1. SNMP Network Management (I)*
*Mani Subramanian “Network Management: Principles and practice”, Addison-Wesley, 2000.

2. SNMP Network Management
Organization Model
Communication Model
Information Model
Structure of Management Information (SMI)
Managed Objects
Management Information Base (MIB)
SNMP Administrative Model
SNMP Protocol Specs

3. Organization Model Describes components of a network management system
Focuses on functions and infrastructure
Objects are network elements such as hubs, bridges, routers, etc.
Managed elements have a process running on them called an agent
Manager queries the agent, gets information, processes it and stores it in the MIB
MIB
SNMP Manager
agent
agent
Managed Objects
Unmanaged Objects
A simplified hierarchical
(2-tier) setup

4. Organization Model Multiple managers, 1 agent
An agent responds to any management system that communicates with it using SNMP
A NMS provided by a vendor is in a better position to manage, monitor and configure all NEs coming from that same vendor
MIB
SNMP Manager
SNMP Manager
Managed
Object
agent
Managed Objects
Managers may have restricted
access to managed objects

5. Organization Model Limiting the data that a manager wishes to obtain!
RMON (Remote Monitoring): acts as an agent and a manager
RMON gathers data from MO, analyses the data, and stores the data
Communicates the statistics to the manager
MIB
SNMP Manager
SNMP Manager
Managed
Object
agent
Managed Objects
RMON Probe
Managers may have restricted
access to managed objects
3-tier architecture

6. Organization Model
Proxy server converts non-SNMP data from non- SNMP objects to SNMP compatible objects and messages
MIB
SNMP Manager
Proxy Server
Managed
Object
agent
Wireless LAN
Managed Objects
unmanaged Objects

7. Introduction to SNMP

8. SNMP Network Management
Organization Model
Communication Model
Information Model
Structure of Management Information (SMI)
Managed Objects
Management Information Base (MIB)
SNMP Administrative Model
SNMP Protocol Specs

9. Communication Model
MANAGER
AGENTS
SNMP Polling
MIB
Trap

10. Communication Model
Communicate mgnt information between network mgnt stations and managed elements
Goals:
Management functions maintained by agents are kept simple
Protocol flexibility (addition of new aspects of operation and management)
Transparency (should not be affected by the architecture of particular hosts and gateways)
Operation: 5 messages
get-request, get-next request, set-request
get-response, trap
SNMP messages are exchanged using UDP (connection less) transport protocol: ports 161 and 162

11. Communication Model Manages objects SNMP messages Network or Internet
SNMP Manager
Application
Get-Response
Get-Request
GetNext-Request
Set-Request
Trap
UDP IP
DLC
PHY
SNMP Agent
SNMP agent
Physical Medium
Manage-
ment
Data
Network or
Internet
Manages objects
SNMP messages

12. Communication Model-SNMP Traps
Type Indication
Cold-start of a system Agent is reinitializing itself since its
configuration has changed
Warm-start of a system Agent is reinitializing itself but
its configuration has not changed
Link down Link failure
Link up Link restoral
Failure of Authentication Request does not have proper authentication
e.g., wrong SNMP community string
EGP neighbor loss Exterior Gateway protocol neighbor gone
Enterprise specific Specific to vendor implementing it

13. Communication Model-SNMP Traps
Type
Cold-start of a system
Warm-start of a system
Link down
Link up
Failure of Authentication
EGP neighbor loss
Enterprise specific
Format
generic-trap INTEGER { coldStart (0), warmStart (1), linkDown (2), linkUp (3), authenticationFailure (4), egpNeighborLoss (5), enterpriseSpecific (6) }

14. SNMP Network Management
Organization Model
Communication Model
Information Model
Structure of Management Information (SMI)
Managed Objects
Management Information Base (MIB)
SNMP Administrative Model
SNMP Protocol Specs

15. Structure of Management Information
RFC 1155: Structure of Management Information
A common representation for data between both manager and agent
Defines the syntax (using ASN.1) to describe management information
Data types and
Rules used to define managed objects in a MIB
Generic objects and private (vendor specific) objects conforming to SMI rules (RFC 1155) can be managed by SNMP

