Quiz 5

Quiz 5

by Joyti Valérian Goel -
Number of replies: 3

Q9 from the Quiz really bothered me:

From what I understood from the course, the HW and the TAs is the following:

(1)Proxy ARP => ARP IP Destination: The End System's Interface IP.                                                        (2)Default Gateway => ARP IP Destination : Default Router's IP. 

Now I can not make sense of how an end system A in IP subnet using (1) would have more/less ARP requests than if in a subnet using (2)... it is simply the Destination Ip address that changes...

And of course... this is again ambiguous because Mac Caching is implementation specific and not seen in the course.... so if Default Gateway => Less Arp Requests.                                                                      Does this => that There is A Cache to map the Ip of default router to its map... and again this cache will have a time limit ... 





In reply to Joyti Valérian Goel

Re: Quiz 5

by Katerina Argyraki -
This was indeed the hardest question on the quiz, Joyti -- I can see how it can be frustrating (even though that was not by intention, of course).

An end-system that uses default gateway, for every packet it wants to send, it maps the default gateway's IP address to a MAC address. So, it needs to perform the *same* ARP request every time (which means that it can cache the result and reuse it).

In contract, an end-system that uses proxy ARP, for every packet it wants to send, it maps the target destination IP address to a MAC address. So, every time it wants to send a packet to a new destination IP address, it needs to perform a new ARP request.

Whatever the caching implementation, in the former approach, the end-system needs to do the *same* mapping again and again, while in the latter approach it needs to do a *new* mapping every time it wants to send a packet to a new destination IP address. I think it's fair to say that we would *expect* the former approach to lead to fewer ARP requests.

I hope this makes sense to you.
In reply to Katerina Argyraki

Re: Quiz 5

by Joyti Valérian Goel -

I think it is clearer, but just to make sure:
if no caching was implemented in either cases then there would be equal number of ARP requests, correct?