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Download speed very slow in Ubuntu 20.04.1 while upload speed is perfectly fine over wifi

cn flag
newka

Im a new Linux user and I am facing this problem with my install. To be very specific, I have tried Ubuntu, Mint and even Kubuntu but this issue persists. The weird part is I am getting the exact same slow download speeds in all the distros which is 1.1Mbps (It should have been 45Mbps up+down) [checked through fast.com], but Im getting the full upload speed. [Using a fiber connection]

Things I have tried -

  • Turning off the power management from this post
  • Turning off IPV6 for that particular interface
  • Updated grub and my system

Here is the output for

ip a

wlp0s20f3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
inet 192.168.1.47/24 brd 192.168.1.255 scope global dynamic noprefixroute wlp0s20f3
   valid_lft 86044sec preferred_lft 86044sec 
   valid_lft forever preferred_lft forever

Here is some information about my Network Controller

Network controller: Intel Corporation Device 43f0 (rev 11)
    Subsystem: Bigfoot Networks, Inc. Device 1652
    Flags: bus master, fast devsel, latency 0, IRQ 16
    Memory at 6205274000 (64-bit, non-prefetchable) [size=16K]
    Capabilities: <access denied>
    Kernel driver in use: iwlwifi
    Kernel modules: iwlwifi

Also

10.817111] iwlwifi 0000:00:14.3: Detected Intel(R) Wi-Fi 6 AX203, REV=0x354

To add further, I dual boot Windows 10 and Ubuntu as of now. The wifi works perfectly fine on windows 10. So after trying everything else I tried to connect my phone to my wifi and then created a hotspot from my phone. I then connected my laptop[with Ubuntu] to that hotspot and it works perfectly fine. The only issue is that I cannot keep doing this forever. Please help me out regarding this and do let me know if there is any command that i specifically need to check.

Thanks a lot for your time.

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24601 avatar
in flag
24601
Does this answer your question? [Wi-Fi on Ubuntu 20.04 is very slow](https://askubuntu.com/questions/1243181/wi-fi-on-ubuntu-20-04-is-very-slow)
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cn flag
newka
@24601 No sadly this doesn't solve the problem because my version is AX203 which is not available in this website (or maybe i am mistaken) https://www.intel.de/content/www/de/de/support/articles/000005511/wireless.html
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user535733 avatar
cn flag
user535733
Are you saying that WiFi works properly when using Windows, and that WiFi works properly when connected to a Hostspot? But WiFi does not work properly when connected to your router's WiFi? If true, then try rebooting your router.
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cn flag
newka
@user535733 yeah i mean exactly that but like it works fine while using windows tho. In any case, let me try rebooting
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Jeremy31 avatar
ke flag
Jeremy31
Sounds like TKIP encryption being used on the router
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Score:1
avatar Ubuntu
cn flag
newka

Alright its totally my fault. The firewall on the router was set to strict and I changed it to be "low" and I'm getting the full bandwidth. Anyways thank you for your time, guys

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Score:1
waltinator avatar Ubuntu
it flag
waltinator

Check your WiFi MTU, using

ip link

or

ip l | grep $(ip r | awk '/default/ {print $5}' ) | awk '{print $2, $4, $5}'

also notice your WiFi interface's name. Your ip a command shows that your WiFi interface is "w1p0s2f3" and your MTU is 1500, which is the cause of your difficulty.

The MTU (Maximum Transmission Unit) is the size of the largest packet that can be sent in a single network transmission. If a packet exceeds the MTU of a link, the data must be split into multiple packets (fragmented). These multiple packets must be sent over the link, received, acknowledged, and reassembled at the far end. If your link is misconfigured, and you have to fragment every packet you send, your actual data transfer rate drops.

Ethernet (wired) networks use an MTU of 1500 bytes.

Due to additional per packet overhead for WiFi (8 bytes PPPoE header), WiFi uses an MTU of 1492.

Your MTU should be set by your DHCP server, check your router's config.

You can set your own MTU (setting does not persist over restarts) with

sudo ip link set dev name mtu 1492

where "name" is the interface name from above.

Here's an example:

walt@squid:~(0)$ ip link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: enp63s0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN mode DEFAULT group default qlen 1000
    link/ether 00:24:21:7f:e5:1c brd ff:ff:ff:ff:ff:ff
3: wlxf46d04b1790f: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN mode DORMANT group default qlen 1000
    link/ether f4:6d:04:b1:79:0f brd ff:ff:ff:ff:ff:ff
walt@squid:~(0)$   sudo ip link set dev wlxf46d04b1790f mtu 1492
[sudo] password for walt: 
walt@squid:~(0)$ ip link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: enp63s0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN mode DEFAULT group default qlen 1000
    link/ether 00:24:21:7f:e5:1c brd ff:ff:ff:ff:ff:ff
3: wlxf46d04b1790f: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1492 qdisc mq state UP mode DORMANT group default qlen 1000
    link/ether f4:6d:04:b1:79:0f brd ff:ff:ff:ff:ff:ff

My WiFi "interface name" is "wlxf46d04b1790f".

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cn flag
newka
No, you have been copy pasting this same answer multiple times where people have the same problem. This answer doesn't help.
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user535733 avatar
cn flag
user535733
@newka the answer is useful for many people, though perhaps not for you today. Historically, an unwise choice for MTU was indeed a common reason for slow connections.
1
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waltinator avatar
it flag
waltinator
@newka All of the Questions I post the canned but detailed (and sometimes customized) answer to look like packet fragmentation (doubles the number of packets) caused by MTU values that are overlarge. If multiple users ask MTU questions (or questions that could be MTU), why shouldn't I reuse the same (correct) answer? Should I come up with a rephrasing of the same answer (check your MTU, change your MTU, change MTU on your router/DHCP server) every time?
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Will avatar
id flag
Will
Well personally I think it’s a little terse and ungrateful to slate an answer in a rather personal way when (regardless of any copy / paste), it’s clearly an attempt to help someone. It’s a relatively long question that @waltinator bothered to read and gave a sensible answer so I think worthy of gratitude rather than criticism (and an up-vote from me!). I learnt something by reading your answer so I’m grateful for that.
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