16. SMI, Objects and Instances
Objects have: object types and object instances
SMI is concerned with types and not instances
Object type
Name (unique descriptor and object identifier)
Syntax (ASN.1)
Encoding (BER)
Object
Instance
Type
Encoding:
BER
Syntax:
ASN.1
Name:
OBJECT
IDENTIFIER
Managed Object : Type and Instance

17. SMI, Objects and Instances
Backbone Network
Hub 1
Hub 2
Router 1
Router 2
NMS
A Managed LAN Network
Object
Instance
Type
Encoding:
BER
Syntax:
ASN.1
Name:
OBJECT
IDENTIFIER
Managed Object : Type and Instance
A hub is an object type
A hub with IP is an
instance of the object

18. SMI, Objects and Instances
Type
Encoding:
BER
Syntax:
ASN.1
Name:
OBJECT
IDENTIFIER
Managed Object : Type with Multiple Instances
Instance 2
Instance 1

19. SMI, Names
root
ccitt(0)
iso(1)
joint-iso-ccitt(2)
org(3)
dod(6)
internet(1)
private(4)
mgmt(2)
experimental(3)
enterprise(1)
mib-2(1)
Each managed object is associated with an identifier (OBJECT IDENTIFIER)
Identifiers are used to name objects and they are unique for managed objects
identifier is a sequence of integers
internet OBJECT IDENTIFIER ::= { iso(1) org(3) dod(6) 1 }
::= { }
::= {iso standard dod internet}
Name of managed object

20. SMI, Names Sub-nodes under Internet To identify objects used
{ }
directory
mgmt
experimental
private
(1)
(2)
(3)
(4)
To identify objects used
in Internet experiments
Reserved for
future use
Used for objects defined in
IAB-approved documents
Used heavily by
commercial vendors
Sub-nodes under Internet

21. SMI, Names Internet {1 3 6 1} directory mgmt experimental private (1)
(2)
(3)
(4)
mib-2
(1)
system (1)
interfaces (2)
at (3)
ip (4)
icmp (5)
snmp (11)
transmission (10)
cmot (9)
egp (8)
udp (7)
tcp (6)

22. SMI, Names Internet {1 3 6 1} directory mgmt experimental private (1)
(2)
(3)
(4)
enterprises
(1) hp
(11)
cisco
(9)
3Com
(43)
Cabletron
(52)

23. SMI, SNMP Syntax SNMP ASN.1 Data Type Defined or Application
Constructor
Structured
Simple
Primitive
Number
Tag
Structure
Class
Universal
Context-
specific
Private

24. SNMP Primitive Data Types
Data Type Comments
INTEGER Subtype INTEGER (n1..nN)
Special case: Enumerated INTEGER type
OCTET STRING bit bytes binary and textual data
Subtypes can be specified by either
range or fixed
OBJECT IDENTIFIER Object position in MIB
NULL Placeholder
Special case of INTEGER data type (enumeration):
Subtype:
INTEGER (0..255)
OCTET STRING (SIZE )
OCTET STRING (SIZE 8)

25. Application-Wide SNMP Types
231
IpAddress ::= [APPLICATION 0] IMPLICIT OCTET STRING (SIZE (4))
Counter ::= [APPLICATION 1] IMPLICIT INTEGER ( )
Gauge ::= [APPLICATION 2] IMPLICIT INTEGER ( )
TimeTicks ::= [APPLICATION 3] IMPLICIT INTEGER ( )
Opaque ::= [APPLICATION 4] IMPLICIT OCTET STRING
[ms] 10 1 20 2 A
Counter, also known as roll over counter (may be incremented but not decremented)
e.g., counts the number of packets sent or received at a particular interface
Gauge: may increase and decrease
e.g., counts the current number of packets stored in the queue.
Time ticks, time is measured relative to some event (such as startup or re- initialization) within the managed system

26. SNMP Structured Types SEQUENCE,SEQUENCE OF
SET and SET OF of ASN.1 are not included in SNMP- based management
Used to build lists and tables
SEQUENCE {<type1>, <type2>,….., <typeN>}
Managed objects
Their location in
the MIB
Their data types

