19-17 ip ospf network point-to-point

Syntax Description:

This command has no arguments.

Purpose: Used to configure an NBMA network as a point-to-point network.

Initial Cisco IOS Software Release: 10.0

Configuration Example: Point-to-Point Partially Meshed OSPF Neighbors

OSPF views networks as being of one of three types:

• A broadcast multiaccess network ” On a broadcast multiaccess network, all routers attached to the network have a direct communication link with all other routers on the network. Examples of a broadcast multiaccess network are Ethernet, Token Ring, and FDDI. When OSPF sends a protocol packet onto a broadcast multiaccess network, all OSPF routers on the network will receive the packet.

• A point-to-point network ” On a point-to-point network, only two routers exist on the network, one at each end of the point-to-point link. Examples of a point-to-point network are HDLC and PPP.

• An NBMA network ” Examples of an NBMA network are Frame Relay and X.25. On an NBMA network, all OSPF routers could possibly have connections to all other OSPF routers on the network but all the connections are logical point-to-point links, so an OSPF protocol packet sent on one link will not reach all OSPF neighbors. NBMA networks can be configured, from an OSPF point of view, as broadcast, point-to-point, or multipoint.

This example investigates configuring Frame Relay as an OSPF point-to-point network.

In Figure 19-13, three OSPF routers are partially meshed over a Frame Relay network. Router A is the hub and routers B and C are spokes . The two PVCs are configured on different IP subnets; therefore, the hub router needs two logical interfaces, one for each IP subnet. Initially the routers in Figure 19-13 are configured without specifying a network type in order to observe the OSPF behavior on an NBMA network. Router C uses a subinterface and Router B uses a major interface to illustrate the configuration differences.

Figure 19-13. A Point-to-Point NBMA Network

 Router A  interface Loopback0   ip address 1.1.1.1 255.255.255.255   interface Serial0/0   bandwidth 64   no ip address   encapsulation frame-relay   frame-relay lmi-type ansi   !   interface Serial0/0.1 point-to-point   ip address 10.1.1.1 255.255.255.252   frame-relay interface-dlci 101   !   interface Serial0/0.2 point-to-point   ip address 10.1.1.5 255.255.255.252   frame-relay interface-dlci 102   !   router ospf 1   network 1.1.1.1 0.0.0.0 area 1   network 10.1.1.0 0.0.0.3 area 0   network 10.1.1.4 0.0.0.3 area 0  _______________________________________________________________ Router B  interface Loopback0   ip address 2.2.2.2 255.255.255.255   !   interface Serial0   ip address 10.1.1.2 255.255.255.252   encapsulation frame-relay   bandwidth 64   frame-relay map ip 10.1.1.1 110 broadcast   no frame-relay inverse-arp   frame-relay lmi-type ansi   !   router ospf 1   network 2.2.2.2 0.0.0.0 area 2   network 10.1.1.0 0.0.0.3 area 0  ____________________________________________________________________________ Router C  interface Loopback0   ip address 3.3.3.3 255.255.255.255   !   interface Serial0   bandwidth 64   no ip address   encapsulation frame-relay   no frame-relay inverse-arp   !   interface Serial0.1 point-to-point   ip address 10.1.1.6 255.255.255.252   frame-relay interface-dlci 120   !   router ospf 1   network 3.3.3.3 0.0.0.0 area 3   network 10.1.1.4 0.0.0.3 area 0  

Frame Relay inverse ARP has been disabled on Router B to prevent Router B from learning about DLCIs that are not being used. Subinterfaces are used on Routers A and C so Frame Relay inverse ARP is automatically disabled. Chapter 11 demonstrates how to use the OSPF neighbor command to configure OSPF over an NBMA network. For this example, the OSPF interface command ip ospf network point-to-point has not been used on any of the routers. Determine if any OSPF neighbor relationships have been formed with Router A.

 rtrA#  show ip ospf neighbor  Neighbor ID     Pri   State           Dead Time   Address         Interface 3.3.3.3           1  FULL/  -  00:00:38    10.1.1.6        Serial0/0.2 

