Our MRT6 code has no compat fallback for the old (> 25year) mrt6msg
format. We only use the new version with the alignment fix.

So there is no need to track mrt6_mrouter_ver since it is always MRT6_INIT
and that will never change. So burn this bridge for good.

Even adding pim support would not require this. So there is really no need
to track this.
-- 
:wq Claudio

Index: netinet6/ip6_mroute.c
===================================================================
RCS file: /cvs/src/sys/netinet6/ip6_mroute.c,v
diff -u -p -r1.159 ip6_mroute.c
--- netinet6/ip6_mroute.c	17 Sep 2026 15:56:59 -0000	1.159
+++ netinet6/ip6_mroute.c	5 Nov 2026 10:03:12 -0000
@@ -133,7 +133,6 @@ struct rwlock mrt6_routerlock = RWLOCK_I
 
 struct rttimer_queue mrt6_timer;
 struct socket	*mrt6_mrouter[RT_TABLEID_MAX + 1];	/* [R] */
-int		 mrt6_mrouter_ver[RT_TABLEID_MAX + 1];	/* [R] */
 int		 ip6_mrtproto;    		/* [I] for netstat only */
 
 struct cpumem *mrt6counters;
@@ -571,7 +570,6 @@ ip6_mrouter_init(struct socket *so, int 
 		return (EADDRINUSE);
 	}
 	mrt6_mrouter[rtableid] = soref(so);
-	mrt6_mrouter_ver[rtableid] = cmd;
 
 	rw_exit_write(&mrt6_routerlock);
 
@@ -631,7 +629,6 @@ ip6_mrouter_done(struct socket *so)
 	}
 
 	mrt6_mrouter[rtableid] = NULL;
-	mrt6_mrouter_ver[rtableid] = 0;
 	sorele(so);
 
 	rw_exit_write(&mrt6_routerlock);
@@ -1072,18 +1069,10 @@ ip6_mforward(struct ip6_hdr *ip6, struct
 
 			rw_enter_read(&mrt6_routerlock);
 
-			switch (mrt6_mrouter_ver[rtableid]) {
-			case MRT6_INIT:
-				im = mtod(mm, struct mrt6msg *);
-				im->im6_msgtype = MRT6MSG_NOCACHE;
-				im->im6_mbz = 0;
-				im->im6_mif = mifp->m6_mifi;
-				break;
-			default:
-				rw_exit_read(&mrt6_routerlock);
-				m_freem(mm);
-				return (EINVAL);
-			}
+			im = mtod(mm, struct mrt6msg *);
+			im->im6_msgtype = MRT6MSG_NOCACHE;
+			im->im6_mbz = 0;
+			im->im6_mif = mifp->m6_mifi;
 
 			sin6.sin6_addr = ip6->ip6_src;
 			if (socket6_send(mrt6_mrouter[rtableid], mm,