27. SNMP Structured Types
ipAddrTable is made up of instances of IpAddrEntry object

28. SMI, Encoding Basic Encoding Rules, BER Data Types and Tags
Type Tag
OBJECT IDENTIFIER UNIVERSAL 6
SEQUENCE UNIVERSAL 16
IpAddress APPLICATION 0
Counter APPLICATION 1
Gauge APPLICATION 2
TimeTicks APPLICATION 3
Opaque APPLICATION 4
Encoding of Object Identifiers: Packs the first two integers into a single sub-identifier

29. SMI, Encoding enterprise OBJECT IDENTIFIER ::=
{iso(1) org(3) dod(6) internet(1) private(4) 1}
Z = 40·X + Y X Y 43 6 1 4 06 05 2B 01 04

30. Managed Objects Textual name: mnemonic; always begins with lower case
sysDescr(1)
sysObjectID(2)
sysContact(4)
sysUpTime(3)
system(1)
Textual name: mnemonic; always begins with lower case
OBJECT IDENTIFIER: unique position of the managed object in the MIB
Syntax: the ASN.1 definition of the object type
Access: read-only, read-write, not-accessible (e.g., tables)
Status: mandatory, optional, obsolete
Definition: textual description of the object type

31. Managed Objects sysDescr(1) sysObjectID(2) sysContact(4) sysUpTime(3)
system(1)

32. Macros for Managed Objects
A formal definition for managed objects

33. SMI Definitions

34. Macros for Managed Objects
Using OBJECT-TYPE MACRO to define a managed object of the system group in the MIB
sysDescr OBJECT-TYPE
SYNTAX DisplayString (SIZE(0..255))
ACCESS read-only
STATUS mandatory
DESCRIPTION
“A textual description of the entity. This value should include the full name and version identification of the system’s hardware type, software operating-system, and networking software. It is mandatory that this only contain printable ASCII characters.”
::= { system 1 }
This is how objects are defined in the MIB
This definition is valid as long as the MACRO OBJECT TYPE is imported from RFC1155

35. Macros for Managed Objects
sysDescr(1)
sysObjectID(2)
sysContact(4)
sysUpTime(3)
system(1)
sysUpTime OBJECT-TYPE
SYNTAX TimeTicks
ACCESS read-only
STATUS mandatory
DESCRIPTION
"The time (in hundredths of a second) since the network management portion of the system was last re-initialized." ::= { system 3 }

36. Aggregate Objects Example: IP address table
A group of related objects (also called tabular objects)
Represented by a table with
Columns of objects
Rows of instances
Example: IP address table
Consists of objects:
IP address
Interface
Subnet mask (which subnet this address belongs to)
Broadcast address (value of l.s.b. in IP broadcast address)
Largest IP datagram that can be assembled
Multiple instances of these objects associated with the node

37. Aggregate Object Macro-ipAddrTable (RFC 1155)
ipAddrTable OBJECT-TYPE
Syntax SEQUENCE OF IpAddrEntry
Access not-accessible
STATUS mandatory
Definition "The table of addressing information
relevant to this entity's IP addresses."
::={ip 20}
ipAddrEntry OBJECT-TYPE
Syntax IpAddrEntry
Definition "The addressing information for one of this
entity's IP addresses..„
INDEX {ipAdEntAddr}
::={ipAddrTable 1}
IpAddrEntry ::= SEQUENCE {
ipAdEntAddr IpAddress,
ipAdEntIfIndex INTEGER,
ipAdEntNetMask IpAddress,
ipAdEntBcastAddr INTEGER,
ipAdEntReasmMaxSize INTEGER ( )}

38. Aggregate Object Macro-ipAddrTable (RFC 1155)
ipAdEntAddr OBJECT-TYPE
Syntax IpAddress
Access read-only
STATUS mandatory
Definition "The IP address to which this entry's
addressing information pertains."
::={ipAddrEntry 1}
ipAdEntIfIndex OBJECT-TYPE
Syntax INTEGER
Definition "The index value that uniquely identifies the interface to which this entry is applicable. The interface identified by a particular value of this index is the same interface as identified by the same value of IfIndex."
INDEX {ipAdEntAddr}
::={ipAddrEntry 2} .

