Cisco NBMA（非广播多址接入）工作原理、优点和用例及配置基于 NBMA 的 OSPF

注：机翻，未校对。

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Rashmi Bhardwaj | Blog,Routing & Switching

Networking protocols use broadcast or not broadcast based communication to establish communication between devices in a network. Broadcast networks such as Ethernet use a broadcast mechanism where data packet is sent to the entire network but imagine a very large network where all devices are broadcasting how much chaos it will create? Or in the case of WAN where there are limitations on bandwidth or infrastructure.
网络协议使用基于广播或非广播的通信来建立网络中设备之间的通信。以太网等广播网络使用广播机制，将数据包发送到整个网络，但想象一下一个非常大的网络，所有设备都在广播，它会产生多少混乱？或者，在带宽或基础设施存在限制的 WAN 中。

Today we look more in detail about a non-broadcast type communication mechanism (NBMA), understand its working, advantages and use cases.
今天，我们更详细地了解了非广播型通信机制（NBMA），了解其工作原理、优点和用例。

What is Non-Broadcast Multiple Access (NBMA)

什么是非广播多址接入 （NBMA）

Non-broadcast multiple access (NBMA), unlike its broadcast counterparts, works on a point-to-point communication model, where every device establishes a direct connection with every other device it needs to communicate to. Creating a virtual circuit or a logical link between devices requires communication with each other. This kind of device communication is usually referred to as nodes.
非广播多址接入 （NBMA） 与其广播对应物不同，它采用点对点通信模型，其中每个设备都与需要通信的每个其他设备建立直接连接。在设备之间创建虚拟电路或逻辑链接需要彼此通信。这种设备通信通常称为节点。

NBMA does not have the broadcast capabilities, so instead of broadcasting messages it relies on unicast and multicast communication modes. Unicast is one to one communication and multicast is one to many or many to one communication. NBMA uses several protocols to achieve this kind of communication in networks such as Network Control Protocol (NCP) to handle negotiation and communication parameters of each virtual circuit, Routing Information protocol (RIP) to enable exchange of routing information between routers.
NBMA 不具备广播功能，因此它依赖于单播和多播通信模式，而不是广播消息。单播是一对一通信，多播是一对多或多对一通信。NBMA 使用多种协议在网络中实现这种通信，例如网络控制协议（NCP）来处理每个虚拟电路的协商和通信参数，路由信息协议（RIP）来启用路由器之间的路由信息交换。

NBMA networks use Data Link Connection Identifiers (DLCIs) to address nodes and establish connections. Multiprotocol Label Switching (MPLS) is used for circuit switching and packet switching for efficient routing of packets across networks.
NBMA 网络使用数据链路连接标识符 （DLCI） 对节点进行寻址并建立连接。多协议标签交换 （MPLS） 用于电路交换和数据包交换，以实现跨网络的数据包高效路由。

How does Non-Broadcast Multiple Access (NBMA) work?

非广播多址接入 （NBMA） 如何工作？

Not all multiaccess technologies support broadcast-based transmissions. Frame relay and ATM are two most common examples of non-broadcast networks which require permanent virtual circuits (PVCs) to be configured between devices as depicted in figure below.
并非所有多址技术都支持基于广播的传输。帧中继和 ATM 是非广播网络的两个最常见的例子，它们需要在设备之间配置永久虚电路（PVC），如下图所示。

In above figure, R1 needs to transmit an individual packet to every device it needs to reach. The router needs to know the address of his neighbours before starting communication with them. NBMA will emulate the function of the broadcast network here. Every router in the segment must be configured with an IP address of each of the neighbours. OSPF hello packets are then individually sent as a unicast packet to each adjacent neighbour in the network.
在上图中，R1 需要向它需要到达的每个设备传输一个单独的数据包。在开始与邻居通信之前，路由器需要知道邻居的地址。NBMA 将在这里模拟广播网络的功能。网段中的每个路由器都必须配置每个邻居的 IP 地址。然后，OSPF hello 数据包将作为单播数据包单独发送到网络中的每个相邻邻居。

