While working on IPv6 for pppd(8), I tried to use the EUI64 address as the PPP
local address and failed because the kernel does not allow to change the netmask
from /64 to /128.
I propose we change the netmask for PPP interfaces to /128. Having a /64 is
useless anyway on a PPP link.

(the alternative would be to generate another local address in pppd(8) but it
seems overkill to me and we end up we 2 link-local addresses).

What do you think ?

Denis

Index: share/man/man4/pppoe.4
===================================================================
RCS file: /cvs/src/share/man/man4/pppoe.4,v
diff -u -p -r1.36 pppoe.4
--- share/man/man4/pppoe.4	27 May 2022 15:45:02 -0000	1.36
+++ share/man/man4/pppoe.4	16 Nov 2024 17:51:53 -0000
@@ -102,7 +102,7 @@ inet 0.0.0.0 255.255.255.255 NONE \e
 dest 0.0.0.1
 inet6 eui64
 !/sbin/route add default -ifp pppoe0 0.0.0.1
-!/sbin/route add -inet6 default -ifp pppoe0 fe80::%pppoe0
+!/sbin/route add -inet6 default -ifp pppoe0 -iface fe80::%pppoe0
 .Ed
 .Pp
 The physical interface must also be marked
Index: sys/netinet6/in6_ifattach.c
===================================================================
RCS file: /cvs/src/sys/netinet6/in6_ifattach.c,v
diff -u -p -r1.122 in6_ifattach.c
--- sys/netinet6/in6_ifattach.c	9 Jul 2023 19:06:48 -0000	1.122
+++ sys/netinet6/in6_ifattach.c	16 Nov 2024 17:51:53 -0000
@@ -266,7 +266,11 @@ in6_ifattach_linklocal(struct ifnet *ifp
 
 	ifra.ifra_prefixmask.sin6_len = sizeof(struct sockaddr_in6);
 	ifra.ifra_prefixmask.sin6_family = AF_INET6;
-	ifra.ifra_prefixmask.sin6_addr = in6mask64;
+	if (ifp->if_type == IFT_PPP)
+		/* There is no need to get a /64 for P2P links */
+		ifra.ifra_prefixmask.sin6_addr = in6mask128;
+	else
+		ifra.ifra_prefixmask.sin6_addr = in6mask64;
 	/* link-local addresses should NEVER expire. */
 	ifra.ifra_lifetime.ia6t_vltime = ND6_INFINITE_LIFETIME;
 	ifra.ifra_lifetime.ia6t_pltime = ND6_INFINITE_LIFETIME;