1473 & 1500 bytes ping drops

MWAM · ‎11-02-2022

I Have intrenet connection through ISP connected to CE router Cisco 888 k9 device

My Lan Subnet configured on int vlan 1

i can reach any site with source int vlan 1 with size 1500 nourmaly and with don't fragment also.

The problem that when i connect laptop to this router can reach to some sites with size 1500 normally and some no and max size can reach is 1472 only as the below.

I need explanation for that please.

C:\WINDOWS\system32>Ping 8.8.8.8 -l 1500

Pinging 8.8.8.8 with 1500 bytes of data:

Request timed out.
Request timed out.

Ping statistics for 8.8.8.8:

Packets: Sent = 3, Received = 0, Lost = 3 (100% loss),

C:\WINDOWS\system32>Ping 8.8.8.8 -l 1472

Pinging 8.8.8.8 with 1472 bytes of data:

Reply from 8.8.8.8: bytes=68 (sent 1472) time=39ms TTL=119

Ping statistics for 8.8.8.8:

Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),

Approximate round trip times in milli-seconds:

Minimum = 39ms, Maximum = 39ms, Average = 39ms

C:\WINDOWS\system32>Ping 8.8.4.4 -l 1500

Pinging 8.8.4.4 with 1500 bytes of data:
Request timed out.
Request timed out.
Ping statistics for 8.8.4.4:

Packets: Sent = 2, Received = 0, Lost = 2 (100% loss),

C:\WINDOWS\system32>Ping 8.8.4.4 -l 1472

Pinging 8.8.4.4 with 1472 bytes of data:

Reply from 8.8.4.4: bytes=68 (sent 1472) time=39ms TTL=119

Ping statistics for 8.8.4.4:

Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:

Minimum = 39ms, Maximum = 39ms, Average = 39ms

Reza Sharifi · ‎11-02-2022

That is because the default payload size is 1472. The other 28 bytes are for IP and ICMP headers. So, the behavior you see is correct.

HTH

MWAM · ‎11-02-2022

Okay , but why can ping the 4.2.2.2 with size 1500 and 1473 nourmally but
cant ping 8.8.8.8 with same size.