Hi, I'd like to report a regression. Currently, if you create GRE interface on the latest stable or LTS kernel (5.4 branch) with unspecified remote destination it's MTU will be adjusted for header size twice. For example:
$ ip link add name test type gre local 127.0.0.32 $ ip link show test | grep mtu 27: test@NONE: <NOARP> mtu 1452 qdisc noop state DOWN mode DEFAULT group default qlen 1000 or with FOU $ ip link add name test2 type gre local 127.0.0.32 encap fou encap-sport auto encap-dport 6666 $ ip link show test2 | grep mtu 28: test2@NONE: <NOARP> mtu 1436 qdisc noop state DOWN mode DEFAULT group default qlen 1000 The same happens with GUE too (MTU is 1428 instead of 1464). As you can see that MTU in first case is 1452 (1500 - 24 - 24) and with FOU it's 1436 (1500 - 32 - 32), GUE 1428 (1500 - 36 - 36). If remote address is specified MTU is correct. This regression caused by fdafed459998e2be0e877e6189b24cb7a0183224 commit.
