IEEE 802.1s: 多生成树协议标准详解

需积分: 5 58 浏览量更新于2024-07-09 收藏 1.75MB PDF 举报

"IEEE 802.1s标准，即多生成树协议（Multiple Spanning Trees，MST），是IEEE 802.1Q虚拟桥接局域网标准的一个重要扩展，旨在解决网络中的环路问题并实现负载均衡。在传统的桥接网络中，生成树协议（Spanning Tree Protocol, STP）被用来消除物理拓扑中的环路，防止广播风暴和帧的无限循环。然而，STP只能提供单一的生成树实例，这限制了网络的灵活性和效率。随着网络规模的扩大和对服务质量（Quality of Service, QoS）需求的提高，单一生成树已无法满足需求。于是，802.1s MST协议应运而生。 802.1s MST协议的核心特性包括： 1. **多实例**：MST允许创建多个独立的生成树实例（MSTI），每个实例可以映射到不同的VLAN，从而实现不同VLAN间的负载均衡。 2. **区域概念**：MST引入了区域（Region）的概念，每个区域有自己的生成树实例配置，这样可以减少STP的开销并提高网络性能。 3. **兼容性**：MST协议保持与传统STP（802.1D）和快速生成树协议（Rapid Spanning Tree Protocol, 802.1w）的兼容性，确保老设备可以顺利工作。 4. **配置和操作**：通过MST配置信息（MST Configuration），网络管理员可以定义VLAN到MSTI的映射，以及每个MSTI的生成树参数，如根桥、路径成本等。 802.1s的应用场景广泛，例如在大型企业网络、数据中心或服务提供商网络中，它可以提供更高效的路径选择、负载均衡和故障恢复能力。通过MST，网络管理员能够更精细地控制数据流，避免单点故障，并提升网络的整体性能。 IEEE 802.1s标准是现代网络设计和管理中不可或缺的一部分，它为复杂网络环境提供了更加灵活和强大的环路消除和流量管理方案。"

IEEE

VIRTUAL BRIDGED LOCAL AREA NETWORKS: AMENDMENT 3 Std 802.1s-2002

SST Single Spanning Tree

ST BPDU Spanning Tree Bridge Protocol Data Unit

STP Spanning Tree Protocol

5. Conformance

5.1 Static conformance requirements

Change list item a) as follows:

a) Conform to the requirements of IEEE Std 802.1D

ISO/IEC 15802-3 andIEEEStd802.1w,asmodi-

fied by the provisions of this standard;

Insert a new list item and sub-items at the end of the numbered list, and a NOTE, as follows, renumbering

the existing NOTE as NOTE 1:

A MAC bridge for which conformance to the provisions of this standard for an MST Bridge is

claimed (5.2, 13) shall:

1) Support the Multiple Spanning Tree Algorithm and Protocol, (MSTP) as specified in Clause 13

and the attendant conformance requirements stated in Clause 5 of IEEE Std 802.1w-2001;

2) Support the CIST plus a stated maximum number of MSTIs, where that number is at least 2

(8.10.7) and at most 64 (13.14);

NOTE 2—In other words, a conformant MST Bridge must support a minimum of three spanning tree instances—the

CIST and at least two additional MSTIs.

3) Support a stated maximum number of FIDs that is at least as large as the number of MSTIs sup-

ported (8.10.7);

4) Support the ability to associate each FID to a spanning tree (8.11.3);

5) Support the transmission and reception of MST Configuration Identifier information (8.11.2).

6) For each Port, be capable of supporting a set of port-state information for each spanning tree

instance supported (8.4.1, 8.4.2, 13.34);

7) For each Port, be capable of supporting an instance of the Spanning Tree Protocol and its asso-

ciated parameters for each spanning tree instance supported (8.12, 13);

8) Use the Bridge Group Address as specified in 8.14.3;

9) Support the default values for Bridge Forward Delay and Bridge Priority parameters specified

in 13.23;

10) Support the operation of GVRP in each supported spanning tree context (11.2.3.3, 11.2.3.4);

11) Support the VLAN bridge management functions for the bridge protocol entity for each sup-

ported spanning tree, independently (12.8)

12) Support, in particular, management of the bridge priority parameters, and of the port priority

and path cost parameters for every port, independently for each supported spanning tree

(12.8.1.1, 12.8.1.3, 13.24);

13) Support the VLAN management functions for each supported spanning tree (12.10.1 and

12.11.1);

14) Support management of the MSTI configuration (12.12).

Authorized licensed use limited to: Weizmann Institute of Science. Downloaded on April 10,2016 at 13:16:17 UTC from IEEE Xplore. Restrictions apply.

IEEE

Std 802.1s-2002 IEEE STANDARD FOR LOCAL AND METROPOLITAN AREA NETWORKS:

5.2 Options

Insert two new list items at the end of the numbered list (note that IEEE Std 802.1u-2001, IEEE Std

802.1v-2001 have added items l, m, and n to this list):

Support MST operation (7, 8.4.1, 8.4.2, 8.6.2, 8.10.7, 8.11, 8.12, 8.14.3, 11.2.3.4, 11.3.1, 13, 14.);

p) A MAC bridge for which support of MSTP is claimed (13) may support a greater number of FIDs

than spanning trees (8.10.7).

Delete the existing contents of Clause 6, rename the clause and insert replacement contents as shown

below.

6. Support of the MAC Service in VLANs

The provisions of Clause 6 of IEEE Std 802.1D apply to this standard, with the additions and modification

defined in this clause.

6.1 Support of the MAC service

The MAC Service provided to end stations attached to a Virtual Bridged LAN is the (unconfirmed) connec-

tionless mode MAC Service defined in ISO/IEC 15802-1. The MAC Service is defined as an abstraction of

the features common to a number of specific MAC Services; it describes the transfer of user data between

source and destination end stations, via MA-UNITDATA request primitives and corresponding MA-UNIT-

DATA indication primitives issued at MAC Service access points. Each MA-UNITDATA request and indica-

tion primitive has four parameters: Destination Address, Source Address, MAC Service data unit (MSDU),

and Priority.

The style of VLAN Bridge operation maximizes the availability of the MAC Service to end stations and

assists in the maintenance of the Virtual Bridged LAN. It is therefore desirable that VLAN Bridges be capa-

ble of being configured in the Virtual Bridged LAN:

a) So as to provide redundant paths between end stations to enable the Virtual Bridged LAN to con-

tinue to provide the Service in the event of component failure (of VLAN Bridge or LAN).

b) So that the paths supported between end stations are predictable and configurable given the avail-

ability of Virtual Bridged LAN components.

The operation of VLAN Bridges supports the provision of the MAC Service only to devices that are authen-

ticated and authorized for such use. Unauthorized devices may be denied access to the Virtual Bridged LAN,

other than as necessary to support the protocol exchanges that are required by any authentication process

that is supported.

NOTE—Authentication and authorization to access a LAN may be achieved by administrative or management mecha-

nisms, or by means of an active authorization mechanism, such as is defined in IEEE Std 802.1X-2001.

6.2 Preservation of the MAC service

The MAC Service offered by a Virtual Bridged LAN consisting of LANs interconnected by VLAN Bridges

is similar to that offered by a single LAN (see 6.3). In consequence,

a) A VLAN Bridge is not directly addressed by communicating end stations, except as an end station

for management purposes: frames transmitted between end stations carry the MAC Address of the

peer-end station in their Destination Address field, not the MAC Address, if any, of the VLAN

Bridge.

Authorized licensed use limited to: Weizmann Institute of Science. Downloaded on April 10,2016 at 13:16:17 UTC from IEEE Xplore. Restrictions apply.

IEEE

VIRTUAL BRIDGED LOCAL AREA NETWORKS: AMENDMENT 3 Std 802.1s-2002

b) All MAC Addresses must be unique within any set of VLANs supported by the Virtual Bridged LAN

that share the same Filtering Identifier (FID).

c) The MAC Addresses of end stations are not restricted by the topology and configuration of the Vir-

tual Bridged LAN.

6.3 Quality of service maintenance

6.3.1 Service availability

Service availability is measured as that fraction of some total time during which the MAC Service is pro-

vided. The operation of a VLAN Bridge can increase or lower the service availability.

The service availability can be increased by automatic reconfiguration of the Virtual Bridged LAN in order

to avoid the use of a failed component (e.g., repeater, cable, or connector) in the data path. The service avail-

ability can be lowered by failure of a VLAN Bridge itself, through denial of service by the VLAN Bridge, or

through frame filtering by the VLAN Bridge. Changes in topology, caused by component failures, the addi-

tion or removal of components, or by administrative changes, are detected and signalled by the following

means:

a) Physical detection of component failure and signalling of that failure by the Enhanced Internal Sub-

layer Service (6.4 and 6.5);

b) Detection of component failure through the operation of a spanning tree algorithm and protocol;

c) Explicit signalling of reconfiguration events through the operation of a spanning tree algorithm and

protocol.

Automatic reconfiguration can be achieved rapidly on the detection of a physical topology change (see

Clause 17 of IEEE Std 802.1w-2001), thus minimizing any service denial that is caused by the reconfigura-

tion.

A VLAN Bridge may deny service and discard frames (6.3.2) in order to preserve other aspects of the MAC

Service (6.3.3 and 6.3.4) when automatic reconfiguration takes place. Service may be denied to end stations

that do not benefit from the reconfiguration; hence, the service availability is lowered for those end stations.

VLAN Bridges may filter frames in order to localize traffic in the Virtual Bridged LAN. Should an end sta-

tion move, it may then be unable to receive frames from other end stations until the filtering information held

by the VLAN Bridges is updated.

To minimize the effects of service denial caused by reconfiguration events, filtering information that has

been dynamically learnt can be modified when automatic reconfiguration takes place, or in preparation for

future reconfiguration events (Clause 17 and 17.10 of IEEE Std 802.1w-2001). However, filtering informa-

tion that is statically configured cannot be modified in this way.

A VLAN Bridge may deny service and discard frames in order to prevent access to the network by devices

that are not authorized for such access.

To maximize the service availability, no loss of service or delay in service provision should be caused by

VLAN Bridges, except as a consequence of a failure, removal, or insertion of a Virtual Bridged LAN com-

ponent, or as a consequence of the movement of an end station, or as a consequence of an attempt to perform

unauthorized access. These are regarded as extraordinary events. The operation of any additional protocol

necessary to maintain the quality of the MAC Service is thus limited to the configuration of the Virtual

Bridged LAN, and is independent of individual instances of service provision.

NOTE 1—This is true only in circumstances where admission control mechanisms are not present, i.e., where the VLAN

Bridges provide a “best effort” service. The specification and applicability of admission control mechanisms in VLAN

Bridges is outside the scope of this standard.

Authorized licensed use limited to: Weizmann Institute of Science. Downloaded on April 10,2016 at 13:16:17 UTC from IEEE Xplore. Restrictions apply.

IEEE

Std 802.1s-2002 IEEE STANDARD FOR LOCAL AND METROPOLITAN AREA NETWORKS:

NOTE 2—The operation of management upon the Bridge can result in the Bridge being reset, either as a result of a spe-

cific Bridge reset operation, or as a consequence of manipulating the Bridge’s configuration. From the point of view of

service availability, resetting the Bridge is an extraordinary event that has a similar effect to physical removal of the

Bridge from the Virtual Bridged LAN, followed by reinsertion of the Bridge into the Virtual Bridged LAN.

