| 10 Feb 2026 |
 kdn | I don't think I have modified it anywhere, should be default 1500 all the way | 13:16:26 |
| kdn | is anything (VLANs?) in such setup chewing through MTU? | 13:16:58 |
 Molly Miller | i don't think so, i haven't ever seen similar problems when working with vlans, but tls handshakes timing out weirdly is often a symptom of mtu problems | 13:21:46 |
| Molly Miller | the sites that do and don't work, are there any patterns to those that do or those that don't? | 13:22:23 |
| 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 |
| kdn | and ipv6 ping stops working at 1449 (20 more bytes), I guess I should move the discussion to #OpenWrt:matrix.org | 14:11:18 |
| kdn | that's curious, I removed some customized configs for devices/links (no idea what I put there, definitely nothing needed), that made me lose internet completely until I rebooted the OpenWRT, now it's functioning correctly all around | 14:40:16 |
| kdn | * that's curious, I removed some customized configs for devices/links (no idea what I put there, definitely nothing needed), that made me lose internet completely until I rebooted the OpenWRT, now it's functioning correctly all around without any custom MTU | 14:40:25 |
|  dadada (er/ihm) changed their display name from dadada to dadada (er/ihm). | 20:02:31 |
|  @Geezus42:matrix.org removed their profile picture. | 22:22:34 |
| @Geezus42:matrix.org left the room. | 22:23:57 |
