch on the
attached multi-access broadcast link. The switch establishes
adjacencies with all other switches attached to the link. The
switch is responsible for originating network link advertisements
for the link, containing link information for all switches
attached to the link, including the designated switch itself.
(See Section 6.3 for more information on the functions performed
by the designated switch.)
3.2 Events Causing Interface State Changes
The state of an interface changes due to an interface event. This
section describes these events.
Interface events are shown as arrows in Figure 1, the graphic
representation of the interface state machine. For more information
on the interface state machine, see Section 3.3.
Kane Informational [Page 18]
RFC 2642 Cabletron's VLS Protocol Specification August 1999
Interface Up
This event is generated by the VlanHello protocol [IDhello] when
it discovers a neighbor switch on the interface. The interface is
now operational. This event causes the interface to change out of
the Down state. The state it enters is determined by the
interface type. If the interface type is broadcast (multi-
access), this event also causes the switch to begin sending
periodic Hello packets out over the interface.
⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -