注：本文为 “OSPF BIT 类型 | LSA 类型 ” 相关文章合辑。

机翻，未校。

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15 OSPF BIT Types Explained

15 种 OSPF BIT 类型说明

Rashmi Bhardwaj

Distribution of routing information within a single autonomous system in larger networks is performed using WAN based protocols such as OSPF, RIP etc. Some of these routing protocols are based on link state algorithms; OSPF is one of them which uses link state algorithm to calculate shortest path tree based on routing table database.
在更大的网络中，单个自治系统内的路由信息分发是通过诸如 OSPF、RIP 等基于广域网（WAN）的协议来实现的。其中一些路由协议基于链路状态算法，OSPF 就是其中一种，它使用链路状态算法根据路由表数据库计算最短路径树。

In today’s topic we will learn about OSPF in general, bit types in OSPF and function of each OSPF bit type.
在今天的主题中，我们将大致了解 OSPF、OSPF 中的位类型以及每种 OSPF 位类型的作用。

About OSPF

关于 OSPF

OSPF is a link state discovery routing protocol. It is designed to run in an internal single autonomous system. Each OSPF router in a network maintains an identical database to describe the topology of the autonomous system. From the OSPF routing database, a shortest path tree is constructed. In the event of topological changes, OSPF quickly utilizes the minimum routing protocol traffic. OSPF supports equal cost multi - pathing. Area routing capability is there to enable an additional level of routing protection and reduction in network traffic. OSPF routing is based on the destination IP address found in the IP packet header.
OSPF 是一种链路状态发现路由协议。它旨在运行内部单个自治系统。网络中的每个 OSPF 路由器都维护相同的数据库来描述自治系统的拓扑。从 OSPF 路由数据库构建最短路径树。在拓扑发生变化时，OSPF 会快速利用最少的路由协议流量。OSPF 支持等价多路径。区域路由功能用于启用更高级别的路由保护和减少网络流量。OSPF 路由基于在 IP 数据包报头中找到的目标 IP 地址。

We will look more in detail about OSPF bit types with their locations in the upcoming section.
在接下来的部分中，我们将更详细地了解 OSPF 位类型及其位置。

OSPF BIT Types

OSPF BIT 类型

OSPF uses various types of bits within its packet headers and Link State Advertisements (LSAs) to communicate specific information between routers. The OSPF bit types are significant because they play a critical role in the operation, efficiency, and flexibility of the OSPF routing protocol. OSPF bit types are fundamental to how OSPF operates, ensuring that the protocol can function effectively in diverse and complex network environments. They help in managing routing information, reducing unnecessary traffic, and ensuring the stability and efficiency of the network.
OSPF 在其数据包报头和链路状态通告（LSA）中使用各种类型的位在路由器之间传递特定信息。OSPF 位类型非常重要，因为它们在 OSPF 路由协议的运作、效率和灵活性中起着关键作用。OSPF 位类型是 OSPF 运行方式的基础，可确保协议能够在各种复杂的网络环境中有效运行。它们有助于管理路由信息、减少不必要的流量以及确保网络的稳定性和效率。

Here are the key OSPF bit types:
以下是关键的 OSPF 位类型：

E-bit

E 位

OSPF areas. can be configured as ‘Stubs’ and AS - external - LSAs will not flood into stub areas. This is represented with E - bit in the OSPF options field. To ensure configuration consistency of stub areas, all routers interfacing such area must have the E - bit cleared in their Hello packets.
OSPF 区域可以配置为 “存根区域”，并且 AS 外部 LSA 不会泛洪到存根区域，这在 OSPF 选项字段中用 E 位表示。为确保存根区域的配置一致性，与该区域接口的所有路由器必须在其 Hello 数据包中将 E 位清零。

M-bit

M 位

Each router’s database description contains an indication that there are more packets to flow using an M - bit. The M - bit is set to the off state when the database exchange process is over.
每个路由器数据库说明都包含一个指示，表明使用 M 位表示是否还有更多数据包要传输。当数据库交换过程结束时，M 位设置为关闭状态。

I-bit and MS-bit

I 位和 MS 位

The initialize (I), more (M) and Master (MS) bits in the options field and the DD sequence number container in the last database description packet arrived from the neighbour are used to determine if the next database description packet received from the neighbour is unique or duplicate.
选项字段中的初始化（I）、更多（M）和主（MS）位以及从邻居到达的最后一个数据库描述数据包中的 DD 序列号容器用于确定从邻居接收的下一个数据库描述数据包是唯一的还是重复的。

B-bit

B 位

B - bit is set whenever the router is actively attached to two or more areas, even if it is not attached to the OSPF backbone area.
每当路由器主动连接到两个或多个区域时，即使它未连接到 OSPF 骨干区域，也会设置 B 位。

V-bit

V 位

In router - LSA, the V - bit is set only if the router is the endpoint of one or more fully adjacent virtual links having Area A as their transit area. The V - bit setting enables other routers in Area A to discover if the area supports transit traffic.
在 router - LSA 中，仅当路由器是一个或多个全相邻的虚拟链路的端点，且区域 A 作为其中转区域时，才设置 V 位。V 位设置使 A 区域中的其他路由器能够发现该区域是否支持中转流量。

R-bit

R 位

Allows for multi - homed hosts to participate in the routing protocol.
允许多归属主机参与路由协议。

V6-bit

V6 位

Specializes the R - bit.
是 R 位的特殊化。

MC-bit

MC 位

Describes whether IP multicast datagrams are forwarded as per specifications.
描述 IP 组播数据报是否按照规范进行转发。

N/P-bit

N/P 位

Describes the handling of type - 7 LSAs.
描述类型 7 LSA 的处理方式。

EA-bit

EA 位

Describes the router’s willingness to forward/receive external - attributes - LSAs.
描述路由器转发 / 接收外部属性 LSA 的意愿。

DC-bit

DC 位

Describes the router’s handling of demand circuits.
描述路由器对按需电路的处理。

DN-bit

DN 位

Is used to prevent loops and it is located in the LSA header in MPLS VPN environments when OSPF is used as the PE - CE protocol.
用于防止环路，当 OSPF 用作 PE - CE 协议时，它位于 MPLS VPN 环境中的 LSA 报头中。

N-bit

N 位

Is used in hello packets. by OSPF NSSA routers.
由 OSPF NSSA 路由器在 hello 数据包中使用。

P-bit

P 位

Is used in the NSSA external header. It allows an ASBR to signal that the ABR router between (0, NSSA area) should translate LSA type 7 to LSA type 5 to be sent to the OSPF backbone area.
用于 NSSA 外部标头。它允许 ASBR 发出信号指示（0，NSSA 区域）之间的 ABR 路由器应将 LSA 类型 7 转换为 LSA 类型 5，以发送到 OSPF 骨干区域。

