Given that Host A and Host B are in different networks. When Host A is trying to communicate with Host B, which step will Host A take first?
A.
Send a TCP SYN and wait for the SYN ACK with the IP address of Host B
B.
Drop the data.
C.
Create an ARP request to get a MAC address for Host B.
D.
Send the data frames to the default gateway.
Explanation:
This question is to examine the ARP working principle.
When Host A doesn’t know the MAC address of Host B, the ARP request will be broadcast so that all hosts on the LAN can see this request. If the IP is not local, the router will check its routing table to see whether there is a route to the destination network. If there is, the router will reply with its own MAC address.
So C is correct.
answer is D because the hosts are on different networks and there’s no need to know the destination MAC (no need for ARP request)
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actually host A should arp the default gateway first if it is not in it’s arp cache, because all communication takes place at l2
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Answer: D
Explanation:
The answer “Create an ARP request to get a MAC address for Host B.” is NOT correct, the host will know if the destination is not on the local network and will send to MAC address of its default gateway setting, it will not ARP for MAC address of remote destination.
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C is correct because you cant send data without knowing the destination mac address, it will arp to get the mac address of the default gateway whc is the router, store the mac in the cache then send the data to the gateway for onward transmission to the destination
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D
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Host A could care less about the MAC address of Host B when it is determined that the address is in another network. If Host A and B shared a common net. Then Host A would be concerned about Host B’s MAC. As B is outside Host A’s net, then Host A only cares about the gateways MAC address. If its MAC is not already know, host will send out the ARP looking for the gateway’s MAC. If it is know, once Host B is known to belong to another net, Host A will send send it to the gateway. From there it is up to the router to do its thing in getting the info to the right place.
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