Technical Tip: How to use ping with data-size
Description
This article describes how to use data size to initiate ping.
Scope
Ping with data-size from the WAN interface going to a specific destination on the internet will be initiated.
Solution
Ping with data-size from the wan interface going to a specific destination on the internet.
- 192.168.254.100 is the WAN1 interface IP.
- 1350 data size will be used to reach Google DNS 8.8.8.8 via ping.
This helps to identify which router in the path is enabled with a lower MTU.
FortiGate # exec ping-option source 192.168.254.100
FortiGate # exec ping-option data-size 1350
FortiGate # exec ping 8.8.8.8
PING 8.8.8.8 (8.8.8.8): 1350 data bytes
76 bytes from 8.8.8.8: icmp_seq=0 ttl=57 time=20.4 ms
76 bytes from 8.8.8.8: icmp_seq=1 ttl=57 time=20.3 ms
76 bytes from 8.8.8.8: icmp_seq=2 ttl=57 time=20.1 ms
76 bytes from 8.8.8.8: icmp_seq=3 ttl=57 time=20.1 ms
76 bytes from 8.8.8.8: icmp_seq=4 ttl=57 time=20.0 ms
Pinging the destination with df bit enabled.
Putty1:
diagnose sniffer packet any "host 173.243.129.16 or host 173.243.140.16" 6 0 l
Putty2:
exe ping-options data-size 1472
exe ping-options df-bit y
exe ping 173.243.129.16
This helps to identify which router in the path is enabled with a lower MTU.
Data-size is the total length of the IP packet. Example below is a ping packet with data-size of 1419.
 
Related article:
Troubleshooting Tip: Using PING options from the FortiGate CLI