diff --git a/sys/net/debugnet_inet.c b/sys/net/debugnet_inet.c
index 837f838fa6d9..e7449113ba10 100644
--- a/sys/net/debugnet_inet.c
+++ b/sys/net/debugnet_inet.c
@@ -1,493 +1,502 @@
 /*-
  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
  *
  * Copyright (c) 2019 Isilon Systems, LLC.
  * Copyright (c) 2005-2014 Sandvine Incorporated. All rights reserved.
  * Copyright (c) 2000 Darrell Anderson
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
 
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 
 #include "opt_inet.h"
 
 #include <sys/param.h>
 #include <sys/systm.h>
 #include <sys/errno.h>
 #include <sys/socket.h>
 #include <sys/sysctl.h>
 
 #include <net/ethernet.h>
 #include <net/if.h>
 #include <net/if_arp.h>
 #include <net/if_dl.h>
 #include <net/if_types.h>
 #include <net/if_var.h>
 
 #include <netinet/in.h>
 #include <netinet/in_systm.h>
 #include <netinet/in_var.h>
 #include <netinet/ip.h>
 #include <netinet/ip_var.h>
 #include <netinet/ip_options.h>
 #include <netinet/udp.h>
 #include <netinet/udp_var.h>
 
 #include <machine/in_cksum.h>
 #include <machine/pcb.h>
 
 #include <net/debugnet.h>
 #define	DEBUGNET_INTERNAL
 #include <net/debugnet_int.h>
 
 int debugnet_arp_nretries = 3;
 SYSCTL_INT(_net_debugnet, OID_AUTO, arp_nretries, CTLFLAG_RWTUN,
     &debugnet_arp_nretries, 0,
     "Number of ARP attempts before giving up");
 
 /*
  * Handler for IP packets: checks their sanity and then processes any debugnet
  * ACK packets it finds.
  *
  * It needs to partially replicate the behaviour of ip_input() and udp_input().
  *
  * Parameters:
  *	pcb	a pointer to the live debugnet PCB
  *	mb	a pointer to an mbuf * containing the packet received
  *		Updates *mb if m_pullup et al change the pointer
  *		Assumes the calling function will take care of freeing the mbuf
  */
 void
 debugnet_handle_ip(struct debugnet_pcb *pcb, struct mbuf **mb)
 {
 	struct ip *ip;
 	struct mbuf *m;
 	unsigned short hlen;
 
+	if (pcb->dp_state < DN_STATE_HAVE_GW_MAC)
+		return;
+
 	/* IP processing. */
 	m = *mb;
 	if (m->m_pkthdr.len < sizeof(struct ip)) {
 		DNETDEBUG("dropping packet too small for IP header\n");
 		return;
 	}
 	if (m->m_len < sizeof(struct ip)) {
 		m = m_pullup(m, sizeof(struct ip));
 		*mb = m;
 		if (m == NULL) {
 			DNETDEBUG("m_pullup failed\n");
 			return;
 		}
 	}
 	ip = mtod(m, struct ip *);
 
 	/* IP version. */
 	if (ip->ip_v != IPVERSION) {
 		DNETDEBUG("bad IP version %d\n", ip->ip_v);
 		return;
 	}
 
 	/* Header length. */
 	hlen = ip->ip_hl << 2;
 	if (hlen < sizeof(struct ip)) {
 		DNETDEBUG("bad IP header length (%hu)\n", hlen);
 		return;
 	}
 	if (hlen > m->m_len) {
 		m = m_pullup(m, hlen);
 		*mb = m;
 		if (m == NULL) {
 			DNETDEBUG("m_pullup failed\n");
 			return;
 		}
 		ip = mtod(m, struct ip *);
 	}
 	/* Ignore packets with IP options. */
 	if (hlen > sizeof(struct ip)) {
 		DNETDEBUG("drop packet with IP options\n");
 		return;
 	}
 
 #ifdef INVARIANTS
 	if ((IN_LOOPBACK(ntohl(ip->ip_dst.s_addr)) ||
 	    IN_LOOPBACK(ntohl(ip->ip_src.s_addr))) &&
 	    (m->m_pkthdr.rcvif->if_flags & IFF_LOOPBACK) == 0) {
 		DNETDEBUG("Bad IP header (RFC1122)\n");
 		return;
 	}
 #endif
 
 	/* Checksum. */
 	if ((m->m_pkthdr.csum_flags & CSUM_IP_CHECKED) != 0) {
 		if ((m->m_pkthdr.csum_flags & CSUM_IP_VALID) == 0) {
 			DNETDEBUG("bad IP checksum\n");
 			return;
 		}
 	} else {
 		/* XXX */ ;
 	}
 
