Network Topology Discovery

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Network Topology Discovery Using SNMP
Tama Mittleman Adam Wolman Advisor Alex
Sprintson
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Project Goal

• Discovery of second layer network topology.
  Why?
• Second layer topology discovery is important for
• network management
• due to the lack of automated solutions, network
  managers are forced to keep layer-2 information
  manually
• providing accurate performance predictions.
• network simulations.
• Most past projects evolved 3rd layer topology
  (e.g, HPs Open View, IBMs Tivoli)
• First use of SNMP in the lab, to collect
  dataabout the network components.

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Network Discovery Challenges

• Limited local information
• Heterogeneity of network elements
• SNMP protocol is not so simple, and neither is
  the MIBs structure.
• Develop a tool without changing the operating
  system

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Working Platform

• Windows 2000, Microsoft visual C with SNMP
  class libraries. Example
• int status
• char sysDescSYS_DESC_LENGTH
• IpAddress ia ipElemPtr-gtm_ipAddress
• Snmp snmp(status) // Create a SNMP
  object
• CTarget ctarget(ia) // Create target with a
  given ip address
• ctarget.set_retry(RETRY_NUM_2) // Set number
  of retries
• ctarget.set_timeout(TIMEOUT_50) // Set number
  of timeouts
• Vb vb(SYS_DESC_OID) // Set pdu to target
• Pdu pdu
• pdu vb
• // Send get query
• if ((status snmp.get(pdu, ctarget))
  SNMP_CLASS_SUCCESS)
• pdu.get_vb(vb, 0)
• vb.get_value(sysDesc)

PDU Protocol Data Unit
VB
OID
value
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Module Diagram
Collection of Network Data using SNMP
Storing in Data Structures
Analysis of Data
Presentation of Network Topology
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Information needed about an IP element

• IP Address (132.68.43.254)
• System Descriptor (Passport)
• Device type (Router, Switch, Host)
• Community (Read Only, Public)
• Connections vector

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Data Structures

• The main data structure - IPElements

IpAddress SysDesc DeviceType Community Connections
ConnectionsUP
IPElement
IPElement

• The dictionary - MAC2IP

Mac
Mac
Mac
IP
IP
IP
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Stages of Data Collection
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Ping query
IPElement
IpAddress 132.68.43.254 SysDesc DeviceType Commu
nity Connections ConnectionsUP
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SNMP basic query
IPElement
IpAddress 132.68.43.254 SysDesc
Passport DeviceType Router Community
Public Connections ConnectionsUP
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SNMP Routers query

• The information we take from the routers is their
  ARP tables.
• The ARP tables give us all the information we
  need in order to create our dictionary - the
  MAC2IP data structure.

Mac 0006290f9898
Mac
Mac
IP 132.68.204.50
IP
IP
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SNMP Switches query

• The information we take from every switch, is the
  Macs of all the elements, which are connected to
  that switch.

Mac A
Mac B
Switch
Mac C
Mac D
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Mac connections to IP connections

• Each Mac address is translated to an IP address
  using our dictionary.
• The IPElement matching that IP address is then
  found in the main data structure.

Mac
IP
IPElement
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SNMP Switches query

• We now know which IPElements are connected to the
  switch.

IPElement A
IPElement B
Switch
IPElement C
IPElement D
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The Network Hierarchy

• This hierarchy is defined according to the
  hierarchy by which packets are passed in the
  network.

Router
Switch
Host
Host with SNMP
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SNMP Switches query

• Now we can determine the Connection and
  ConnectionUP fields of the switches and routers.

Router
Host with SNMP
Switch
Host
Switch
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SNMP Switches query
IPElement
IpAddress 132.68.43.254 SysDesc
Passport DeviceType Router Community
Public Connections 132.68.43.253,
132.68.43.252 ConnectionsUP
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Testing on a known subnet
See results in a txt file ...snmpTopo_43.txt
Router
Switch
Host
Host
Host
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Suggestions for future work

• Extend our project to discover both 2 and 3 layer
  topologies
• Use the topology discovery tool as a building
  block for various applications
• network management (e.g., identification of
  bottlenecks, failure detection, topology changes)
• research on layer 2 topology
• Allow the program to receive a few subnets, and
  not only one.
• Print trace route information, and port numbers.
• Adjusting the program so that the network manager
  can determine and update the network components
  names.