Question

[tibys05]

A host is attempting to send data to another host on a different network. What is the first action that the sending host will take?

A. Drop the data.
B. Send the data frames to the default gateway.
C. Create an ARP request to get a MAC address for the receiving host.
D. Send a TCP SYN and wait for the SYN ACK with the IP address of the receiving host.

I believe the correct answer is B. But i'm not sure. can you help me?

[Big Evil]

I also think B. The host will forward a frame to its default gateway. The caveat is if the default gateway does not exist in the host's arp table, it will need to send an arp for the ip address of its default gateway.


Just for reference though if a computer does not have a gateway configured, but still needs to communicate with a remote device, is it possible for this communication to happen? The answer is it depends. Depends on the host, if any other routers are on the same network as the host, and if those routers have a route to the remote network. So, with that in mind, and this wasn't the CCNA, C could be a possibility.

[tibys05]

Thank you very much! :)

[Big Evil]

No problem - for new people to networking B would stand right out. For those that have some real world years experience you will see yourself over think the question. Todd mentions this in his book a few times where he say - "This is true for the CCNA exam". :)

[lammle]

I saw this yesterday.
And really, there is no good answer to this, but the "best" answer is "B".
The host would never broadcast for a remote MAC (knowing that this is a remote host), so it would always go to the DG.
Now, if this was a few years ago, Cisco used Proxy ARP on the objectives, and C would have been correct.
With proxy ARP, you never set a default gateway so the hosts would just broadcast an ARP request looking for the destination host.
All Cisco routers run Proxy ARP by default (still to this day), so the router would respond that "I am the remote host", and your host would then send the data to the router, which in turn would route it to the remote host.
So "C" is correct if you would think there is no default gateway set on the transmitting host. However, we don't have that information so "B" is probably the best "wrong" answer.
Why wrong? Because the first thing that the host does is hand the packet to IP, and IP determines if it is a local or remote host, and then looks up the default gateway in the registry.
Please read "Todd's 36 Steps to Understanding Simple IP Routing" in my chapter 8.
In summary, I am changing my answer to B.
Todd Lammle

[bs_kwaj]

Well, you may say 'wrong' based on a broad knowledge of the topic, but from a simplistic CCNA view point, isn't B just the only answer in 'the list' that is correct.

It says, 'What is the first action the sending host will take...' based on the list of events given.

Just my 2cents. :cool: I have a nickle, but I'm trying to conserve. ;)

[lammle]

Yes, B is the best answer.
The question is just too damn simple, period.
That is the most simplistic answer and the only correct one in the list, but that is not really how it happens, but again, I am changing the answer to B.
Todd