1. Chapter 6 Overview Simple Network Management Protocol
SNMPv1
SNMP packet format
Structure of MIB tree
MIB-2 objects
SNMP commands
SNMP security
Network mgmt system functions
Chapter 6  SNMP

2. SNMP Recall that SNMP is SNMP is part of network management
An application layer protocol
Used to transfer info between mgmt station and mgmt agent
SNMP is part of network management
Like HTTP is part of Web browsing
Chapter 6  SNMP

3. Web Browsing Web browsing requires Web browser on your computer HTTP
Web server(s) with data
Software on Web server
Communication architecture
Chapter 6  SNMP

4. Network Management Network management requires
Management application, mgmt processes, management MIB
SNMP
Agent process, agent MIB
Communication architecture
Chapter 6  SNMP

5. Management Environment
Components of mgmt environment
Chapter 6  SNMP

6. Mgmt Application This is the main part of NMS software
Application that requests and manages info from agents
Display results in a usable format
Graphs, pictures, etc.
May display data in the ISO mgmt categories
Chapter 6  SNMP

7. Mgmt Process Mgmt processes support mgmt application
Application programs that do necessary functions
For example, process accesses MIB variable and passes it to SNMP
Chapter 6  SNMP

8. Mgmt Station SNMP
Processes packet to be sent to agent, and those received from agent
Note that SNMP packet contains
Version number
Community string
SNMP command
List of variables
Chapter 6  SNMP

9. Mgmt Agent SNMP Like previous slide, but on agent
For received SNMP packet
Extract MIB variable
Pass MIB variable to agent process
Chapter 6  SNMP

10. Agent Process Purpose is to get the requested data
Agent must locate the data in “virtual database”
Then prepare date for
Mgmt agent SNMP (previous slide)
Chapter 6  SNMP

11. Essential Mgmt Components
Essential mgmt components include…
MIB on Mgmt Station
Stores MIB variables
NMS application software
Display, analyze data
SNMP
Format used for request/reply messages
Agent process
Gathers data from virtual database
Chapter 6  SNMP

12. SNMPv1 Packet SNMPv1 packet has the form Version  the version of SNMP
SNMPv1 is “0” in version field
Community name  like a password
Agent can limit who can see what
Sent “in the clear”, so not very secure
Chapter 6  SNMP

13. SNMPv1 PDU
PDU for Get-Request, Get-Next-Request and Set-Request has fields:
Request ID  like a sequence number
Error status  error in Get-Response
Error index  first variable in VarBindList that caused error
Chapter 6  SNMP

14. SNMPv1 PDU Error status 0 = noError
1 = tooBig (PDU has too many bytes)
2 = noSuchName (no object with requested name)
3 = badValue (invalid no. for PDU type)
4 = readOnly (incorrect implementation of SNMP)
5 = genErr (any other error)
Chapter 6  SNMP

15. SNMPv1 PDU VarBindList  list of pairs of the form
Variable ID  Object Identifier as defined in SMI specification
Variable value  actual value, which could be integer, IP address, etc.
Chapter 6  SNMP

16. SNMP Commands SNMP commands (numbered 0 thru 4)
Get-Request  request value(s) from agent MIB
Get-Next-Request  next MIB element (based on object identifier) in lexicographic order
Can use this to “walk” the MIB tree
Get-Response  response from agent
Set-Request  write a value in agent’s MIB
For example, the value might shut down device
Trap  unsolicited msg from agent
Chapter 6  SNMP

17. SNMP Trap Trap PDU is of the form
Enterprise  Object Identifier for device that created trap message
Agent address  IP address of device
Generic trap number  7 categories
Specific trap number  code number
Time stamp  time since device initialized
VarBindList  same as defined previously
Chapter 6  SNMP

18. SMI Structure of Management Info The data structure on the agent
RFC 1155
The data structure on the agent
Object Identifier mapped to value stored on subsystem
NIC is example of a subsystem
MAC address could be desired value
Chapter 6  SNMP

19. SMI Each object has a name Each object has a type Types can be
Groups of related objects also defined
Each object has a type
For example, “integer”
Types can be
Simple  a single value
Constructed  multiple objects of simple type
Chapter 6  SNMP

20. SMI
SMI specification uses subset of Abstract Syntax Notation One (ASN.1)
Formal specification of MIB objects
ASN.1 used to specify
Name of object
Type of object
Read, read-write, or not accessible
Brief description of object
See Appendix B for info on ASN.1
Chapter 6  SNMP

