[PATCH v6 02/13] ip: Introduce unified multi-address data structures

[Jon Maloy <jmaloy@redhat.com>]

As preparation for supporting multiple addresses per interface,
we replace the single addr/prefix_len fields with an array. The
array consists of a new struct inany_addr_entry containing an
address and prefix length, both in inany_addr format.

Despite some code refactoring, there are only two real functional
changes:
- The indicated IPv6 prefix length is now properly stored, instead
  of being ignored and overridden with the hardcoded value 64, as
  as has been the case until now.
- Since even IPv4 addresses now are stored in IPv6 format, we
  also store the corresponding prefix length in that format,
  i.e. using the range [96,128] instead of [0,32].

Signed-off-by: Jon Maloy <jmaloy@redhat.com>

---
v2: -Using inany_addr instead of protocol specific addresses as
     entry address field.

v3: -Merging into one array, directly in struct ctx
    -Changed prefix_len and flags fields in struct inany_addr_entry
     to uint8_t, since that makes the struct directly migratable

v4: -Updated according to changes in previous commits
    -Updated according to feedback from David G.
    -Squashed IP4_MASK macro commit into this one

v6: -Renamed and moved some definitions
    -Introduced fwd_set_addr() and fwd_get_addr() already in this commit
    -Eliminated first_v4/v6() functions, replaced with fwd_get_addr()
    -Some other changes as suggested by David G.
    -I kept the flag CONF_ADDR_LINKLOCAL, since it will be
     needed later in an address selection function.
---
 arp.c    |  10 +++-
 conf.c   | 142 +++++++++++++++++++++++++++++--------------------------
 dhcp.c   |  13 +++--
 dhcpv6.c |  15 ++++--
 fwd.c    | 104 +++++++++++++++++++++++++++++++++-------
 fwd.h    |   4 ++
 igmp.c   |   1 +
 ip.h     |   2 +
 ndp.c    |  16 +++++--
 passt.h  |  82 ++++++++++++++++++++++++++++----
 pasta.c  |  21 ++++----
 tap.c    |   7 ++-
 12 files changed, 302 insertions(+), 115 deletions(-)

diff --git a/arp.c b/arp.c
index bb042e9..18ff5de 100644
--- a/arp.c
+++ b/arp.c
@@ -41,6 +41,8 @@
 static bool ignore_arp(const struct ctx *c,
 		       const struct arphdr *ah, const struct arpmsg *am)
 {
+	const struct guest_addr *a = fwd_get_addr(c, AF_INET, 0, 0);
+
 	if (ah->ar_hrd != htons(ARPHRD_ETHER)	||
 	    ah->ar_pro != htons(ETH_P_IP)	||
 	    ah->ar_hln != ETH_ALEN		||
@@ -54,7 +56,7 @@ static bool ignore_arp(const struct ctx *c,
 		return true;
 
 	/* Don't resolve the guest's assigned address, either. */
-	if (!memcmp(am->tip, &c->ip4.addr, sizeof(am->tip)))
+	if (a && !memcmp(am->tip, inany_v4(&a->addr), sizeof(am->tip)))
 		return true;
 
 	return false;
@@ -123,12 +125,16 @@ int arp(const struct ctx *c, struct iov_tail *data)
  */
 void arp_send_init_req(const struct ctx *c)
 {
+	const struct guest_addr *a = fwd_get_addr(c, AF_INET, 0, 0);
 	struct {
 		struct ethhdr eh;
 		struct arphdr ah;
 		struct arpmsg am;
 	} __attribute__((__packed__)) req;
 
+	if (!a)
+		return;
+
 	/* Ethernet header */
 	req.eh.h_proto = htons(ETH_P_ARP);
 	memcpy(req.eh.h_dest, MAC_BROADCAST, sizeof(req.eh.h_dest));
@@ -145,7 +151,7 @@ void arp_send_init_req(const struct ctx *c)
 	memcpy(req.am.sha,	c->our_tap_mac,		sizeof(req.am.sha));
 	memcpy(req.am.sip,	&c->ip4.our_tap_addr,	sizeof(req.am.sip));
 	memcpy(req.am.tha,	MAC_BROADCAST,		sizeof(req.am.tha));
-	memcpy(req.am.tip,	&c->ip4.addr,		sizeof(req.am.tip));
+	memcpy(req.am.tip,	inany_v4(&a->addr),	sizeof(req.am.tip));
 
 	debug("Sending initial ARP request for guest MAC address");
 	tap_send_single(c, &req, sizeof(req));
diff --git a/conf.c b/conf.c
index 9bcd9de..8f02494 100644
--- a/conf.c
+++ b/conf.c
@@ -728,13 +728,15 @@ static int conf_ip4_prefix(const char *arg)
 
 /**
  * conf_ip4() - Verify or detect IPv4 support, get relevant addresses
+ * @c:		Execution context
  * @ifi:	Host interface to attempt (0 to determine one)
- * @ip4:	IPv4 context (will be written)
  *
  * Return: interface index for IPv4, or 0 on failure.
  */
-static unsigned int conf_ip4(unsigned int ifi, struct ip4_ctx *ip4)
+static unsigned int conf_ip4(struct ctx *c, unsigned int ifi)
 {
+	struct ip4_ctx *ip4 = &c->ip4;
+
 	if (!ifi)
 		ifi = nl_get_ext_if(nl_sock, AF_INET);
 
@@ -753,60 +755,57 @@ static unsigned int conf_ip4(unsigned int ifi, struct ip4_ctx *ip4)
 		}
 	}
 