 	/* Convert fields to host byte order. */
 	ip->ip_len = ntohs(ip->ip_len);
 	if (ip->ip_len < hlen) {
 		DNETDEBUG("IP packet smaller (%hu) than header (%hu)\n",
 		    ip->ip_len, hlen);
 		return;
 	}
 	if (m->m_pkthdr.len < ip->ip_len) {
 		DNETDEBUG("IP packet bigger (%hu) than ethernet packet (%d)\n",
 		    ip->ip_len, m->m_pkthdr.len);
 		return;
 	}
 	if (m->m_pkthdr.len > ip->ip_len) {
 		/* Truncate the packet to the IP length. */
 		if (m->m_len == m->m_pkthdr.len) {
 			m->m_len = ip->ip_len;
 			m->m_pkthdr.len = ip->ip_len;
 		} else
 			m_adj(m, ip->ip_len - m->m_pkthdr.len);
 	}
 
 	ip->ip_off = ntohs(ip->ip_off);
 
 	/* Check that the source is the server's IP. */
 	if (ip->ip_src.s_addr != pcb->dp_server) {
 		DNETDEBUG("drop packet not from server (from 0x%x)\n",
 		    ip->ip_src.s_addr);
 		return;
 	}
 
 	/* Check if the destination IP is ours. */
 	if (ip->ip_dst.s_addr != pcb->dp_client) {
 		DNETDEBUGV("drop packet not to our IP\n");
 		return;
 	}
 
 	if (ip->ip_p != IPPROTO_UDP) {
 		DNETDEBUG("drop non-UDP packet\n");
 		return;
 	}
 
 	/* Do not deal with fragments. */
 	if ((ip->ip_off & (IP_MF | IP_OFFMASK)) != 0) {
 		DNETDEBUG("drop fragmented packet\n");
 		return;
 	}
 
 	if ((m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR) != 0) {
 		if ((m->m_pkthdr.csum_flags & CSUM_DATA_VALID) == 0) {
 			DNETDEBUG("bad UDP checksum\n");
 			return;
 		}
 	} else {
 		/* XXX */ ;
 	}
 
 	/* UDP custom is to have packet length not include IP header. */
 	ip->ip_len -= hlen;
 
 	/* Checked above before decoding IP header. */
 	MPASS(m->m_pkthdr.len >= sizeof(struct ipovly));
 
 	/* Put the UDP header at start of chain. */
 	m_adj(m, sizeof(struct ipovly));
 	debugnet_handle_udp(pcb, mb);
 }
 
 /*
  * Builds and sends a single ARP request to locate the L2 address for a given
  * INET address.
  *
  * Return value:
  *	0 on success
  *	errno on error
  */
 static int
 debugnet_send_arp(struct debugnet_pcb *pcb, in_addr_t dst)
 {
 	struct ether_addr bcast;
 	struct arphdr *ah;
 	struct ifnet *ifp;
 	struct mbuf *m;
 	int pktlen;
 
 	ifp = pcb->dp_ifp;
 
 	/* Fill-up a broadcast address. */
 	memset(&bcast, 0xFF, ETHER_ADDR_LEN);
 	m = m_gethdr(M_NOWAIT, MT_DATA);
 	if (m == NULL) {
 		printf("%s: Out of mbufs\n", __func__);
 		return (ENOBUFS);
 	}
 	pktlen = arphdr_len2(ETHER_ADDR_LEN, sizeof(struct in_addr));
 	m->m_len = pktlen;
 	m->m_pkthdr.len = pktlen;
 	MH_ALIGN(m, pktlen);
 	ah = mtod(m, struct arphdr *);
 	ah->ar_hrd = htons(ARPHRD_ETHER);
 	ah->ar_pro = htons(ETHERTYPE_IP);
 	ah->ar_hln = ETHER_ADDR_LEN;
 	ah->ar_pln = sizeof(struct in_addr);
 	ah->ar_op = htons(ARPOP_REQUEST);
 	memcpy(ar_sha(ah), IF_LLADDR(ifp), ETHER_ADDR_LEN);
 	((struct in_addr *)ar_spa(ah))->s_addr = pcb->dp_client;
 	bzero(ar_tha(ah), ETHER_ADDR_LEN);
 	((struct in_addr *)ar_tpa(ah))->s_addr = dst;
 	return (debugnet_ether_output(m, ifp, bcast, ETHERTYPE_ARP));
 }
 