Check the summarized table below:
查看下面的汇总表：

S.No.	OSPF BIT Type	Description
1	E-bit	The OSPF area can be configured as a “Stub” area. AS external LSAs (Link State Advertisements) will not flood into the stub area, which is indicated by the E - bit in the OSPF option field. To ensure consistent stub area configuration, all routers connected to the area must clear the E - bit in their Hello packets. OSPF 区域可配置为 “Stub”（存根区域），AS 外部 LSA（链路状态通告）不会泛洪到存根区域，这在 OSPF 选项字段中由 E-bit 表示。为确保存根区域配置一致，连接该区域的所有路由器在其 Hello 包中必须将 E-bit 清零。
2	M-bit	The database description of each router contains an indication, using the M - bit to represent whether there are more packets to be transmitted. When the database exchange process is complete, the M - bit is set to the off state. 每个路由器的数据库描述包含一个指示，即使用 M-bit 表示是否还有更多数据包要传输。数据库交换过程结束时，M-bit 被设置为关闭状态。
3 & 4	I-bit and MS-bit	The Initialization (I), More (M), and Master (MS) bits in the option field, along with the DD sequence number container in the last database description packet received from the neighbor, are used to determine whether the next database description packet received from the neighbor is unique or a duplicate. 选项字段中的初始化（I）、更多（M）和主（MS）位，以及从邻居收到的最后一个数据库描述包中的 DD 序列号容器，用于确定从邻居接收到的下一个数据库描述包是唯一的还是重复的。
5	B-bit	The B-bit is set as long as the router is actively connected to two or more areas, even if it is not connected to the OSPF backbone area. 只要路由器主动连接到两个或更多区域，即使它未连接到 OSPF 骨干区域，B-bit 也会被设置。
6	V-bit	The V-bit is set in the router LSA only when the router is the endpoint of one or more fully adjacent virtual links with area A as the transit area. The setting of the V - bit enables other routers in area A to discover whether the area supports transit traffic. 仅当路由器是一个或多个以区域 A 为中转区域的全相邻虚拟链路的端点时，在路由器 LSA 中才会设置 V-bit。V-bit 的设置使区域 A 中的其他路由器能够发现该区域是否支持中转流量。
7	R-bit	Allows a multi - homed host to participate in the routing protocol. 允许多归属主机参与路由协议。
8	V6-bit	Specializes R-bit. It is a specialization of the R-bit. R-bit 的特殊化。
9	MC-bit	Describes whether IP multicast datagrams are forwarded according to the specification. 描述 IP 组播数据报是否按照规范进行转发。
10	N/P-bit	Describes the processing method of type 7 LSA. 描述类型 7 LSA 的处理方式。
11	EA-bit	Describes the router’s willingness to forward/receive external - attributes - LSAs. 描述路由器转发 / 接收外部属性 LSA 的意愿。
12	DC-bit	Describes the router’s handling of demand circuits. 描述路由器对按需电路的处理。
13	DN-bit	Is used to prevent loops. In an MPLS VPN environment where OSPF is used as the PE - CE protocol, it is located in the LSA header. 用于防止环路，在使用 OSPF 作为 PE-CE 协议的 MPLS VPN 环境中，它位于 LSA 头部。
14	N-bit	Used by OSPF NSSA (Not-So-Stubby Area) routers in Hello packets. OSPF NSSA（非纯末梢区域）路由器在 Hello 包中使用。
15	P-bit	Used for the NSSA external header. It allows an ASBR (Autonomous System Boundary Router) to signal an ABR (Area Border Router) between (0, NSSA area) that the ABR should convert a type 7 LSA to a type 5 LSA and send it to the OSPF backbone area. 用于 NSSA 外部头部。它允许 ASBR（自治系统边界路由器）向（0，NSSA 区域）之间的 ABR（区域边界路由器）发出信号指示，指示 ABR 应将类型 7 LSA 转换为类型 5 LSA 并发送到 OSPF 骨干区域。

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OSPF LSA Types: The Ultimate Guide

OSPF LSA 类型：终极指南

Rashmi Bhardwaj

OSPF LSA Types –

OSPF LSA 类型 –

OSPF uses LSAs or Link state Advertisements to share information of each network and populate the LSDB (Link State Database). The LSAs are used by routers to exchange topology information. An LSA contains routing and topology information that describe a part of an OSPF network. Routers exchange LSAs and learn the complete topology of the network until all routers have the exact same topology database. Infact, OSPF sends updates (LSAs) when there is a change to one of its links. LSAs are additionally refreshed every 30 minutes.
OSPF 使用 LSA 或链路状态通告来共享每个网络的信息并填充 LSDB（链路状态数据库）。路由器使用 LSA 来交换拓扑信息。LSA 包含描述 OSPF 网络一部分的路由和拓扑信息。路由器交换 LSA 并了解网络的完整拓扑，直到所有路由器都具有完全相同的拓扑数据库。事实上，OSPF 会在其其中一个链路发生更改时发送更新 （LSA）。LSA 每 30 分钟刷新一次。

All OSPF LSA Types are mentioned in below table –

下表中提到了所有 OSPF LSA 类型 –

Types	Description
LSA Type 1	Router LSA
LSA Type 2	Network LSA
LSA Type 3 or 4	Summary LSA & ASBR LSA
LSA Type 5	Autonomous System External LSA
LSA Type 6	Multicast OSPF LSA Type
LSA Type 7	Defined for Not-So-Stubby-Areas
LSA Type 8	External Attribute LSA for BGP
LSA Type 9,10,11	Opaque LSA

