Is this Boson Question wrong?

Deathmage

hey guys,

So I think this Boson question is wrong.

Shouldn't the correct answer be: ' network 192.168.100.16 0.0.0.15 area 0'?

To me if it was .30 0.0.0.15 then then ip address range would be 33 to 46.

The correct range should be .17 to .30 .....

Let me know what you think?

Stevecb06

You have to understand that the network command in OSPF is not necessarily to define a network, but instead telling any interface in that network to participate in OSPF. The network 192.168.100.30 command isn't saying "The network is .30" , it's saying "Any interface in the same network as .30 should participate in OSPF". In this case, any interface with an address that falls between 192.168.100.17 and 192.168.100.30 will participate. The 192.168.100.18 a dress falls within this range, and nothing else does, so this answer is correct. Not sure where you are getting the 33-46 range from?

Nans

Deathmage wrote: »

hey guys,


To me if it was .30 0.0.0.15 then then ip address range would be 33 to 46.

What the network command does is look for the interfaces that's in the network specified in the ip address which may not be the network address and the wildcard mask helps in further narrowing the issue and letting OSPF decide which network it is part of (which is this case). So when you input .30 and a mask of 0.0.0.15 then it would automaically calcuate the network address and looks the interfaces that are in valid network address range to pull into OSPF routing and sends hello packets to form adjacencies.

Hope this helps and correct me if I am wrong

techfiend

network 192.168.100.16 0.0.0.15 area 0 would work as it's .16-31 but the choice is actually 100.15, which would be .0-15

satishtech

192.168.100.30 0.0.0.15 area 0
is correct

30 IP with 15 wild card mask , range will be .17 to .30 ,.16 network number and .31 broadcast number

Blocks are 0 to 15 , 16 to 31 , 32 to 47,
.0 , .16 , .32 are network numbers
.15,.31,.47 are broadcast numbers
kindly correct me if I am wrong
wild card masking is like subnetting in the reverse

If one assigns network 192.168.100.30 0.0.0.15 area 0
and checks ru conf , it is subnetted to 192.168.100.16

DPN1

As the guys above have said basically its going up in blocks of 16 ( you can tell this by the wildcard mask) so when you see 0.0.0.15 you first thought should of been that .30 would be in the .16 network due to the block sizes. I see where you have went wrong you've assumed that .30 was the starting address rather than a single address inside a block

james43026

First I would like to say, you should never assume that the entire network goes up in blocks of 16 just because that is what this subnet appears to be doing, as VLSM will cause problems, and VLSM is heavily used in real networks. You should always be doing a logical "and" with the given IP address and the subnet mask, which you can derive from the wildcard mask. As this will always take you to that examples exact network address / range. Which is 192.168.100.16 255.255.255.240 - 192.168.100.31 255.255.255.240, with 192.168.100.16 being the unusable network address and 192.168.100.31 being the broadcast address. This example is trying to be tricky, and in a real network you would never want to do this, Cisco's best practice is to only issue the network statement for a single network address only, for this example it would be "network 192.168.100.18 0.0.0.0 area 0". So answer A is the best answer for this question.

Deathmage

Thanks for the feedback guys.

"A" seemed like the only answer that was sort of right since it did fall into the /28 block range but I just was curious if it was intentionally made to make me scratch my head just a little bit, I was like "like wait huh, well it looks like it's right cause all of the other are way our of the scope of the block size. - I knew it was one of the 0.0.0.15 wildcards and 'A" just looked like the right answer.".

I see after reading everyone response my logic was correct just never saw a addresses written with a address at the tail end of block range being used. For that question I literally had to write out the answer and waste 7 minutes cause I was like my head is saying it's this, but my eyes are saying my brain is stupid, ultimately I listen to my head and went with "A".

With this being said just for clarification the D answer would be a 'network 192.168.100.15 0.0.0.15 area 0' range for the 192.168.100.0 range, presuming ip subnet-zero is enable, which is the 1st block range of the /28.

Again glad I trusted my gut, but I don't normally start my block range at the end of a available IP addresses so it was interesting to see. If I didn't fully understand block sizes I could have seen D as the answer I chose. This just goes to show: "Every question is basically a subnetting question in some way".

Deathmage

A few weeks ago this kind of question would have boggled my head. Now after really painfully reading each paragraph in my books I know the answer is D. I think questions like these is why I got such poor scoring on IP data Operations.

Nans

Deathmage wrote: »

A few weeks ago this kind of question would have boggled my head. Now after really painfully reading each paragraph in my books I know the answer is D. I think questions like these is why I got such poor scoring on IP data Operations.

Well that was a head stumper for me before 3 days. I took it to my mind now so that i can hit it next time

JUst a small question for the heads up with your preperation do you remember the protocols used for etherchannel and their modes..

satishtech

thank you for the switching questions , yes D is the answer
I was thinking what if all source mac's from all vlan2 ports
are in the mac-address-table,makes no difference I guess.