 /*
  * Handler for ARP packets: checks their sanity and then
  * 1. If the ARP is a request for our IP, respond with our MAC address
  * 2. If the ARP is a response from our server, record its MAC address
  *
  * It needs to replicate partially the behaviour of arpintr() and
  * in_arpinput().
  *
  * Parameters:
  *	pcb	a pointer to the live debugnet PCB
  *	mb	a pointer to an mbuf * containing the packet received
  *		Updates *mb if m_pullup et al change the pointer
  *		Assumes the calling function will take care of freeing the mbuf
  */
 void
 debugnet_handle_arp(struct debugnet_pcb *pcb, struct mbuf **mb)
 {
 	char buf[INET_ADDRSTRLEN];
 	struct in_addr isaddr, itaddr;
 	struct ether_addr dst;
 	struct mbuf *m;
 	struct arphdr *ah;
 	struct ifnet *ifp;
 	uint8_t *enaddr;
 	int req_len, op;
 
 	m = *mb;
 	ifp = m->m_pkthdr.rcvif;
 	if (m->m_len < sizeof(struct arphdr)) {
 		m = m_pullup(m, sizeof(struct arphdr));
 		*mb = m;
 		if (m == NULL) {
 			DNETDEBUG("runt packet: m_pullup failed\n");
 			return;
 		}
 	}
 
 	ah = mtod(m, struct arphdr *);
 	if (ntohs(ah->ar_hrd) != ARPHRD_ETHER) {
 		DNETDEBUG("unknown hardware address 0x%2D)\n",
 		    (unsigned char *)&ah->ar_hrd, "");
 		return;
 	}
 	if (ntohs(ah->ar_pro) != ETHERTYPE_IP) {
 		DNETDEBUG("drop ARP for unknown protocol %d\n",
 		    ntohs(ah->ar_pro));
 		return;
 	}
 	req_len = arphdr_len2(ifp->if_addrlen, sizeof(struct in_addr));
 	if (m->m_len < req_len) {
 		m = m_pullup(m, req_len);
 		*mb = m;
 		if (m == NULL) {
 			DNETDEBUG("runt packet: m_pullup failed\n");
 			return;
 		}
 	}
 	ah = mtod(m, struct arphdr *);
 
 	op = ntohs(ah->ar_op);
 	memcpy(&isaddr, ar_spa(ah), sizeof(isaddr));
 	memcpy(&itaddr, ar_tpa(ah), sizeof(itaddr));
 	enaddr = (uint8_t *)IF_LLADDR(ifp);
 
 	if (memcmp(ar_sha(ah), enaddr, ifp->if_addrlen) == 0) {
 		DNETDEBUG("ignoring ARP from myself\n");
 		return;
 	}
 
 	if (isaddr.s_addr == pcb->dp_client) {
 		printf("%s: %*D is using my IP address %s!\n", __func__,
 		    ifp->if_addrlen, (u_char *)ar_sha(ah), ":",
 		    inet_ntoa_r(isaddr, buf));
 		return;
 	}
 
 	if (memcmp(ar_sha(ah), ifp->if_broadcastaddr, ifp->if_addrlen) == 0) {
 		DNETDEBUG("ignoring ARP from broadcast address\n");
 		return;
 	}
 
 	if (op == ARPOP_REPLY) {
 		if (isaddr.s_addr != pcb->dp_gateway &&
 		    isaddr.s_addr != pcb->dp_server) {
 			inet_ntoa_r(isaddr, buf);
 			DNETDEBUG("ignoring ARP reply from %s (not configured"
 			    " server or gateway)\n", buf);
 			return;
 		}
+		if (pcb->dp_state >= DN_STATE_HAVE_GW_MAC) {
+			inet_ntoa_r(isaddr, buf);
+			DNETDEBUG("ignoring server ARP reply from %s (already"
+			    " have gateway address)\n", buf);
+			return;
+		}
+		MPASS(pcb->dp_state == DN_STATE_INIT);
 		memcpy(pcb->dp_gw_mac.octet, ar_sha(ah),
 		    min(ah->ar_hln, ETHER_ADDR_LEN));
 		
 		DNETDEBUG("got server MAC address %6D\n",
 		    pcb->dp_gw_mac.octet, ":");
 
-		MPASS(pcb->dp_state == DN_STATE_INIT);
 		pcb->dp_state = DN_STATE_HAVE_GW_MAC;
 		return;
 	}
 
 	if (op != ARPOP_REQUEST) {
 		DNETDEBUG("ignoring ARP non-request/reply\n");
 		return;
 	}
 
 	if (itaddr.s_addr != pcb->dp_client) {
 		DNETDEBUG("ignoring ARP not to our IP\n");
 		return;
 	}
 
 	memcpy(ar_tha(ah), ar_sha(ah), ah->ar_hln);
 	memcpy(ar_sha(ah), enaddr, ah->ar_hln);
 	memcpy(ar_tpa(ah), ar_spa(ah), ah->ar_pln);
 	memcpy(ar_spa(ah), &itaddr, ah->ar_pln);
 	ah->ar_op = htons(ARPOP_REPLY);
 	ah->ar_pro = htons(ETHERTYPE_IP);
 	m->m_flags &= ~(M_BCAST|M_MCAST);
 	m->m_len = arphdr_len(ah);
 	m->m_pkthdr.len = m->m_len;
 
 	memcpy(dst.octet, ar_tha(ah), ETHER_ADDR_LEN);
 	debugnet_ether_output(m, ifp, dst, ETHERTYPE_ARP);
 	*mb = NULL;
 }
 