-	if (IN4_IS_ADDR_UNSPECIFIED(&ip4->addr)) {
+	if (!fwd_get_addr(c, AF_INET, 0, 0)) {
+		struct in_addr addr;
+		int prefix_len;
 		int rc = nl_addr_get(nl_sock, ifi, AF_INET,
-				     &ip4->addr, &ip4->prefix_len, NULL);
+				     &addr, &prefix_len, NULL);
 		if (rc < 0) {
 			debug("Couldn't discover IPv4 address: %s",
 			      strerror_(-rc));
 			return 0;
 		}
-	}
+		if (IN4_IS_ADDR_UNSPECIFIED(&addr))
+			return 0;
 
-	if (!ip4->prefix_len) {
-		in_addr_t addr = ntohl(ip4->addr.s_addr);
-		if (IN_CLASSA(addr))
-			ip4->prefix_len = (32 - IN_CLASSA_NSHIFT);
-		else if (IN_CLASSB(addr))
-			ip4->prefix_len = (32 - IN_CLASSB_NSHIFT);
-		else if (IN_CLASSC(addr))
-			ip4->prefix_len = (32 - IN_CLASSC_NSHIFT);
-		else
-			ip4->prefix_len = 32;
+		fwd_set_addr(c, &inany_from_v4(addr), CONF_ADDR_HOST,
+			     prefix_len + 96);
+		ip4->addr_seen = addr;
 	}
 
-	ip4->addr_seen = ip4->addr;
-
 	ip4->our_tap_addr = ip4->guest_gw;
 
-	if (IN4_IS_ADDR_UNSPECIFIED(&ip4->addr))
-		return 0;
-
 	return ifi;
 }
 
 /**
  * conf_ip4_local() - Configure IPv4 addresses and attributes for local mode
- * @ip4:	IPv4 context (will be written)
+ * @c:		Execution context (will be written)
  */
-static void conf_ip4_local(struct ip4_ctx *ip4)
+static void conf_ip4_local(struct ctx *c)
 {
-	ip4->addr_seen = ip4->addr = IP4_LL_GUEST_ADDR;
-	ip4->our_tap_addr = ip4->guest_gw = IP4_LL_GUEST_GW;
-	ip4->prefix_len = IP4_LL_PREFIX_LEN;
+	struct ip4_ctx *ip4 = &c->ip4;
 
+	ip4->addr_seen = IP4_LL_GUEST_ADDR;
+	ip4->our_tap_addr = ip4->guest_gw = IP4_LL_GUEST_GW;
 	ip4->no_copy_addrs = ip4->no_copy_routes = true;
+	fwd_set_addr(c, &inany_from_v4(IP4_LL_GUEST_ADDR),
+		     CONF_ADDR_HOST | CONF_ADDR_LINKLOCAL,
+		     IP4_LL_PREFIX_LEN + 96);
 }
 
 /**
  * conf_ip6() - Verify or detect IPv6 support, get relevant addresses
+ * @c:		Execution context
  * @ifi:	Host interface to attempt (0 to determine one)
- * @ip6:	IPv6 context (will be written)
  *
  * Return: interface index for IPv6, or 0 on failure.
  */
-static unsigned int conf_ip6(unsigned int ifi, struct ip6_ctx *ip6)
+static unsigned int conf_ip6(struct ctx *c, unsigned int ifi)
 {
+	const struct guest_addr *a = fwd_get_addr(c, AF_INET6, 0, 0);
+	struct ip6_ctx *ip6 = &c->ip6;
+	union inany_addr addr;
 	int prefix_len = 0;
 	int rc;
 
@@ -827,21 +826,24 @@ static unsigned int conf_ip6(unsigned int ifi, struct ip6_ctx *ip6)
 		}
 	}
 
-	rc = nl_addr_get(nl_sock, ifi, AF_INET6,
-			 IN6_IS_ADDR_UNSPECIFIED(&ip6->addr) ? &ip6->addr : NULL,
+	rc = nl_addr_get(nl_sock, ifi, AF_INET6, &addr.a6,
 			 &prefix_len, &ip6->our_tap_ll);
 	if (rc < 0) {
 		debug("Couldn't discover IPv6 address: %s", strerror_(-rc));
 		return 0;
 	}
 
-	ip6->addr_seen = ip6->addr;
+	if (!a) {
+		fwd_set_addr(c, &addr, CONF_ADDR_HOST, prefix_len);
+		ip6->addr_seen = addr.a6;
+	} else {
+		ip6->addr_seen = a->addr.a6;
+	}
 
 	if (IN6_IS_ADDR_LINKLOCAL(&ip6->guest_gw))
 		ip6->our_tap_ll = ip6->guest_gw;
 
-	if (IN6_IS_ADDR_UNSPECIFIED(&ip6->addr) ||
-	    IN6_IS_ADDR_UNSPECIFIED(&ip6->our_tap_ll))
+	if (IN6_IS_ADDR_UNSPECIFIED(&ip6->our_tap_ll))
 		return 0;
 
 	return ifi;
@@ -849,13 +851,13 @@ static unsigned int conf_ip6(unsigned int ifi, struct ip6_ctx *ip6)
 
 /**
  * conf_ip6_local() - Configure IPv6 addresses and attributes for local mode
- * @ip6:	IPv6 context (will be written)
+ * @c:		Execution context (will be written)
  */
-static void conf_ip6_local(struct ip6_ctx *ip6)
+static void conf_ip6_local(struct ctx *c)
 {
-	ip6->our_tap_ll = ip6->guest_gw = IP6_LL_GUEST_GW;
+	c->ip6.our_tap_ll = c->ip6.guest_gw = IP6_LL_GUEST_GW;
 