21. SMI Object Tree 0 is the root Example:
Object ID of sysDescr(1) is
Chapter 6  SNMP

22. SMI Object Tree MIB objects identified as on previous slide
Tree can be arbitrarily deep
MIB-2 defined with 10 groups
System, interfaces, address translation, IP, ICMP, TCP, UDP, EGP, transmission, SNMP
Later added 13 more groups (extensions)
Group can contain many objects, and these objects can be “constructed” type
Chapter 6  SNMP

23. Proprietary MIBs and RMON
If not enough groups in MIB-2…
…can create a proprietary MIB
Proprietary MIBs are listed under enterprise
Enterprise is a sub-node of private (4)
RMON
Remote Monitoring Standard
An extension of MIB-2
Deals with traffic on a network segment
Chapter 6  SNMP

24. SMI Tree MIB-2 (1) IP has 23 objects ipRouteTable (21)
ipRouteEntry (1), consists of 13 column objects
Chapter 6  SNMP

25. ipRouteEntry
An instance of ipRouteEntry consists of all 13 columns in the table above
How to select column 7?
Note that the result is a column, not a value
How to specify row 3 of column 7?
ipRouteDest serves as Index Object
Chapter 6  SNMP

26. wsnmp wsnmp is SNMP command line program
Suppose we want to get sysDescr
Why does “get sysDescr” fail?
Get-Request returns an instance (a value)
sysDescr is an object
Must include Index Object of 0
Chapter 6  SNMP

27. wsnmp
Recall Get-Next-Request gets next object in MIB tree (in lexicographic order)
getnext sysDescr
sysDescr is at in MIB tree
sysDescr.0, i.e., , is next location in MIB tree that contains a value
The value at sysDescr.0 is “Hardware: x86 … “
Chapter 6  SNMP

28. wsnmp
Recall Get-Next-Request gets next object in MIB tree (in lexicographic order)
getnext sysDescr.0
sysDescr.0 is at in MIB tree
, sysObjectID.0, is next location with a value
Value of sysObjectID.0 is
Chapter 6  SNMP

29. MIB-2 System Group Note that “311” (on previous slide) stands for IBM
Chapter 6  SNMP

30. Get-Request vs Get-Next-Request
Spse you use Get-Request
If no value for requested object (or other error), NULL and error returned
As we saw with “get sysDescr”
Spse you use Get-Next-Request
If no value for specified object, you will still get next value in MIB tree
This is a good thing!
Chapter 6  SNMP

31. Get-Request vs Get-Next-Request
What is result of GetNextRequest(ipRouteEntry)?
Address of ipRouteEntry is
Next value in MIB is at index
Result: ipRouteDest =
What is GetNextRequest(ipRouteDest )?
ipRouteDest is
Next value in MIB tree is at
Result: ipRouteifIndex = 1
Chapter 6  SNMP

32. Get-Request vs Get-Next-Request
What is GetNextRequest(ipRouteifIndex )?
ipRouteifIndex is
Next value in MIB tree is at
Result: ipRouteifIndex = 2
What is result of GetNextRequest(ipRouteTable)?
Recall address of ipRouteTable is
Next value in MIB is at index
Result: ipRouteDest =
Chapter 6  SNMP

33. Get-Next-Request
Can use Get-Next-Request to access all values in a table
Even if we don’t know how many rows in table
Can access values in MIB tree from a given starting point on
Can “walk” the MIB tree in lexicographic order
A nice feature!
Chapter 6  SNMP

34. Set Command Recall Set-Request used to remotely “set” (write) a value
For example,
SetRequest(sysContact = Frank)
Would change value of sysContact to “Frank”
Response to this would be Get-Response with sysContact = Frank
Chapter 6  SNMP

35. Security We mentioned previously the SNMP method of authentication
A community name acts like a password
More than one mgmt station may have access
Authorization is also a concern
Assuming that you have access…
…then what are you allowed to do?
Chapter 6  SNMP

36. Security SNMP security features SNMP community profile
Access mode specifies type of access
MIB view specifies access or not
Chapter 6  SNMP

37. Security SNMP security features SNMP Access Policy
Combination of all of the above
Chapter 6  SNMP

38. Security SNMP Access Mode  MIB Access
Mapping between these given below
Chapter 6  SNMP

39. Proxy SNMP agent can act as a proxy Device might not support SNMP
To collect mgmt values
Device might not support SNMP
Might be used to improve performance
Chapter 6  SNMP

40. Meterware NMS MIB browser screen Much easier than command line mode!
Chapter 6  SNMP

41. Meterware NMS
Meterware “decodes” the information and presents it in a readable form
Also presents hex view
See book for more pictures of Meterware output
Chapter 6  SNMP

42. Chapter 6 Summary Components of mgmt environment
Format of SNMP messages
Get-Request
Get-Next-Request
Command line
Security (or lack thereof)
Meterware NMS
Chapter 6  SNMP