39. Columnar Objects Aggregate objects type contains one or more subtypes
each could have multiple instances, with a value associated with each instance
It is convenient to conceptually define a tabular structure for objects with multiple values
e.g., IP address table
TABLE T
ENTRY E
COLUMNAR
OBJECT 5
Multiple Instance Managed Object
OBJECT 4
OBJECT 3
OBJECT 1
OBJECT 2
The objects TABLE T and ENTRY E are logical objects
define grouping, are not accessible
Columnar objects are objects that represent the attributes
hence are accessible
Each instance of E is a row of columnar objects 1 through 5
Multiple instances of E are represented by multiple rows

40. Columnar Objects T
T.E
T.E.1.1
T.E.5.1
T.E.2.1
T.E.3.1
T.E.4.1
T.E.1.2
T.E.5.2
T.E.2.2
T.E.3.2
T.E.4.2
T.E.1.3
T.E.5.3
T.E.2.3
T.E.3.3
T.E.4.3
T.E.1.4
T.E.5.4
T.E.2.4
T.E.3.4
T.E.4.4
Example of 5 Columnar Object with 4 Instances (rows)
Object ID
Not accessible
{Table, Entry, Object, Index}
Row 3:
the third instance of
the object
Notice that the column-row numeric designation is reverse of that used in matrix representation (row-column)

41. Columnar Objects - Example
ipAddrTable { }
ipAddrEntry (1)
ipAdEntAddr (1)
ipAdEntIfIndex (2)
ipAdEntNetMask (3)
ipAdEntBcastAddr (4)
ipAdEntReasmMaxSize (5)
Columnar object ID of
ipAdEntBcastAddr is ( ):
iso org
dod internet mgmt
mib ip
ipAddrTable
ipAddrEntry
ipAdEntBcastAddr
Columnar objects under ipAddrEntry
Row
ipAdEntAddr
ipAdEntIfIndex
IpAdEntNetMask
IpAdEntBcastAddr
IpAdEntReasmMaxSize 1
12000 2 3
10000 4
15000
4 instances of the
Columnar object
Index of table
Object instances of ipAddrTable ( )

42. Columnar Objects - Example
Row
ipAdEntAddr
ipAdEntIfIndex
IpAdEntNetMask
IpAdEntBcastAddr
IpAdEntReasmMaxSize 1
12000 2 3
10000 4
15000
Object instances of ipAddrTable ( )
Node 1 under
ipAddrEntry
Columnar Object
Row #
Object Identifier
ipAdEntAddr 2
{ }
ipAdEntIfIndex 3
{ }
ipAdEntBcastAddr 1
{ }
IpAdEntReasmMaxSize 4
{ }
Index of the
object instance
Object ID for
ipAddrEntry
Object Id for specific instances

43. Management Information Base (MIB)
RFC 1213
MIB is a database containing information about elements to be managed
For SNMP, the MIB is a structured database (tree)
Each resource to be managed is represented by an object
Each system (e.g., a router) maintains a MIB that reflects the status of its managed resources
A NMS monitors/controls the resources by reading/modifying the values of objects in the MIB

44. MIB, RFC1213
mgmt
(2)
directory
(1)
experimental
(3)
private
(4)
Internet
{ }
mib-2
Internet MIB-II Group
system (1)
interfaces (2)
at (3)
ip (4)
icmp (5)
snmp (11)
transmission (10)
cmot (9)
egp (8)
udp (7)
tcp (6)
Implementation can be done as needed (e.g., objects essential for fault or configuration management are added)
If a group is implemented by a vendor, all its components are implemented (e.g. OSPF and all its group objects)
<module name> DEFINITIONS ::= BEGIN
<imports>
<definitions>
END