-	ip6->no_copy_addrs = ip6->no_copy_routes = true;
+	c->ip6.no_copy_addrs = c->ip6.no_copy_routes = true;
 }
 
 /**
@@ -1137,6 +1139,7 @@ enum passt_modes conf_mode(int argc, char *argv[])
 static void conf_print(const struct ctx *c)
 {
 	char buf[INET6_ADDRSTRLEN];
+	const struct guest_addr *a;
 	int i;
 
 	if (c->ifi4 > 0 || c->ifi6 > 0) {
@@ -1182,19 +1185,19 @@ static void conf_print(const struct ctx *c)
 			     inet_ntop(AF_INET, &c->ip4.map_host_loopback,
 				       buf, sizeof(buf)));
 
-		if (!c->no_dhcp) {
+		a = fwd_get_addr(c, AF_INET, 0, 0);
+		if (a && !c->no_dhcp) {
 			uint32_t mask;
 
-			mask = htonl(0xffffffff << (32 - c->ip4.prefix_len));
+			mask = IN4_MASK(inany_prefix_len(a));
 
 			info("DHCP:");
-			info("    assign: %s",
-			     inet_ntop(AF_INET, &c->ip4.addr, buf, sizeof(buf)));
-			info("    mask: %s",
-			     inet_ntop(AF_INET, &mask,        buf, sizeof(buf)));
-			info("    router: %s",
-			     inet_ntop(AF_INET, &c->ip4.guest_gw,
-				       buf, sizeof(buf)));
+			inany_ntop(&a->addr, buf, sizeof(buf));
+			info("    assign: %s", buf);
+			inet_ntop(AF_INET, &mask, buf, sizeof(buf));
+			info("    mask: %s", buf);
+			inet_ntop(AF_INET, &c->ip4.guest_gw, buf, sizeof(buf));
+			info("    router: %s", buf);
 		}
 
 		for (i = 0; i < ARRAY_SIZE(c->ip4.dns); i++) {
@@ -1228,13 +1231,14 @@ static void conf_print(const struct ctx *c)
 		else
 			goto dns6;
 
-		info("    assign: %s",
-		     inet_ntop(AF_INET6, &c->ip6.addr, buf, sizeof(buf)));
-		info("    router: %s",
-		     inet_ntop(AF_INET6, &c->ip6.guest_gw, buf, sizeof(buf)));
-		info("    our link-local: %s",
-		     inet_ntop(AF_INET6, &c->ip6.our_tap_ll,
-			       buf, sizeof(buf)));
+		a = fwd_get_addr(c, AF_INET6, 0, CONF_ADDR_LINKLOCAL);
+		if (a)
+			inany_ntop(&a->addr, buf, sizeof(buf));
+		info("    assign: %s", !a ? "" : buf);
+		inet_ntop(AF_INET6, &c->ip6.guest_gw, buf, sizeof(buf));
+		info("    router: %s", buf);
+		inet_ntop(AF_INET6, &c->ip6.our_tap_ll, buf, sizeof(buf));
+		info("    our link-local: %s", buf);
 
 dns6:
 		for (i = 0; i < ARRAY_SIZE(c->ip6.dns); i++) {
@@ -1887,16 +1891,12 @@ void conf(struct ctx *c, int argc, char **argv)
 			    IN6_IS_ADDR_V4COMPAT(&addr.a6))
 				die("Invalid address: %s", optarg);
 
-			if (inany_v4(&addr)) {
-				c->ip4.addr = *inany_v4(&addr);
-				c->ip4.prefix_len = prefix_len - 96;
-				if (c->mode == MODE_PASTA)
-					c->ip4.no_copy_addrs = true;
-			} else {
-				c->ip6.addr = addr.a6;
-				if (c->mode == MODE_PASTA)
-					c->ip6.no_copy_addrs = true;
-			}
+			/* Legacy behaviour: replace existing address if any */
+			fwd_set_addr(c, &addr, CONF_ADDR_USER, prefix_len);
+			if (inany_v4(&addr))
+				c->ip4.no_copy_addrs = true;
+			else
+				c->ip6.no_copy_addrs = true;
 			break;
 		}
 		case 'n': {
@@ -1910,7 +1910,13 @@ void conf(struct ctx *c, int argc, char **argv)
 				die("Invalid prefix length: %s", optarg);
 
 			prefix_len_from_opt = plen + 96;
-			c->ip4.prefix_len = plen;
+
+			for (int i = 0; i < c->addr_count; i++) {
+				if (!inany_v4(&c->addrs[i].addr))
+					continue;
+				c->addrs[i].prefix_len = prefix_len_from_opt;
+				break;
+			}
 			break;
 		}
 		case 'M':
@@ -2104,9 +2110,9 @@ void conf(struct ctx *c, int argc, char **argv)
 
 	nl_sock_init(c, false);
 	if (!v6_only && !c->splice_only)
-		c->ifi4 = conf_ip4(ifi4, &c->ip4);
+		c->ifi4 = conf_ip4(c, ifi4);
 	if (!v4_only && !c->splice_only)
-		c->ifi6 = conf_ip6(ifi6, &c->ip6);
+		c->ifi6 = conf_ip6(c, ifi6);
 
