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Created September 12, 2025 05:23
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Wireguard Optimal MTU
Raw
optimal_mtu.md

About

I faced bandwidth issues when trying to connect from a WG Peer to a WG server. Download bandwidth was reduced significantly and upload bandwidth was practically non existent. I followed this tutorial to setup my Wireguard configurations. I found a few reddit posts that said that we need to choose the right MTU. So I wrote a script to find an optimal MTU. Ideally I would have liked to have run all possible MTU configurations for both WG Server and WG Peer but for simplicity I choose to fix the WG Server to the original 1420 MTU and tried all MTUs from 1280 to 1500 for the WG Peer.

Testing

  • On WG server, I started an iperf3 server
  • On WG peer, I wrote a script that does the following:
    • wg-quick down wg0
    • Edit MTU in the /etc/wireguard/wg0.conf file
    • wg-quick up wg0
    • iperf3 -c 172.123.0.1 -J -t 5 -i 5
      • This runs an iperf3 client that connects to 172.123.0.1 which is the WG Server gateway
      • The iperf3 client runs for 5 seconds and stops and dumps a JSON output

Setup

  • Max bandwidth provided by my ISP (1000Mbps Download, 50Mbps Upload)
  • WG Server is a VPS running Ubuntu 20.04 on a cloud provider.
  • WG Peer is a PC running Ubuntu 20.04 locally at home.

Config

WG-server

# /etc/wireguard/wg0.conf
[Interface]
Address = 172.123.0.1/24
MTU = 1420
SaveConfig = true
PostUp = iptables -A FORWARD -i wg0 -j ACCEPT; iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE; ip6tables -A FORWARD -i wg0 -j ACCEPT; ip6tables -t nat -A POSTROUTING -o eth0 -j MASQUERADE; iptables -t nat -A POSTROUTING -o ens10 -j MASQUERADE; ip6tables -t nat -A POSTROUTING -o ens10 -j MASQUERADE
PostDown = iptables -D FORWARD -i wg0 -j ACCEPT; iptables -t nat -D POSTROUTING -o eth0 -j MASQUERADE; ip6tables -D FORWARD -i wg0 -j ACCEPT; ip6tables -t nat -D POSTROUTING -o eth0 -j MASQUERADE; iptables -t nat -D POSTROUTING -o ens10 -j MASQUERADE; ip6tables -t nat -D POSTROUTING -o ens10 -j MASQUERADE
ListenPort = 51820
PrivateKey = xxxxxxxxxxxxxxxxxx

[Peer]
PublicKey = xxxxxxxxxxxxxxxxxx
AllowedIPs = 172.123.0.2/32
Endpoint = X.X.X.X:61426

WG-peer

# /etc/wireguard/wg0.conf
[Interface]
PrivateKey = xxxxxxxxxxxxxxxxxx
ListenPort = 51820
Address = 172.123.0.2/24
MTU = 1384

[Peer]
PublicKey = xxxxxxxxxxxxxxxxxx
AllowedIPs = 172.123.0.0/24, 10.1.0.0/24
Endpoint = Y.Y.Y.Y:51820
PersistentKeepalive = 5

Conclusions

  • As you can see in the image peer_mtu_vs_bandwidth.png, the original MTU settings for 1420 both peer and server gives abysmal bandwdith.
  • I found that that MTU 1384 on the WG peer with 1420 on the WG server seems to almost have the best bandwidth.
  • For MTU 1384, the max upload bandwidth of 50Mbps for my ISP connection is achieved but I was only able to hit 550 Mbps for the download bandwidth where the max download bandwidth for my ISP connection is 1000 Mbps. This reduction in download bandwidth might be due to other factors but 550 Mbps was sufficient for my use cases so I stopped testing it further.

In case any one has any explanations for this behavior or have found some mistakes in my configurations or tests, please let me know.

