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SNMP Dissector error when object length > 4 bytes
From: Francesco Ruta <p29731 () yahoo com>
Date: Mon, 12 Jul 2010 17:39:25 -0700 (PDT)
When an SNMP packets contains an object with a length > 4 bytes, the dissector returns the following error: Dissector bug, protocol SNMP: proto.c:1047: failed assertion "DISSECTOR_ASSERT_NOT_REACHED" Unfortunately it is not very difficult to have values with a length greater than 4 bytes. As example, the following requests would generate the error described before --when the relevant SMI file is loaded--: snmpset -v2c -d -c public 10.215.98.1 .1.3.6.1.4.1.111.1.1.0 u 4294967295 snmpset -v2c -d -c public 10.215.98.1 .1.3.6.1.4.1.111.1.1.0 u 4026531840 A SMI file could be as follow (this file must be loaded in the "SMI (MIB and PIB) modules" to see the problem or the dissector would return "Missing MIB"): MY-MIB DEFINITIONS ::= BEGIN IMPORTS MODULE-IDENTITY, Unsigned32, enterprises FROM SNMPv2-SMI; myModule MODULE-IDENTITY LAST-UPDATED "201007120000Z" ORGANIZATION " " CONTACT-INFO " " DESCRIPTION " " ::= { enterprises my(111) 1 } myObject OBJECT-TYPE SYNTAX Unsigned32 MAX-ACCESS read-write STATUS current DESCRIPTION "= " ::= { myModule 1 } END The problem is visible (at least) with the following Window releases: 1.2.1 and 1.2.9. Frame 2 (91 bytes on wire, 91 bytes captured) Ethernet II, Src: Motorola_24:01:9a (00:16:26:24:01:9a), Dst: Motorola_24:01:9a (00:16:26:24:01:9a) Internet Protocol, Src: 192.168.236.162 (192.168.236.162), Dst: 10.215.98.1 (10.215.98.1) User Datagram Protocol, Src Port: 53719 (53719), Dst Port: snmp (161) Simple Network Management Protocol version: v2c (1) community: public data: set-request (3) set-request request-id: 1210029970 error-status: noError (0) error-index: 0 variable-bindings: 1 item VarBind Object Name: 1.3.6.1.4.1.111.1.1.0 (MY-MIB::myObject.0) Scalar Instance Index: 0 [Dissector bug, protocol SNMP: proto.c:1047: failed assertion "DISSECTOR_ASSERT_NOT_REACHED"] [Expert Info (Error/Malformed): proto.c:1047: failed assertion "DISSECTOR_ASSERT_NOT_REACHED"] [Message: proto.c:1047: failed assertion "DISSECTOR_ASSERT_NOT_REACHED"] [Severity level: Error] [Group: Malformed]
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- SNMP Dissector error when object length > 4 bytes Francesco Ruta (Jul 12)