NBMA (non-broadcast multiple access) is one of four network types in the OSPF (Open Shortest Path First) communications protocol. NBMA is used to accurately model X.25 and frame relay environments in multiple-access networks where there are no intrinsic broadcast and multicast capabilities. The other OSPF network types are: broadcast, point-to-point, and point-to-multipoint. In an NBMA configuration, OSPF sends HELLO packets (packets sent periodically to establish and confirm neighbor relationships between routers) to each router one at a time rather than multicasting them. The HELLO timer (which tells the router how often to send HELLO packets) is extended from 10 to 30 seconds and the dead router timer (which tells the router how long to wait before it decides that a neighboring router is not functioning) is extended from 40 to 120 seconds.
译文:
NBMA（非广播多路访问网络）是OSPF（开放最短路径优先）通信协议中四种网络的一种。NBMA用于精确模型X2.5和帧延迟环境，这些模型不具备内部广播和多点传送能力。其他的OSPF网络类型有：广播、点对点和点对多点。在NBMA设置里，OSPF一次只发送一个呼叫包（在路由器间周期性发送的建立和确认临近关系的包）而不是多广播是的发送给他们。呼叫计时器（它控制路由器每发送一个呼叫包需要隔多少时间）需要延迟10到30秒，死路由器计时器（它控制在决定临近路由器失效时应该等待多少时间）需要延迟40到120秒。
例子
Rakc01R1#sh run
Building configuration...
Current configuration : 693 bytes
!
version 12.2
no service single-slot-reload-enable
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname Rakc01R1
!
logging rate-limit console 10 except errors
!
ip subnet-zero
no ip finger
no ip domain-lookup
!
no ip dhcp-client network-discovery
!
!
!
!
interface Ethernet0
ip address 172.10.14.1 255.255.255.0
ip router isis
!
interface Serial0
no ip address
shutdown
!
interface Serial1
no ip address
shutdown
!
router isis
net 49.0002.1420.0000.1001.00
!
ip kerberos source-interface any
ip classless
no ip http server
!
!
!
line con 0
exec-timeout 0 0
logging synchronous
transport input none
line aux 0
line vty 0 4
!
end
Rakc01R1#
---------------------------------------------------------------------------------------
Rakc01R3#sh run
Building configuration...
Current configuration : 1149 bytes
!
version 12.1
no service single-slot-reload-enable
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
service udp-small-servers
service tcp-small-servers
!
hostname Rakc01R3
!
logging rate-limit console 10 except errors
!
ip subnet-zero
no ip finger
no ip domain-lookup
!
clns routing
cns event-service server
!
!
!
!
!
interface Ethernet0
ip address 192.168.0.21 255.255.255.0
no ip route-cache
no ip mroute-cache
!
interface Serial0
no ip address
no ip route-cache
no ip mroute-cache
shutdown
!
interface Serial1
ip address 198.10.235.3 255.255.255.0
ip router isis
encapsulation frame-relay
no ip route-cache
no ip mroute-cache
frame-relay map clns 302 broadcast
frame-relay map clns 306 broadcast
no frame-relay inverse-arp
!
interface BRI0
no ip address
no ip route-cache
no ip mroute-cache
shutdown
!
router isis
net 49.0001.1420.0000.3003.00
!
ip default-gateway 192.168.0.20
ip kerberos source-interface any
ip classless
no ip http server
!
!
!
line con 0
exec-timeout 0 0
logging synchronous
transport input none
line aux 0
transport input all
line vty 0 4
login
!
end
Rakc01R3#
--------------------------------------------------------------------------
Rakc01R2#sh run
Building configuration...
Current configuration : 890 bytes
!
version 12.2
no service single-slot-reload-enable
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname Rakc01R2
!
logging rate-limit console 10 except errors
!
ip subnet-zero
no ip finger
no ip domain-lookup
!
no ip dhcp-client network-discovery
clns routing
!
!
!