45. MIB, RFC1213 -- groups in MIB-II RFC1213-MIB DEFINITIONS ::= BEGIN
system OBJECT IDENTIFIER ::= { mib-2 1}
interfaces OBJECT IDENTIFIER ::= { mib-2 2 }
at OBJECT IDENTIFIER ::= { mib-2 3 }
ip OBJECT IDENTIFIER ::= { mib-2 4 }
icmp OBJECT IDENTIFIER ::= { mib-2 5 }
tcp OBJECT IDENTIFIER ::= { mib-2 6 }
udp OBJECT IDENTIFIER ::= { mib-2 7 }
egp OBJECT IDENTIFIER ::= { mib-2 8 }
cmot OBJECT IDENTIFIER ::= { mib-2 9 }
transmission OBJECT IDENTIFIER ::= {mib-2 10}
snmp OBJECT IDENTIFIER ::= { mib-2 11 } .
END
RFC1213-MIB DEFINITIONS ::= BEGIN
IMPORT mgmt, NetworkAddress, IpAddress, Counter, Gauge, TimeTicks FROM RFC1155-SMI
OBJECT-TYPE FROM RFC-1212;
-- This MIB module uses the extended
-- OBJET-TYPE macro as defined in [14];
-- MIB-II (same prefix as MIB-I)
mib OBJECT IDENTIFIER ::= { mgmt 1 }
-- textual conventions
DisplayString ::=
OCTET STRING
-- This data type is used to model textual information taken from the NVT ASCII character -- set. By convention, objects
-- with this syntax are declared as having --
SIZE (0..255)
PhysAddress ::=
-- This data type is used to model media
-- addresses. For many types of media, this will
-- be in a binary representation. For example,
-- an ethernet address would be represented as
-- a string of 6 octets.

46. MIB, System Group sysServices (7) sysLocation (6) sysDescr (1) system
-- the System group
-- Implementation of the System group is
-- mandatory for all systems. If an agent is not
-- configured to have a value for any of these
-- variables, a string of length 0 is returned.
sysDescr OBJECT-TYPE
SYNTAX DisplayString (SIZE (0..255))
ACCESS read-only
STATUS mandatory
DESCRIPTION "A textual description of the entity. ……."
::= { system 1 }
sysServices (7)
sysLocation (6)
sysDescr (1)
system
(mib-2 1)
sysObjectId
(2)
sysUpTime (3)
sysName (5)
sysContact (4)
sysObjectID OBJECT-TYPE
SYNTAX OBJECT IDENTIFIER
ACCESS read-only
STATUS mandatory
DESCRIPTION "The vendor's authoritative identification of the network management subsystem contained in the entity."
::= { system 2 }
sysUpTime OBJECT-TYPE
SYNTAX TimeTicks
ACCESS read-only
STATUS mandatory
DESCRIPTION
"The time (in hundredths of a second) since the network management portion of the system was last reinitialized."
::= { system 3 }

47. MIB, System Group Fault monitoring:
By periodically polling each agent for this value; if the current
value is less than the most recent value, then the agent has
been restarted since last poll!
Programmed by vendor of objects during manufacturing time

48. MIB, Interface Group
ifTable
(2)
ifNumber
(1)
interfaces
(mib-2 2)
ifEntry
ifIndex (1)
ifDescr (2)
ifType (3)
ifMtu (4)
ifSpeed (5)
ifPhysAddress (6)
ifAdminstatus (7)
ifOperStatus (8)
ifLastChange (9)
ifInOctets (10)
ifInUcastPkts (11)
ifSpecific (22)
ifOutQLen (21)
ifOutErrors (20)
ifOutDiscards (19)
ifOutNUcastPkts (18)
ifOutUcastPkts (17)
ifOutOctets (16)
ifUnknownProtos (15)
ifInErrors (14)
ifInDiscards (13)
ifInNUcastPkts (12)
It specifies the number of interfaces in a network component and the managed objects associated with each interface
E.g., Ethernet bridge with many network interface cards
Implementation: mandatory
interfaces OBJECT IDENTIFIER ::= { mib-2 2 }

