WAN Packet Overhead / Best MTU for 4G LTE? (2023)


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05/08/2021, 03:46 PM (This post was last modified: 05/08/2021, 03:51 PM by Lynx.)

I have beenexperimenting with QoS-CAKE, in which ideallythe 'WAN packet overhead' is ascertained.

Since I use a VPN, by using 'tcpdump -vpni' on 'eth0' vs 'tun11' interfaces, I have determined that the OpenVPN encapsulation adds 53 bytes to each packet.

But I need to enter the overhead associated with 4G LTE transmission. That is a harder number to determine.

Mindful of, e.g.:

Quote:Over the Iu-ps interface 1400 byte will avoid fragmentation. This is a conservative value to accommodate the protocol layer header overheads. The possible overheads over the Iu-ps interface (GTP/UDP/lower-IP) are the following: GTP main header = 12 bytes GTP extension header = 4 bytes UDP header = 8 bytes IPv4 header = 20 bytes (without optional IPv4 fields), or IPv6 header = 40 bytes (without optional IPv6 headers). The maximum headers size is then 12+4+8+40=64 bytes. The MTU for IPv4 and IPv6 is 1500 bytes. So, the maximum SDU size would be 1500-64=1436 bytes. 1400 bytes is a safer value.


(as an aside,this makes me wonder:what is the optimal MTU set for a 4G LTE connection?Should this value be the same in OpenVPN?)

Any idea of the 'WAN packet overhead' for use with 4G LTE? I mean, what is the WAN packet overhead in bytes associated with the 4G LTE encapsulation around the payload? Is it fixed?




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05/08/2021, 07:45 PM (This post was last modified: 05/08/2021, 07:47 PM by Seán.)

You can determine the MTU of your 4G connection with a ping test. ICMP has an overhead of 28 bytes for the packet size, so by determining the largest packet size you can ping a host such as with without packet fragmentation, you can add 28 bytes to determine the optimal MTU for your 4G connection.

Try the following in the command line without the VPN connection:
ping -f -l 1472

The '-f' means do not fragment and the '-l' specifies the ping byte size.

If you get a"Packet needs to be fragmented but DF set" or "Request timed out" reply, reduce the 1472 value by 10 or 20 and repeat until you get a "Reply from". Then repeat increasing the value by 2 until it stops replying.

Whatever is the highest value to give a reply, add 28 and this is the optimal MTU.

On my 4G connection, I get a reply at 1472, i.e. adding 28 gives the standard IPv4 MTU size. However, I have used 4G connections that have a much lower MTU size such as 1440, particularly with the Eir 4G network here. PPPoE connections such as DSL based typically have an MTU size of 1492. VPNs typically have the MTU size set at 1400, so you'll likely find that 1372 is the largest value that will give a ping reply above while connected to the VPN.

Cloudflare seems to use an MTU of 1300 based on 1272 largest size before it fragments.

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05/08/2021, 08:45 PM (This post was last modified: 05/08/2021, 08:49 PM by Lynx.)

Thanks Seán. Like you I get 1472 (for both output through WAN and also via OpenVPN), making my optimal MTU 1500 according to the above technique. However, I am a little suspicious that this technique works for 4G LTE given the 4G LTE overhead itself. Does this necessarily show that we are not getting fragmentation at the 4G LTE transmission level? I read somewhere that actually a lower/higher value might be more appropriate for 4G LTE given the 4G LTE overhead.

In terms of the complete overhead, I am trying to ascertain the overhead in speed terms and also in byte terms. Given that speedtest.net and the like reports 'goodput', or 'net speed', do you know what the 'gross speed' is given overheads that is transmitted to result in that 'goodput'? Like how many bytes/second gross are needed to give, say, 50Mbit/s on speedtest.net? I suppose if we know how many encapsulation bytes 4G LTE uses, we could estimate this?

I am optimizing my QoS-CAKE implementation, and I somehow need to determine:

a) LTE/4G overhead bytes associated with the 1500 byte payload

b) the gross speed to be determined based on the bandwidth measurement and a) above.




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05/08/2021, 09:58 PM

The 4G overhead goes outside the Ethernet packet, which is transparently taken care of by the modem, so the cellular network can carry Ethernet packets with the full 1500 byte payload. This is different to a PPPoE or VPN connection that goes inside the Ethernet payload.

