Tuesday, March 2, 2010

OSPF Area 555 - Now what the hack is that ?

Here is another OSPF twist. Although in my point of view it's just a stupid router trick which can appear in CCIE R&S lab cause that's the lab where they ask lots of Router tricks too along with the deep understanding of different Internetwork Technologies. But in some other people's opinion it could be something related to deep understanding of OSPF protocol.

Anyways here is your CCIE Lab task under OSPF Section worth 5 Points: :)
Q - Router R2 has been configured under OSPF AREA 555. Now configure Router R1 to peer with Router R2 using OSPF. But do not use "area 555" key-word any where in configuration.

Hmmm....Isn't that interesting enough ?

Looks like that proctor is not happy with you and that's why he asked for this.

Any-ways...lets try to find this under DOC CD (12.4T - As per lab version)


I quickly browse through DOC CD and didn't find anything helpful there...So what now? ...As our best friend in Exam - DOC CD - is not able to help us with this.

Now lets come back to the basics...how we can configure ospf area on router...Hmmm....1.) Under the OSPF Process...2.) Under the interface configuration mode using " ip ospf" command...hmmm...but in both ways commands asks for " area 555" key-word to be entered.

So are we gonna loose 5 Point Now ?

and Answer is ....YES...I mean chances are pretty high for that if you haven't read about this earlier somewhere. Also this may lead us to loose further points along the way if this peering needs to be functional for BGP, Multicast, QOS and other tasks to work properly.

So lets talk about how we can do it now :)

Well...Actually Area IDs are 32-bit numbers. Although they can be expressed into Decimal format for our sake but they can also be expressed in a Dotted-Decimal format. Also some vendors does support the Dotted Decimal format as default way to configure OSPF Area IDs.

So lets convert 555 into binary first:

555 = 1000101011 <- Used windows Calculator Here :)

so in better way we can write it as follows:

00000000.00000000.00000010.00101011  <- Now lets break it further

00000000 = 0

00000000 = 0

00000010 = 2

00101011 = 32+8+2+1 = 43

00000010.00101011 = 2.43 or

Hmmm....wasn't that fun ?????

Now lets put the following command under OSPF router configuration mode, but same format will also work for OSPF interface configuration mode too.

R1(config)#router ospf 1
R1(config-router)#net a

So soon after this you will see the magical peering coming UP :)

So I hope you will enjoy it. Below is the complete config though for detailed review:


R1(config)#do sh prot | e do
Global values:
  Internet Protocol routing is enabled
Serial0/0 is up, line protocol is up
  Internet address is < - This is another fun too :) to add here
Loopback11 is up, line protocol is up
  Internet address is

R1(config)#router ospf 1
R1(config-router)#net 0.0.00 a


R2(config-router)#do sh prot | e do
Global values:
  Internet Protocol routing is enabled
Serial0/0 is up, line protocol is up
  Internet address is
Loopback22 is up, line protocol is up
  Internet address is

R2(config-router)#net a 555

R2(config-router)#do sh run | s rout
router ospf 1
 network area 555

R2(config-router)#do ping r 10 so lo 22

Type escape sequence to abort.
Sending 10, 100-byte ICMP Echos to, timeout is 2 seconds:
Packet sent with a source address of
Success rate is 100 percent (10/10), round-trip min/avg/max = 4/24/140 ms

Happy Studying...

Best Regards,
Deepak Arora

1 comment:

luichi said...

i looked all over the net for a simple explanation, yours is the winner, great job