An OSPF neighbor relationship has been established between Routers A and C, but not Routers A and B. To understand why, you need to look at the OSPF network type that is being used on the Frame Relay interfaces.

 rtrA#  show ip ospf int s0/0.1  Serial0/0.1 is up, line protocol is up   Internet Address 10.1.1.1/30, Area 0   Process ID 1, Router ID 1.1.1.1,  Network Type POINT_TO_POINT  , Cost: 1562   Transmit Delay is 1 sec, State POINT_TO_POINT,   Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5     Hello due in 00:00:07   Index 1/1, flood queue length 0   Next 0x0(0)/0x0(0)   Last flood scan length is 1, maximum is 6   Last flood scan time is 0 msec, maximum is 0 msec   Neighbor Count is 0, Adjacent neighbor count is 0   Suppress hello for 0 neighbor(s) rtrA#  show ip ospf int s0/0.2  Serial0/0.2 is up, line protocol is up   Internet Address 10.1.1.5/30, Area 0   Process ID 1, Router ID 1.1.1.1,  Network Type POINT_TO_POINT  , Cost: 1562   Transmit Delay is 1 sec, State POINT_TO_POINT,   Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5     Hello due in 00:00:07   Index 2/2, flood queue length 0   Next 0x0(0)/0x0(0)   Last flood scan length is 1, maximum is 2   Last flood scan time is 0 msec, maximum is 0 msec   Neighbor Count is 1, Adjacent neighbor count is 1     Adjacent with neighbor 3.3.3.3   Suppress hello for 0 neighbor(s) ____________________________________________________________________________ rtrC#  show ip ospf int s0.1  Serial0.1 is up, line protocol is up   Internet Address 10.1.1.6/30, Area 0   Process ID 1, Router ID 3.3.3.3,  Network Type POINT_TO_POINT  , Cost: 1562   Transmit Delay is 1 sec, State POINT_TO_POINT,   Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5     Hello due in 00:00:06   Neighbor Count is 1, Adjacent neighbor count is 1     Adjacent with neighbor 1.1.1.1   Suppress hello for 0 neighbor(s) 

When the subinterfaces were created on Routers A and C, the type was set to point-to-point; therefore, the interface command ip ospf network point-to-point is not needed. Router B is not using a subinterface and the default OSPF network type is nonbroadcast.

 rtrB#  show ip ospf interface serial 0  Serial0 is up, line protocol is up   Internet Address 10.1.1.2/30, Area 0   Process ID 1, Router ID 2.2.2.2,  Network Type NON_BROADCAST  , Cost: 1562   Transmit Delay is 1 sec, State DR, Priority 1   Designated Router (ID) 2.2.2.2, Interface address 10.1.1.2   No backup designated router on this network   Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5     Hello due in 00:00:16   Neighbor Count is 0, Adjacent neighbor count is 0   Suppress hello for 0 neighbor(s) 

The neighbor command (Chapter 11) or the ip ospf network point-to-point command can be used on Router B to enable OSPF over the Frame Relay link. Modify Router B using the ip ospf network command.

 Router B  interface Serial0   ip address 10.1.1.2 255.255.255.252   encapsulation frame-relay    ip ospf network point-to-point    bandwidth 64   frame-relay map ip 10.1.1.1 110 broadcast   no frame-relay inverse-arp   frame-relay lmi-type ansi  

Verification

Verify that OSPF is treating the Frame Relay network as a point-to-point network on Router B.

 rtrB#  show ip ospf interface serial 0  Serial0 is up, line protocol is up   Internet Address 10.1.1.2/30, Area 0   Process ID 1, Router ID 2.2.2.2,  Network Type POINT_TO_POINT  , Cost: 1562   Transmit Delay is 1 sec, State POINT_TO_POINT,   Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5     Hello due in 00:00:02   Neighbor Count is 1, Adjacent neighbor count is 1     Adjacent with neighbor 1.1.1.1   Suppress hello for 0 neighbor(s) 

Verify that the OSPF neighbor relationships are established.

