OSPF Broadcast Mode over Full-Mesh Frame Relay Network with One IP Subnet
Below shows the OSPF neighbors and IP routing table on RT1:
RT1#sh ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 200.1.1.2 0 FULL/DROTHER 00:00:39 200.1.1.2 Serial0/0 200.1.1.3 0 FULL/DROTHER 00:00:33 200.1.1.3 Serial0/0 RT1# RT1#sh ip route Gateway of last resort is not set C 200.1.1.0/24 is directly connected, Serial0/0 172.16.0.0/24 is subnetted, 3 subnets C 172.16.1.0 is directly connected, FastEthernet1/0 O 172.16.2.0 [110/65] via 200.1.1.2, 00:01:00, Serial0/0 O 172.16.3.0 [110/65] via 200.1.1.3, 00:01:00, Serial0/0 RT1#
OSPF Broadcast Mode over Partial-Mesh Frame Relay Network with One IP Subnet
The frame-relay map ip {ip-addr} {dlci} interface subcommand is required on spoke routers as there are no PVCs between spoke routers. The broadcast keyword is optional for this setup.
Below shows the OSPF neighbors and IP routing table on RT2:
RT2#sh frame-relay map Serial0/0 (up): ip 200.1.1.1 dlci 101(0x65,0x1850), dynamic, broadcast,, status defined, active Serial0/0 (up): ip 200.1.1.3 dlci 101(0x65,0x1850), static, CISCO, status defined, active RT2# RT2#sh ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 200.1.1.1 255 FULL/DR 00:00:39 200.1.1.1 Serial0/0 RT2# RT2#sh ip route Gateway of last resort is not set C 200.1.1.0/24 is directly connected, Serial0/0 172.16.0.0/24 is subnetted, 3 subnets O 172.16.1.0 [110/65] via 200.1.1.1, 00:00:17, Serial0/0 C 172.16.2.0 is directly connected, FastEthernet1/0 O 172.16.3.0 [110/65] via 200.1.1.3, 00:00:17, Serial0/0 RT2#
OSPF Non-Broadcast Mode over Full-Mesh Frame Relay Network with One IP Subnet
Below shows the OSPF neighbors on RT1, RT2, and RT3:
RT1#sh ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface N/A 0 ATTEMPT/DROTHER 00:01:42 200.1.1.2 Serial0/0 N/A 0 ATTEMPT/DROTHER 00:01:42 200.1.1.3 Serial0/0 RT1# 00:07:04: %OSPF-5-ADJCHG: Process 100, Nbr 200.1.1.2 on Serial0/0 from LOADING to FULL, Loading Done 00:07:04: %OSPF-5-ADJCHG: Process 100, Nbr 200.1.1.3 on Serial0/0 from LOADING to FULL, Loading Done RT1#sh ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 200.1.1.2 0 FULL/DROTHER 00:01:45 200.1.1.2 Serial0/0 200.1.1.3 0 FULL/DROTHER 00:01:45 200.1.1.3 Serial0/0 RT1# ====================================================================== RT2#sh ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 200.1.1.1 255 FULL/DR 00:01:55 200.1.1.1 Serial0/0 RT2# ====================================================================== RT3#sh ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 200.1.1.1 255 FULL/DR 00:01:47 200.1.1.1 Serial0/0 RT3#
OSPF Non-Broadcast Mode over Partial-Mesh Frame Relay Network with One IP Subnet
The frame-relay map ip {ip-addr} {dlci} interface subcommand is required on spoke routers as there are no PVCs between spoke routers. The broadcast keyword is optional for this setup.
Below shows the OSPF neighbors on RT1, RT2, and RT3:
RT1#sh ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 200.1.1.2 0 FULL/DROTHER 00:01:55 200.1.1.2 Serial0/0 200.1.1.3 0 FULL/DROTHER 00:01:55 200.1.1.3 Serial0/0 RT1# ====================================================================== RT2#sh ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 200.1.1.1 255 FULL/DR 00:01:58 200.1.1.1 Serial0/0 RT2# ====================================================================== RT3#sh ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 200.1.1.1 255 FULL/DR 00:01:42 200.1.1.1 Serial0/0 RT3#
The neighbor {ip-addr} [cost num] [database-filter all out] [poll-interval sec] [priority num] router subcommand specifies a neighboring OSPF router that connects to a NBMA network. The priority option specifies the router priority for a neighboring router. The default priority value is 0, which designates that the neighboring routers as a DROTHER.
Note: The priority configured with the ip ospf priority interface subcommand on spoke router would override the priority configured with the neighbor router subcommand on the hub router.
When a neighboring router has become inactive or dead (Hello packets have not been received for RouterDeadInterval), it may still be necessary to send Hello packets to the dead neighbor. These Hello packets will be sent at the reduced rate – PollInterval, which should be much larger than HelloInterval. The default PollInterval value is 120 seconds (2 minutes).
The interval between Hello packets is determined by the state of the neighbor. If the neighbor is in the DOWN state, Hello packets are sent every PollInterval; otherwise, the Hello packets are sent every HelloInterval.
When an OSPF router first starts up, it sends only Hello packets to other routers with non-zero priority – routers that are eligible to become DR and BDR. After the DR election, DR and BDR will then start sending Hello packets to all other neighboring routers in order to form adjacencies.