LSA Type 1: Router LSA

LSA 类型 1：路由器 LSA

• This LSA type is flooded by every router within an area
  此 LSA 类型由区域内的每台路由器泛洪
• The LSA consists of information about directly connected links
  LSA 包含有关直接连接链路的信息
• It is identified by the Router ID. or the originating router
  它由路由器 ID 或始发路由器标识
• It floods within an area and the LSA Type 1 does not cross the ABR.
  它会在一个区域内泛洪，并且 LSA 类型 1 不会穿过 ABR。
• We see this as “O” routes in the routing table
  我们在路由表中将其视为 “O” 路由
• LSA 1 – O, Router LSA contains all Link IDs – network, generated by every router and is local to the area.
  LSA 1 – O，路由器 LSA 包含所有链路 ID – 网络，由每个路由器生成，并且是该区域的本地。
• This LSA does not cross ABR.
  此 LSA 不跨越 ABR。

LSA Type 2: Network LSA

LSA 类型 2：网络 LSA

• Generated by the DR Router on the broadcast network
  由广播网络上的 DR 路由器生成
• It includes the network ID, subnet mask and also the list of attached routers in the transit
  它包括网络 ID、子网掩码以及传输中连接的路由器列表
• In OSPF we can have one Network LSA or Type 2 LSA for each transit broadcast of NBMA Network.
  在 OSPF 中，我们可以为 NBMA 网络的每个中转广播提供一个网络 LSA 或第 2 类 LSA
• This LSA also can be flooded only within the area and cannot cross the ABR
  此 LSA 也只能在区域内泛洪，不能穿过 ABR
• We see this as “O” routes in the routing table
  我们在路由表中将其视为 “O” 路由
• LSA 2 – O, Network LSA contains all routers attached to the segment, generated by DR and is local to the area
  LSA 2 — O，网络 LSA 包含连接到网段的所有路由器，由 DR 生成，并且是该区域的本地路由器

LSA Type 3: Summary LSA

LSA 类型 3：摘要 LSA

• The Type 3 LSA is used to share the network information with other areas. Inter-area ( IA)
  Type 3 LSA 用于与其他区域共享网络信息。区域间 （IA）
• These LSAs are advertised by the ABR Router
  这些 LSA 由 ABR 路由器通告
• These LSA are represented in the routing table as “OIA” routes
  这些 LSA 在路由表中表示为“OIA”路由
• To flood the information through the Autonomous System, they are regenerated by the ABRs following subsequently
  为了通过自治系统泛洪信息，它们随后由 ABR 重新生成
• LSA 3 – O IA, Network Summary LSA describes network from another area, generated by ABR and is propagated between areas
  LSA 3 – O IA，网络摘要 LSA 描述来自另一个区域的网络，由 ABR 生成并在区域之间传播
• It contains network ID and subnet mask
  它包含网络 ID 和子网掩码

LSA Type 4: Summary ASBR LSA

LSA 类型 4：摘要 ASBR LSA

• This LSA type is also known as summary LSA is used to advertise about the ASBR to other areas in the same autonomous system.
  此 LSA 类型也称为摘要 LSA，用于向同一自治系统中的其他区域通告 ASBR。
• It is generated by the ABR of the originating area.
  它由原始区域的 ABR 生成。
• These type of LSAs are flooded throughout the Autonomous System
  这些类型的 LSA 在整个自治系统中泛洪
• These LSA will contain the Router ID of the ASBR only
  这些 LSA 将仅包含 ASBR 的路由器 ID
• LSA 4 – O IA, Summary ASB Link States, generated by the ABR and is propagated between areas
  LSA 4 - O IA，摘要 ASB 链路状态，由 ABR 生成并在区域之间传播