49. MIB, Interface Group ifNumber OBJECT-TYPE SYNTAX INTEGER
ifTable
(2)
ifNumber
(1)
interfaces
(mib-2 2)
ifEntry
ifNumber OBJECT-TYPE
SYNTAX INTEGER
ACCESS read-only
STATUS mandatory
DESCRIPTION "The number of network interfaces (regardless of their current state) present on this system."
::= { interfaces 1 }
ifEntry OBJECT-TYPE
SYNTAX IfEntry
ACCESS not-accessible
STATUS mandatory
DESCRIPTION "An interface entry containing objects at the sub-network layer and below for a particular interface."
INDEX { ifIndex }
::= { ifTable 1 }
ifTable OBJECT-TYPE
SYNTAX SEQUENCE OF IfEntry
ACCESS not-accessible
STATUS mandatory
DESCRIPTION "A list of interface entries. The number of entries is given by the value of ifNumber."
::= { interfaces 2 }
IfEntry ::= SEQUENCE {ifIndex INTEGER, ifDescr DisplayString, ifType INTEGER,
ifMtu INTEGER, ifSpeed Gauge, ifPhysAddress PhysAddress, ifAdminStatus INTEGER,
ifOperStatus INTEGER, ifLastChange TimeTicks, ifInOctets Counter, ……}

50. MIB, Interface Group
ifTable
(2)
ifNumber
(1)
interfaces
(mib-2 2)
ifEntry
ifIndex (1)
ifDescr (2)
ifType (3)
ifMtu (4)
ifSpeed (5)
ifPhysAddress (6)
ifAdminstatus (7)
ifOperStatus (8)
ifLastChange (9)
ifInOctets (10)
ifInUcastPkts (11)
ifSpecific (22)
ifOutQLen (21)
ifOutErrors (20)
ifOutDiscards (19)
ifOutNUcastPkts (18)
ifOutUcastPkts (17)
ifOutOctets (16)
ifUnknownProtos (15)
ifInErrors (14)
ifInDiscards (13)
ifInNUcastPkts (12)
Basic information useful for network management such as performance monitoring and fault control
Examples
1)-measuring the queue length or the total number of octets into/out of the system--
indicators for detecting congestion
2)- measuring the traffic rate on a given interface!
ifInUcastPkts/second, ifOutUcastPkts/second
Counter data types, always incrementing!

51. MIB, IP Group
ipRoutingDiscards (23) ip
(mib-2 4)
ipForwarding (1)
ipDefaultTTL (2)
ipInReceives (3)
ipInHdrErrors (4)
ipInAddrErrors (5)
ipForwDatagrams (6)
ipInUnknownProtos (7)
ipInDiscards (8)
ipInDelivers (9)
ipOutRequests(10)
ipNetToMediaTable (22)
ipRouteTable (21)
ipAddrTable (20)
ipFragCreates (19)
ipFragFails (18)
ipFragOKs (17)
ipReasmFails (16)
ipReasmOKs (15)
ipReasmReqds (14)
ipOutDiscards (11)
ipReasmTimeout (13)
ipOutNoRoutes (12)
Contains information relevant to the implementation and operation of IP at a node
Routers periodically execute routing algorithms and update routing tables
IP Address Table contains table of IP addresses
IP Route Table contains an entry for each route
IP Network-to-Media Table is address translation table mapping IP addresses to physical addresses

52. MIB, IP Group Gateway or router TTL in IP header Total # packets
ipRoutingDiscards (23) ip
(mib-2 4)
ipForwarding (1)
ipDefaultTTL (2)
ipInReceives (3)
ipInHdrErrors (4)
ipInAddrErrors (5)
ipForwDatagrams (6)
ipInUnknownProtos (7)
ipInDiscards (8)
ipInDelivers (9)
ipOutRequests(10)
ipNetToMediaTable (22)
ipRouteTable (21)
ipAddrTable (20)
ipFragCreates (19)
ipFragFails (18)
ipFragOKs (17)
ipReasmFails (16)
ipReasmOKs (15)
ipReasmReqds (14)
ipOutDiscards (11)
ipReasmTimeout (13)
ipOutNoRoutes (12)
Gateway or router
TTL in IP header
Total # packets
received from interfaces
# of discarded datagrams
due to header errors

53. MIB, IP Group ipAddrTable (ip 20) ipAddrEntry (ipAddrTable 1)
ipAdEntAddr (1)
ipAddrEntry
(ipAddrTable 1)
ipAdEntReasmMaxSize (5)
ipAdEntBcastAddr (4)
ipAddrTable
(ip 20)
ipAdEntIfIndex (2)
ipAdEntNetMask
(3)

