OSPF 1秒未満Hello
設定
192.168.xy.0/24
Loopback: x.x.x.x/8
全I/FにてOSPFを起動
前提知識
OSPFのHello/DeadはBroadcastで10/40(s)がデフォなのは常識。
iosv-3#sh ip o int gi0/0
GigabitEthernet0/0 is up, line protocol is up
Internet Address 192.168.23.3/24, Area 0, Attached via Interface Enable
Process ID 1, Router ID 3.3.3.3, Network Type BROADCAST, Cost: 1
Topology-MTID Cost Disabled Shutdown Topology Name
0 1 no no Base
Enabled by interface config, excluding secondary ip addresses
Transmit Delay is 1 sec, State BDR, Priority 1
Designated Router (ID) 2.2.2.2, Interface address 192.168.23.2
Backup Designated router (ID) 3.3.3.3, Interface address 192.168.23.3
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
oob-resync timeout 40
Hello due in 00:00:02
Supports Link-local Signaling (LLS)
Cisco NSF helper support enabled
IETF NSF helper support enabled
Index 1/1/1, flood queue length 0
Next 0x0(0)/0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 1
Last flood scan time is 1 msec, maximum is 1 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 2.2.2.2 (Designated Router)
Suppress hello for 0 neighbor(s)Helloを1秒未満にしたい
DeadはHelloの1/4秒になっているので、逆もしかり、Deadを1秒にすれば0.25秒になるのではという算段。
iosv-3(config)#int gi0/0
iosv-3(config-if)#ip o dead 1
iosv-3(config-if)#do sh ip o int gi0/0
GigabitEthernet0/0 is up, line protocol is up
Internet Address 192.168.23.3/24, Area 0, Attached via Interface Enable
Process ID 1, Router ID 3.3.3.3, Network Type BROADCAST, Cost: 1
Topology-MTID Cost Disabled Shutdown Topology Name
0 1 no no Base
Enabled by interface config, excluding secondary ip addresses
Transmit Delay is 1 sec, State DR, Priority 1
Designated Router (ID) 3.3.3.3, Interface address 192.168.23.3
No backup designated router on this network
Timer intervals configured, Hello 10, Dead 1, Wait 1, Retransmit 5
oob-resync timeout 40
Hello due in 00:00:09
Supports Link-local Signaling (LLS)
Cisco NSF helper support enabled
IETF NSF helper support enabled
Index 1/1/1, flood queue length 0
Next 0x0(0)/0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 1
Last flood scan time is 1 msec, maximum is 1 msec
Neighbor Count is 0, Adjacent neighbor count is 0
Suppress hello for 0 neighbor(sまあならないんですねこれが。Helloは変わらずDeadだけ変わる。
ip o dead minimal hello x
iosv-2(config-if)#ip o dead minimal hello 4
iosv-2(config-if)#
iosv-2(config-if)#do sh ip o int gi0/1 | i Hello
Timer intervals configured, Hello 250 msec, Dead 1, Wait 1, Retransmit 5
Hello due in 107 msec正式には
(config-if)#ip ospf dead-interval minimal hello-multiplier 4
因みに
Helloを1秒未満にすると不一致でもネイバーを確立する。
厳密には、OSPFパケット上ではHelloが０として送信されるため、対向と０で一致してネイバーを形成している。
iosv-2(config-if)#do sh ip o nei
Neighbor ID Pri State Dead Time Address Interface
iosv-3 1 FULL/DR 815 msec 192.168.23.3 GigabitEthernet0/1
iosv-1 1 FULL/BDR 00:00:30 192.168.12.1 GigabitEthernet0/0
iosv-2(config-if)#
iosv-2(config-if)#do sh ip o int gi0/1 | i Hello
Timer intervals configured, Hello 200 msec, Dead 1, Wait 1, Retransmit 5
Hello due in 118 msec
iosv-3(config-if)#do sh ip o nei
Neighbor ID Pri State Dead Time Address Interface
2.2.2.2 1 FULL/BDR 955 msec 192.168.23.2 GigabitEthernet0/0
iosv-3(config-if)#do sh ip o int gi0/0 | i Hello
Timer intervals configured, Hello 250 msec, Dead 1, Wait 1, Retransmit 5
Hello due in 147 msec上記ではiosv-2が200msec, iosv-3が250msecだがネイバーが形成されている。
参考
CCIE Enterprise Infrastructure Foundation, 2nd Edition
OSPFのネイバーを張る為にはHello/Deadタイマーは一致する必要がある？その2（回答編）