A standard Ethernet packet (without VLAN) has 26 bytes of overhead and a 12 byte interpacket gap. With an MTU size of 1500, the total Physical Layer 1 size is 1538 bytes. TCP has between 20 and 60 bytes of overhead that goes inside the Ethernet payload. For a payload throughput of 50Mbps (such as Speed test.net), MTU size of 1500 and assuming a 20 byte TCP overhead and no retransmissions, the RAW throughput would be ~51.89Mbps (50 / 1480 * 1538).

For the reverse such as the router showing 20Mbps current download activity, this would work out at 19.25Mbps TCP payload traffic.

Wikipedia article on the Ethernet frame overhead:

Wikipedia article on the Transmission Control Protocol:




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09/08/2021, 02:11 PM (This post was last modified: 09/08/2021, 02:22 PM by Lynx.)

Thanks a lot for this insight. I have set WAN packet overhead to 91 (53 for VPN overhead + 38 for ethernet overhead). Not sure if this is correct, but seems best guess. I don't see bufferbloat now at what for me is an acceptable dl/ul (30/25 Mbit/s net).

Are you at all tempted to try one of the Asus routers with the Asus Merlin custom firmware? I have had so much fun with this option. It feels to me like I get so much more out of my LTE connection now.

I bought the RT-AX86u. It gets very good reviews online for Wi-Fi performance and overall specs: CPU quad-core 1.8GHz Broadcom BCM4908KFEBG SoC (ARM Cortex A53); and RAM 1GB (2x 512MB) Nanya NT5CC256M16ER-EK. See, e.g.:


And put on this software:


Earlier I tried OpenWRT on another device, but what I like about the Asus option is the mix of proprietary (e.g. for good Wi-Fi drivers) and configurability with custom firmware.

I am super impressed with what I have been able to implement on mine:

- OpenVPN encryption performed by the router
- DNSFilter: enables you to set up specific DNS servers for particular devices. I haveCleanBrowsing (Family) set globally, but DNS queries from television MAC addresses are hijacked and redirected via VPN tunnelto keep Amazon Prime and Netflix happy through VPN (with choice of location).
- Cake-QOS to fix max dl/ul to handle bufferbloat. I find taking big bandwidth hit to work with e.g. 30/25 preferable to the latency spike I see with bufferbloat.
- USB 3.0 port that can take SSD / USB stick. I have 16GB USB stick plugged into back of router. Can be shared as samba share. Can also plug in SSD drive.
- sophisticated AD blocking via 'Diversion': https://diversion.ch/diversion/faq.html
- dual WAN options with balancing / failover
- SSH interface exposing linux architecture that can allow installing all sorts of software / scripts / network monitoring.

To give anexample of the flexibility afforded by setting upa custom script,I have set up a USB samba share that my scanner can write to, then file system change detection that detects write to directory, then uses 'rclone' to send scanned file to OneDrive for business:


admin@RT-AX86U-4168:/tmp/home/root# cat /jffs/scripts/upload-scans

upload_dir="OneDrive:/Scanned Documents/"

while [[ true ]]; do

if ! rclone --config "$rclone_config_file" move "$scans_dir" "$upload_dir" --include "*.pdf" >"$log_file" 2>&1; then
sleep 1m

if ! inotifywait -r -e modify,create,move --include "\.pdf" --format '%T %:e %f' --timefmt '%c' "$scans_dir" >"$log_file" 2>&1; then
sleep 1m



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What is the MTU size for 4G LTE? ›

By default, the MTU is 1500 bytes for the LTE cellular interfaces or LTE channel interfaces.

What is the best MTU for WAN? ›

It is generally recommended that the MTU for a WAN interface connected to a PPPoE DSL network be 1492. In fact, with auto MTU discovery, 1492 is discovered to be the maximum allowed MTU. However, having an MTU of 1452 is most optimal.

What is the max MTU size for LTE? ›

The MTU for LTE is 1428 and WiMax is 1400. By changing the MTU and\or MSS you can achieve greater reliability when using cellular data services by avoiding fragmentation.

What is the MTU size for WAN setup? ›

The default MTU size is 1500, however for some networking technologies reducing the MTU size and allowing fragmentation can help eliminate some connectivity problems occurring at the protocol level.