6.3.2 Frame loss

The MAC Service does not guarantee the delivery of Service Data Units. Frames transmitted by a source sta-

tion arrive, uncorrupted, at the destination station with high probability. The operation of a VLAN Bridge

introduces minimal additional frame loss.

A frame transmitted by a source station can fail to reach its destination station as a result of

a) Frame corruption during physical layer transmission or reception.

b) Frame discard by a VLAN Bridge because

1) It is unable to transmit the frame within some maximum period of time and, hence, must dis-

card the frame to prevent the maximum frame lifetime (6.3.6) from being exceeded.

2) It is unable to continue to store the frame due to exhaustion of internal buffering capacity as

frames continue to arrive at a rate in excess of that at which they can be transmitted.

3) The size of the service data unit carried by the frame exceeds the maximum supported by the

MAC procedures employed on the LAN to which the frame is to be relayed.

4) Changes in the connected topology of the Virtual Bridged LAN necessitate frame discard for a

limited period of time to maintain other aspects of Quality of Service (see 8.3.3 of IEEE Std

802.1D, 1998 Edition, and 17.9 of IEEE Std 802.1w-2001).

5) The device attached to the Port is not authorized for access to the network.

6) The configuration of Static Filtering Entries or Static VLAN Registration Entries in the Filter-

ing Database (8.11.1, 8.11.2) disallows the forwarding of frames with particular destination

addresses or VLAN classifications on specific Ports.

NOTE—As Static Filtering Entries and Static VLAN Registration Entries are associated with particular Ports or combi-

nations of Ports, there is a possibility that mis-configuration of such entries will lead to unintended frame discard during

or following automatic reconfiguration of the Virtual Bridged LAN.

6.3.3 Frame misordering

The MAC Service (9.2 of ISO/IEC 15802-1) permits a negligible rate of reordering of frames with a given

user priority for a given combination of destination address and source address, transmitted on a given

VLAN. MA_UNITDATA.indication service primitives corresponding to MA_UNITDATA.request primi-

tives, with the same requested priority and for the same combination of VLAN classification, destination and

source addresses, are received in the same order as the request primitives were processed.

NOTE 1—The operation of the Forwarding Process in VLAN Bridges (8.7) is such that the frame-ordering characteris-

tics of the MAC Service are preserved.

Where VLAN Bridges in a Virtual Bridged LAN are capable of connecting the individual MACs in such a

way that multiple paths between any source station–destination station pairs exist, the operation of a proto-

col is required to ensure that a single path is used.

NOTE 2—Where STP is in use (see Clause 8 of IEEE Std 802.1D, 1998 Edition), frame misordering cannot occur dur-

ing normal operation. Where RSTP is in use (see Clause 17 of IEEE Std 802.1w-2001), there is an increased probability

that frames that are in transit through the Virtual Bridged LAN will be misordered, due to the fact that a VLAN Bridge

can buffer frames awaiting transmission through its Ports. The probability of misordering occurring as a result of such an

event is dependent upon implementation choices, and is associated with Spanning Tree reconfiguration events. Some

known LAN protocols, for example, LLC Type 2, are sensitive to frame duplication; in order to allow VLAN Bridges

that support RSTP to be used in environments where sensitive protocols are in use, the forceVersion parameter (17.16.1

of IEEE Std 802.1w-2001) can be used to force a VLAN Bridge that supports RSTP to operate in an STP-compatible

manner. A more detailed discussion of misordering in RSTP can be found in F.2.4 of IEEE Std 802.1w-2001.

Authorized licensed use limited to: Weizmann Institute of Science. Downloaded on April 10,2016 at 13:16:17 UTC from IEEE Xplore. Restrictions apply.

IEEE

VIRTUAL BRIDGED LOCAL AREA NETWORKS: AMENDMENT 3 Std 802.1s-2002

6.3.4 Frame duplication

The MAC Service (9.2 of ISO/IEC 15802-1) permits a negligible rate of duplication of frames. The opera-

tion of VLAN Bridges introduces a negligible rate of duplication of user data frames.

