Question about ARP, default gateways, subnet on ENARSI exam

[hfakoor222]

Taking the exam soon.

The first chapter first two questions:

Question 1 answer is b ,d

Question 2 answer is a, c

I'm trying to figure out why.

Here's what I think.

Question 1 

10.1.1.27/28

is a 2^4   is a 16 subnet

so it goes in blocks of 10.1.1.15,  10.1.1.31,  10.1.1.47,   10.1.1.63,   10.1.1.79  and so forth.

Since 10.1.1.18 and 10.1.1.27 are in the same sumbnets the device is broadcasting on the devices on the local subnet for a mac address, and the receiving device (PC2) should be on this subnet.

In question 2 since the subnets are in blocks of 6, 10.1.1.18 and 10.1.1.27  so the PC is forwarding to the

default gateway

  Am i correct in assuming this?

Thanks

[M02@rt37 · Accepted solution]

Hello @hfakoor222,

You correctly identified that

10.1.1.27/28

represents a subnet with 16 addresses (from 10.1.1.16 to 10.1.1.31).

Both 10.1.1.18 and 10.1.1.27 are within this subnet, so they are on the same local subnet. When a device in this subnet wants to communicate with another device within the same subnet, it uses

ARP

to find the MAC address of the destination device. So, PC1 broadcasts for the MAC address of 10.1.1.27, which PC2 responds to because it's in the same subnet.

As concerned Q2, you're also correct. 

10.1.1.18 and 10.1.1.27 are in different subnets. In this scenario, if PC1 wants to communicate with PC2 (10.1.1.27), it will send the packet to its

default gateway

(the router) using

ARP

to get gateway MAC.

The router will then forward the packet to the appropriate subnet (10.1.1.24/29) where PC2 resides.

[hfakoor222]

Thanks