Troubleshoot
"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
MTU
MTU MSS Article MSS/MTU
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.