When I use highest ip address of active interface as a Router-Id of the router if its active interface goes down then the router must reestablishing adjacency with other neighbor router or not.
please clarify or provide helpful link.
Thank in advance
If the interface associated with this IP address is ever brought down, or if the IP address is removed/replaced, the OSPF process must recalculate a new router ID and resend all its routing information out its interfaces. Yes, it will reestablish adjacency - check "show ip ospf neighbor".
By experience, I recommend you statically assign a router-id and it should be a loopback interface IP Address
Agree with most of what you said. However i believe even if the interface that has the IP address being used as the router-id goes down OSPF will still continue to use that IP address.
The only time the router-id changes is if you manually change it with the "router-id" command or if the OSPF process itself restarts.
Hi guys Thank for input.
So, the neighbor routers that associate with active interfaces must reestablish adjacency again but the router-id in hello packet has not been changed,
please clear me out
Yes new adjancencises will need to be establised but the router-id will not change unless you manually change it with the router-id command or restart the OSPF process.
interesting link - and dead wrong in this specific point, as already pointed out. Each OSPF process needs a router ID for identification. There is no requirement, that it belongs to an active interface IP. You can f.e. use an OSPF router ID of 255.255.255.255 without any problem as long as it is unique.
If you need the confirmation: Jon is absolutely right.
P.S.: Just configured it as a demonstration by adding a Loopback with IP 192.168.1.1, starting OSPF and deleting the Loopback:
(Hope this clarifies it):
R1#sh ip int brie
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 unassigned YES TFTP administratively down down
Serial1/0 unassigned YES NVRAM administratively down down
Serial1/1 unassigned YES NVRAM administratively down down
Serial1/2 unassigned YES NVRAM administratively down down
Serial1/3 unassigned YES NVRAM administratively down down
R1#show ip ospf
Routing Process "ospf 10" with ID 192.168.1.1
Start time: 00:00:33.660, Time elapsed: 00:02:35.148
Supports only single TOS(TOS0) routes
Supports opaque LSA
Supports Link-local Signaling (LLS)
Supports area transit capability
Router is not originating router-LSAs with maximum metric
Initial SPF schedule delay 5000 msecs
Minimum hold time between two consecutive SPFs 10000 msecs
Maximum wait time between two consecutive SPFs 10000 msecs
Minimum LSA interval 5 secs
Minimum LSA arrival 1000 msecs
LSA group pacing timer 240 secs
Interface flood pacing timer 33 msecs
Retransmission pacing timer 66 msecs
Number of external LSA 0. Checksum Sum 0x000000
Number of opaque AS LSA 0. Checksum Sum 0x000000
Number of DCbitless external and opaque AS LSA 0
Number of DoNotAge external and opaque AS LSA 0
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
Number of areas transit capable is 0
External flood list length 0
Area BACKBONE(0) (Inactive)
Number of interfaces in this area is 0
Area has no authentication
SPF algorithm last executed 00:01:44.688 ago
SPF algorithm executed 3 times
Area ranges are
Number of LSA 1. Checksum Sum 0x00B9B0
Number of opaque link LSA 0. Checksum Sum 0x000000
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0
Many thanks for that Martin.
I remembered reading a long time ago that the router-id did not actually change when the interface went down but I'd never actually tested it.