| 10 Feb 2026 |
 Molly Miller | especially IPv4/IPv6 | 13:22:26 |
 Marcel | Otherwise you could trz to use traceroute (or tracepath) to check if there is a difference in the mtu to the target host. I always forget if traceroute or tracepath also determinates the mtu. | 13:25:12 |
 kdn | will check, I could issue pings of specific sizes to pinpoint at which connection the issue occurs? | 13:26:47 |
| Molly Miller | yes, that's an option | 13:30:16 |
| kdn | so curl -v https:// works for facebook.com, doesn't for news.ycombinator.com & nc.nazarewk.pw (my Hetzner nextcloud) | 13:32:48 |
| kdn | ping -s XXXX nc.nazarewk.pw seems to work fine between 1200 and 1700 | 13:34:56 |
| kdn | * ping -s XXXX nc.nazarewk.pw seems to work fine between 1200 and 1700 over IPv6, let's try other options | 13:35:10 |
| kdn | ping -4 -s XXXX nc.nazarewk.pw works for 1460, doesn't for 1470, let's try narrowing it down | 13:36:24 |
| kdn | 1468 is the last one that works, 1469 doesn't | 13:37:12 |
| kdn | yeah, it's the same for router's IP | 13:46:48 |
 magic_rb | Yeah last time i did it its just trial and error seeing what mtu works or not | 13:47:39 |
| magic_rb | If you know its 1468 then increase your routers uplink mtu to 1532 | 13:47:58 |
| magic_rb | Do you happen to be going over pppoe? That number seems familiar to me (i am going over pppoe) | 13:48:15 |
| magic_rb | Ideally your internal network mtu remains at 1500 | 13:48:31 |
| kdn | no, I'm not going over PPPoE, the connectivity fails over LAN address space too (from Wifi AP to the router over 2 switches) | 13:50:19 |
| kdn | I'm trying to find some MTU settings on AP (EAP773) or zyxel XGS1250-12, but so far no luck | 13:50:42 |
| kdn | that seems useful (from Kagi Assistant):
Why 1468 Bytes?
Normal MTU: 1500 bytes
Your effective MTU: 1468 + 28 (ICMP/IP headers) = 1496 bytes
Missing: 4 bytes = exactly the size of a VLAN 802.1Q tag
1
When VLAN tagging is added, frames grow from 1500 to 1504 bytes. If any device in the path doesn't account for this, it causes fragmentation or drops. | 13:51:23 |
| kdn | doh, increasing MTU on the router to 1504 didn't help | 13:53:24 |
| kdn | pinging another device plugged in directly to Mikrotik works fine with whatever MTU, so if I'm correct it must be some issue with the router? | 14:03:58 |
| kdn | yeah, wired 1469 to the router doesn't work either | 14:05:02 |
| 19 May 2021 |
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