Raw
wireguard_peer_mtu.csv
MTU_server MTU_peer upload_rcv_mbps upload_send_mbps download_rcv_mbps download_send_mbps
1420 1280 9.779 10.085 363.282 367.822
1420 1281 10.037 10.221 365.3 367.071
1420 1282 11.266 11.709 304.065 309.068
1420 1283 16.128 16.773 436.708 440.421
1420 1284 9.085 9.32 439.456 442.93
1420 1285 14.175 14.784 405.159 409.575
1420 1286 15.324 17.204 461.383 464.782
1420 1287 9.089 10.135 393.274 396.265
1420 1288 13.843 14.456 417.028 420.83
1420 1289 8.903 9.154 365.598 368.779
1420 1290 9.465 9.741 374.178 377.272
1420 1291 13.716 14.789 513.172 516.836
1420 1292 11.127 11.686 449.897 452.991
1420 1293 17.062 17.937 373.172 375.754
1420 1294 8.913 9.336 506.806 508.484
1420 1295 11.947 12.288 409.137 412.493
1420 1296 8.825 9.102 439.877 442.88
1420 1297 9.073 9.256 384.711 388.869
1420 1298 19.563 21.517 456.428 460.047
1420 1299 8.732 8.942 412.162 415.124
1420 1300 11.78 13.12 458.38 460.836
1420 1301 13.143 13.835 345.283 348.746
1420 1302 17.922 18.753 405.418 409.175
1420 1303 13.009 14.061 393.397 397.085
1420 1304 14.858 16.404 550.447 552.679
1420 1305 10.502 10.884 377.632 381.924
1420 1306 8.892 9.62 391.268 394.983
1420 1307 11.758 12.459 430.463 434.699
1420 1308 12.74 13.193 478.767 481.101
1420 1309 8.037 8.403 376.72 380.583
1420 1310 10.473 11.855 497.612 500.3
1420 1311 10.782 11.032 411.316 415.38
1420 1312 18.371 20.796 411.914 415.025
1420 1313 8.627 8.813 380.383 384.415
1420 1314 10.49 10.996 413.854 416.949
1420 1315 15.525 17.196 517.402 519.832
1420 1316 11.548 12.51 426.626 431.252
1420 1317 20.41 22.89 374.859 378.885
1420 1318 11.807 12.317 410.784 414.048
1420 1319 17.487 18.05 386.323 390.693
1420 1320 19.413 21.036 451.24 453.66
1420 1321 40.135 42.82 455.563 459.274
1420 1322 44.686 47.313 433.582 436.076
1420 1323 43.2 45.824 422.772 426.286
1420 1324 41.241 43.648 412.187 415.485
1420 1325 40.672 43.91 504.611 509.149
1420 1326 39.525 42.257 433.56 437.778
1420 1327 42.659 45.424 518.56 521.709
1420 1328 40.767 43.171 451.313 455.999
1420 1329 44.862 47.07 541.91 544.553
1420 1330 42.012 45.087 446.963 450.593
1420 1331 42.473 45.097 491.676 495.083
1420 1332 43.203 46.347 485.328 489.416
1420 1333 43.597 46.58 376.498 381.03
1420 1334 45.479 47.653 499.392 502.72
1420 1335 42.135 44.841 507.46 510.794
1420 1336 45.487 48.443 439.534 443.768
1420 1337 41.627 44.141 438.988 442.439
1420 1338 45.14 48.169 512.471 515.087
1420 1339 44.749 47.02 507.913 510.595
1420 1340 43.1 46.089 510.18 513.517
1420 1341 44.901 48.07 428.675 432.339
1420 1342 37.157 39.991 554.82 557.78
1420 1343 36.424 38.485 382.8 386.083
1420 1344 40.27 43.063 434.334 438.187
1420 1345 40.031 42.848 428.99 432.84
1420 1346 36.87 39.092 375.337 378.224
1420 1347 39.407 41.866 468.454 470.649
1420 1348 38.104 40.695 438.86 443.512
1420 1349 44.343 46.408 457.244 461.109
