Networking gurus of GATT, I seek your assistance.

[Spazosaurus]

Based on the ideology behind the last one, I am at a glance thinking the answer is A. Simple reason being that the Main office has an IP address 10.10.11.x - It's important to know that the 3rd octet is 11 not 10 as is in the Server 1 address space. Remember how subnets work 255==11111111 it also means that all parts of that octet MUST match.

If I have an address 172.16.1.x 255.255.255.0 - It means the first 3 octet MUST match i.e. 172, 16, 1
If the subnet mask was 255.255.0.0 - This means the first 2 octets MUST match i.e. 172, 16

Since the 3rd Octet in the example you gave does NOT match this suggest that the 3 octet in the MASK could be a 0 meaning 255.255.0.0
Likewise we can go to even a class A 255.0.0.0 meaning ONLY the FIRST octect MUST match.
10.1.1.0/8 (10.1.1.0 255.0.0.0) can communicate with EVERYTHING below it, meaning once the FIRST octet is 10, that's all that matters.
10.1.1.0/8 can directly communicate with ANY IP between 10.0.0.1-10.255.255.255

I understand up to this part.

I even understand that 255.255.255.129 is the first valid address in the 128 subnet. What I dont understand is the relationship between the ip 10.10.10.222 and the subnet 255.255.255.128. Is it because its one of the options in the question?

[W1nTry]

Essentially every IP address in a given subnet is capable of communicating with each other. So let's use the 128 subnet /25.
192.168.1.1/25 can ping every IP address between 192.168.1.2-192.168.1.127 however EVEN if say a PC was configured with 192.168.1.129/25 was on the SAME SWITCH they would NOT be able to talk to each other because of the subnet mask.

I said that 129 CAN communicate with 222 because it is an IP address within its own subnet meaning 129-254 can talk to each other.

[Spazosaurus]

Please bear with me. I still dont understand how a subnet could be arrived at if the extended address is not given.


If I understand what I know correctly, 255.255.255.128 gives you a total of 2 subnets, each having 126 usable hosts. How does this fit in with the IP address of 10.10.10.222?

[W1nTry]

Not a problem. The router acts as the gateway for that LAN segment, like the gateway IP in windows. (Please forgive me if I go too simple, I am just trying to be as clear as I can). The gateway IP of any network device is the address through which unknown destination IPs are sent. A device can only communicate directly with another device on the same subnet. When it tries to send to another subnet, it will send it to the gateway IP.

The router has the gateway IP of 10.10.10.129. So when 10.10.10.222 tries to send a packet to 10.10.11.x, this is no longer in it's subnet and as such it wil forward all packets destined to 10.10.11.x to 10.10.10.129. Which will in turn forward it to 10.10.11.x on another interface it may have on the same subnet or it will route it via alternative IP schemes to the router that sits on the 10.10.11.x network.

If 10.10.10.222 was required to DIRECTLY communicate with 10.10.11.x the subnet is how that would be accomplished. In NORMAL environments though traffic for different subnet are usually ROUTED using a Layer 3 device such as a router so that it does not HAVE to have a large subnet mask.

The inherent benefit of using seperate subnets and routers is that it breaks up both collision and broadcast domains. Of course the downside is more overhead and increased latency. With the power of routers today though, that is pretty minimal save in very high utilization situations.

[Spazosaurus]

So tell me if my logic is correct here...

We can pretty much ignore the main office in this scenario because its on a totally different subnet, meaning that the branch office and main office routers would take care of any traffic going to and fro between the main office and branch office.

Assuming that 255.255.255.128 is the subnet mask for server 1, that means that there can be a max of 2 subnets with 126 hosts per right? So if that's the case, you have server 1 with an ip of 10.10.10.222 and the branch office can have any ip address between 10.10.10.129 and 10.10.10.255, except of course 10.10.10.222?

They didnt put any computers in the branch office, which making me wonder.

Any holes in that logic?

[SPK]

That's pretty much it, yeah.

[Spazosaurus]

Yay meeee

[W1nTry]

A router is it's namesake, a 'router' routes traffic between its interfaces. Necessarily the interfaces MUST be on different subnet, otherwise if the interfaces were to have the same ip or reside on the same subnet it'd be called a switch XD

[Spazosaurus]

192.168.1.64/26

4 subnets, 64 (62) hosts per subnet.

0-64 (1-63)
65-128 (66-127)

192.168.1.64 is the broadcast address. Am I to think that in a case where the network address is the last ip in the subnet, you have to use the next subnet? I dont know how to ask that question.

192.168.1.64 is part of the first or second subnet? How and why?

[W1nTry]

Alright in this e.g. the subnets are 64 addresses
0-63
64-127
etc

That being said the first IP is the subnet IP and the last IP is the Broadcast IP, thus, 1-62 are USEABLE IP addresses. 64 is the SUBNET address of the 2nd subnet in this scheme. 65-126 are the useable IP addresses and 127 is the Broadcast address of the .64 subnet.

[SPK]

Had now seen this, W1n has it spot on.

Usable addresses in the first subnet would have been from 1-62 (0 and 63 are subnet and broadcast addresses for the specific subnet respectively).
Usable addresses in the second subnet would have been from 65-126 (64 and 127 are subnet and broadcast)
Third subnet from 129-190 (128 and 191 are subnet and broadcast) etc etc etc...

For the specific answers in the question:

A - Usable address in 1st subnet.
B - Broadcast address in 1st subnet.
C - Usable address in 2nd subnet.
D - Usable address in 4th subnet.

[Spazosaurus]

Orrr ok I understand. My mistake was to count an extra host, i.e. 0-64 is really 65 addresses right?

[SPK]

Yup, that's correct.

[Spazosaurus]

You guys are the best. Chakra iymc