54. MIB, IP Group Contains information used for Internet routing
ipRouteEntry
ipRouteTable (1)
ipRouteDest
(1)
ipRouteIfIndex (2)
ipRouteMetric1 (3)
ipRouteMetric2 (4)
ipRouteMetric3 (5)
ipRouteInfo (13)
ipRouteMetric5
(12)
ipRouteMask 11)
ipRouteAge (10)
ipRouteProto (9)
ipRouteMetric4 (6)
ipRouteType (8)
ipRouteNextHop (7)
ipRouteTable
(ip 21)
Contains information used for Internet routing
ipRouteTable information is useful for: configuration monitoring, controlling the routing process as well as fault isolation

55. MIB, TCP Group
Contains info. relevant to the implementation/operation of connection-oriented TCP
tcp
(mib-2 6)
tcpRtoAlgorithm
(1)
tcpRtoMin (2)
tcpRtoMax (3)
tcpMaxConn (4)
tcpActiveOpens (5)
tcpOutRsts (15)
tcpInErrors (14)
tcpConnTable 13)
tcpRetranSegs (12)
tcpOutSegs (11)
tcpPassiveOpens (6)
tcpInSegs (10)
tcpCurrEstab (9)
tcpAttemptFails (7)
tcpEstabResets (8)
Timeout algorithm for retransmission
Minimum value for
retransmission timer
# segments
retransmitted
Maximum value for
retransmission timer
# segments
received
# segments
sent
Maximum nb of
TCP connections

56. MIB, TCP Group tcpConnEntry (1) tcpConnState (1)
tcpConnLocalAddress (2)
tcpCommRemPort (5)
tcpConnRemAddress(4)
tcpConnLocalPort (3)
tcpConnTable
(tcp 13)

57. SNMP Network Management
Organization Model
Communication Model
Information Model
Structure of Management Information (SMI)
Managed Objects
Management Information Base (MIB)
SNMP Administrative Model
SNMP Protocol Specs

58. SNMPv1 Administrator Model
SNMP Entities:
SNMP application entities
Reside in management stations and network elements
Manager and agent
Pairing of both entities forms SNMP community
SNMP protocol entities
Communication processes (PDU handlers)
Peer processes that support application entities
Administrative model defines administrative relationship between communicating entities
Management stations, each manages all or a subset of the managed stations in the configuration
Subsets may overlap
Each managed station controls its local MIB
control the use of MIB by a number of management stations

59. SNMPv1 Administrator Model
SNMP Community
It is a relation:
between one SNMP agent and a set of managers
defines authentication, access control and proxy charct.
SNMP Manager
Authentication Scheme
SNMP Agent
Authentic Messages
Multiple pairs can belong to the same community
A community name is a string of octets
Two application entities in the same community can communicate with each other
This essentially defines a filter module or authentication scheme between manager and agent
Security in SNMPv1 is therefore community-based
no encryption

60. SNMPv1 Administrator Model
SNMP Community Profile
Operations such as get, set and trap
can be performed on objects 2,3,4
SNMP Agent
Object 2
read-only
READ-
ONLY
WRITE
SNMP Access Mode
SNMP MIB View
MIB Access
Object 3
write-only
Object 1
not-accessible
Object 4
read-write
only get, and trap are
performed on objects 2,3,4
Community profile: MIB view + SNMP access mode
MIB View: a subset of the managed objects an agent is permitted to manage/view
A community name is also assigned an SNMP access mode
READ ONLY, READ-WRITE
Operations on an object is determined by community profile and the access mode of the object
Total of four access privileges
Read-only, write-only, read- write, not-accessible
Some objects, such as table and table entry, are non-accessible

61. SNMPv1 Administrator Model
SNMP Access Policy
Community
Community Profile 1
Community Profile 2
Agent 2
Agent 1
Manager
Pair of “SNMP community” and “community profile” define SNMP access policy
Access policy allow a managed agent to give different access privileges to different managers
Manager manages network components of communities 1 and 2 via Agents 1 and 2
Agent 1 has only view of Community Profile 1, e.g. Cisco components
Agent 2 has only view of Community Profile 2, e.g. 3Com components
Manager has total view of both Cisco and 3Com components

