Noticed this warning building systemd-252 with glibc-2.37 and linux-6.1 UAPI headers: In file included from ../src/libsystemd/sd-netlink/netlink-types-genl.c:10: ../src/basic/linux/l2tp.h:16: warning: "IPPROTO_L2TP" redefined 16 | #define IPPROTO_L2TP 115 | In file included from ../src/libsystemd/sd-netlink/netlink-types-genl.c:3: /usr/include/netinet/in.h:85: note: this is the location of the previous definition 85 | #define IPPROTO_L2TP IPPROTO_L2TP |