1420 1350 41.43 43.773 439.033 442.085
1420 1351 44.566 46.729 486.283 490.222
1420 1352 43.826 46.653 411.147 415.675
1420 1353 37.991 41.169 462.502 466.677
1420 1354 44.502 47.079 457.439 461.368
1420 1355 42.396 45.164 389.4 392.718
1420 1356 38.012 40.918 419.988 423.808
1420 1357 41.4 44.477 485.799 490.087
1420 1358 42.438 44.904 545.914 549.605
1420 1359 42.562 45.459 447.518 450.806
1420 1360 45.411 47.928 393.015 396.515
1420 1361 43.693 45.798 476.769 479.518
1420 1362 41.835 44.81 420.56 423.304
1420 1363 41.241 44.067 469.51 474.006
1420 1364 47.234 50.056 416.02 419.452
1420 1365 46.766 49.922 522.7 526.512
1420 1366 42.228 44.471 469.826 473.419
1420 1367 45.386 48.233 481.835 484.83
1420 1368 40.473 43.29 394.326 397.456
1420 1369 45.624 47.933 421.451 424.758
1420 1370 45.554 47.232 426.004 429.556
1420 1371 45.72 48.316 505.968 509.855
1420 1372 40.715 43.042 463.434 466.39
1420 1373 44.388 46.817 394.342 399.014
1420 1374 44.234 47.081 414.499 417.601
1420 1375 44.987 47.772 511.849 515.524
1420 1376 43.949 46.898 413.523 417.787
1420 1377 42.328 44.548 564.274 567.8
1420 1378 39.379 41.955 489.432 493.637
1420 1379 42.114 44.552 517.783 520.464
1420 1380 40.725 43.098 456.699 459.31
1420 1381 42.542 45.402 523.891 526.872
1420 1382 42.395 44.906 514.792 518.786
1420 1383 45.63 48.434 482.853 485.493
1420 1384 45.023 47.23 514.259 517.485
1420 1385 43.41 45.675 443.337 446.342
1420 1386 38.452 40.952 496.755 500.859
1420 1387 41.681 43.994 582.79 586.792
1420 1388 43.156 45.636 517.781 521.409
1420 1389 41.981 44.336 478.165 481.941
1420 1390 43.159 45.298 533.484 536.138
1420 1391 41.629 44.981 411.492 415.005
1420 1392 45.42 47.612 400.268 403.638
1420 1393 44.537 47.562 91.884 93.101
1420 1394 47.322 50.432 74.137 75.698
1420 1395 47.792 50.713 124.13 126.563
1420 1396 44.564 47.602 171.668 175.504
1420 1397 42.817 45.856 70.946 72.115
1420 1398 43.047 46.05 146.641 151.438
1420 1399 47.634 50.21 138.423 143.805
1420 1400 47.693 50.47 124.784 130.186
1420 1401 0.002 0.112 110.135 111.815
1420 1402 0.002 0.112 123.79 126.142
1420 1403 0.002 0.112 103.124 105.616
1420 1404 0 0.112 86.977 88.483
1420 1405 0.002 0.112 97.243 99.735
1420 1406 0.002 0.113 144.839 148.922
1420 1407 0.002 0.113 157.802 160.497
1420 1408 0.002 0.113 64.273 65.018
1420 1409 0 0.113 128.295 131.228
1420 1410 0.002 0.113 62.276 63.044
1420 1411 0.002 0.113 109.99 111.325
1420 1412 0.002 0.113 102.435 106.584
1420 1413 0 0.113 79.216 80.371
1420 1414 0.002 0.113 100.332 102.214
1420 1415 0.002 0.113 114.64 116.9
1420 1416 0.002 0.113 160.194 163.28
1420 1417 0.002 0.113 128.546 131.178
1420 1418 0 0.114 106.562 108.683
1420 1419 0.002 0.114 228.267 231.989
1420 1420 0.002 0.114 100.311 102.456
1420 1421 0.002 0.114 68.612 69.437
1420 1422 0 0.114 222.877 227.281
1420 1423 0 0.114 114.47 116.175
