TCP IP Illustrated

8 whose object identifier is 13612171 is referenced

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Unformatted text preview: tings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/snmp_sim.htm (8 of 33) [12/09/2001 14.47.40] Chapter 25. SNMP: Simple Network Management Protocol These diagrams were used during the development of the MIB to verify that all data paths for a packet were accounted for. [Rose 1994] shows Case Diagrams for all the groups in the MIB. 25.6 Instance Identification Every variable in the MIB must be identified when SNMP is referencing it, to fetch or set its value. First, only leaf nodes are referenced. SNMP does not manipulate entire rows or columns of tables. Returning to Figure 25.7, the leaf nodes are the four that we described in Figure 25.8 and the two in Figure 25.9. mib, udp, udpTabie, and udpEntry are not leaf nodes. Simple Variables Simple variables are referenced by appending ".0" to the variable's object identifier. For example, the counter udpInDatagrams from Figure 25.8, whose object identifier is 1.3.6.1.2.1.7.1, is referenced as 1.3.6.1.2.1.7.1.0. The textual name of this reference is iso.org.dod.internet.mgmt.mib.udp.udpInDatagrams.0. Although references to this variable are normally abbreviated as just udpInDatagrams.0, we reiterate that the name of the variable that appears in the SNMP message (Figure 25.2) is the object identifier 1.3.6.1.2.1.7.1.0. Tables Instance identification of table entries is more detailed. Let's return to the UDP listener table (Figure 25.7). One or more indexes are specified in the MIB for each table. For the UDP listener table, the MIB defines the index as the combination of the two variables udpLocalAddress, which is an IP address, and udpLocalPort, which is an integer. (We showed this index in the top row in Figure 25.9.) Assume there are three rows in the UDP listener table: the first row is for IP address 0.0.0.0 and port 67, the second for 0.0.0.0 and port 161, and the third for 0.0.0.0 and port 520. Figure 25.11 shows this table. udpLocalAddress udpLocalPort 0.0.0.0 67 0.0.0.0 161 0.0.0.0 520 Figure 25.11...
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.

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