OpenWrt/LEDE Project

  • Status Unconfirmed
  • Percent Complete
  • Task Type Bug Report
  • Category Base system
  • Assigned To No-one
  • Operating System All
  • Severity Low
  • Priority Very Low
  • Reported Version openwrt-19.07
  • Due in Version Undecided
  • Due Date Undecided
  • Private
Attached to Project: OpenWrt/LEDE Project
Opened by Mikhail f. Shiryaev - 09.09.2020

FS#3330 - ds-lite: too low default MTU

Supply the following if possible:
- Device problem occurs on TP-Link Archer C7 v5
- Software versions of OpenWrt/LEDE release, packages, etc.

OpenWrt 19.07.3 r11063-85e04e9f46 / LuCI openwrt-19.07 branch git-20.136.49537-fb2f363
ds-lite 7-4

- Steps to reproduce: install system, install ds-lite, the mtu for all dslite connections will be [1280|] by default.

Because of it, if a VPN with ipv6 is used over ipv4, it’s completely broken.

tun0 w/ ipv6 -> [vpn client -> [dslite with mtu 1280] -> vpn server] -> private network

As far as I see, it should be relatively easy to make default MTU autoconfigurable with parent’s MTU-x (where 30 is 30, if I’m right)

Mikhail f. Shiryaev commented on 09.09.2020 11:00

* MTU-x (where x is 40, if I'm right)


Paul Oranje commented on 12.10.2020 18:50

I do not know whether this is really a bug, but with DS-Lite the IPv4 interface is itself a tunnel over IPv6 and as such an IPv6 tunnel over IPv4 is a tunnel in a tunnel. Also with DS-Lite the IPv4 address is non-global address that may change anytime and connections over IPv4 are handled with CGNAT.

Practical: why not run your IP46 tunnel over the IPv6 interface of DS-Liet ?

Mikhail f. Shiryaev commented on 30.11.2020 16:09

Hello Paul.

I'm quite not sure, what could I do here as a user. I have a VPN on work, it has A and AAAA records. So I can end up on both. And I need to tweak the MTU manually in the script.

Or, as I just found, I could tweak it in hotplug

# /etc/hotplug.d/iface/00-netstate [..]

if [ ifup = "$ACTION" ] && [ wan6_4 = "$INTERFACE" ] ; then
        ip link set ds-wan6_4 mtu 1452


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