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Title: Advanced Network Protocols


1
Advanced Network Protocols
  • CSCI 5132
  • Chapter 30
  • Simple Network Management Protocol
  • By
  • Chetan Singh
  • Haaris Sheikh
  • Lakshmi Menon
  • Kavita Sarma

2
Level of Management Protocols
Wide area networks include management protocols
as part Of their link level protocols. Control
packets are used by the receiver to respond to
commends from the manager to handle packet switch
misbehaving. The switch can resume normal
operation once the problem is fixed. TCP/IP does
not have a single link level protocol as the
internet consists of multiple physical networks
interconnected by IP routers.
3
Level of Management Protocols (Cont..)
The differences between internet management
are - A single manager can control
heterogeneous devices. - The controlled
entities may not share common link level
protocol. - The manager controls a set of
machines that may lie in different physical
networks. The internet management protocol used
with TCP/IP operates above the transport level
i.e the application level.
4
Level of Management Protocols (Cont..)
Advantages of using the internet management
software in the application layer - One set
of protocols can be used for all networks. -
One set of protocols can be used for all managed
devices. - Routers can be
managed without direct attachment to
every physical network or router. Disadvantages
- Routers con not be contacted if either the
operating system, IP software or
transport software fail.
5
Architectural Model
Client software runs on the managers
machine. The management agent(server program) is
run on each participating router or host. A
manager tells a client about the agent it wants
to communicate with. The client sends commands
or queries to the agent. The management software
uses an authentication mechanism to ensure that
only authorized managers can access or control a
particular device.
6
Protocol Framework
TCP/IP management protocols divide the management
problem into two parts specifying separate
standards for each part. The first part specifies
hoe the client communicates with the agent. The
second part specifies which data item a managed
device must keep. Simple Network Management
Protocol (SNMP) is the TCP/IP standard for
network management.
7
Standard For Managed Information
A device being managed must keep control and
status information that the manager can
access. SNMP allows a manager to access the
statistics but does not specify which data can
be accessed. Management Information Base (MIB) is
a standard that specifies what data items a
managed device must keep and the operations
allowed on each. MIB divides management
information into many categories and the choice
of categories are important because identifiers
used to specify items include a code for the
category.
8
Examples of MIB Variables

Separate RFCs exist that specify MIB variables
associated with different devices. Also many
vendors have specified MIB variables for
their products. Refer to Figure 30.3. for a small
list of MIB variables. MIB variables present
only a logical definition of each data item. The
internal data structures a router uses may differ
from the MIB definition.
9
THE STRUCTURE OF MANAGEMENT INFORMATION (SMI)
  • SMI is a set of rules used to define and identify
    MIB variables.
  • It places restrictions on types of variables
    allowed in MIB.
  • Specifies rules for naming variables.
  • Creates rules for defining variable types.

10
THE STRUCTURE OF MANAGEMENT INFORMATION (SMI)
  • Example
  • SMI standard includes definitions of terms like
  • IPAddress as a 4-octet string,
  • Counter, an integer in the range of 0 to 223-1.
  • Also specifies that these are the terms used to
    define MIB variables.
  • The rules in SMI, most importantly, describe how
    MIB refers to tables of values (e.g., IP routing
    table).

11
FORMAL DEFINITIONS USING ASN.1
  • The TCP/IP network mangement protocols use a
    formal notation called Abstract Syntax Notation
    (ASN.1) to define names and types for variables
    in the management information base. The precise
    notation makes the form and contents of variables
    unambiguous.
  • Precision is important when implementations
    include hetrogeneous computers that do not all
    use the same representations for data items.

12
FORMAL DEFINITIONS USING ASN.1
  • Example
  • A protocol using ASN.1 must state exact form and
    range of numeric values instead of simply
    specifying that a variable contains an integer
    value.
  • ASN.1 also simplifies the implementation of
    network management and guarantees
    interoperability.

13
STRUCTURE AND REPRESENTATION OF MIB OBJECT NAMES
  • Names for MIB variables are taken from the object
    identifier namespace administered by ISO ITU.
  • Object Identifier provides a namespace in which
    all possible objects can be designated. The
    namespace includes variables used in network
    management and names for arbitrary objects.
  • Object Identifier namespace is absolute(global)
    and hierarchical (Fig 30.4).

14
STRUCTURE AND REPRESENTATION OF MIB OBJECT NAMES
  • The name of an object in the hierarchy is a
    sequence of numeric labels, separated with
    periods to identify an individual component, on
    the nodes along a path from the node to the
    object.
  • Example
  • The name 1.3.6.1.2 denotes the node mgmt (Fig
    30.4).

15
STRUCTURE AND REPRESENTATION OF MIB OBJECT NAMES
  • MIB groups variables into categories.
  • The categories are the subtrees of the MIB node
    of the object identifier namespace (Fig 30.5).
  • Examples
  • Refer to Fig 30.5.
  • MIB standards do not dictate the implementation,
    instead provides a uniform and virtual interface
    to access data.

