How to fix this "unreachable - need to frag (mtu 1365)"

Installing and Using OpenWrt
#1

i am getting this icmp message how can i fix it ?

i tried to lower mtu from 1492 to 1365 and it still show up

15:07:04.204080 IP OpenWrt.lan > PS4-GAMING-CONSOLE.lan: ICMP ec2-3-86-1-110.compute-1.amazonaws.com unreachable - need to frag (mtu 1365), length 556
15:10:55.259244 IP OpenWrt.lan > PS4-GAMING-CONSOLE.lan: ICMP ec2-52-70-153-127.compute-1.amazonaws.com unreachable - need to frag (mtu 1365), length 556
15:15:56.129102 IP OpenWrt.lan > PS4-GAMING-CONSOLE.lan: ICMP ec2-107-20-42-120.compute-1.amazonaws.com unreachable - need to frag (mtu 1365), length 556
15:20:57.102437 IP OpenWrt.lan > PS4-GAMING-CONSOLE.lan: ICMP ec2-54-175-149-153.compute-1.amazonaws.com unreachable - need to frag (mtu 1365), length 556
How can i increase packets per second for ip?
How to enable ip packets fragmentation in OpenWrt?
Need help to set [DF] flag on all udp outgoing packets?
#2

You fix this by putting your MTU on the correct setting. For normal Ethernet, that number is 1500. Also, you may want to note to others you're doing this because you believe your Fortnite game has a problem; because it sends small packets and/or not/using the fragmentation flags.

You will never reach the Fortnite server at Amazon if you keep lowering the MTU of the packets and refuse to fragment them. I think you may need to understand what you're doing and why it's actually causing your problem:

Also see:

4 Likes
#3

but i get that message even with mtu = 1492

#4

What did Fortnite support say?

#5

they didn't email me back

#6

OK, since the server is sending this message, you cannot control that. If you are not altering packets and properly using an 1492 MTU, then you'll have to ask Fortnite why they drop packets >= 1493.

Since you never mentioned this issue before; and given packets in your other threads were <= 150, I'm somewhat confused how you're now experiencing the exact opposite situation. Are you doing anything to these packets?

1 Like
Need help to set [DF] flag on all udp outgoing packets?
#7

i didn't do anything

#8

If this is a PPPoE connection, then 1492 is max packet size, so anything larger than that will not reach fortnight un-fragmented.

1 Like
#9

See original post and title...or maybe you don't understand the MTU issue...

It's very abnormal for a 1492 packet to be fragmented across internet routing equipment - especially since the common MTU is 1500. Additionally, the OP had an issue with "too small" packets; now suddenly Amazon is requesting fragmentation on packets at thier maximum size...?

And, I hope we all know that:

1365 < 1492

:thinking:

The problem here is the server appears to be sending the ICMP messages.

This usually means the sender could be altering packets; and the server doesn't expect to receive them. It is a game after all - probably anti-cheating features in place.

I think Epic Games should be more than happy to assist you then.

2 Likes
#10

Am I interpreting the messages wrong, or is OP experiencing fragmentation when sending 556 byte packets over a line with a MTU of 1365?

#11

556 is the size of the ICMP message itself, not the original traffic (which is assumed to be >= 1366).