 	if (c->ifi4 && c->mtu < IPV4_MIN_MTU) {
 		warn("MTU %"PRIu16" is too small for IPv4 (minimum %u)",
@@ -2129,7 +2135,7 @@ void conf(struct ctx *c, int argc, char **argv)
 	if (!c->ifi4 && !v6_only) {
 		if (!c->splice_only) {
 			info("IPv4: no external interface as template, use local mode");
-			conf_ip4_local(&c->ip4);
+			conf_ip4_local(c);
 		}
 		c->ifi4 = -1;
 	}
@@ -2137,7 +2143,7 @@ void conf(struct ctx *c, int argc, char **argv)
 	if (!c->ifi6 && !v4_only) {
 		if (!c->splice_only) {
 			info("IPv6: no external interface as template, use local mode");
-			conf_ip6_local(&c->ip6);
+			conf_ip6_local(c);
 		}
 		c->ifi6 = -1;
 	}
@@ -2202,7 +2208,7 @@ void conf(struct ctx *c, int argc, char **argv)
 	if (!c->ifi6) {
 		c->no_ndp = 1;
 		c->no_dhcpv6 = 1;
-	} else if (IN6_IS_ADDR_UNSPECIFIED(&c->ip6.addr)) {
+	} else if (!fwd_get_addr(c, AF_INET6, 0, 0)) {
 		c->no_dhcpv6 = 1;
 	}
 
diff --git a/dhcp.c b/dhcp.c
index 1ff8cba..6d9def5 100644
--- a/dhcp.c
+++ b/dhcp.c
@@ -302,6 +302,7 @@ static void opt_set_dns_search(const struct ctx *c, size_t max_len)
  */
 int dhcp(const struct ctx *c, struct iov_tail *data)
 {
+	const struct guest_addr *a = fwd_get_addr(c, AF_INET, 0, 0);
 	char macstr[ETH_ADDRSTRLEN];
 	size_t mlen, dlen, opt_len;
 	struct in_addr mask, dst;
@@ -313,6 +314,7 @@ int dhcp(const struct ctx *c, struct iov_tail *data)
 	const struct udphdr *uh;
 	struct msg m_storage;
 	struct msg const *m;
+	struct in_addr addr;
 	struct msg reply;
 	unsigned int i;
 
@@ -344,6 +346,9 @@ int dhcp(const struct ctx *c, struct iov_tail *data)
 	    m->op != BOOTREQUEST)
 		return -1;
 
+	ASSERT(a);
+	addr = *inany_v4(&a->addr);
+
 	reply.op		= BOOTREPLY;
 	reply.htype		= m->htype;
 	reply.hlen		= m->hlen;
@@ -352,7 +357,7 @@ int dhcp(const struct ctx *c, struct iov_tail *data)
 	reply.secs		= 0;
 	reply.flags		= m->flags;
 	reply.ciaddr		= m->ciaddr;
-	reply.yiaddr		= c->ip4.addr;
+	reply.yiaddr		= addr;
 	reply.siaddr		= 0;
 	reply.giaddr		= m->giaddr;
 	memcpy(&reply.chaddr,	m->chaddr,	sizeof(reply.chaddr));
@@ -404,7 +409,7 @@ int dhcp(const struct ctx *c, struct iov_tail *data)
 
 	info("    from %s", eth_ntop(m->chaddr, macstr, sizeof(macstr)));
 
-	mask.s_addr = htonl(0xffffffff << (32 - c->ip4.prefix_len));
+	mask.s_addr = IN4_MASK(inany_prefix_len(a));
 	memcpy(opts[1].s,  &mask,                sizeof(mask));
 	memcpy(opts[3].s,  &c->ip4.guest_gw,     sizeof(c->ip4.guest_gw));
 	memcpy(opts[54].s, &c->ip4.our_tap_addr, sizeof(c->ip4.our_tap_addr));
@@ -412,7 +417,7 @@ int dhcp(const struct ctx *c, struct iov_tail *data)
 	/* If the gateway is not on the assigned subnet, send an option 121
 	 * (Classless Static Routing) adding a dummy route to it.
 	 */
-	if ((c->ip4.addr.s_addr & mask.s_addr)
+	if ((addr.s_addr & mask.s_addr)
 	    != (c->ip4.guest_gw.s_addr & mask.s_addr)) {
 		/* a.b.c.d/32:0.0.0.0, 0:a.b.c.d */
 		opts[121].slen = 14;
@@ -471,7 +476,7 @@ int dhcp(const struct ctx *c, struct iov_tail *data)
 	if (m->flags & FLAG_BROADCAST)
 		dst = in4addr_broadcast;
 	else
-		dst = c->ip4.addr;
+		dst = addr;
 
 	tap_udp4_send(c, c->ip4.our_tap_addr, 67, dst, 68, &reply, dlen);
 
diff --git a/dhcpv6.c b/dhcpv6.c
index 97c04e2..3a007bf 100644
--- a/dhcpv6.c
+++ b/dhcpv6.c
@@ -318,7 +318,7 @@ static bool dhcpv6_opt(struct iov_tail *data, uint16_t type)
  *         false otherwise and @data is unmodified
  */
 static bool dhcpv6_ia_notonlink(struct iov_tail *data,
-				struct in6_addr *la)
+				const struct in6_addr *la)
 {
 	int ia_types[2] = { OPT_IA_NA, OPT_IA_TA };
 	struct opt_ia_addr opt_addr_storage;
@@ -566,6 +566,7 @@ int dhcpv6(struct ctx *c, struct iov_tail *data,
 	struct opt_hdr client_id_storage;
 	/* cppcheck-suppress [variableScope,unmatchedSuppression] */
 	struct opt_ia_na ia_storage;
+	const struct guest_addr *a;
 	const struct in6_addr *src;
 	struct msg_hdr mh_storage;
 	const struct msg_hdr *mh;
@@ -573,6 +574,8 @@ int dhcpv6(struct ctx *c, struct iov_tail *data,
 	const struct udphdr *uh;
 	size_t mlen, n;
 
