ping size matters?

[admin_2]

I was troubleshooting a network problem related to the size of packets, and for fun I pinged yahoo.com and found that the size of the ping matters. If I do a "ping yahoo.com -l 1272" the ping will work, but 1273 bytes or larger times out.

I've pinged some other internet servers and found that the 1272 byte thing holds true for them as well.

What is going on here?

[steven-dunn]

As you are seeing the small ping sizes work for many internet sites, I belived you may have a common point in the network with this smaller MTU. I ran a ping to yahoo (everybody else is blocking ping ;) with a packet size of 1400 and the DF tag which is just less than my MTU of 1500. The ping worked. I think the ping size limit is in your network.

[aslam]

Hi,

First thing that we need to understand is that the value 1272 / 1400 is not the actual Packet Size is the size of the payload that the ping packet is going to carry.

By defult the MTU on the network is 1518, so now removing 18 bytes for ethernet, 20 bytes of IP header and 8 bytes for Echo Reply Message header, you are left with 1472 bytes of payload. I did ping Yahoo with 1472 payload successfully. Buy if you exceed 1472 then the packet becomes a giant and will most probably be dropped.

So, I think that there must be some limitation on you network or machine which is not allowing you to cross 1272.

HTH