Router 1

R1 (config)# router ospf 1
R1 (config-router)# neighbor 10.0.0.2
R1 (config-router)# neighbor 10.0.0.3
R1 (config-router)# neighbor 10.0.0.4

Router 2

R2 (config)# router ospf 1
R2 (config-router)# neighbor 10.0.0.3
R2 (config-router)# neighbor 10.0.0.4

Router 3

R3 (config)# router ospf 1
R3 (config-router)# neighbor 10.0.0.4

Router 4

R4 (config)# router ospf 1
R4 (config-router)# neighbor 10.0.0.3

R4 and R3 are elected as DR and BDR in above configuration
在上述配置中，R4 和 R3 被选为 DR 和 BDR

In case of point-to-multipoint configuration NBMA organizes PVCs into a collection of Point-to-Point networks. Hello packets are sent individually to each neighbour. It does not require DR/BDR and emulated point-to-point links can use a common subnet. All routers required to be manually configured to recognize it as point-to-multipoint segment using below command:
在点对多点配置的情况下，NBMA 将 PVC 组织成点对点网络的集合。Hello 数据包将单独发送给每个邻居。它不需要 DR/BDR，模拟的点对点链路可以使用公共子网。所有路由器都需要手动配置，以使用以下命令将其识别为点对多点网段：

Router (config-if)# ip ospf network point-to-multipoint [non-broadcast] 

Advantages of Non-broadcast Multiaccess Networks

非广播多址网络的优势

• Improved network efficiency especially in case of large networks and networks having limited bandwidth
  提高网络效率，特别是在大型网络和带宽有限的网络的情况下

• Reduction in network congestion and performance improvement
  减少网络拥塞并提高性能

• Better scalability as bandwidth utilization is more efficient
  由于带宽利用率更高，因此具有更好的可扩展性

• Enhanced security with point-to-point communication model which ensure data packets are only received by targeted recipients reducing risk of unauthorized access and eavesdropping
  通过点对点通信模型增强安全性，确保数据包仅由目标接收者接收，从而降低未经授权的访问和窃听的风险

• Better control over network resources with bandwidth allocation , prioritization of traffic based on needs
  通过带宽分配更好地控制网络资源，根据需要确定流量的优先级

• Enablement of efficient management of resources and Quality of service (QoS)
  实现资源和服务质量 （QoS） 的高效管理

Limitations of Non-broadcast Multiaccess Networks

非广播多址网络的局限性

• Increased complexity of configuration and management as compared to broadcast networks
  与广播网络相比，配置和管理的复杂性增加

• Time consuming as it involves setting up individual connections and maintain them
  非常耗时，因为它涉及设置单个连接并维护它们

• Increased reliance of routing protocols as routing protocols determines delivery paths in the absence of broadcast-based communications
  由于在没有基于广播的通信的情况下，路由协议决定了传递路径，因此对路由协议的依赖性增加

• Scalability could a challenge as number of nodes and logical links increase routing and addressing complexities also increase
  随着节点和逻辑链路数量的增加，可扩展性可能是一个挑战，路由和寻址的复杂性也会增加

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Configuring OSPF Over Non-Broadcast Multiaccess Networks (NBMA)

在非广播多址网络 （NBMA） 上配置 OSPF

Rashmi Bhardwaj | Blog,Config & Troubleshoot,Routing & Switching

All network communication happens using the standard OSI framework. At each layer a set of protocols work which standardize the requirements of communication and prepare data which is universally acceptable to the next layer. Of network communication the most important aspect is data packet routing – there are several protocols available to support routing such as TCP/IP, OSPF etc. The one which gives the optimal route from source to destination is preferably considered for communication over large heterogeneous networks.
所有网络通信都使用标准 OSI 框架进行。在每一层都有一组协议工作，这些协议标准化了通信要求并准备了下一层普遍接受的数据。在网络通信中，最重要的方面是数据包路由 - 有几种协议可用于支持路由，例如 TCP/IP、OSPF 等。在大型异构网络上进行通信时，最好考虑提供从源到目的地的最佳路由的那一种。

