So while testing my WAN speed for SQM, I used the OpenWRT terminal ping command to test MTU. When I ping google using “ping 8.8.8.8 -s 1500” the response shows 1508 bytes. I’m assuming the extra 8 bytes are the PPPoE header because I am on a coax cable internet connection but after researching this a bit, I am not sure if I am supposed to configure my WAN MTU as 1508 or 1492?
Nope, ping does not see encap headers, and busybox ping does not set DF bit so it is not valid for mtu test.
Is your wan connection ppp or dhcp? Coax docsis internet usually provides later on your client port.
1 Like
Oh interesting, I was just assuming based on articles on the help guide that my ISP would be PPPoE but Google says my ISP uses DHCP. So why does the OpenWRT ping return 1508 bytes on a 1500 ping?
The 8 extra bytes displayed in a ping reply account for the ICMP packet header.
Ahh ok. It makes sense now. So if my ISP is DHCP based then I should leave the MTU at 1500 and set SQM to “Ethernet with Overhead” and the value at 22 bytes?
No basis to add overhead. "ethernet" and thats all.