Why openwrt won't fragment large packets using ping

Hi Guys,

When I ping with size larger than 1464 I gets packet loss why this behavior happen, it suppose to fragment the large packets? Can anyone explain to me why this happen I am using mtu 1492 as my internet service is pppoe and is possible to enforce fragment ??

@Miko, welcome to the community!

Can you show the command you used...and perhaps the output?

(Please use the </> button to place output in codeboxes.)

user@machine:~$ ping 8.8.8.8 -s 1500 -c 3
PING 8.8.8.8 (8.8.8.8) 1500(1528) bytes of data.

--- 8.8.8.8 ping statistics ---
3 packets transmitted, 0 received, 100% packet loss, time 2045ms

user@machine:~$ ping 8.8.8.8 -s 1500 -M do -c 3
PING 8.8.8.8 (8.8.8.8) 1500(1528) bytes of data.
ping: local error: message too long, mtu=1500
ping: local error: message too long, mtu=1500
ping: local error: message too long, mtu=1500

--- 8.8.8.8 ping statistics ---
3 packets transmitted, 0 received, +3 errors, 100% packet loss, time 2029ms
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Thank you when I ping it shows like this:

-----------------------------------------------------
 OpenWrt SNAPSHOT, r2473-3bb1af32
 -----------------------------------------------------
root@OpenWrt:~# ping 8.8.8.8 -s 1500
PING 8.8.8.8 (8.8.8.8): 1500 data bytes

I am getting no reply it keeps like this

root@OpenWrt:~# ping 8.8.8.8 -s 1500 -c 3
PING 8.8.8.8 (8.8.8.8): 1500 data bytes

--- 8.8.8.8 ping statistics ---
3 packets transmitted, 0 packets received, 100% packet loss
root@OpenWrt:~# y

The ICMP messages typically report errors in the processing of
datagrams. To avoid the infinite regress of messages about messages
etc., no ICMP messages are sent about ICMP messages. Also ICMP
messages are only sent about errors in handling fragment zero of
fragemented datagrams. (Fragment zero has the fragment offeset equal
zero).

~ RFC792

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Thanks for you reply, So this mean that someone is hacking me :flushed::flushed::flushed: how can I fix it

No, I think you did not understood @lleachii's post. What he is saying is that ICMP packets do not get fragmented, they are just dropped. In other words, what you are experiencing is expected behavior.

2 Likes

Huh!
...no

I'm lost at why you would think that because you're initiating a ping. As @eduperez noted, pings simply do not produce ICMP errors, hence no fragmentation.

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