 rtrA#  show ip ospf neighbor  Neighbor ID     Pri   State           Dead Time   Address         Interface 3.3.3.3           1  FULL/  -  00:00:31    10.1.1.6        Serial0/0.2 2.2.2.2           1  FULL/  -  00:00:36    10.1.1.2        Serial0/0.1 

Each router is advertising its loopback network into OSPF. Check the routing tables on Routers A, B, and C to determine if the routes are being advertised to all routers.

 rtrA#  show ip route  Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP        D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area        N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2        E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP        i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area        * - candidate default, U - per-user static route, o - ODR        P - periodic downloaded static route Gateway of last resort is not set      1.0.0.0/32 is subnetted, 1 subnets C       1.1.1.1 is directly connected, Loopback0      2.0.0.0/32 is subnetted, 1 subnets  O IA    2.2.2.2 [110/1563] via 10.1.1.2, 00:45:57, Serial0/0.1  3.0.0.0/32 is subnetted, 1 subnets  O IA    3.3.3.3 [110/1563] via 10.1.1.6, 00:45:57, Serial0/0.2  10.0.0.0/30 is subnetted, 2 subnets C       10.1.1.0 is directly connected, Serial0/0.1 C       10.1.1.4 is directly connected, Serial0/0.2 ___________________________________________________________________________________ rtrB#  show ip route  Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP        D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area        N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2        E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP        i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default        U - per-user static route, o - ODR Gateway of last resort is not set      1.0.0.0/32 is subnetted, 1 subnets  O IA    1.1.1.1 [110/1563] via 10.1.1.1, 00:46:46, Serial0  2.0.0.0/32 is subnetted, 1 subnets C       2.2.2.2 is directly connected, Loopback0      3.0.0.0/32 is subnetted, 1 subnets  O IA    3.3.3.3 [110/3125] via 10.1.1.1, 00:46:46, Serial0  10.0.0.0/30 is subnetted, 2 subnets C       10.1.1.0 is directly connected, Serial0 O       10.1.1.4 [110/3124] via 10.1.1.1, 00:46:46, Serial0 _________________________________________________________________ rtrC#  show ip route  Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP        D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area        N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2        E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP        i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default        U - per-user static route, o - ODR Gateway of last resort is not set      1.0.0.0/32 is subnetted, 1 subnets  O IA    1.1.1.1 [110/1563] via 10.1.1.5, 00:47:13, Serial0.1  2.0.0.0/32 is subnetted, 1 subnets  O IA    2.2.2.2 [110/3125] via 10.1.1.5, 00:47:13, Serial0.1  3.0.0.0/32 is subnetted, 1 subnets C       3.3.3.3 is directly connected, Loopback0      10.0.0.0/30 is subnetted, 2 subnets O       10.1.1.0 [110/3124] via 10.1.1.5, 00:47:14, Serial0.1 C       10.1.1.4 is directly connected, Serial0.1 

Even though the routes are being advertised, they may not be reachable . Use the ping command to see if the routes can be reached.

 rtrA#  ping 2.2.2.2  Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 4/5/8 ms rtrA#  ping 3.3.3.3  Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 3.3.3.3, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 4/5/8 ms ______________________________________________________________________________ rtrB#  ping 1.1.1.1  Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 4/5/8 ms rtrB#  ping 3.3.3.3  Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 3.3.3.3, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 8/8/12 ms ______________________________________________________________________________ rtrC#  ping 1.1.1.1  Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/8 ms rtrC#  ping 2.2.2.2  Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 8/8/12 ms 

Troubleshooting

Step 1. Verify the IP address and netmask assignments used on the NBMA network interfaces.

Step 2. Verify that the proper DLCIs and IP addresses are being used. These can be checked using the show frame-relay map command.

 rtrA#  show frame-relay map  Serial0/0.2 (up): point-to-point dlci, dlci 102(0x66,0x1860), broadcast           status defined, active Serial0/0.1 (up): point-to-point dlci, dlci 101(0x65,0x1850), broadcast status defined, active 

Step 3. Before configuring OSPF, check IP connectivity by pinging the other end of each Frame Relay link.

Step 4. If you are mixing network types (multipoint and point-to-point), verify that the Hello intervals match on all routers.