Got 2.5G networking working on first try, one question about jumbo frames

[rbmatt1s]

I read that 2.5G networking has been a mixed bag, but I went for it anyway. I bought the TRENDnet 2.5GBase-T PCIe Network Adapter, TEG-25GECTX which uses the Realtek 8125 chipset. I installed it, then switched the interface rules to put "r8169" as eth0, turned it off, moved the cat7 cable to the 2.5G port, booted up and everything just worked.

Now my question is, I set "Desired MTU: 9000" but I don't know if that was wise, I get one Jumbo Frame warning in Fix Common Problems.

Any thoughts?

 

 

[Barry Staes]

Not sure on Jumbo frames and that MTU setting, except that i have had Jumbo frames enabled on most devices i see the option, for many years without issue. Also many devices have it enabled by default.. for what i'm concerned it all works with the default values and for me thats the " automatic MTU " option.

 

But somewhat related, i just upgraded my server with new motherboards and such, that has two 1G and two 2.5G ethernet ports. (Shuttle SW580R8)

These all work without an issue, first has Unraid update to the latest 6.11.5 version.

 

What pleasantly surprised me Unraid chose to use a 2.5G port as the primary ethernet adapter.

[MAM59]

Jumbo Frames were a try when 1G LANs came up. The basic idea behind them was that larger frames need fewer headers so the throughput would increase.

It does, but not really much. And when LAN cards started to manange headers themselfs "in hardware" the header thing got even less important.

Today the benefit from Jumbo frames is almost not existent anymore. You can perfectly live without them. They do not harm unless your transmissions are not clear and need retries (larger packets need longer times to be resend). But they also do not improve anything.

IF you want to use them, you need to configure ALL comunication partners (PC - switch - PC) to use the same MTU, else you slow down the transmissions because the computers need to find out by try & error (aaaah... "resend & fragment") which value is suitable for the partner.

And, to make things even more complicated, some count the MTU without headers ("9000"), some count them in ("9114"). You have to find out which setting is correct for your cards/switches.

Nice job if you want to kill a rainy day, but also not needed at all.

 

[rbmatt1s]

Awesome, thanks a ton MAM59

[JorgeB]

Like MAM59 mentioned there's usually not much difference, except sometimes with 10GbE, but you can easily test with iperf and then set accordingly, after confirming that everything in the network supports jumbo frames, just recently was installing a couple of 2.5GbE NICs and since these are going to be used for direct connection it won't cause any issues, still with 2.5GbE there's not much difference.

 

Intel I225V -> Realtek 8125

 

root@Tower15:~# iperf3 -c 10.0.0.2
Connecting to host 10.0.0.2, port 5201
[  5] local 10.0.0.1 port 58158 connected to 10.0.0.2 port 5201
[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[  5]   0.00-1.00   sec   283 MBytes  2.38 Gbits/sec    0    300 KBytes       
[  5]   1.00-2.00   sec   282 MBytes  2.36 Gbits/sec    0    322 KBytes       
[  5]   2.00-3.00   sec   280 MBytes  2.35 Gbits/sec    0    300 KBytes       
[  5]   3.00-4.00   sec   281 MBytes  2.36 Gbits/sec    0    303 KBytes       
[  5]   4.00-5.00   sec   280 MBytes  2.35 Gbits/sec    0    297 KBytes       
[  5]   5.00-6.00   sec   281 MBytes  2.36 Gbits/sec    0    303 KBytes       
[  5]   6.00-7.00   sec   280 MBytes  2.35 Gbits/sec    0    300 KBytes       
[  5]   7.00-8.00   sec   280 MBytes  2.35 Gbits/sec    0    297 KBytes       
[  5]   8.00-9.00   sec   281 MBytes  2.36 Gbits/sec    0    300 KBytes       
[  5]   9.00-10.00  sec   280 MBytes  2.35 Gbits/sec    0   5.66 KBytes       
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-10.00  sec  2.74 GBytes  2.36 Gbits/sec    0             sender
[  5]   0.00-10.00  sec  2.74 GBytes  2.35 Gbits/sec                  receiver

 

Jumbo frames

 

root@Tower15:~# iperf3 -c 10.0.0.2
Connecting to host 10.0.0.2, port 5201
[  5] local 10.0.0.1 port 50186 connected to 10.0.0.2 port 5201
[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[  5]   0.00-1.00   sec   296 MBytes  2.49 Gbits/sec    0    262 KBytes       
[  5]   1.00-2.00   sec   294 MBytes  2.47 Gbits/sec    0    419 KBytes       
[  5]   2.00-3.00   sec   295 MBytes  2.47 Gbits/sec    0    262 KBytes       
[  5]   3.00-4.00   sec   295 MBytes  2.47 Gbits/sec    0    262 KBytes       
[  5]   4.00-5.00   sec   293 MBytes  2.46 Gbits/sec    0    280 KBytes       
[  5]   5.00-6.00   sec   295 MBytes  2.48 Gbits/sec    0    262 KBytes       
[  5]   6.00-7.00   sec   295 MBytes  2.47 Gbits/sec    0    262 KBytes       
[  5]   7.00-8.00   sec   294 MBytes  2.46 Gbits/sec    0    262 KBytes       
[  5]   8.00-9.00   sec   295 MBytes  2.47 Gbits/sec    0    280 KBytes       
[  5]   9.00-10.00  sec   295 MBytes  2.47 Gbits/sec    0   35.0 KBytes       
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-10.00  sec  2.88 GBytes  2.47 Gbits/sec    0             sender
[  5]   0.00-10.00  sec  2.88 GBytes  2.47 Gbits/sec                  receiver