Note
Use the ip ospf mtu-ignore command for OSPFv2 or ipv6 ospf mtu-ignore command for OSPFv3 to disable MTU mismatch detection on an interface. By default, OSPF checks whether neighbors use the same MTU on a common interface. If the receiving MTU is higher than the IP MTU configured on the incoming interface, OSPF does not establish adjacencies. The mtu-ignore command will disable this check and allow adjacencies when the MTU value differs between OSPF neighbors. This command will help only if the OSPF LSA database packet size is less than the lowest interface MTU. If the OSPF LSA packet is greater than the interface MTU, the physical interface will drop the packet as defragment disabled, and the OSPF neighbor will continuously change state between Down and Full.
Note
The dead interval default will be 4xhello-interval. In this example, it is set to 100 seconds. You can set the dead interval using the OSPF interface command ospf dead-interval seconds.
Example 1-4 OSPF Authentication Shared Key Configuration
SW9621-1(config)#
key chain mypass
SW9621-1(config-keychain)#
key 0
SW9621-1(config-keychain-key)#
key-string cisco
SW9621-1(config-keychain-key)#
exit
SW9621-1(config-keychain)#
exit
Examples 1-5 and 1-6 show the SW9621-1 OSPF status.
Example 1-5 OSFPv2 ABR Verification (SW9621-1)
SW9621-1#
show ip ospf neighbors
OSPF Process ID 21 VRF default
Total number of neighbors: 3
Neighbor ID Pri State Up Time Address Interface
1.1.1.10 10 FULL/BDR 00:20:19 10.10.10.2 Eth2/1
1.1.1.11 1 FULL/ – 00:20:48 10.10.10.6 Eth2/2
1.1.1.15 1 FULL/BDR 00:04:39 10.10.10.10 Eth2/3
SW9621-1#
show ip ospf
Routing Process 21 with ID 1.1.1.1 VRF default
Routing Process Instance Number 1
Stateful High Availability enabled
Graceful-restart is configured
Grace period: 60 state: Inactive
Last graceful restart exit status: None
Supports only single TOS(TOS0) routes
Supports opaque LSA
This router is an area border
Administrative distance 110
Reference Bandwidth is 40000 Mbps
SPF throttling delay time of 200.000 msecs,
SPF throttling hold time of 1000.000 msecs,
SPF throttling maximum wait time of 5000.000 msecs
LSA throttling start time of 0.000 msecs,
LSA throttling hold interval of 5000.000 msecs,
LSA throttling maximum wait time of 5000.000 msecs
Minimum LSA arrival 1000.000 msec
LSA group pacing timer 10 secs
Maximum paths to destination 8
Number of external LSAs 0, checksum sum 0
Number of opaque AS LSAs 0, checksum sum 0
Number of areas is 2, 1 normal, 1 stub, 0 nssa
Number of active areas is 2, 1 normal, 1 stub, 0 nssa
Install discard route for summarized external routes.
Install discard route for summarized internal routes.
Area BACKBONE(0.0.0.0)
Area has existed for 00:37:14
Interfaces in this area: 3 Active interfaces: 3
Passive interfaces: 0 Loopback interfaces: 1
Message-digest authentication
SPF calculation has run 20 times
Last SPF ran for 0.000420s
Area ranges are
Number of LSAs: 7, checksum sum 0x363a9
Area (0.0.0.5)
Area has existed for 00:37:14
Interfaces in this area: 1 Active interfaces: 1
Passive interfaces: 0 Loopback interfaces: 0
This area is a STUB area
Generates stub default route with cost 1
No authentication available
SPF calculation has run 20 times
Last SPF ran for 0.000078s
Area ranges are
Number of LSAs: 11, checksum sum 0x5306a
SW9621-1#
show ip ospf interface brief
OSPF Process ID 21 VRF default
Total number of interface: 4
Interface ID Area Cost State Neighbors Status
Lo0 1 0.0.0.0 1 LOOPBACK 0 up
Eth2/1 4 0.0.0.0 40 DR 1 up
Eth2/2 3 0.0.0.0 40 P2P 1 up
Eth2/3 2 0.0.0.5 40 DR 1 up
SW9621-1#
show ip ospf interface
loopback0 is up, line protocol is up
IP address 1.1.1.1/32
Process ID 21 VRF default, area 0.0.0.0
Enabled by interface configuration
State LOOPBACK, Network type LOOPBACK, cost 1
Index 1
Ethernet2/1 is up, line protocol is up
IP address 10.10.10.1/30
Process ID 21 VRF default, area 0.0.0.0
Enabled by interface configuration
State DR, Network type BROADCAST, cost 40
Index 4, Transmit delay 1 sec, Router Priority 1
Designated Router ID: 1.1.1.1, address: 10.10.10.1
Backup Designated Router ID: 1.1.1.10, address: 10.10.10.2
1 Neighbors, flooding to 1, adjacent with 1
Timer intervals: Hello 10, Dead 40, Wait 40, Retransmit 5
Hello timer due in 00:00:05
Message-digest authentication, using keychain mypass (ready)
Number of opaque link LSAs: 0, checksum sum 0
Ethernet2/2 is up, line protocol is up
IP address 10.10.10.5/30
Process ID 21 VRF default, area 0.0.0.0
Enabled by interface configuration
State P2P, Network type P2P, cost 40
Index 3, Transmit delay 1 sec
1 Neighbors, flooding to 1, adjacent with 1
Timer intervals: Hello 10, Dead 40, Wait 40, Retransmit 5
Hello timer due in 00:00:02
Message-digest authentication, using keychain mypass (ready)
Number of opaque link LSAs: 0, checksum sum 0
Ethernet2/3 is up, line protocol is up
IP address 10.10.10.9/30
Process ID 21 VRF default, area 0.0.0.5
Enabled by interface configuration
State DR, Network type BROADCAST, cost 40
Index 2, Transmit delay 1 sec, Router Priority 1
Designated Router ID: 1.1.1.1, address: 10.10.10.9
Backup Designated Router ID: 1.1.1.15, address: 10.10.10.10
1 Neighbors, flooding to 1, adjacent with 1
Timer intervals: Hello 25, Dead 100, Wait 100, Retransmit 5
Hello timer due in 00:00:06
No authentication
Number of opaque link LSAs: 0, checksum sum 0
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