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Troubleshooting

Connectivity tools​

  • ipconfig
  • ping
  • tracert
  • telnet

ipconfig​

  • Internet Protocol Configuration
  • View Network configuration
  • Release and Renew DHCP address
ipconfig /renew
ipconfig /all

ping​

  • Verifies connectivity to another computer
  • Uses TCP/IP
  • Uses ICMP echo requests

tracert​

  • Trace Route
  • Determine route to destination
  • Uses ICMP packets
  • Calculates Time-To-Live (TTL)
tracert <ip>

telnet​

  • Protocol to interact with remote computers
  • Used to test TCP connections
  • Combine host name/IP address and port
telnet <default gateway>

Example (Windows)​

ncpa.cpl
Network adapter -> Properties -> IPv4 -> Use following IP address
ping 127.0.0.1
ping <default gateway>

Name Resolution​

  • ipconfig
  • nslookup
  • nbtstat
  • arp

ipconfig​

  • Purge local DNS cache
  • Re-register DNS names
ipconfig /flushdns
ipconfig /registerdns

nslookup​

  • Name Server lookup
  • Diagnose DNS infrastructure
  • Look up host name records
nslookup -type mx cybrary.it
nslookup cybrary.it 8.8.8.8
nslookup cybrary.it 1.1.1.1

nbtstat​

  • NetBIOS over TCP/IP Statistics
  • Verifies NetBIOS name resolution
  • Windows Internet Naming Services (WINS)
nbtstat -c

arp​

  • Address Resolution Protocol
  • IP Addresses and physical addresses
  • Display and modifies entries in cache
arp -a
arp -s <ip> <MAC>

Advance tools​

  • netstat
  • route
  • netsh

netstat​

  • Network Statistics
  • Display active connections
  • Verify Ports computer is listening on
netstat
netstat -f
netstat -a
netstat -ano

route​

  • Displays local IP routing table
  • Add static routes to control network traffic
route print
route ADD <IP> MASK <SUBNET> <GATEWAY> METRIC <METRIC> IF <INTERFACE>
route DELETE <IP>

netsh​

  • Network Shell
  • Display and configure network communication settings
  • Reset network adapter
netsh
netsh winsock reset

Capturing Network Traffic​

  • netsh

netsh​

  • Capture network traffic
  • Persist through system restarts
netsh trace start persistent=yes capture=yes tracefile=C:\netshtrace\demo.etl
netsh trace stop

Wireshark​

  • Open-source
  • Network Packet Analyzer
  • Filters like ip.addr == <ip>

Fiddler​

  • Capture HTTP traffic
  • Decrypt to view secure sessions
  • Acts as a proxy

Troubleshoot Network Devices​

Physical Connections​

  • Verify network cable
  • Verify network card
  • Network activity lights

Network Devices​

  • Power and network connectivity
  • Access admin interface (GUI, SSH)
  • Direct connection

Configuration​

  • Port connectivity
  • Port enablement
  • Port speed

Network Architecture​

  • Documentation and diagrams
  • Understand traffic flows
  • Security devices (firewalls, proxies)