+	a = fwd_get_addr(c, AF_INET6, 0, CONF_ADDR_LINKLOCAL);
+
 	uh = IOV_REMOVE_HEADER(data, uh_storage);
 	if (!uh)
 		return -1;
@@ -628,7 +631,7 @@ int dhcpv6(struct ctx *c, struct iov_tail *data,
 		if (mh->type == TYPE_CONFIRM && server_id)
 			return -1;
 
-		if (dhcpv6_ia_notonlink(data, &c->ip6.addr)) {
+		if (a && dhcpv6_ia_notonlink(data, &a->addr.a6)) {
 
 			dhcpv6_send_ia_notonlink(c, data, &client_id_base,
 						 ntohs(client_id->l), mh->xid);
@@ -682,7 +685,8 @@ int dhcpv6(struct ctx *c, struct iov_tail *data,
 
 	tap_udp6_send(c, src, 547, tap_ip6_daddr(c, src), 546,
 		      mh->xid, &resp, n);
-	c->ip6.addr_seen = c->ip6.addr;
+	if (a)
+		c->ip6.addr_seen = a->addr.a6;
 
 	return 1;
 }
@@ -693,6 +697,7 @@ int dhcpv6(struct ctx *c, struct iov_tail *data,
  */
 void dhcpv6_init(const struct ctx *c)
 {
+	const struct guest_addr *a;
 	time_t y2k = 946684800; /* Epoch to 2000-01-01T00:00:00Z, no mktime() */
 	uint32_t duid_time;
 
@@ -706,5 +711,7 @@ void dhcpv6_init(const struct ctx *c)
 	memcpy(resp_not_on_link.server_id.duid_lladdr,
 	       c->our_tap_mac, sizeof(c->our_tap_mac));
 
-	resp.ia_addr.addr	= c->ip6.addr;
+	a = fwd_get_addr(c, AF_INET6, 0, CONF_ADDR_LINKLOCAL);
+	if (a)
+		resp.ia_addr.addr = a->addr.a6;
 }
diff --git a/fwd.c b/fwd.c
index bedbf98..9101d6d 100644
--- a/fwd.c
+++ b/fwd.c
@@ -249,6 +249,64 @@ void fwd_neigh_table_init(const struct ctx *c)
 		fwd_neigh_table_update(c, &mga, c->our_tap_mac, true);
 }
 
+/**
+ * fwd_set_addr() - Add or update an address in the unified address array
+ * @c:		Execution context
+ * @addr:	Address to add (IPv4-mapped or IPv6)
+ * @flags:	CONF_ADDR_* flags for this address
+ * @prefix_len:	Prefix length in IPv6/mapped format, 0-128
+ *
+ * Find the first existing entry of the same address family and
+ * overwrite it, or create a new one if none exists
+ */
+void fwd_set_addr(struct ctx *c, const union inany_addr *addr,
+		  uint8_t flags, int prefix_len)
+{
+	struct guest_addr *a;
+
+	for (int i = 0; i < c->addr_count; i++) {
+		a = &c->addrs[i];
+		if ((inany_v4(addr) && inany_v4(&a->addr)) ||
+		    (!inany_v4(addr) && !inany_v4(&a->addr)))
+			goto found;
+	}
+
+	if (c->addr_count >= MAX_GUEST_ADDRS)
+		return;
+
+	a = &c->addrs[c->addr_count++];
+
+found:
+	a->addr = *addr;
+	a->prefix_len = prefix_len;
+	a->flags = flags;
+}
+
+/**
+ * fwd_get_addr() - Get guest address entry matching criteria
+ * @c:		Execution context
+ * @af:		Address family (AF_INET, AF_INET6, or 0 for any)
+ * @incl:	Flags that must be present (any-match)
+ * @excl:	Flags that must not be present
+ *
+ * Return: first address entry matching criteria, or NULL
+ */
+const struct guest_addr *fwd_get_addr(const struct ctx *c, sa_family_t af,
+				      uint8_t incl, uint8_t excl)
+{
+	const struct guest_addr *a;
+
+	for_each_addr(a, c, af) {
+		if (incl && !(a->flags & incl))
+			continue;
+		if (a->flags & excl)
+			continue;
+		return a;
+	}
+
+	return NULL;
+}
+
 /** fwd_probe_ephemeral() - Determine what ports this host considers ephemeral
  *
  * Work out what ports the host thinks are emphemeral and record it for later
@@ -941,8 +999,10 @@ static bool is_dns_flow(uint8_t proto, const struct flowside *ini)
  *         translation, false otherwise
  */
 static bool fwd_guest_accessible4(const struct ctx *c,
-				    const struct in_addr *addr)
+				  const struct in_addr *addr)
 {
+	const struct guest_addr *a = fwd_get_addr(c, AF_INET, 0, 0);
+
 	if (IN4_IS_ADDR_LOOPBACK(addr))
 		return false;
 
@@ -957,7 +1017,7 @@ static bool fwd_guest_accessible4(const struct ctx *c,
 	/* For IPv4, addr_seen is initialised to addr, so is always a valid
 	 * address
 	 */
-	if (IN4_ARE_ADDR_EQUAL(addr, &c->ip4.addr) ||
+	if ((a && IN4_ARE_ADDR_EQUAL(addr, inany_v4(&a->addr))) ||
 	    IN4_ARE_ADDR_EQUAL(addr, &c->ip4.addr_seen))
 		return false;
 
