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rxavier
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Packet loss above 1472 bytes

I have noticed some packet loss recently on my broadband connection.

After doing some investigatory ping tests I noticed that packets above 1472 bytes were being dropped within the Virgin media network.  Pings above this size worked fine to the next hop address after my VM Hub, and below this size work all the way through.  Anything above this size is dropped at brnt-core-2b-xe-202-0.network.virginmedia.net [62.252.212.37]

This suggests that the DF flag (don't fragment) is set somewhere in the network and would be dropping large packets (above 1500 bytes) instead of fragmenting and forwarding them on.  There is a possibility that a firewall rule is blocking large ICMP packets but usually these rules are set to block all ICMP.

I'm sure this was not the case before, and I have noticed recently dropouts in team video conf calls.

I did log an email explaining this but got the usual standard bull$*** response.

Can someone at VM  2nd line support look into this?  Is anyone else noticing packet loss (poor quality video calls)?

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legacy1
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Re: Packet loss above 1472 bytes

VM don't need to fragment your packets anything above 1472 for ICMP you send the fragments.

Then fact that 62.252.212.37 dose not reply to a ICMP + fragment thats above 1472 should not be a problem its the remote end you want to get the ICMP + fragment should it allow it a hop that you directly ping too is not important.

But even if VM did block ICMP fragments as a whole its not that important but what is important is UDP and even TCP so thats want needs to be made sure...
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Tudor
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Re: Packet loss above 1472 bytes

Who are you trying to ping? 1.1.1.1 supports above this size, but 8.8.8.8 will not even accept 80.


Tudor
There are 10 types of people: those who understand binary and those who don't and F people out of 10 who do not understand hexadecimal c1a2a285948293859940d9a49385a2
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legacy1
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Re: Packet loss above 1472 bytes

Try a ping to www.kloth.net over 1472 bytes works fine here.
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rxavier
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Re: Packet loss above 1472 bytes

I had jumboframes enabled on my network, but even after turning off the same result.  So your answer makes sense, thanks.

Just a bit strange that ICMP fragments are responded to by the next hop, but nothing further.

Yes possibly fragmented UDP packets are being dropped in the network.  I've also noticed packet loss recently in some online games (only for downlink).

Not sure how to prove this though.

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legacy1
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Re: Packet loss above 1472 bytes

Netalyzr was a great way to test if UDP fragments was allowed.

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rxavier
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Re: Packet loss above 1472 bytes

Thanks all for the responses.  I'm now guessing that there is just congestion somewhere in the network causing the problem as pings above 1472 bytes are working to some internet destinations.

It would be more noticeable for real time traffic like gaming and video calls which would explain what I've been experiencing. 

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legacy1
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Re: Packet loss above 1472 bytes

You can use this UDP tool to test fragments by a 4G connection and Wireshark to a destination port say 49141 to VM
http://startrinity.com/VoIP/NetworkTester/NetworkTester.aspx
Then to test back on your VM connection send a connect back on the same SNAT source port used for 4G as destination from and source port 49141 (49140 as it ups the port you set by 1)


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Adduxi
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Re: Packet loss above 1472 bytes

I’ve my MTU set to 1472 on my Router and don’t seem to have any problems? Am I missing something here? 

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legacy1
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Re: Packet loss above 1472 bytes

MTU should be 1500
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