62. SNMPv1 Administrator Model
SNMP Access Policy
Community 1
Community Profile 1
Community Profile 2
Manager 3
(Community 1, Community 2)
Agent 2
Agent 1
Community 2
Community Profile 3
Community Profile 4
Agent 4
Agent 3
Manager 2
(Community 2)
Manager 1
(Community 1)
Manager 1 manages community 1, manager 2 community 2,and manager 3 (MoM) both communities 1 and 2
Example: Enterprise management

63. SNMPv1 Administrator Model
SNMP Proxy Access Policy
Proxy agent enables non- SNMP community elements to be managed by an SNMP manager
An SNMP MIB is created to handle the non-SNMP objects
SNMP Community
non-SNMP
Community
Proxy Agent
SNMP
Agent
SNMP Manager
(Community 1)

64. SNMP Network Management
Organization Model
Communication Model
Information Model
Structure of Management Information (SMI)
Managed Objects
Management Information Base (MIB)
SNMP Administrative Model
SNMP Protocol Specs

65. Message Format version community data
Protocol entities support application entities
Communication between remote peer processes Message consists of :
Version identifier
Community name
Protocol Data Unit
Message encapsulated in UDP datagrams and transmitted
SNMP uses two well-known ports to operate:
UDP Port SNMP Messages
UDP Port SNMP Trap Messages

66. Message Format
version
community
data
SNMP message format is defined using ASN.1, encoded for transmission over UDP using BER
Message ::= SEQUENCE { version INTEGER {version-1(0)}, community OCTET STRING, data PDUs }
3 different versions:
SNMPv1, SNMPv2, SNMPv3

67. Message Format-Set/Get PDU
version
community
data
Message ::= SEQUENCE { version INTEGER {version-1(0)}, community OCTET STRING, data PDUs }
PDUs::= CHOICE { get-request [0] IMPLICIT PDU, get-next-request [1] IMPLICIT PDU, get-response [2] IMPLICIT PDU, set-request [3] IMPLICIT PDU, trap [4] IMPLICIT Trap-PDU }

68. Message Format-Set/Get PDU
request- id
error- status
variable-bindings
error- index
PDU-
type
request-id: track a message and indicate loss of a message (e.g., timeout, etc.)
error-status: indicate the occurrence of error
error-index: indicate the occurrence of error (position in the list of variables)
variable-bindings: grouping of number of operations in a single message:
e.g., one request to get all values and one response listing all values
PDU ::= SEQUENCE { request-id INTEGER, error-status INTEGER { noError (0), tooBig (1), noSuchName(2), badValue (3), readOnly (4), genErr (5) }, error-index INTEGER, variable-bindings VarBindList }

69. Message Format-variable bindings
name
value
var-bind 1
var-bind 2
var-bind n
. . .
VarBindList ::= SEQUENCE OF VarBind
VarBind ::= SEQUENCE { name ObjectName, value ObjectSyntax }
ObjectName ::= OBJECT IDENTIFIER
ObjectSyntax ::= CHOICE { simple SimpleSyntax, application-wide ApplicationSyntax }

70. Message Format-variable bindings
SimpleSyntax ::= CHOICE { number INTEGER, string OCTET STRING, object OBJECT IDENTIFIER, empty NULL }
ApplicationSyntax::= CHOICE { address NetworkAddress, counter Counter, gauge Gauge, ticks TimeTicks, arbitrary Opaque }
NetworkAddress::= CHOICE { internet IpAddress }

71. Message Format-Trap PDU
Entreprise
Agent
Address
variable-bindings
Generic
Trap Type
PDU-
type
Specific
Time
Stamp
Trap-PDU ::= SEQUENCE { enterprise OBJECT IDENTIFIER, agent-addr NetworkAddress, generic-trap INTEGER { coldStart (0), warmStart (1), linkDown (2), linkUp (3), authenticationFailure(4), egpNeighborLoss (5), enterpriseSpecific (6) }, specific-trap INTEGER, time-stamp TimeTicks, variable-bindings VarBindList }
Pertain to the system generating
the trap (sysObjectID)
-IP address of the objetc
Specific code to identify the
trap cause…
Elapsed time since last re-initialization