!
interface Ethernet0
no ip address
shutdown
!
interface Serial0
ip address 198.10.235.2 255.255.255.0
ip router isis
encapsulation frame-relay
frame-relay map clns 203 broadcast
frame-relay map clns 206 broadcast
no frame-relay inverse-arp
frame-relay lmi-type cisco
!
interface Serial1
ip address 192.168.24.2 255.255.255.0
ip router isis
!
router isis
net 49.0001.1420.0000.2002.00
!
ip kerberos source-interface any
ip classless
ip http server
!
!
!
line con 0
exec-timeout 0 0
logging synchronous
transport input none
line aux 0
line vty 0 4
!
end
Rakc01R2#
-----------------------------------------------------------------------
----------------------------------
R2-----R4-----R1 |
/ \|
/\ |
R5 ----R3 |
---------------------------------
拓扑如上
R2、R3、R5之间为FULL MESH的NBMA网络， 区域1, R4、R1组成区域2
R2: 49.0001.1420.0000.2002.00
R3: 49.0001.1420.0000.3003.00
R5: 49.0001.1420.0000.5005.00
-------------------------------------------------
R4: 49.0002.1420.0000.4004.00
R1: 49.0002.1420.0000.1001.00
在这里要要注意一些CLNS的特性，CLNS是独立于IP网络的协议，在FR中Map时不能象以前那样，
map ip XXX.XXX.XXX.XXX DLCI，这样去做了，只要map clns DLCI Bro就可以了。ISIS不在P2MP的环境运行，但是可以在P2P的环境下运行。ISIS不想OSPF有，ip ospf network [类型]命令可以让我们来更改网络类型，所有既要注意CLNS的一些特性。 在出现错误时，常用sh clns nei来查看ISIS的邻居关系有没有建立，deb isis is-nei de来查看ISIS的邻居关系的详细情况，sh isis da来看有没有接受到hello包。
之后可以用sh int s 0命令来查看接口上有没有严重的误码率，来排除是否是物理链路的错误
LZ问这两个网络类型能否配置OSPF问题？可见是你对其中理解的不是太透彻，呵呵。没关系，其实很简单。首先NBMA与多点网络（更确切的叫法是“点到多点网络”）就是OSPF协议的4种主要网络类型的两种，已经是NBMA和点到多点了，就是说明这条网络的路由协议里面主要用的就是OSPF了。
点到多点（PTMP）与NBMA（非广播多路访问网络）的区别主要是他们是否要选举DR和BDR。
NBMA中，每个路由必须手工配置出邻居路由器信息，根据这写信息，路由器们再自动选举出DR与BDR。它主要用在互联网的主要结构上，稳定安全。因为在NBMA中DR与BDR要知道每条路由的信息，需要你动脑子，需要复杂的计算，但复杂也会导致路由器的开销很大。
点到多点中，路由器将自动识别邻居路由器的信息，就不用去选举DR或BDR了，手工配置少，省力。但比不上NMBA的稳定，但简单，路由开销小。用在非主干的网络上，方便管理维护。
OSPF网络类型广播、NBMA（非广播点达）、P2MP、P2P广播、NBMA需要选举DR、BDR
P2MP、P2P需要选举DR、BDR
广播、NBMADR选举：
首先两台设备交互hello报文比较Hello报文参数参数相同才进行DR/BDR选举否则能通讯
1、Area ID
2、Hello/Dead 间间隔
3、认证类型认证密钥
4、特 殊区域类型Stub Flag
5、网掩码
面参数都首先比较端口优先级端口优先级选DR第二选BDR优先级相同则需要比较Router IDRouter ID选DR、第二选BDR优先级0则参与DR、BDR选举查看设备OSPF状态进入2-way状态
面限于第DR、BDR选举优先级更高加入现网络于安全稳定考虑新加入设备参加DR、BDR选举知道DR、BDR现故障才参与选举
选举DR、BDR原防止设备间相互发送OSPF交互报文每台设备都交互OSPF报文网络带宽快消耗掉都与DR、BDR交互报文由DR发减少OSPF报文交互提高网络带宽利用率
P2MP、P2P需要选举DR、BDR使用组播址224.0.0.5 224.0.0.6直接交互OSPF报文 些厂商（H3C）没按照RFC文档制作OSPF协议debug查看OSPF交互报文使用组播224.0.0.5.