16
Simple Network Management Protocol
  • Network management protocols specify
    communication between the network management
    client and a network management server program
    that executes at the host or the router
  • The protocol needs to be flexible and compatible
    to changes.
  • Does not define a large set of commands.
  • Uses the fetch and store paradigm

17
SNMP contd
  • Taking a conceptual view of SNMP it contains only
    2 commands
  • Example if you want to reboot
  • Declare a data item that gives the time until
    the next reboot and allows the manager to assign
    a value to the item like 0

18
Advantages
  • Stability Definitions remain fixed even if new
    items are added.
  • Simplicity Saves the complexity of having
    special cases for each command
  • Flexibility Accommodates arbitrary commands in
    an elegant frame work

19
SNMP hidden facts!
  • Looking at the managers point of view SNMP
    remains hidden
  • SNMP software comes with a GUI interface that
    displays diagrams of network connectivity and
    uses the point and click interaction technique
  • figure 30.6 in the book shows the fetch and
    store commands
  • Get request fetch
  • Set request store
  • Response provides a reply.

20
SNMP operations
  • atomicIf the SNMP message specifies operations
    on multiple variables the server either performs
    all operations on all of them or on none of them
  • trap
  • Allows managers to program servers to send
    information when an event occurs.

21
Searching table using names
  • ASN.1 does not provide mechanisms for declaring
    arrays or indexing.
  • In order to iterate through the table the client
    can use the get-next-request operation which does
    the iteration

22
An Example
  • An example search
  • The client is not aware of the IP addresses
    that are currently
  • The client uses the prefix in order to
  • get-next request
  • iso.org.dod.internet.mgmt.mib.ip.ipAddrEntry.i
    pAdEntNetMask
  • The server then returns the network mask
    field of the first entry in ipAddrTable .

23
SNMP Message Format
  • SNMP messages do not have fixed fields
  • They use standard ASN.1 encoding which is not in
    human readable form
  • It consists of a descriptive name followed by
    the declaration of the items type.
  • msgVersion INTEGER(0..2147483647)
  • a non negative number lt 2147483647

24
SNMP Message formats
  • Integer identifies the protocol version
  • Header data
  • ref figure 30.8 page 567
  • Security parameters
  • Data Area
  • this is divided into PDU Protocol data
    unitsPDU consists of a request and a response
    from the client and the agent respectively.This
    also offers a choice of plain text or encrypted
    text
  • Notestechnically called discriminated union

25
SNMP Message contd.
  • SNMPv3 distinguishes between an application that
    uses the service SNMP supplies and an engine that
    is the underlying software
  • The encrypted text PDU begins with a identifier
    for the engine along with the engine ID.
  • data ANY implies that the context field has the
    exact details of the data.

26
SNMP Definitions -ERRORS
  • Error-status and Error-indexthese are single
    octet integers which contain the value zero in a
    request.
  • If an error occurs the values in the response
    identify the cause
  • The last parameter VarBindList is a sequence of
    pairs of object name and value.

27
Example Encode SNMP Message
  • Encoded form of ASN.1 uses variable length fields
    to represent items.
  • Each field begins with a header that specifies
    the type of object and its length in bytes.
  • The msg starts with a code for SEQUENCE which has
    a length of 103 octets.
  • 1st item 1 octet integer protocol version.

28
  • Successive fields indicate msg ID and the maximum
    message size the sender can accept in a reply.
  • Security information follows the msg header.
  • GetRequest-PDU occupies the tail of the message.
  • ScopedPDU specifies a context in which to
    interpret the remainder of the message.
  • Octet A0 specifies the operation as a
    get-Request.(Since high order bit is turned on
    the interpretation is context specific).

29
  • The length octet specifies the request is 26
    octets long.
  • The request ID is 2 octets.
  • Each of the error-status and error-index are 1
    octet.
  • Finally, the sequence pairs contains one binding.
    A binding is a single object identifier bound to
    a null value.
  • The identifier is encoded. The first two numeric
    labels are combined into a single octet.

30
New Features In SNMPv3
  • The primary changes are in the areas of security
    and administration.
  • First, SNMPv3 is designed to have both general
    and flexible security policies.
  • SNMPv3 includes facilities for several aspects
    of security, and allows each to be configured
    independently.

31
  • Second, the system is designed to make
    administration of security easy.
  • V3 allows remote configuration, meaning that an
    authorized manager can change the configuration
    of security items listed above without being
    physically present at the device.

32
Summary
  • Network Management Protocols allow a manager to
    monitor and control routers and hosts.
  • A network management client program executing on
    the managers workstation contacts one or more
    servers, called agents, running on the devices to
    be controlled.
  • As an internet consists of heterogeneous machines
    and networks, TCP/IP management software executes
    as application programs and uses internet
    transport protocols for communication.

33
Summary Contd.
  • SNMP , the standard TCP/IP network management
    protocol defines a low-level management protocol
    that performs two conceptual operations
  • Fetch a value from a variable or store a value
    into a variable.
  • SNMP defines the format of messages that travel
    between a managers computer and a managed entity.

34
Summary Contd.
  • A set of companion standards to SNMP define the
    set of variables that a managed entity maintains.
  • The set of variables comprise a Management
    Information Base(MIB) variables described using
    ASN.1, a formal language that provides a concise
    encoded form , also human readable notation for
    names and objects.
  • ASN.1 uses a hierarchical namespace to guarantee
    that all MIB names are globally unique while
    still allowing subgroups to assign parts of the
    namespace.

35
Any Questions?
36
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