EE450_HW_2_solutions - EE450: Computer Networks, Fall 2007...

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EE450: Computer Networks, Fall 2007 Homework #2, Solutions (100 points) Textbook Problems: Chapter 4: Problems #11, Answer: (10 points) If the timeout value is too small, we clutter the network with unnecessary re-requests, and halt transmission until the re-request is answered. When a host’s Ethernet address changes, e.g. because of a card replacement, then that host is unreachable to others that still have the old Ethernet address in their ARP cache. 10-15 minutes is a plausible minimal amount of time required to shut down a host, swap its Ethernet card, and reboot. While self-ARP (described in the following exercise) is arguably a better solution to the problem of a too-long ARP timeout, coupled with having other hosts update their caches whenever they see an ARP query from a host already in the cache, these features were not always universally implemented. A reasonable upper bound on the ARP cache timeout is thus necessary as a backup. Problems #12, Answer: (10 points) The answer is no in practice, but yes in theory. MAC address is statically assigned to each hardware. ARP mapping enables indirection from IP addresses to the hardware MAC addresses. This allows IP addresses to be dynamically reallocated when the hardware moves to the different network. So using MAC addresses as IP addresses would mean that we would have to use static IP addresses. Since the Internet routing takes
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This note was uploaded on 05/05/2008 for the course EE 450 taught by Professor Zahid during the Fall '06 term at USC.

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EE450_HW_2_solutions - EE450: Computer Networks, Fall 2007...

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