In today’s article we will look more in detail about how OSPF (Open Shortest Path First) link state routing protocols work over non broadcast networks (NBMA), how to configure OSPF over NBMA, its features and limitations.
在今天的文章中，我们将更详细地了解 OSPF（开放最短路径优先）链路状态路由协议如何在非广播网络 （NBMA） 上工作，如何在 NBMA 上配置 OSPF，其功能和限制。

OSPF Over Non-Broadcast Networks (NBMA)

基于非广播网络的 OSPF （NBMA）

OSPF is a link state routing protocol (used mostly widely) which uses information about the state of network links to ascertain or determine the best path for data packets. There are three types of network types in OSPF which determine how OSPF will route data packets across networks.
OSPF 是一种链路状态路由协议（主要使用广泛），它使用有关网络链路状态的信息来确定或确定数据包的最佳路径。OSPF 中有三种类型的网络类型，它们决定了 OSPF 如何在网络之间路由数据包。

• Broadcast 广播
• Point-to-Point 点对点
• No Broadcast 无广播

In addition to above there are two more Cisco proprietary network types
除上述网络外，还有两种思科专有网络类型

• Point to Multipoint 点对多点
• Point to Multipoint Non broadcast 点对多点非广播

Since the point of focus in this article is No Broadcast networks (NBMA), we will go deeper into this. Non broadcast OSPF networks used in point-to-point links where multiple OSPF routers are connected such as frame relay, X.25, ATM virtual circuits (not used nowadays). For all hosts in a single NBMA network, data is sent from one host to another without broadcasting information across all hosts. Switched networks or virtual circuits provide direct routing of data packets. NMBA communicates directly to other hosts but on the same physical link other hosts can’t connect to it. NBMA uses next hop resolution protocol (NHRP) to find routes automatically through the network
由于本文的重点是无广播网络 （NBMA），因此我们将对此进行更深入的探讨。非广播 OSPF 网络，用于连接多个 OSPF 路由器的点对点链路，如帧中继、X.25、ATM 虚拟电路（目前不使用）。对于单个 NBMA 网络中的所有主机，数据会从一台主机发送到另一台主机，而不会在所有主机之间广播信息。交换网络或虚拟电路提供数据包的直接路由。NMBA 直接与其他主机通信，但在同一物理链路上，其他主机无法连接到它。NBMA 使用下一跳解析协议 （NHRP） 通过网络自动查找路由

Configure OSPF Over Non-Broadcast Networks (NBMA)

配置基于非广播网络 （NBMA） 的 OSPF

Non broadcast Multiaccess (NBMA) broadcast model based on selection of designated router (DR) and a backup designated router (BDR). There are two ways to deploy this: defining the network type as broadcast with the IP OSPF network broadcast interface sub command or configure the neighbor statements using router OSPF command.
基于指定路由器 （DR） 和备用指定路由器 （BDR） 选择的非广播多访问 （NBMA） 广播模型。有两种方法可以部署它：使用 IP OSPF network broadcast interface sub 命令将网络类型定义为广播，或使用 router OSPF 命令配置 neighbor 语句。

1. Configuration for NBMA (use Network Type Broadcast)

Router 1 Configuration

Interface loopback0
Ip address 168.0.2.3 255.255.255.255
!
!
Interface serial2 
Ip address 168.0.2.1 255.255.255.0 
Encapsulation frame-relay
Ip ospf network broadcast
No keepalive 
Frame-relay map ip 168.0.2.1 16 broadcast
!
!
Router ospf 1
Network 168.0.2.0 0.0.0.255 area 0

Router 2 Configuration

Interface loopback0
Ip address 168.0.0.2 255.255.255.255 
! 
Interface serial1/0 
Ip address 168.0.2.1 255.255.255.0
Encapsulation frame-relay
Ip ospf network broadcast
No keepalive
Clockrate 2000000
Frame-relay map ip 168.0.2.1 16 broadcast
!
Router ospf 1 
Network 168.0.2.0 0.0.0.255 area 0

