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NixOS Networking

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10 Feb 2026
@nazarewk:matrix.orgkdn ping -4 -s XXXX nc.nazarewk.pw works for 1460, doesn't for 1470, let's try narrowing it down 13:36:24
@nazarewk:matrix.orgkdn 1468 is the last one that works, 1469 doesn't 13:37:12
@nazarewk:matrix.orgkdnyeah, it's the same for router's IP13:46:48
@magic_rb:matrix.redalder.orgmagic_rbYeah last time i did it its just trial and error seeing what mtu works or not13:47:39
@magic_rb:matrix.redalder.orgmagic_rbIf you know its 1468 then increase your routers uplink mtu to 153213:47:58
@magic_rb:matrix.redalder.orgmagic_rbDo you happen to be going over pppoe? That number seems familiar to me (i am going over pppoe)13:48:15
@magic_rb:matrix.redalder.orgmagic_rbIdeally your internal network mtu remains at 150013:48:31
@nazarewk:matrix.orgkdnno, 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
@nazarewk:matrix.orgkdnI'm trying to find some MTU settings on AP (EAP773) or zyxel XGS1250-12, but so far no luck13:50:42
@nazarewk:matrix.orgkdnthat 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
@nazarewk:matrix.orgkdndoh, increasing MTU on the router to 1504 didn't help13:53:24
@nazarewk:matrix.orgkdnpinging 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
@nazarewk:matrix.orgkdnyeah, wired 1469 to the router doesn't work either14:05:02
@nazarewk:matrix.orgkdn and ipv6 ping stops working at 1449 (20 more bytes), I guess I should move the discussion to #OpenWrt:matrix.org 14:11:18
@nazarewk:matrix.orgkdnthat'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
@nazarewk:matrix.orgkdn* 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 MTU14:40:25
19 May 2021
@grahamc:nixos.org@grahamc:nixos.org set the history visibility to "world_readable".19:20:58
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