LSA Type 5: External LSA

LSA 类型 5：外部 LSA

• These are advertised by the ASBR only and also owned by the ASBR
  这些仅由 ASBR 公布，也归 ASBR 所有
• These LSAs are used to advertise networks from other Autonomous systems
  这些 LSA 用于通告来自其他自治系统的网络
• These LSAs are flooded throughout the entire Autonomous System
  这些 LSA 在整个自治系统中泛洪
• The advertising router ID is not changed throughout the AS when it is propagating.
  广告路由器 ID 在传播时不会在整个 AS 中更改。
• An LSA Type 4 is used to find an ASBR
  LSA 类型 4 用于查找 ASBR
• Routes are not summarized by default
  默认情况下，不汇总路由
• LSA 5 – O E1, O E2, External Link States, generated by ASBR and is propagated
  LSA 5 – O E1、O E2、外部链路状态，由 ASBR 生成并传播

LSA Type 6: Multicast OSPF LSA

LSA 类型 6：组播 OSPF LSA

• These are used when routing using multicast (the MODPF Routing protocol)
  这些在使用多播（MODPF 路由协议）进行路由时使用
• These LSAs are not supported by Cisco Routers
  Cisco 路由器不支持这些 LSA

LSA Type 7: External LSA

LSA 类型 7：外部 LSA

• As LSA Type 5 is not allowed in NSSA Areas, a solution to that was thought as LSA 7.
  由于 NSSA 区域不允许使用 LSA 类型 5，因此该解决方案被认为是 LSA 7。
• It carries similar information as a Type 5 LSA but this is not blocked in the NSSA Area.
  它携带与 5 类 LSA 类似的信息，但这在 NSSA 区域中未被阻止。
• When it reached the ABR it is translated back to Type 5 LSA and flooded into other areas.
  当它到达 ABR 时，它被转换回 5 型 LSA 并泛洪到其他区域。
• LSA 7 – O N1, O N2, NSSA External Link States, generated by ASBR into NSSA area and is propagated into area 0 as E1 or E2
  LSA 7 – O N1、O N2、NSSA 外部链路状态，由 ASBR 生成到 NSSA 区域，并作为 E1 或 E2 传播到区域 0

LSA Type 8: External attributes LSA for Border Gateway Protocol (BGP)

LSA 类型 8：边界网关协议 （BGP） 的外部属性 LSA

This LSA Types is used to work with BGP.
此 LSA 类型用于与 BGP 配合使用。

Note – Below list of LSA9, 10 and 11 are called Opaque LSAs. Further detail on these LSA types is shared below –
注意 – 以下 LSA9、10 和 11 列表称为不透明 LSA。有关这些 LSA 类型的更多详细信息，请参见下文 –

LSA Type 9: Opaque LSA

LSA 类型 9：不透明 LSA

This LSA types is Link-state in scope and is not flooded beyond the local network.
此 LSA 类型在范围内是链路状态，不会泛洪到本地网络之外。

LSA Type 10: Opaque LSA

LSA 类型 10：不透明 LSA

The scope of this type of LSA is area-local. This LSA is not flooded beyond the borders of their associated area.
此类 LSA 的范围是区域本地的。此 LSA 不会在其关联区域的边界之外泛洪。

LSA Type 11: Opaque LSA

LSA 类型 11：不透明 LSA

This LSA is flooded throughout the Autonomous System (AS). Somewhat is can be related to Type-5 LSA is terms of flooding scope.
此 LSA 在整个自治系统 （AS） 中泛洪。在某种程度上可能与 5 型 LSA 有关，是泛洪范围的术语。

There are 3 key features of Type11 LSAs –
Type11 LSA 有 3 个关键功能 –

• These are flooded throughout the transit areas
  这些在整个过境区域都被泛洪了
• Not flooded into stub areas from the backbone
  未从主干泛洪到存根区域
• Not originated by routers having connected stub areas
  不是由具有连接的存根区域的路由器发起的

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via：

• 15 OSPF BIT Types Explained - IP With Ease
  https://ipwithease.com/15-ospf-bit-types-explained/

• Uptimate Guide on OSPF LSA Types
  https://ipwithease.com/ospf-lsa-types/