Hi all.

I have some files on an apache server (localhost) and i'm using simple AJAX commands to pull the files from the server. Whilst doing this, I am running wireshark to analyze the way in which the packets are received and acknowledged.

To replicate ethernet stardards, I set the MTU at 1500 using the following command:
sudo ifconfig lo mtu 1500

Following that, ifconfig states:

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:1500 Metric:1
RX packets:3187 errors:0 dropped:0 overruns:0 frame:0
TX packets:3187 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:9154900 (9.1 MB) TX bytes:9154900 (9.1 MB)


However when running wireshark, packets are of sizes in excess of 1500 such as: 8694, 5814, 7734 etc

Any idea why the packets would be larger than the MTU specified?

Hi,

I've just a guess:
Is the client using a different MTU?

Wouldn't the loopback interface cover both the client request and server response on a single machine?

I didn't know that it was just the same machine.
Maybe you should check the other NICs on that machine.

Good idea, I tried modifying the mtu on both my wlan & ethernet and it when reduced the packet trace reflected the reduced mtu.

I can't figure out why lo won't follow suit!

OK
Each host has its own MTU (per NIC or interface). This value is being obeyed by the host for sending packets. If the host is receiving
packets the receiving host "can not do" anything to it.
If you have a router between server and client the situation might be different.
A router can (if capable) take received packets and generate more than one packet to send (split up packets to obey the MTU).

I hope this will help you to understand.

Not sure lo is a good choice to use logic on. Some odd things happen there.