 /*
  * Sends ARP requests to locate the server and waits for a response.
  * We first try to ARP the server itself, and fall back to the provided
  * gateway if the server appears to be off-link.
  *
  * Return value:
  *	0 on success
  *	errno on error
  */
 int
 debugnet_arp_gw(struct debugnet_pcb *pcb)
 {
 	in_addr_t dst;
 	int error, polls, retries;
 
 	dst = pcb->dp_server;
 restart:
 	for (retries = 0; retries < debugnet_arp_nretries; retries++) {
 		error = debugnet_send_arp(pcb, dst);
 		if (error != 0)
 			return (error);
 		for (polls = 0; polls < debugnet_npolls &&
 		    pcb->dp_state < DN_STATE_HAVE_GW_MAC; polls++) {
 			debugnet_network_poll(pcb);
 			DELAY(500);
 		}
 		if (pcb->dp_state >= DN_STATE_HAVE_GW_MAC)
 			break;
 		printf("(ARP retry)");
 	}
 	if (pcb->dp_state >= DN_STATE_HAVE_GW_MAC)
 		return (0);
 	if (dst == pcb->dp_server) {
 		printf("\nFailed to ARP server");
 		if (pcb->dp_gateway != INADDR_ANY) {
 			printf(", trying to reach gateway...\n");
 			dst = pcb->dp_gateway;
 			goto restart;
 		} else
 			printf(".\n");
 	} else
 		printf("\nFailed to ARP gateway.\n");
 
 	return (ETIMEDOUT);
 }
 
 /*
  * Unreliable IPv4 transmission of an mbuf chain to the debugnet server
  * Note: can't handle fragmentation; fails if the packet is larger than
  *	 ifp->if_mtu after adding the UDP/IP headers
  *
  * Parameters:
  *	pcb	The debugnet context block
  *	m	mbuf chain
  *
  * Returns:
  *	int	see errno.h, 0 for success
  */
 int
 debugnet_ip_output(struct debugnet_pcb *pcb, struct mbuf *m)
 {
 	struct udphdr *udp;
 	struct ifnet *ifp;
 	struct ip *ip;
 
 	MPASS(pcb->dp_state >= DN_STATE_HAVE_GW_MAC);
 
 	ifp = pcb->dp_ifp;
 
 	M_PREPEND(m, sizeof(*ip), M_NOWAIT);
 	if (m == NULL) {
 		printf("%s: out of mbufs\n", __func__);
 		return (ENOBUFS);
 	}
 
 	if (m->m_pkthdr.len > ifp->if_mtu) {
 		printf("%s: Packet is too big: %d > MTU %u\n", __func__,
 		    m->m_pkthdr.len, ifp->if_mtu);
 		m_freem(m);
 		return (ENOBUFS);
 	}
 
 	ip = mtod(m, void *);
 	udp = (void *)(ip + 1);
 
 	memset(ip, 0, offsetof(struct ip, ip_p));
 	ip->ip_p = IPPROTO_UDP;
 	ip->ip_sum = udp->uh_ulen;
 	ip->ip_src = (struct in_addr) { pcb->dp_client };
 	ip->ip_dst = (struct in_addr) { pcb->dp_server };
 
 	/* Compute UDP-IPv4 checksum. */
 	udp->uh_sum = in_cksum(m, m->m_pkthdr.len);
 	if (udp->uh_sum == 0)
 		udp->uh_sum = 0xffff;
 
 	ip->ip_v = IPVERSION;
 	ip->ip_hl = sizeof(*ip) >> 2;
 	ip->ip_tos = 0;
 	ip->ip_len = htons(m->m_pkthdr.len);
 	ip->ip_id = 0;
 	ip->ip_off = htons(IP_DF);
 	ip->ip_ttl = 255;
 	ip->ip_sum = 0;
 	ip->ip_sum = in_cksum(m, sizeof(struct ip));
 
 	return (debugnet_ether_output(m, ifp, pcb->dp_gw_mac, ETHERTYPE_IP));
 }