OSPF–Point To Multipoint Networks
using the same setup we used in the last 2 posts for Broadcast and Non-Broadcast Networks, but we will create multipoint interface on each router
R1 interface Serial0/0 no ip address encapsulation frame-relay no frame-relay inverse-arp ! interface Serial0/0.123 multipoint ip address 10.1.123.1 255.255.255.0 frame-relay map ip 10.1.123.2 102 broadcast frame-relay map ip 10.1.123.3 103 broadcast R2 interface Serial0/0 no ip address encapsulation frame-relay no frame-relay inverse-arp ! interface Serial0/0.123 multipoint ip address 10.1.123.2 255.255.255.0 frame-relay map ip 10.1.123.1 201 broadcast R3 interface Serial1/0 no ip address encapsulation frame-relay no frame-relay inverse-arp ! interface Serial0/0.123 multipoint ip address 10.1.123.3 255.255.255.0 frame-relay map ip 10.1.123.1 301 broadcast |
interf s0/0.123 ip ospf 1 area 0 R2 interf s0/0.123 ip ospf 1 area 0 R3 interf s1/0.123 ip ospf 1 area 0 |
R3(config)#do sh ip os inter Serial1/0.123 is up, line protocol is up Internet Address 10.1.123.3/24, Area 0 Process ID 1, Router ID 3.3.3.3, Network Type NON_BROADCAST, Cost: 781 Enabled by interface config, including secondary ip addresses |
We will change R1 s0/0.123 and see what happens
interf s0/0.123 ip ospf network point-to-multipoint |
R1
R1(config-router)#do sh ip os inter Serial0/0.123 is up, line protocol is up Internet Address 10.1.123.1/24, Area 0 Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_MULTIPOINT, Cost: 64 Enabled by interface config, including secondary ip addresses Transmit Delay is 1 sec, State POINT_TO_MULTIPOINT, Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5 R1(config-router)#do sh ip ospf ne Neighbor ID Pri State Dead Time Address Interface 2.2.2.2 0 FULL/ - 00:01:37 10.1.123.2 Serial0/0.123 3.3.3.3 0 FULL/ - 00:01:46 10.1.123.3 Serial0/0.123 R1(config-router)#do sh ip route ospf R1(config-router)# |
R2(config)#do sh ip os ne Neighbor ID Pri State Dead Time Address Interface 1.1.1.1 1 FULL/BDR 00:01:35 10.1.123.1 Serial0/0.123 R2(config)#do sh ip route ospf R2(config)# |
R3(config)#do sh ip os ne Neighbor ID Pri State Dead Time Address Interface 1.1.1.1 1 FULL/BDR 00:01:50 10.1.123.1 Serial1/0.123 |
Things should be sorted out after changing the OSPF network types on R2 and R3
R1(config)#do sh ip os ne Neighbor ID Pri State Dead Time Address Interface 2.2.2.2 0 FULL/ - 00:01:55 10.1.123.2 Serial0/0.123 3.3.3.3 0 FULL/ - 00:01:58 10.1.123.3 Serial0/0.123 R1(config)#do sh ip route R1(config)#do sh ip route os 2.0.0.0/32 is subnetted, 1 subnets O 2.2.2.2 [110/65] via 10.1.123.2, 00:00:30, Serial0/0.123 3.0.0.0/32 is subnetted, 1 subnets O 3.3.3.3 [110/65] via 10.1.123.3, 00:00:30, Serial0/0.123 10.0.0.0/8 is variably subnetted, 3 subnets, 2 masks O 10.1.123.2/32 [110/64] via 10.1.123.2, 00:00:30, Serial0/0.123 O 10.1.123.3/32 [110/64] via 10.1.123.3, 00:00:30, Serial0/0.123 |
R2(config)#do sh ip os ne Neighbor ID Pri State Dead Time Address Interface 1.1.1.1 0 FULL/ - 00:01:47 10.1.123.1 Serial0/0.123 R2(config)#do sh ip route ospf 1.0.0.0/32 is subnetted, 1 subnets O 1.1.1.1 [110/65] via 10.1.123.1, 00:04:40, Serial0/0.123 3.0.0.0/32 is subnetted, 1 subnets O 3.3.3.3 [110/129] via 10.1.123.3, 00:04:40, Serial0/0.123 10.0.0.0/8 is variably subnetted, 3 subnets, 2 masks O 10.1.123.1/32 [110/64] via 10.1.123.1, 00:04:40, Serial0/0.123 O 10.1.123.3/32 [110/128] via 10.1.123.1, 00:04:40, Serial0/0.123 |
R3(config)#do sh ip os ne Neighbor ID Pri State Dead Time Address Interface 1.1.1.1 0 FULL/ - 00:01:43 10.1.123.1 Serial1/0.123 R3(config)#do sh ip route ospf 1.0.0.0/32 is subnetted, 1 subnets O 1.1.1.1 [110/782] via 10.1.123.1, 00:24:25, Serial1/0.123 2.0.0.0/32 is subnetted, 1 subnets O 2.2.2.2 [110/846] via 10.1.123.2, 00:24:25, Serial1/0.123 10.0.0.0/8 is variably subnetted, 3 subnets, 2 masks O 10.1.123.1/32 [110/781] via 10.1.123.1, 00:24:25, Serial1/0.123 O 10.1.123.2/32 [110/845] via 10.1.123.1, 00:24:25, Serial1/0.123 |
- We can see that point-to-multipoint OSPF networks don’t require DR/BDR election
- We can also see the next hop for R2/R3 loopback interfaces on R3/R2 respectively are pointing to R1 as the Hub that's why we don't need the extra frame relay mapping on the spokes unlike broadcast and non broadcast networks
- Finally we can see the host routes on the three routers, while the major subnets are suppressed and not being advertised by the Hub
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