2. Configuration for NBMA (use Neighbour statements)

Router 1 Configuration

Interface loopback0
Ip address 168.0.2.3 255.255.255.255
! 
Interface Serial2 
Ip address 168.0.2.1 255.255.255.0
Encapsulation frame-relay
Ip ospf priority 2 
No keepalive
Frame-relay map ip 168.0.2.1 16 
!
Router ospf 1
Network 168.0.2.0 0.0.0.255 area 0
Neighbor 168.0.2.1 
!

Router 2 Configuration

Interface loopback0
Ip address 168.0.2.2 255.255.255.255
! 
Interface Serial0/1
Ip address 168.0.2.1 255.255.255.0
Encapsulation frame-relay
Ip ospf priority 2 
No keepalive
Clockrate 2000000
Frame-relay map ip 168.0.2.1 16 
!
Router ospf 1
Network 168.0.2.0 0.0.0.255 area 0
Neighbor 168.0.2.1 
!

Use show command to verify configuration

Router1 # Show ip ospf neighbors

OSPF Non-broadcast Network Features

OSPF 非广播网络特性

• Network can connect more than two routers but by default they cannot broadcast
  网络可以连接两个以上的路由器，但默认情况下它们无法广播

• Multipoint frame relay interfaces are default network type for OSPF
  多点帧中继接口是 OSPF 的默认网络类型

• OSPF routers on NBMA networks choose a DR (Designated router) and a BDR (backup designated router), all OSPF packets are unicast between each neighbor specified with ‘neighbor’ command
  NBMA 网络上的 OSPF 路由器选择 DR（指定路由器）和 BDR（备份指定路由器），所有 OSPF 数据包在使用 “neighbor” 命令指定的每个邻居之间进行单播

• The next hop IP do not change and remains same as IP address of the router which sent the packet
  下一跳 IP 不会更改，并且与发送数据包的路由器的 IP 地址相同

• The assigned priority by default is ‘1’ and should be set to = 0 (turned off) on ALL SPOKES to stop spoke from becoming a blackhole DR/BDR
  默认情况下，分配的优先级为 “1”，应在所有辐条上设置为 = 0（关闭），以阻止辐条成为黑洞 DR/BDR

• 30 seconds is Hello interval and 120 seconds is dead interval in OSPF
  在 OSPF 中，30 秒是 Hello 间隔，120 秒是死间隔

Pros & Cons of OSPF over NBMA

OSPF 相对于 NBMA 的优点和缺点

PROS

• Easier to control traffic flow on network and also helpful to limit amount of traffic goes through a particular link
  更容易控制网络上的流量，也有助于限制通过特定链路的流量

• Non broadcast network types are secure since hackers can easily intercept broadcast which will not happen here
  非广播网络类型是安全的，因为黑客可以很容易地拦截广播，而这在这里不会发生

CONS

• Difficult to configure as it requires manual neighbor configuration
  难以配置，因为它需要手动邻居配置

• Difficult to scale on OPSF networks as compared to other network types
  与其他网络类型相比，难以在 OPSF 网络上扩展

• Limited feature availability of OSPF features when this network type is used
  使用此网络类型时，OSPF 功能的功能可用性有限

• Susceptible to certain types of faults
  容易受到某些类型的故障的影响

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via:

Author / Editor Rashmi Bhardwaj

• What is Non-Broadcast Multiple Access (NBMA)? - IP With Ease

  https://ipwithease.com/what-is-non-broadcast-multiple-access-nbma/

• Configuring OSPF Over Non-Broadcast Multiaccess Networks (NBMA) - IP With Ease

  https://ipwithease.com/ospf-over-non-broadcast-multiaccess-networks-nbma/

原文地址：https://blog.csdn.net/u013669912/article/details/140705217

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