《ospf network types》由会员分享，可在线阅读，更多相关《ospf network types（53页珍藏版）》请在金锄头文库上搜索。
1、Configuring OSPF,OSPF Network Types,OSPF Network Types,The three types of networks defined by OSPF are: Point-to-point: A network that joins a single pair of routers. Broadcast: A multiaccess broadcast network, such as Ethernet. Nonbroadcast multiaccess (also called NBMA): A network that interconnec
2、ts more than two routers but that has no broadcast capability. Frame Relay, ATM, and X.25 are examples of NBMA networks. Five modes of OSPF operation are available for NBMA networks.,Point-to-Point Links,Usually a serial interface running either PPP or HDLC. May also be a point-to-point subinterface
3、 running Frame Relay or ATM. No DR or BDR election required. OSPF autodetects this interface type. OSPF packets are sent using multicast 224.0.0.5.,Multiaccess Broadcast Network,Generally these are, LAN technologies like Ethernet and Token Ring. DR and BDR selection are required. All neighbor router
4、s form full adjacencies with the DR and BDR only. Packets to the DR and the BDR use 224.0.0.6. Packets from DR to all other routers use 224.0.0.5.,Electing the DR and BDR,Hello packets are exchanged via IP multicast. The router with the highest OSPF priority is selected as the DR. The router with th
5、e second-highest priority value is the BDR. Use the OSPF router ID as the tiebreaker. The DR election is nonpreemptive.,Setting Priority for DR Election,This interface configuration command assigns the OSPF priority to an interface. Different interfaces on a router may be assigned different values.
6、The default priority is 1. The range is from 0 to 255. 0 means the router cannot be the DR or BDR. A router that is not the DR or BDR is DROTHER.,ip ospf priority number,Router(config-if)#,NBMA Topology,A single interface interconnects multiple sites. NBMA topologies support multiple routers, but wi
7、thout broadcasting capabilities.,DR Election in NBMA Topology,OSPF considers NBMA to be like other broadcast media. The DR and BDR need to have fully meshed connectivity with all other routers, but NBMA networks are not always fully meshed. The DR and BDR need a list of neighbors. OSPF neighbors are
8、 not automatically discovered by the router.,Frame Relay Topologies,OSPF over NBMA Topology Modes of Operation,RFC 2328-compliant modes are as follows: Nonbroadcast (NBMA) Point-to-multipoint Additional modes from Cisco are as follows: Point-to-multipoint nonbroadcast Broadcast Point-to-point,Select
9、ing the OSPF Network Type for NBMA Networks,ip ospf network broadcast | non-broadcast | point-to-multipoint non-broadcast | point-to-point,Defines OSPF network type,Router(config-if)#,Router(config)#interface serial 0/0/0 Router(config-if)#encapsulation frame-relay Router(config-if)#ip ospf network
10、broadcast,Example: Broadcast Mode,Nonbroadcast Mode (NBMA Mode),Treated as a broadcast network by OSPF (acts like a LAN). All serial ports are part of the same IP subnet. Frame Relay, X.25, and ATM networks default to nonbroadcast mode. Neighbors must be statically configured. Duplicates LSA updates
11、. Complies with RFC 2328.,Using the neighbor Command,Used to statically define neighbor relationships in an NBMA network,neighbor ip-address priority number poll-interval number cost number database-filter all,Router(config-router)#,neighbor Command Example,RouterA(config)# router ospf 100 RouterA(c
12、onfig-router)# network 192.168.0.0 0.0.255.255 area 0 RouterA(config-router)# neighbor 192.168.1.2 priority 0 RouterA(config-router)# neighbor 192.168.1.3 priority 0 RouterA(config-router)# network 172.16.0.0 0.0.255.255 area 0,RouterA# show ip ospf neighborNeighbor ID Pri State Dead Time Address In
13、terface 192.168.1.3 0 FULL/DROTHER 00:01:57 192.168.1.3 Serial0/0/0 192.168.1.2 0 FULL/DROTHER 00:01:33 192.168.1.2 Serial0/0/0 172.16.1.1 1 FULL/BDR 00:00:34 172.16.1.1 FastEthernet0/0,The show ip ospf neighbor Command,Point-to-Multipoint Mode,The point-to-multipoint mode allows for NBMA networking
14、. The point-to-multipoint mode fixes partial-mesh and star topologies. No DR is required and only a single subnet is used. A 30-second hello is used. This mode is RFC 2328-compliant.,Point-to-Multipoint Configuration,interface Serial0/0/0ip address 192.168.1.1 255.255.255.0encapsulation frame-relayi
15、p ospf network point-to-multipointrouter ospf 100log-adjacency-changesnetwork 172.16.0.0 0.0.255.255 area 0network 192.168.0.0 0.0.255.255 area 0,interface Serial0/0/0ip address 192.168.1.3 255.255.255.0encapsulation frame-relayip ospf network point-to-multipointip ospf priority 0,Router A,Router C,
16、Point-to-Multipoint Example,RouterA#sh ip ospf int s0/0/0 Serial0/0/0 is up, line protocol is upInternet Address 192.168.1.1/24, Area 0Process ID 100, Router ID 192.168.1.1, Network Type POINT_TO_MULTIPOINT, Cost: 781Transmit Delay is 1 sec, State POINT_TO_MULTIPOINTTimer intervals configured, Hello
17、 30, Dead 120, Wait 120, Retransmit 5oob-resync timeout 120Hello due in 00:00:26Supports Link-local Signaling (LLS)Index 2/2, flood queue length 0Next 0x0(0)/0x0(0)Last flood scan length is 1, maximum is 1Last flood scan time is 0 msec, maximum is 4 msecNeighbor Count is 2, Adjacent neighbor count is 2Adjacent with neighbor 192.168.1.3Adjacent with neighbor 192.168.1.2Suppress hello for 0 neighbor(s) RouterA#,
