Transcript Chapter 8
Network Management Security Ola Flygt Växjö University, Sweden http://w3.msi.vxu.se/users/ofl/ [email protected] +46 470 70 86 49 1 Outline Basic Concepts of SNMP SNMPv1 Community Facility SNMPv3 2 The Internet Standard Management Framework SNMP network management consists of four parts: Management Information Base (MIB) A map of the hierarchical order of all managed objects and how they are accessed Structure of Management Information (SMI) Rules specifying the format used to define objects managed on the network that the SNMP protocol accesses SNMP Protocol Defines format of messages exchanged by management systems and agents. Specifies the Get, GetNext, Set, and Trap operations Security and administration capabilities The addition of these capabilities represents the major enhancement in SNMPv3 over SNMPv2 3 Basic Concepts of SNMP An integrated collection of tools for network monitoring and control. Single operator interface Minimal amount of separate equipment. Software and network communications capability built into the existing equipment SNMP key elements: Management station Management agent Management information base Network Management protocol Get, Set and Notify 4 Management Information Bases (MIB) SNMP agent is software that runs on a piece of network equipment (host, router, printer, or others) and that maintains information about its configuration and current state in a database Information in the database is described by Management Information Bases (MIBs) The MIB specifies the managed objects 5 Management Information Bases (MIB) The MIB is a text file that describes managed objects using the syntax of ASN.1 (Abstract Syntax Notation 1) ASN.1 is a formal language for describing data and its properties In Linux, MIB files are in the directory /usr/share/snmp/mibs Multiple MIB files MIB-II (defined in RFC 1213) defines the managed objects of TCP/IP networks 6 Managed Objects Each managed object is assigned an object identifier (OID) The OID is specified in a MIB file. An OID can be represented as a sequence of integers separated by decimal points or by a text string. Example: 1.3.6.1.2.1.4.6. iso.org.dod.internet.mgmt.mib-2.ip.ipForwData When an SNMP manager requests an object, it sends the OID to the SNMP agent. 7 MIB Example ipForwDatagrams OBJECT-TYPE SYNTAX Counter ACCESS read-only STATUS mandatory DESCRIPTION "The number of input datagrams for which this entity was not their final IP destination, as a result of which an attempt was made to find a route to forward them to that final destination. In entities which do not act as IP Gateways, this counter will include only those packets which were Source-Routed via this entity, and the SourceRoute option processing was successful." ::= { ip 6 } 8 Protocol context of SNMP 9 Proxy Configuration 10 11 SNMP v1 and v2 Trap – an unsolicited message (reporting an alarm condition) SNMPv1 is ”connectionless” since it utilizes UDP (rather than TCP) as the transport layer protocol. SNMPv2 allows the use of TCP for ”reliable, connection-oriented” service. 12 Comparison of SNMPv1 and SNMPv2 SNMPv1 PDU SNMPv2 PDU Direction Description GetRequest GetRequest Manager to agent Request value for each listed object GetRequest GetRequest Manager to agent Request next value for each listed object ------ GetBulkRequest Manager to agent Request multiple values SetRequest SetRequest Manager to agent Set value for each listed object ------ InformRequest Manager to manager Transmit unsolicited information GetResponse Response Agent to manager or Manage to manager(SNMPv2) Respond to manager request Trap SNMPv2-Trap Agent to manager Transmit unsolicited information 13 SNMPv1 Community Facility SNMP Community – Relationship between an SNMP agent and SNMP managers. Three aspect of agent control: Authentication service Access policy Proxy service 14 SNMPv1 Administrative Concepts 15 SNMPv3 SNMPv3 defines a security capability to be used in conjunction with SNMPv1 or v2 16 SNMPv3 Flow 17 Typical SNMP Manager 18 Typical SNMP Agent 19 User Security Model (USM) Designed to secure against: Modification of information Masquerade Message stream modification Disclosure Not intended to secure against: Denial of Service (DoS attack) Traffic analysis 20 SNMP3 Message Format with USM 21 USM Encryption Authentication (using authKey) HMAC-MD5-96 HMAC-SHA1-96 Encryption (using privKey) DES CBC Uses first 64 bits of the 16-octet privKey Last 64 bits used as IV to DES CBC Key values not accessible from SNMP 22 Authoritative Engine SNMP messages with payloads that expect a response (Get…, Set, Inform) Receiver of message is authoritative SNMP messages with payload that does not expect response (Trap, Response, Report) Sender is authoritative 23 Key Localization Allows single user to own keys stored in multiple engines Key localized to each authoritative engine using hash functions Avoids problem of a single key being stored in many places Greatly slows brute force attack 24 Key Localization 25 Timeliness Determined by a clock kept at the authoritative engine When authoritative engine sends a message, it includes the current clock value Nonauthoritative agent synchronizes on clock value When nonauthoritative engine sends a message, it includes the estimated destination clock value These procedures allow assessing message timeliness 26 View-Based Access Control Model (VACM) VACM has two characteristics: Determines whether access to a managed object should be allowed. Make use of an MIB that: Defines the access control policy for this agent. Makes it possible for remote configuration to be used. 27 Access control decision 28 SNMPv3 Security SNMPv3 solves SNMP security problems, right? NOT! Decent security implementation, but reality is: SNMPv1 still holds ~95% of the market (2005) Even SNMPv2 not widely deployed Upgrading to SNMPv3 is difficult and costly (sort of like moving from WinXP to WinVista all at once) There is the issue of proxies and foreign clients SNMPv3 is the clear long-term choice 29