@@ -975,10 +1035,12 @@ static bool fwd_guest_accessible4(const struct ctx *c,
 static bool fwd_guest_accessible6(const struct ctx *c,
 				  const struct in6_addr *addr)
 {
+	const struct guest_addr *a = fwd_get_addr(c, AF_INET6, 0, 0);
+
 	if (IN6_IS_ADDR_LOOPBACK(addr))
 		return false;
 
-	if (IN6_ARE_ADDR_EQUAL(addr, &c->ip6.addr))
+	if (a && IN6_ARE_ADDR_EQUAL(addr, &a->addr.a6))
 		return false;
 
 	/* For IPv6, addr_seen starts unspecified, because we don't know what LL
@@ -1023,14 +1085,19 @@ static bool fwd_guest_accessible(const struct ctx *c,
 static void nat_outbound(const struct ctx *c, const union inany_addr *addr,
 			 union inany_addr *translated)
 {
+	const struct guest_addr *ga;
+
 	if (inany_equals4(addr, &c->ip4.map_host_loopback))
 		*translated = inany_loopback4;
 	else if (inany_equals6(addr, &c->ip6.map_host_loopback))
 		*translated = inany_loopback6;
-	else if (inany_equals4(addr, &c->ip4.map_guest_addr))
-		*translated = inany_from_v4(c->ip4.addr);
-	else if (inany_equals6(addr, &c->ip6.map_guest_addr))
-		translated->a6 = c->ip6.addr;
+	else if (inany_equals4(addr, &c->ip4.map_guest_addr)) {
+		ga = fwd_get_addr(c, AF_INET, 0, 0);
+		*translated = ga ? ga->addr : inany_any4;
+	} else if (inany_equals6(addr, &c->ip6.map_guest_addr)) {
+		ga = fwd_get_addr(c, AF_INET6, 0, 0);
+		translated->a6 = ga ? ga->addr.a6 : in6addr_any;
+	}
 	else
 		*translated = *addr;
 }
@@ -1137,16 +1204,21 @@ bool nat_inbound(const struct ctx *c, const union inany_addr *addr,
 	} else if (!IN6_IS_ADDR_UNSPECIFIED(&c->ip6.map_host_loopback) &&
 		   inany_equals6(addr, &in6addr_loopback)) {
 		translated->a6 = c->ip6.map_host_loopback;
-	} else if (!IN4_IS_ADDR_UNSPECIFIED(&c->ip4.map_guest_addr) &&
-		   inany_equals4(addr, &c->ip4.addr)) {
-		*translated = inany_from_v4(c->ip4.map_guest_addr);
-	} else if (!IN6_IS_ADDR_UNSPECIFIED(&c->ip6.map_guest_addr) &&
-		   inany_equals6(addr, &c->ip6.addr)) {
-		translated->a6 = c->ip6.map_guest_addr;
-	} else if (fwd_guest_accessible(c, addr)) {
-		*translated = *addr;
 	} else {
-		return false;
+		const struct guest_addr *ga4 = fwd_get_addr(c, AF_INET, 0, 0);
+		const struct guest_addr *ga6 = fwd_get_addr(c, AF_INET6, 0, 0);
+
+		if (!IN4_IS_ADDR_UNSPECIFIED(&c->ip4.map_guest_addr) &&
+		    ga4 && inany_equals(addr, &ga4->addr)) {
+			*translated = inany_from_v4(c->ip4.map_guest_addr);
+		} else if (!IN6_IS_ADDR_UNSPECIFIED(&c->ip6.map_guest_addr) &&
+			   ga6 && inany_equals(addr, &ga6->addr)) {
+			translated->a6 = c->ip6.map_guest_addr;
+		} else if (fwd_guest_accessible(c, addr)) {
+			*translated = *addr;
+		} else {
+			return false;
+		}
 	}
 
 	return true;
diff --git a/fwd.h b/fwd.h
index 958eee2..c5a1068 100644
--- a/fwd.h
+++ b/fwd.h
@@ -23,6 +23,8 @@ struct flowside;
 
 void fwd_probe_ephemeral(void);
 bool fwd_port_is_ephemeral(in_port_t port);
+const struct guest_addr *fwd_get_addr(const struct ctx *c, sa_family_t af,
+				      uint8_t incl, uint8_t excl);
 
 /**
  * struct fwd_rule - Forwarding rule governing a range of ports
@@ -141,5 +143,7 @@ void fwd_neigh_table_free(const struct ctx *c,
 void fwd_neigh_mac_get(const struct ctx *c, const union inany_addr *addr,
 		       uint8_t *mac);
 void fwd_neigh_table_init(const struct ctx *c);
+void fwd_set_addr(struct ctx *c, const union inany_addr *addr,
+		  uint8_t flags, int prefix_len);
 
 #endif /* FWD_H */
diff --git a/igmp.c b/igmp.c
index a3971fc..0e77584 100644
--- a/igmp.c
+++ b/igmp.c
@@ -13,4 +13,5 @@
  */
 