1420 1424 0.002 0.114 87.183 88.719
1420 1425 0.002 0.114 111.124 115.439
1420 1426 0.002 0.114 136.311 139.502
1420 1427 0 0.114 123.442 126.936
1420 1428 0 0.114 146.415 151.041
1420 1429 0.002 0.114 140.015 144.193
1420 1430 0.002 0.114 137.163 141.625
1420 1431 0 0.114 101.918 104.045
1420 1432 0.002 0.114 109.205 111.651
1420 1433 0.002 0.114 102.198 104.472
1420 1434 0.002 0.114 94.156 96.912
1420 1435 0 0.114 274.923 278.557
1420 1436 0 0.114 89.887 91.313
1420 1437 0.002 0.114 89.854 90.785
1420 1438 0.002 0.114 149.419 154.718
1420 1439 0 0.114 162.98 168.52
1420 1440 0 0.114 129.754 131.415
1420 1441 0.002 0.114 136.865 138.569
1420 1442 0.002 0.114 95.295 97.197
1420 1443 0.002 0.114 150.988 154.865
1420 1444 0 0.114 79.417 81.118
1420 1445 0.002 0.114 134.379 136.362
1420 1446 0.002 0.114 72.408 73.436
1420 1447 0.002 0.114 134.539 137.73
1420 1448 0 0.114 121.354 123.645
1420 1449 0.002 0.114 69.386 72.186
1420 1450 0.002 0.114 155.168 160.252
1420 1451 0.002 0.114 95.625 98.829
1420 1452 0 0.114 154.402 158.912
1420 1453 0.002 0.114 77.676 81.093
1420 1454 0 0.114 151.933 155.661
1420 1455 0.002 0.114 127.309 132.258
1420 1456 0.002 0.114 148.996 153.324
1420 1457 0.002 0.114 92.367 95.644
1420 1458 0.002 0.114 144.232 148.894
1420 1459 0.002 0.114 77.765 80.336
1420 1460 0.002 0.114 133.286 138.711
1420 1461 0 0.114 129.757 135.053
1420 1462 0.002 0.114 203.826 209.096
1420 1463 0.002 0.114 71.752 74.063
1420 1464 0.002 0.114 159.222 164.221
1420 1465 0 0.114 119.811 124.256
1420 1466 0 0.114 105.249 110.749
1420 1467 0.002 0.114 60.189 62.376
1420 1468 0.002 0.114 213.514 217.745
1420 1469 0 0.114 64.601 66.069
1420 1470 0.002 0.114 138.102 142.246
1420 1471 0 0.114 148.872 152.626
1420 1472 0.002 0.114 212.529 216.044
1420 1473 0.002 0.114 104.654 108.83
1420 1474 0 0.114 137.298 142.16
1420 1475 0.002 0.114 93.042 96.909
1420 1476 0.002 0.114 150.276 154.835
1420 1477 0.002 0.114 80.563 85.272
1420 1478 0 0.114 114.828 119.55
1420 1479 0.002 0.114 65.511 67.377
1420 1480 0.002 0.114 141.206 146.038
1420 1481 0.002 0.114 210.533 215.735
1420 1482 0.002 0.114 133.742 138.278
1420 1483 0 0.114 127.18 130.657
1420 1484 0.002 0.114 169.513 174.231
1420 1485 0.002 0.114 155.057 158.817
1420 1486 0.002 0.114 112.984 117.463
1420 1487 0 0.114 122.723 127.679
1420 1488 0 0.114 127.9 132.621
1420 1489 0.002 0.114 131.65 136.616
1420 1490 0.002 0.114 60.408 62.315
1420 1491 0.002 0.114 107.486 111.7
1420 1492 0 0.114 113.105 116.995
1420 1493 0.002 0.114 161.789 167.387
1420 1494 0.002 0.114 87.811 90.931
1420 1495 0.002 0.114 96.189 99.908
1420 1496 0 0.114 83.761 86.526
1420 1497 0 0.114 80.308 82.488
1420 1498 0.002 0.114 124.105 128.196
1420 1499 0.002 0.114 120.256 124.763
1420 1500 0 0.114 184.46 189.222
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