OSPF Router Id
Before OSPF sends any messages it must choose 32 bit id.
Desicion process:
router id command
Launched on Router without configured ip addresses:
(config)#router ospf 1
*Aug 6 22:03:30.995: %OSPF-4-NORTRID: OSPF process 1 failed to allocate unique router-id and cannot start
R1(config-router)#rout
R1(config-router)#router-id 1.1.1.1
R1(config-router)#do sho ip ospf
Routing Process "ospf 1" with ID 1.1.1.1
highes ip address of no shut loopback interface
R1(config-router)#int lo0
*Aug 6 22:06:16.975: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback0, changed state to up
R1(config-if)#ip address 2.2.2.2 255.255.255.255
R1(config-if)#do sho ip ospf
Routing Process "ospf 1" with ID 1.1.1.1
R1(config-if)#router ospf 1
R1(config-router)#no rou
R1(config-router)#no router-id 1.1.1.1
R1(config-router)#do show ip ospf
Routing Process "ospf 1" with ID 2.2.2.2
highest Ip address on no shut, nonloopback interface
(config-if)#do show ip int br
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 192.168.12.1 YES manual administratively down down
FastEthernet1/0 192.168.23.1 YES manual administratively down down
GigabitEthernet2/0 unassigned YES unset administratively down down
Loopback0 2.2.2.2 YES manual up up
R1(config-if)#do show ip ospf
Routing Process "ospf 1" with ID 2.2.2.2
R1(config-if)#no int lo0
*Aug 6 22:11:58.663: %LINK-5-CHANGED: Interface Loopback0, changed state to administratively down
*Aug 6 22:11:59.663: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback0, changed state to down
R1(config)#do show ip ospf
Routing Process "ospf 1" with ID 2.2.2.2
R1#clear ip ospf process
Reset ALL OSPF processes? [no]:
R1#show ip ospf
Routing Process "ospf 1" with ID 2.2.2.2
Start time: 00:00:30.932, Time elapsed: 00:11:12.396
R1# show ip int br
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 192.168.12.1 YES manual administratively down down
FastEthernet1/0 192.168.23.1 YES manual administratively down down
GigabitEthernet2/0 unassigned YES unset administratively down down
R1#
R1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#no router ospf 1
R1(config)#router ospf 1
R1(config-router)#do s
*Aug 6 22:17:47.827: %OSPF-4-NORTRID: OSPF process 1 failed to allocate unique router-id and cannot start
Even if links are not administratively shut
R1(config-if)#router ospf 1
R1(config-router)#do show ip ospf
%OSPF: Router process 1 is not running, please configure a router-id
R1(config-router)#do show ip ospf
%OSPF: Router process 1 is not running, please configure a router-id
R1(config-router)#do show ip int br
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 192.168.12.1 YES manual down down
FastEthernet1/0 192.168.23.1 YES manual down down
GigabitEthernet2/0 unassigned YES unset administratively down down
R1(config-router)#
R1(config-router)#int lo0
R1(config-if)#ip add
R1(config-if)#ip address 2.2
*Aug 6 22:23:11.799: %LINK-3-UPDOWN: Interface Loopback0, changed state to up
*Aug 6 22:23:12.799: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback0, changed state to up
R1(config-if)#ip address 2.2.2.2 255.255.255.0
R1(config-if)#do show ip ospf
Routing Process "ospf 1" with ID 2.2.2.2
Router Id doesn’t change from the start even loopback is deleted
*Aug 6 22:23:58.987: %LINK-3-UPDOWN: Interface FastEthernet0/0, changed state to up
*Aug 6 22:23:59.987: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed state to up
*Aug 6 22:24:03.983: %LINK-3-UPDOWN: Interface FastEthernet1/0, changed state to up
*Aug 6 22:24:04.983: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet1/0, changed state to up
R1(config-if)#no int lo0
*Aug 6 22:24:30.635: %LINK-5-CHANGED: Interface Loopback0, changed state to administratively down
*Aug 6 22:24:31.635: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback0, changed state to down
R1(config)#do show ip ospf
Routing Process "ospf 1" with ID 2.2.2.2
R1(config)#no router ospf 1
R1(config)#router ospf 1
R1(config-router)#do show ip ospf
Routing Process "ospf 1" with ID 192.168.23.1
Each OSPF process want to have unique router id, so same desicion path except it will not choose alredy used as router id ip address
R1(config-router)#do show ip ospf
Routing Process "ospf 2" with ID 192.168.12.1