I'm currently prepared my BSCI certification Exam, my studdy process is on OSPF Protocol for now. In my certification documentation the author say the link ID and the advertized ID are generally the same value in " show ip ospf database " output command.
In my fisrt reading on this subject I was understand from this output command I can manually rebuild network desing as it is also possible with the output commande of "show ip EIGRP topology" in case of eigrp routing protocol is use.
I had supposed the link ID was the network adverstized and advertized router the router ID is directly connected to. But today read something different and I also remark in this output command no network mask is advertized with the link ID which make my first understanding incorrect, because OSPF is class we can assume the network mask.
Since my fisrt understanding is now invalidate, I can't understand how the routing table is construct with the information contain in the output of this command, if nothing is mention about the IP network of each router interface's is belong to.
I would also would understand what is the purpose of the link ID and Advertize Router if those as most of the time set as the same value ?
Tthanks a lot in advance !
Don't worry about your rating. We're not here to run for ratings but to help each other.
The terminology in OSPF is hard to read, that's for sure. Also, the OSPF is really an applied chapter from the graph theory (a mathematical discipline). Explaining the OSPF to someone who has had the graph theory subject during his studies is much easier, otherwise, it is necessary to find workarounds around terms and concepts and to basically re-explain the required topics of graph theory in layman terms :) And sometimes, I don't find the shortest or easiest way to do it. Fortunately, you eventually managed to get through my posts.
The area number written as IP number? Well, basically, the area number is a 4B number. You can write any 4B number by its individual bytes even it is not supposed to be interpreted as an IP address. The main reason here is that the dotted-decimal notation is easier to work with and remember for a human than expressing the entire 4B value, be it an IP address or area number or any other number. For example, what would be more easy to remember - 22.214.171.124 or 2663483944? They both express the same IP address:
[email protected]:~$ ping 2663483944 -c 3
PING 2663483944 (126.96.36.199) 56(84) bytes of data.
64 bytes from 188.8.131.52: icmp_seq=1 ttl=55 time=31.5 ms
64 bytes from 184.108.40.206: icmp_seq=2 ttl=55 time=32.4 ms
64 bytes from 220.127.116.11: icmp_seq=3 ttl=55 time=32.4 ms
--- 2663483944 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2003ms
rtt min/avg/max/mdev = 31.544/32.172/32.492/0.444 ms
Surely, the dotted-decimal notation is much more readable here. Working with 4B area numbers is pretty much the same. You just simplify their notation by writing out their numbers in dotted-decimal form if that's more convenient for you. If it's not, then you are free to use the linear number. Depending on your addressing customs, you may also make an area number to resemble the IP addressing used in that area, thereby making your area numbering plan easier to read.
But all this basically boils down to the fact that you can write an area number in the dotted-decimal format simply because nobody tells you that you cannot :)