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"Not working" network

  • Duplex
  • Cable
  • Firewall - disable it
  • DNS filtering - public DNS
  • ISP outage - ping its address
  • Path outage - MTR tool
  • ARP old record
  • MAC collision
  • STP loop/Broadcast storm
  • Route missing
  • LACP/PAGP must be on both ends configured
  • Zombie process and station or froze
  • Local firewall on device, or network type (windows-public)
  • NAT
  • Cache browser - try incognito mode

Slow network

  • Path drop - MTR tool
  • Number of active sessions on device
  • Packet/Frame size
  • Number of ACL on device
  • Wireless is slower + wireless noise
  • Duplex
  • Cable
  • Link type overhead + MTU
  • Aggregated interfaces - hashing type (source+destination IP)
  • CPU and RAM low especially tunneling encryption (AES-CBC not paralelized)
  • Rate limiting
  • No offloading



Testing max MTU

The important thing to remember is that an ICMP header is 8 bits so the ping test from CMD should be whatever number is your max without fragmenting PLUS 8 which gives your value for the router.

Testing Max MTU/MSS