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FS#3330 - ds-lite: too low default MTU #8190

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openwrt-bot opened this issue Sep 9, 2020 · 3 comments
Open

FS#3330 - ds-lite: too low default MTU #8190

openwrt-bot opened this issue Sep 9, 2020 · 3 comments
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flyspray release/19.07 pull request/issue targeted (also) for OpenWrt 19.07 release

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@openwrt-bot
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Felixoid:

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|https://github.com/openwrt/openwrt/blob/master/package/network/ipv6/ds-lite/files/dslite.sh#L66] 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)

@openwrt-bot
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Felixoid:

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

fixed

@openwrt-bot
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por:

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 ?

@openwrt-bot
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Felixoid:

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
fi

@aparcar aparcar added the release/19.07 pull request/issue targeted (also) for OpenWrt 19.07 release label Feb 22, 2022
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