What is a good 4G LTE signal strength? ›

The closer the number is to 0, the better the signal strength. For example, -50 dBm is a strong signal; anything lower than -85 dBm can cause slow or no connection. Through this tool, you can determine if the location of your device is causing a weak signal.

What is the bandwidth of 4G LTE? ›

LTE offers only 100 Mbps, while true 4G offers up to 1,000 Mbps. However, if we take a look at the LTE-A speeds, the difference disappears as it also offers 1,000 Mbps.

What is the MTU size for 5G LTE? ›

By default, the MTU of a 5G cellular interface or 5G cellular channel interface is 1500 bytes.

What happens if MTU is too high? ›

Routers that support IPv6 will not fragment IPv6 packets, so if the test packets exceed the MTU, the routers drop the packets and send back corresponding ICMP messages without checking for a Don't Fragment flag.

Does increasing MTU increase Internet speed? ›

One of the easiest things you can do to increase your Internet speed is to adjust your router's MTU setting. MTU stands for Maximum Transmission Unit. It is essentially the setting that limits the maximum size of a packet that can be sent across a network.

How many Mbps should 4G LTE be? ›

Cable. Verizon 4G LTE wireless broadband is 10 times faster than 3G — able to handle download speeds between 5 and 12 Mbps (Megabits per second) and upload speeds between 2 and 5 Mbps, with peak download speeds approaching 50 Mbps. Cable speeds vary, but 4 to 12 Mbps are common. Why are megabits per second important?

Is an MTU of 1480 Good? ›

1480 is just fine. If you are using wireless then try wired. Also the hubs have dodgy UPnP which either isn't fully compatible with Xbox one or just randomly stops working depending on the hub version.

What is the maximum data rate in 4G? ›

4G users get speeds of up to 100 Mbps, while 3G only promised a peak speed of 14 Mbps. With 4G download speeds, wireless users can stream high-definition video and audio.

Why MTU 1472? ›

The reason for this is that by default, Juniper uses the standard IP MTU of 1500. Along with the default size, you have to account for 8 bytes being used for the ICMP header and another 20 bytes for the IP address. As such, 1472 bytes is the largest payload that you can set where you have "do fragment" turned off.

Does changing MTU size affect speed? ›

The MTU size of the network can have a large impact on performance. The use of large MTU sizes allows the operating system to send fewer packets of a larger size to reach the same network throughput.

Should I set MTU to 9000? ›

Generally, switches and routers should have an MTU of 9216 while nodes have the MTU set to 9000 bytes. When devices are configured incorrectly problems will usually be intermittent.

How can I improve my 4G signal strength? ›

How Can I Improve My 4G LTE or 5G Speed?
  1. Get a New Phone/Hotspot. If you're using an old device, a new phone or hotspot may allow you to connect to new bands. ...
  2. Use External Antennas [Best for Hotspots] ...
  3. Use a MIMO Signal Booster [Best for Phones]
Jan 23, 2023

Which LTE frequency is best? ›

Band 3 (1800 MHz): The most popular global band for LTE.

What is the fastest speed for LTE? ›

LTE wireless broadband is about 10x faster than the 3G network and has an average download speed of 12-30 Megabits per second. It can also handle uploads to the internet at 2-5 MBps. There is no set standard for LTE speed.

Which 4G band is fastest? ›

  • Frequencies that can provide LTE: Band 2 (1900 MHz) Band 5 (850 MHz) Band 4 (1700/2100 MHz) ...
  • 4G LTE offers fast download speeds, up to 50% faster speeds than 3G. See Data speeds.
  • Voice and data services only work at the same time when on you have VoLTE enabled on your device. Otherwise, LTE only provides data.

Should I add 28 to MTU? ›

Add 28 to that number (IP/ICMP headers) to get the optimal MTU setting. For example, if the largest packet size from ping tests is 1462, add 28 to 1462 to get a total of 1490 which is the optimal MTU setting.

What is correct MTU size? ›

The standard size MTU for Ethernet is 1,500 bytes. This does not include the Ethernet header of 18 or 20 bytes, and is the theoretical maximum amount of data that can be transmitted by the physical link. The MTU of any higher-level protocols must fit within this MTU.