The potential for frame duplication in a Virtual Bridged LAN arises through the possibility of duplication of

received frames on subsequent transmission within a VLAN Bridge, or through the possibility of multiple

paths between source and destination end stations.

Where VLAN Bridges in a Virtual Bridged LAN are capable of connecting the individual MACs in such a

way that multiple paths between any source station–destination station pairs exist, the operation of a proto-

col is required to ensure that a single path is used.

NOTE—Where RSTP is in use (see Clause 17 of IEEE Std 802.1w-2001), there is an increased probability that a Span-

ning Tree reconfiguration event can cause frames that are in transit through the Virtual Bridged LAN to be duplicated,

due to the fact that a VLAN Bridge can buffer frames awaiting transmission through its Ports. As the probability of

duplication occurring as a result of such an event is small, and the frequency of Spanning Tree reconfiguration events is

also small, the degradation of the properties of the MAC service caused by this source of frame duplication is considered

to be negligible. A more detailed discussion of frame duplication in RSTP can be found in F.2.4 of IEEE Std 802.1w-

2001.

6.3.5 Transit delay

The MAC Service introduces a frame transit delay that is dependent on the particular media and MAC

method employed. Frame transit delay is the elapsed time between an MA_UNITDATA.request primitive

and the corresponding MA_UNITDATA.indication primitive. Elapsed time values are calculated only on

Service Data Units that are successfully transferred.

Since the MAC Service is provided at an abstract interface within an end station, it is not possible to specify

precisely the total frame transit delay. It is, however, possible to measure those components of delay associ-

ated with media access and with transmission and reception; and the transit delay introduced by an interme-

diate system, in this case a VLAN Bridge, can be measured.

The minimum additional transit delay introduced by a VLAN Bridge is the time taken to receive a frame

plus that taken to access the media onto which the frame is to be relayed. Note that the frame is completely

received before it is relayed as the Frame Check Sequence (FCS) is to be calculated and the frame discarded

if in error.

6.3.6 Frame lifetime

The MAC Service ensures that there is an upper bound to the transit delay experienced for a particular

instance of communication. This maximum frame lifetime is necessary to ensure the correct operation of

higher layer protocols. The additional transit delay introduced by a VLAN Bridge is discussed in 6.3.5.

To enforce the maximum frame lifetime, a VLAN Bridge may be required to discard frames. Since the

information provided by the MAC Sublayer to a VLAN Bridge does not include the transit delay already

experienced by any particular frame, VLAN Bridges must discard frames to enforce a maximum delay in

each VLAN Bridge.

The value of the maximum bridge transit delay is based on both the maximum delays imposed by all the

VLAN Bridges in the Virtual Bridged LAN and the desired maximum frame lifetime. A recommended and

an absolute maximum value are specified in Table 8-2 of IEEE Std 802.1D, 1998 Edition.

Authorized licensed use limited to: Weizmann Institute of Science. Downloaded on April 10,2016 at 13:16:17 UTC from IEEE Xplore. Restrictions apply.

剩余221页未读，继续阅读

zxzzzzzxxx

粉丝: 0
资源: 1

IEEE 802.1s: 多生成树协议标准详解

IEEE-Std-802.3bm-(40GE-100GE-标准).pdf

IEEE_802.3-2018.pdf

IEEE-802.3-2018.pdf

IEEE Std 802.3-2008 section 1-20.pdf

IEEE Std 802.3-2008 section 34-43.pdf

IEEE802.3-2018.pdf

802.1s-D8.pdf

IEEE802.3BS-2017.pdf

IEEE802.3dj-800GBASE FR4-welch-3dj-01a-2401 .pdf

IEEE Std 802.3-2018_IEEE802.3-2018_IEEE802.3_802.3_802.3-2018_IE

最新资源