kern/60071: The kernel stop sending ARP/NS packets on ping/ping6

["ozaki-r%iij.ad.jp@localhost via gnats" <gnats-admin%NetBSD.org@localhost>]

>Number:         60071
>Category:       kern
>Synopsis:       The kernel stop sending ARP/NS packets on ping/ping6
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Mar 12 04:20:00 +0000 2026
>Originator:     Ryota Ozaki
>Release:        current, 11, 10
>Organization:
IIJ
>Environment:
NetBSD kvm 11.99.5 NetBSD 11.99.5 (KVM) #32: Thu Mar 12 11:48:45 JST 2026  (hidden) amd64
>Description:
ping(8) with no option sends ICMP echo requests periodically.  If a target host is not available, the kernel keeps sending ARP packets per the ICMP packets.  This is probably the typical and expected behavior.  NetBSD 9, NetBSD 8, FreeBSD 11 and Linux 6.0 acts like so.

However, recent NetBSD kernels (10~) stop sending ARP packets at most net.inet.arp.nd_bmaxtries times.

ping6 (IPv6 NS) is the same situation.
>How-To-Repeat:
Run tcpdump on a host (or another host in the same network) and ping to a nonexistence host from the host, and see tcpdump's outputs.
>Fix:
One possible fix:

@@ -361,10 +361,6 @@ nd_resolve(struct llentry *ln, const struct rtentry *rt, struct mbuf *m,
         * does not exceed maxqueuelen.  When it exceeds maxqueuelen,
         * the oldest packet in the queue will be removed.
         */
-       if (ln->ln_state == ND_LLINFO_NOSTATE ||
-           ln->ln_state == ND_LLINFO_WAITDELETE)
-               ln->ln_state = ND_LLINFO_INCOMPLETE;
-
 #ifdef MBUFTRACE
        m_claimm(m, ln->lle_tbl->llt_mowner);
 #endif
@@ -406,6 +402,12 @@ nd_resolve(struct llentry *ln, const struct rtentry *rt, struct mbuf *m,
        else
                error = EWOULDBLOCK;
 
+       if (ln->ln_state == ND_LLINFO_NOSTATE ||
+           ln->ln_state == ND_LLINFO_WAITDELETE) {
+               ln->ln_asked = 0;
+               ln->ln_state = ND_LLINFO_INCOMPLETE;
+       }
+
        /*
         * If there has been no NS for the neighbor after entering the
         * INCOMPLETE state, send the first solicitation.