INT20CN Computer Networks

Tutorial #17

1. How would you request a router to return the actual values of the objects ipForwarding, icmpInEchoes and tcpMaxConn? Give solutions using each of the get and get-next commands. Use a command syntax of your choice, although the CMU SNMPlib syntax given in the lecture notes would be the most appropriate.

2. The following is a diagrammatic view of portion of a table (ifTable) in the interfaces portion of the standard MIB, edited to fit the page. The table consists of a sequence of ifEntry elements. Values shown are from the router r-bgowan at Bendigo, which is nowadays used as a backup (over ISDN) to the microwave link to Bundoora.

   

   1. Describe interface 3 on this router.
   2. Draw the OBJECT IDENTIFIER subtree, in "tree" format, in the region which defines the various ifSpeed entries. You might find it helpful to refer to your lecture notes for some useful information here.
   3. What would be the structure of an SNMP get-request to discover the speed, in bps, of interface 1.
   4. What value would be returned by get-next(...ifSpeed.2) ?

3. Why do SNMP proponents use the expression "powerful get-next"? In other words, what problem does the get-next operation solve very elegantly?

4. (Philosophical, but still practical, question) In this section of the unit, we have played pretty "fast and loose" with abbreviations of OBJECT IDENTIFIERs, eg { system sysDescr }. Of course, in the "Real World", we would normally have to be more careful to ensure that the software we were using was able to unambiguously fetch the variable we desired. How should SNMP software resolve such abbreviations, especially with numeric OBJECT IDENTIFIER strings? Hint: think of how Fully Qualified Domain Names (FQDNs) are specified, compared to abbreviated versions.

5. (Philosophical question) What is the purpose of the SNMP portion of the MIB?