 /* TO BE IMPLEMENTED */
+/* cppcheck-suppress unusedFunction */
 __attribute__((__unused__)) static void unused(void) { }
diff --git a/ip.h b/ip.h
index d0de6c8..933d98c 100644
--- a/ip.h
+++ b/ip.h
@@ -19,6 +19,8 @@
 	(ntohl(((struct in_addr *)(a))->s_addr) >> IN_CLASSA_NSHIFT == IN_LOOPBACKNET)
 #define IN4_IS_ADDR_MULTICAST(a) \
 	(IN_MULTICAST(ntohl(((struct in_addr *)(a))->s_addr)))
+#define IN4_MASK(prefix) \
+	((prefix) <= 0 ? 0 : htonl(0xffffffff << (32 - (prefix))))
 #define IN4_ARE_ADDR_EQUAL(a, b) \
 	(((struct in_addr *)(a))->s_addr == ((struct in_addr *)b)->s_addr)
 #define IN4ADDR_LOOPBACK_INIT \
diff --git a/ndp.c b/ndp.c
index 1f2bcb0..3750fc5 100644
--- a/ndp.c
+++ b/ndp.c
@@ -257,7 +257,6 @@ static void ndp_ra(const struct ctx *c, const struct in6_addr *dst)
 			.valid_lifetime		= ~0U,
 			.pref_lifetime		= ~0U,
 		},
-		.prefix = c->ip6.addr,
 		.source_ll = {
 			.header = {
 				.type		= OPT_SRC_L2_ADDR,
@@ -265,8 +264,13 @@ static void ndp_ra(const struct ctx *c, const struct in6_addr *dst)
 			},
 		},
 	};
+	const struct guest_addr *a = fwd_get_addr(c, AF_INET6, 0, 0);
 	unsigned char *ptr = NULL;
 
+	ASSERT(a);
+
+	ra.prefix = a->addr.a6;
+
 	ptr = &ra.var[0];
 
 	if (c->mtu) {
@@ -460,6 +464,7 @@ first:
  */
 void ndp_send_init_req(const struct ctx *c)
 {
+	const struct guest_addr *a = fwd_get_addr(c, AF_INET6, 0, 0);
 	struct ndp_ns ns = {
 		.ih = {
 			.icmp6_type		= NS,
@@ -468,8 +473,13 @@ void ndp_send_init_req(const struct ctx *c)
 			.icmp6_solicited	= 0, /* Reserved */
 			.icmp6_override		= 0, /* Reserved */
 		},
-		.target_addr = c->ip6.addr
+		.target_addr = IN6ADDR_ANY_INIT
 	};
+
+	if (!a)
+		return;
+
+	ns.target_addr = a->addr.a6;
 	debug("Sending initial NDP NS request for guest MAC address");
-	ndp_send(c, &c->ip6.addr, &ns, sizeof(ns));
+	ndp_send(c, &a->addr.a6, &ns, sizeof(ns));
 }
diff --git a/passt.h b/passt.h
index b614bdf..6bca778 100644
--- a/passt.h
+++ b/passt.h
@@ -64,11 +64,31 @@ enum passt_modes {
 	MODE_VU,
 };
 
+/* Maximum number of addresses in context address array */
+#define MAX_GUEST_ADDRS		32
+
+/* Flags indicating origin and role of a guest address
+ * To be used in struct guest_addr
+ */
+#define CONF_ADDR_USER		BIT(0)		/* User set via -a */
+#define CONF_ADDR_HOST		BIT(1)		/* From host interface */
+#define CONF_ADDR_LINKLOCAL	BIT(2)		/* Link-local address */
+
+/**
+ * struct guest_addr - Unified IPv4/IPv6 address entry
+ * @addr:	IPv4 (as mapped) or IPv6 address
+ * @prefix_len:	Prefix length in IPv6/IPv4-mapped [0,128]/[96,128] format
+ * @flags:	CONF_ADDR_* flags
+ */
+struct guest_addr {
+	union inany_addr addr;
+	uint8_t prefix_len;
+	uint8_t flags;
+};
+
 /**
  * struct ip4_ctx - IPv4 execution context
- * @addr:		IPv4 address assigned to guest
  * @addr_seen:		Latest IPv4 address seen as source from tap
- * @prefixlen:		IPv4 prefix length (netmask)
  * @guest_gw:		IPv4 gateway as seen by the guest
  * @map_host_loopback:	Outbound connections to this address are NATted to the
  *                      host's 127.0.0.1
@@ -84,10 +104,7 @@ enum passt_modes {
  * @no_copy_addrs:	Don't copy all addresses when configuring namespace
  */
 struct ip4_ctx {
-	/* PIF_TAP addresses */
-	struct in_addr addr;
 	struct in_addr addr_seen;
-	int prefix_len;
 	struct in_addr guest_gw;
 	struct in_addr map_host_loopback;
 	struct in_addr map_guest_addr;
@@ -107,7 +124,6 @@ struct ip4_ctx {
 
 /**
  * struct ip6_ctx - IPv6 execution context
- * @addr:		IPv6 address assigned to guest
  * @addr_seen:		Latest IPv6 global/site address seen as source from tap
  * @addr_ll_seen:	Latest IPv6 link-local address seen as source from tap
  * @guest_gw:		IPv6 gateway as seen by the guest
@@ -125,8 +141,6 @@ struct ip4_ctx {
  * @no_copy_addrs:	Don't copy all addresses when configuring namespace
  */
 struct ip6_ctx {
-	/* PIF_TAP addresses */
-	struct in6_addr addr;
 	struct in6_addr addr_seen;
 	struct in6_addr addr_ll_seen;
 	struct in6_addr guest_gw;
@@ -181,6 +195,8 @@ struct ip6_ctx {
  * @fqdn:		Guest FQDN
  * @ifi6:		Template interface for IPv6, -1: none, 0: IPv6 disabled
  * @ip6:		IPv6 configuration
+ * @addrs:		Unified address array for both IPv4 (mapped) and IPv6
+ * @addr_count:		Number of active entries in @addrs array
  * @pasta_ifn:		Name of namespace interface for pasta
  * @pasta_ifi:		Index of namespace interface for pasta
  * @pasta_conf_ns:	Configure namespace after creating it
@@ -260,6 +276,9 @@ struct ctx {
 	int ifi6;
 	struct ip6_ctx ip6;
 
