OSPF IP priority

There is one description that in below in 'CCNA Study Guide'

By default, OSPF uses the highest IP address on any active interface at the
moment of OSPF startup. However, this can be overridden by a logical inter-
face. The highest IP address of any logical interface will always become a
router’s RID.

Question: Which one will be highest IP in below IP?
192.168.0.1
10.56.39.254

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Comments

amb1s1

o1n wrote: »

There is one description that in below in 'CCNA Study Guide'

By default, OSPF uses the highest IP address on any active interface at the
moment of OSPF startup. However, this can be overridden by a logical inter-
face. The highest IP address of any logical interface will always become a
router’s RID.

Question: Which one will be highest IP in below IP?
192.168.0.1
10.56.39.254

192.168.0.1 would be highter.

Take a look at the OSPF Wiki, read the Designated router section.

Open Shortest Path First - Wikipedia, the free encyclopedia

MickQ

amb1s1 wrote: »

192.168.0.1 would be highter.

Take a look at the OSPF Wiki, read the Designated router section.

Open Shortest Path First - Wikipedia, the free encyclopedia

192.168.0.1 if both of the addresses are on physical interfaces. Eg. FA0/1 and FA0/2.

If one of them is a "loopback" (logical) interface, then that'll take preference.

CodeBlox

if 192.168.0.1 is on an ethernet interface and 10.56.39.254 is on a loopback interface, then 10.56.39.254 would be the RID

o1n

Thanks for all the answer. I got it!

ccnaomkar

Cisco routers derive their Router IDs by the following means:

1. If the Router ID has been manually configured using the router-id command (can use any value unlike BGP which can use o*nly up to 223.255.255.255 which is the last unicast IP), that Router ID is used.

2. If no Router ID has been manually configured, the router chooses the numerically highest IP address on any of its loopback interfaces.

3. If no loopback interfaces are configured with IP addresses, the router chooses the numerically highest IP address on any of its UP/UP physical interfaces. (accordingly you won’t have OSPF running unless one interface is UP/UP and the router will issue this log message “%OSPF-4-NORTRID: OSPF process 1 cannot start. There must be at least o*ne “up” IP interface, for OSPF to use as router ID”).

for more link
OSPF RID Story