Is 1500 MTU good? ›

The MTU (Maximum Transmission Unit) states how big a single packet can be. Generally speaking, when you are talking to devices on your own LAN the MTU will be around 1500 bytes and the internet runs almost universally on 1500 as well.

What is normal MTU size? ›

The normal or default MTU size typically used is 1500 bytes and for a larger MTU size 9000 bytes tends to be the common choice. While 9000 bytes is typically used as a large MTU size, it also spans more than two physical 4K pages of memory.

What happens if MTU is too small? ›

The main problem with MTU size being reduced across the network is that some applications may not work well in this environment. To complicate matters, some routers ignore packet-too-big messages and keep sending packets that exceed the MTU.

Is it better to have a lower MTU? ›

Increasing the MTU can improve performance, and decreasing the MTU can resolve packet loss and fragmentation problems when it is too high.

What is MTU size in IPv4? ›

MTUs for common media

The MTU should not be confused with the minimum datagram size that all hosts must be prepared to accept. This is 576 bytes for IPv4 and of 1280 bytes for IPv6. Systems may use Path MTU Discovery to find the actual path MTU. Routing from larger MTU to smaller MTU causes IP fragmentation.

Is 4G and 4G LTE the same thing? ›

First, “4G” represents the fourth generation of mobile technology, the next big advancement after 3G. And “long-term evolution,” or “LTE,” is industry jargon used to describe the particular type of 4G that delivers the fastest mobile internet experience.

Is 4G LTE faster than 5G? ›

5G is significantly quicker than LTE. In 2008, the International Telecommunications Union (ITU) recommended that data throughput on LTE networks needs to be as high as 1 Gb/s in ideal low-mobility circumstances.

Is 4G LTE faster than Wi-Fi? ›

Speed: The standard data transfer speed for Wi-Fi is between 11Mbps to 1Gbps depending on its specifications. LTE, on the other hand, offers data transfer speeds between 100 Mbps and 1Gbps.

Is it safe to change MTU size? ›

Changing the maximum transfer unit (MTU) setting on your router may boost your overall network speed performance significantly. However, choosing the wrong setting could cripple your router and crush your overall network speeds to a level that is unbearable.

Does 4G use alot of bundles? ›

4G networks provide higher Internet speeds when compared to a 3G network. The difference between these two networks does not affect your mobile data consumption.

Is MTU 1500 or 1472? ›

For our transmission media, the TCP and IP headers make up a total of 28 bytes (8 bytes + 20 bytes). Therefore, 1472 bytes + 28 bytes gives us the actual MTU size, which is 1500 bytes. This is typically the MTU size allowed by most Ethernet networks at the network layer.

Does 4G use massive MIMO? ›

As a massive-antenna technology in the 4G era, Massive MIMO has been widely regarded as an ever-energizing technology since 4G roll out. This revolutionary technology is a great prelude to the future-oriented network.

What is the maximum bandwidth of 4G? ›

4G offers maximum real-world download speeds up to around 100Mbps, making it over 20 times faster than 3G. Theoretical maximum 4G speeds are significantly higher at 300Mbps, although such speeds are only achievable in controlled laboratory environments.

Which bandwidth is best for 4G network *? ›

Each generation of wireless cellular technology has introduced increased bandwidth speeds and network capacity. 4G users get speeds of up to 100 Mbps, while 3G only promised a peak speed of 14 Mbps.

Does changing MTU increase speed? ›

Increasing the MTU can improve performance, and decreasing the MTU can resolve packet loss and fragmentation problems when it is too high.

Does LTE support different MIMO? ›

LTE uses MIMO for transmit diversity, spatial multiplexing (to transmit spatially separated independent channels), and single-user and multiuser systems. MIMO in LTE enables more reliable transmission of data, while also increasing data rates. It separates the data into individual streams before transmission.

Is 4x4 MIMO better than 2x2 MIMO? ›

Under strong signal conditions 4x4 provides around a 90% improvement over 2x2 MIMO, and under weak conditions as high as 160% faster than 2x2.

What protocol does 4G use? ›

4G is All-IP

Like 3G, 4G networks are IP-based (Internet protocol), meaning that it uses a standard communications protocol to send and receive data in packets. Unlike 3G, however, 4G uses IP even for voice data. It is an all-IP standard.


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