From: Leon Schuermann <firstname.lastname@example.org> This patch series is an attempt to integrate a per-peer MTU setting into WireGuard. With matching changes to the wireguard-tools, individual MTU values can be set and retrieved for each registered peer.
While Linux supports setting an MTU metric for specific FIB route entries [which I've only found out after implementing this :)], and thus allows to lower the MTU for individual peers, this appears to disable regular path MTU discovery (PMTUD) entirely on the route. While regular PMTUD does not work over the tunnel link, it should still be usable on the rest of the route. Furthermore, with the goal of eventually introducing an in-band per-peer PMTUD mechanism, keeping an internal per-peer MTU value does not require modifying the FIB and thus potentially interfere with userspace. In an effort to solve this issues, this patch series introduces a rather generic framework for implementing these kinds of dynamic MTU policies. By providing a hook in the netdevice implementation to decide on the applicable MTU, very flexible designs can be built. I suppose that these changes are rather controversial, or at least require some more discussion. I'm sending this patchset to the WireGuard development list in hopes to get some initial feedback on the idea and implementation and would like to eventually submit the non-WireGuard changes directly to the netdev ML. The patches are currently based on v5.10, as that happens to be what I was developing on. I'll gladly rebase to the latest revision / wireguard-devel if requested. Thanks! Leon Leon Schuermann (4): netdevice: add ndo_lookup_mtu for dynamically determining MTU net/ipv4: respect MTU determined by `ndo_lookup_mtu` net/ipv6: respect MTU determined by `ndo_lookup_mtu` net/wireguard: add per-peer MTU setting drivers/net/wireguard/allowedips.c | 2 +- drivers/net/wireguard/allowedips.h | 2 +- drivers/net/wireguard/device.c | 20 ++++++++++++++++-- drivers/net/wireguard/netlink.c | 8 +++++++ drivers/net/wireguard/peer.c | 1 + drivers/net/wireguard/peer.h | 1 + drivers/net/wireguard/queueing.h | 2 +- include/linux/netdevice.h | 12 +++++++++++ include/net/ip.h | 34 ++++++++++++++++++++++-------- include/net/ip6_route.h | 14 ++++++++++-- include/uapi/linux/wireguard.h | 5 +++++ net/ipv4/ip_forward.c | 2 +- net/netfilter/nf_flow_table_core.c | 2 +- 13 files changed, 87 insertions(+), 18 deletions(-) base-commit: 2c85ebc57b3e1817b6ce1a6b703928e113a90442 -- 2.33.1