Computer Networks

Tutorial #14

1. What information can the network manager obtain from the ping command? What does ping actually do?

2. What does the traceroute command do? How does it do it?

3. The following are some (highly edited) entries from the standard Unix MIB definition, in file /etc/mib.txt.

   ipForwarding OBJECT-TYPE ::= { ip 1 }
   icmpInEchos OBJECT-TYPE ::= { icmp 8 }
   tcpMaxConn OBJECT-TYPE ::= { tcp 4 }
   

   What are the numeric OBJECT IDENTIFIERS of the objects ipForwarding, icmpInEchoes and tcpMaxConn.

4. One interesting aspect of the ASN.1/BER is the way in which OBJECT IDENTIFIERS are encoded. In general, the integers which specify the OBJECT IDENTIFIER are simply encoded in BER as a SEQUENCE of single byte values. However, the first two integers (let's call them a and b) are encoded in a compact form, taking only a single byte, of the form 40a + b. So, for the Internet, the first two integers are 1.3, therefore they are encoded as the single byte value 43. Can you imagine a reason why this is done? What does it say about the values of these first two integers?

5. Marshall T. Rose[1] espouses the fundamental axiom of network management, which is: The impact of adding management to managed nodes must be minimal, reflecting a lowest common denominator. Discuss.

Practical Exercises:

• Use the ping[2] command to check reachability of various hosts at Bendigo and elsewhere. Now investigate the command line options of ping. Be sure to to try it on both the Indys and redgum.

• The traceroute command is available on redgum. Use traceroute (judiciously - see the man page). Now have a look at ntping on the SGI systems (Indys, ironbark).