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nourathar

Member

From: Bxl

Registered: 2013-04-26

Posts: 112

https slowness and mtu size ?

Hello,

for some time I have been experiencing excruciatingly slow loading times for websites that heavily use https, such as banking sites.
I seem to remember this started with a system update of my adsl modem (a FritzBox wlan 7340), but I'm not sure anymore, since that was quite some time ago and I did not make the connection to the slowdown at the time.

when looking around in the documentation and on the forum, one possible reason seems to be an incorrect packet size, and it does seem that setting it smaller changes things a bit.
But it doesn't remediate the issue, and when I am downloading slightly larger files over https, it often stalls completely.

below the current info shown by ip link and confirmation that packets bigger than the mtu size do not go through:

$ ip link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: enp3s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1492 qdisc fq_codel state UP mode DEFAULT group default qlen 2000
    link/ether 14:da:e9:f5:de:33 brd ff:ff:ff:ff:ff:ff

$ ping -c 3 -s 1464 www.google.com
PING www.google.com (173.194.65.106) 1464(1492) bytes of data.
72 bytes from ee-in-f106.1e100.net (173.194.65.106): icmp_seq=1 ttl=49 (truncated)
72 bytes from ee-in-f106.1e100.net (173.194.65.106): icmp_seq=2 ttl=49 (truncated)
72 bytes from ee-in-f106.1e100.net (173.194.65.106): icmp_seq=3 ttl=49 (truncated)

--- www.google.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2002ms
rtt min/avg/max/mdev = 22.344/22.685/23.289/0.461 ms

$ ping -c 3 -s 1465 www.google.com
PING www.google.com (173.194.65.106) 1465(1493) bytes of data.

--- www.google.com ping statistics ---
3 packets transmitted, 0 received, 100% packet loss, time 1999ms

I now set the mtu size manually to 1492 and that seems a bit better than the 1500 it was originally set to.
But it is still unreasonably slow and downloads still stall.

What can I do ?
Is there something else than an incorrect mtu size that could cause such behaviour ?

kind regards,

Joost.

tohojo

Member

From: Sweden

Registered: 2010-10-06

Posts: 4

Re: https slowness and mtu size ?

What line rate is your ADSL connection, and how is your computer connected to the ADSL modem? Also, is there any other devices on your LAN sharing the connection?

graysky

Wiki Maintainer

From: :wq

Registered: 2008-12-01

Posts: 10,731

Website

Re: https slowness and mtu size ?

I ran with non-standard MTU sizes without noticing this.  I switched back due to my LAN driver not allowing C7 sleep states with them enabled... your LAN might be different than mine though.

Modem <--> Router <---> Gigalan switch <==> All PCs

Dunno if larger MTUs would mess up traffic without the switch.

Last edited by graysky (2014-11-27 16:52:29)

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brebs

Member

Registered: 2007-04-03

Posts: 3,742

Re: https slowness and mtu size ?

Is there something else than an incorrect mtu size that could cause such behaviour ?

Are you running a firewall which over-zealously blocks ICMP? If so, don't block ICMP.