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So after discovering I can increase internet speed by tweaking the MTU, it appears I have a MTU of only 96 bytes. Any idea why that is?

ping -c 3 -M do -s 68 google.com
PING google.com (172.217.169.46) 68(96) bytes of data.
76 bytes from lhr48s08-in-f14.1e100.net (172.217.169.46): icmp_seq=1 ttl=119 time=20.2 ms
76 bytes from lhr48s08-in-f14.1e100.net (172.217.169.46): icmp_seq=2 ttl=119 time=21.7 ms
76 bytes from lhr48s08-in-f14.1e100.net (172.217.169.46): icmp_seq=3 ttl=119 time=19.7 ms

--- google.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2003ms
rtt min/avg/max/mdev = 19.742/20.546/21.664/0.815 ms

Lets increase that by a single byte:

ping -c 3 -M do -s 69 google.com
PING google.com (172.217.169.46) 69(97) bytes of data.

--- google.com ping statistics ---
3 packets transmitted, 0 received, 100% packet loss, time 2002ms

Running on Ubuntu 20.04.3 LTS

enkor
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  • What's the question? – Halfgaar Feb 04 '22 at 16:14
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    See this answer: https://networkengineering.stackexchange.com/a/28487 "Every internet module must be able to forward a datagram of 68 octets without further fragmentation. This is because an internet header may be up to 60 octets, and the minimum fragment is 8 octets." – Greg Askew Feb 04 '22 at 16:34
  • @Halfgaar, So the question is :Any idea why that is? The default appears to be around 1500 for others, somehow mine is a great deal lower than that. – enkor Feb 06 '22 at 12:41
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    Google is just blocking big ICMP packets. Try pinging something else. – Halfgaar Feb 06 '22 at 16:56

1 Answers1

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As per @Halfgaar 's comment, Google is blocking big ICMP packets. So lets try something else:

ping -c 3 -M do -s 1464 bbc.co.uk
PING bbc.co.uk (151.101.0.81) 1464(1492) bytes of data.
1472 bytes from 151.101.0.81 (151.101.0.81): icmp_seq=1 ttl=60 time=20.0 ms
1472 bytes from 151.101.0.81 (151.101.0.81): icmp_seq=2 ttl=60 time=20.2 ms
1472 bytes from 151.101.0.81 (151.101.0.81): icmp_seq=3 ttl=60 time=20.5 ms

--- bbc.co.uk ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2003ms
rtt min/avg/max/mdev = 20.007/20.214/20.478/0.196 ms
enkor
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