The cost option assigns a cost to the link to a neighboring router to reflect the link bandwidth.
The database-filter all out keyword filters outgoing LSAs to a neighboring router.
The poll-interval and priority options are allowed only for non-broadcast interface type; while the cost and database-filter options are allowed only for point-to-multipoint and point-to-multipoint non-broadcast interface types.
In non-broadcast mode, the neighbor statements are required only on the DR and BDR. In a hub-and-spoke partial-mesh topology, the neighbor statements are required on the hub router, which must also be configured to become a DR by being assigned a higher priority; while the neighbor statements are not required on the spoke routers. In a full-mesh topology, the neighbor statements are required on all routers unless the DR and BDR are manually configured using the ip ospf priority interface subcommand.
In point-to-multipoint mode, the DR and BDR are not elected. Multicast Hello packets are used to automatically discover the neighbors, and manual neighbor configuration is not required. The Network-LSAs are not exchanged between neighboring routers; instead, routers exchange additional LSAs to describe the underlying network topology (be it full-mesh or partial-mesh).
The point-to-multipoint mode reduces the number of VCs required for complete connectivity, as it does not require a full-mesh topology. It allows routing between routers that are not directly connected via a VC but are connected through a (hub) router that has VCs connected to them.
The point-to-multipoint mode treats a NBMA network as a collection of point-to-point links rather than a multi-access network, which is not suitable for networks with dynamic connections, in which SVCs are being used instead of PVCs. The Cisco-proprietary point-to-multipoint non-broadcast extension mode should be used instead.
Note: Cisco routers only support Frame Relay SVC in Data Terminal Equipment (DTE) mode. The Cisco Frame Relay switching feature does not support SVC. Due to the limitation of hardware availability and limited deployment of SVCs in current networking industry, the configuration for point-to-multipoint non-broadcast mode will not be discussed.
OSPF Point-to-Multipoint Mode over Full-Mesh Frame Relay Network with One IP Subnet
Below shows the OSPF neighbors, IP routing table, and OSPF link-state database on RT1:
RT1#sh ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 200.1.1.3 0 FULL/ - 00:01:48 200.1.1.3 Serial0/0 200.1.1.2 0 FULL/ - 00:01:51 200.1.1.2 Serial0/0 RT1# RT1#sh ip route Gateway of last resort is not set 200.1.1.0/24 is variably subnetted, 3 subnets, 2 masks C 200.1.1.0/24 is directly connected, Serial0/0 O 200.1.1.2/32 [110/64] via 200.1.1.2, 00:00:05, Serial0/0 O 200.1.1.3/32 [110/64] via 200.1.1.3, 00:00:05, Serial0/0 172.16.0.0/24 is subnetted, 3 subnets C 172.16.1.0 is directly connected, FastEthernet1/0 O 172.16.2.0 [110/65] via 200.1.1.2, 00:00:05, Serial0/0 O 172.16.3.0 [110/65] via 200.1.1.3, 00:00:05, Serial0/0 RT1# RT1#sh ip ospf database OSPF Router with ID (200.1.1.1) (Process ID 100) Router Link States (Area 0) Link ID ADV Router Age Seq# Checksum Link count 200.1.1.1 200.1.1.1 32 0x80000003 0x00AB84 4 200.1.1.2 200.1.1.2 32 0x80000002 0x00F239 4 200.1.1.3 200.1.1.3 27 0x80000003 0x0042E3 4 RT1#
OSPF Point-to-Multipoint Mode over Partial-Mesh Frame Relay Network with One IP Subnet
Note: The frame-relay map ip {ip-addr} {dlci} interface subcommand is NOT required on spoke routers even there are no PVCs between spoke routers.
Below shows the OSPF neighbors on RT1, RT2, and RT3:
RT1#sh ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 200.1.1.3 0 FULL/ - 00:01:45 200.1.1.3 Serial0/0 200.1.1.2 0 FULL/ - 00:01:45 200.1.1.2 Serial0/0 RT1# ====================================================================== RT2#sh ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 200.1.1.1 0 FULL/ - 00:01:40 200.1.1.1 Serial0/0 RT2# ====================================================================== RT3#sh ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 200.1.1.1 0 FULL/ - 00:01:58 200.1.1.1 Serial0/0 RT3#
Note: The network setup above is operational when Serial0/0 on RT2 and RT3 is configured with ip ospf network point-to-point. However, the ip ospf hello-interval 10 interface subcommand must be configured on RT1 Serial0/0 or else the adjacencies will not be established due to mismatched Hello parameters – 10 seconds for P2P and 40 seconds for NBMA.
OSPF Point-to-Point Mode over Partial-Mesh Frame Relay Network with One IP Subnet Per VC
Below shows the OSPF neighbors on RT1, RT2, and RT3:
RT1#sh ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 172.16.3.1 0 FULL/ - 00:00:36 11.11.11.2 Serial0/0.103 172.16.2.1 0 FULL/ - 00:00:34 10.10.10.2 Serial0/0.102 RT1# ====================================================================== RT2#sh ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 172.16.1.1 0 FULL/ - 00:00:33 10.10.10.1 Serial0/0.101 RT2# ====================================================================== RT3#sh ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 172.16.1.1 0 FULL/ - 00:00:34 11.11.11.1 Serial0/0.101 RT3#
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