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Commit 34d43616 authored by Maciej Żenczykowski's avatar Maciej Żenczykowski
Browse files

Reduce advertised ipv6 mtu by 16 to fit ethernet header 



This is a temporary hack to workaround the inability of current
kernel's ebpf bpf_skb_change_mode() function to prefix a 14-byte
ethernet header on to a packet without going over the upstream
(source, rawip) interface's mtu *before* we bpf_redirect() to
the downstream (destination, ethernet) interface.

Test: build, atest, atest TetheringTests
Bug: 149816401
Signed-off-by: default avatarMaciej Żenczykowski <maze@google.com>
Change-Id: I646148ebfd978a2489c0cd065e4b671b01150add
parent 91bb789c

packages/Tethering/src/android/net/ip/IpServer.java

+6 −1
Original line number Original line Diff line number Diff line
@@ -541,7 +541,12 @@ public class IpServer extends StateMachine { 




        if (v6only != null) {

        if (v6only != null) {

            params = new RaParams();

            params = new RaParams();

            params.mtu = v6only.getMtu();

            // We advertise an mtu lower by 16, which is the closest multiple of 8 >= 14,

            // the ethernet header size.  This makes kernel ebpf tethering offload happy.

            // This hack should be reverted once we have the kernel fixed up.

            // Note: this will automatically clamp to at least 1280 (ipv6 minimum mtu)

            // see RouterAdvertisementDaemon.java putMtu()

            params.mtu = v6only.getMtu() - 16;

            params.hasDefaultRoute = v6only.hasIpv6DefaultRoute();

            params.hasDefaultRoute = v6only.hasIpv6DefaultRoute();





            if (params.hasDefaultRoute) params.hopLimit = getHopLimit(v6only.getInterfaceName());

            if (params.hasDefaultRoute) params.hopLimit = getHopLimit(v6only.getInterfaceName());