+	struct guest_addr addrs[MAX_GUEST_ADDRS];
+	int addr_count;
+
 	char pasta_ifn[IF_NAMESIZE];
 	unsigned int pasta_ifi;
 	int pasta_conf_ns;
@@ -301,6 +320,53 @@ struct ctx {
 	bool migrate_exit;
 };
 
+/**
+ * inany_prefix_len() - Get address-family-appropriate prefix length
+ * @a:		Address entry
+ *
+ * Return: prefix length in native format (0-32 for IPv4, 0-128 for IPv6)
+ */
+static inline int inany_prefix_len(const struct guest_addr *a)
+{
+	if (inany_v4(&a->addr))
+		return a->prefix_len - 96;
+	return a->prefix_len;
+}
+
+/**
+ * _next_addr_idx() - Find next address index matching family filter
+ * @c:		Pointer to struct ctx
+ * @i:		Starting index
+ * @af:		Address family filter: AF_INET, AF_INET6, or 0 for all
+ *
+ * Return: next matching index, or addr_count if none found
+ */
+static inline int _next_addr_idx(const struct ctx *c, int i, sa_family_t af)
+{
+	for (; i < c->addr_count; i++) {
+		sa_family_t entry_af;
+
+		entry_af = inany_v4(&c->addrs[i].addr) ? AF_INET : AF_INET6;
+
+		if (af == AF_UNSPEC || af == entry_af)
+			return i;
+	}
+	return i;
+}
+
+/**
+ * for_each_addr() - Iterate over addresses in unified array
+ * @a:		Pointer variable for current entry (struct guest_addr *)
+ * @c:		Pointer to struct ctx
+ * @af:		Address family filter: AF_INET, AF_INET6, or 0 for all
+ *
+ * Note: @_i is the internal loop counter, uses _next_addr_idx() helper
+ */
+#define for_each_addr(a, c, af)						\
+	for (int _i = _next_addr_idx((c), 0, (af));			\
+	     _i < (c)->addr_count && ((a) = &(c)->addrs[_i], true);	\
+	     _i = _next_addr_idx((c), _i + 1, (af)))
+
 void proto_update_l2_buf(const unsigned char *eth_d);
 
 #endif /* PASST_H */
diff --git a/pasta.c b/pasta.c
index bab945f..e88a893 100644
--- a/pasta.c
+++ b/pasta.c
@@ -330,6 +330,7 @@ void pasta_ns_conf(struct ctx *c)
 
 	if (c->pasta_conf_ns) {
 		unsigned int flags = IFF_UP;
+		const struct guest_addr *a;
 
 		if (c->mtu)
 			nl_link_set_mtu(nl_sock_ns, c->pasta_ifi, c->mtu);
@@ -341,10 +342,12 @@ void pasta_ns_conf(struct ctx *c)
 
 		if (c->ifi4) {
 			if (c->ip4.no_copy_addrs) {
-				rc = nl_addr_set(nl_sock_ns, c->pasta_ifi,
-						 AF_INET,
-						 &c->ip4.addr,
-						 c->ip4.prefix_len);
+				a = fwd_get_addr(c, AF_INET, 0, 0);
+				if (a)
+					rc = nl_addr_set(nl_sock_ns,
+							 c->pasta_ifi, AF_INET,
+							 inany_v4(&a->addr),
+							 a->prefix_len - 96);
 			} else {
 				rc = nl_addr_dup(nl_sock, c->ifi4,
 						 nl_sock_ns, c->pasta_ifi,
@@ -397,11 +400,13 @@ ipv4_done:
 					  0, IFF_NOARP);
 
 			if (c->ip6.no_copy_addrs) {
-				if (!IN6_IS_ADDR_UNSPECIFIED(&c->ip6.addr)) {
+				a = fwd_get_addr(c, AF_INET6, 0, 0);
+				if (a)
 					rc = nl_addr_set(nl_sock_ns,
-							 c->pasta_ifi, AF_INET6,
-							 &c->ip6.addr, 64);
-				}
+							 c->pasta_ifi,
+							 AF_INET6,
+							 &a->addr.a6,
+							 a->prefix_len);
 			} else {
 				rc = nl_addr_dup(nl_sock, c->ifi6,
 						 nl_sock_ns, c->pasta_ifi,
diff --git a/tap.c b/tap.c
index eaa6111..78a494a 100644
--- a/tap.c
+++ b/tap.c
@@ -951,8 +951,11 @@ resume:
 				c->ip6.addr_seen = *saddr;
 			}
 
-			if (IN6_IS_ADDR_UNSPECIFIED(&c->ip6.addr))
-				c->ip6.addr = *saddr;
+			if (!fwd_get_addr(c, AF_INET6, 0, 0)) {
+				union inany_addr addr = { .a6 = *saddr };
+
+				fwd_set_addr(c, &addr, CONF_ADDR_LINKLOCAL, 64);
+			}
 		} else if (!IN6_IS_ADDR_UNSPECIFIED(saddr)){
 			c->ip6.addr_seen = *saddr;
 		}
-- 
2.52.0