Re: [PATCH v7 02/13] passt, pasta: Introduce unified multi-address data structures

[Stefano Brivio <sbrivio@redhat.com>]

On Sun, 12 Apr 2026 20:53:08 -0400
Jon Maloy <jmaloy@redhat.com> wrote:

> 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 a lot of 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
>   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.
> 
> v7: -Introduced CONF_ADDR_GENERATED flag
>     -Other fixes based on feedback from David and Stefano.
>     -I changed signature of inany_prefix_len(), but I did not change
>      its semantics, since the premise of David's comment is wrong: the
>      caller does *not* explicitly know he is dealing with an IPv4 address.
>      In fact, there are examples later in this series where it may be an
>      IPv6 address, and the caller just trusts he gets the return value in
>      the appropriate format.
>     -Introduced the inverse of inany_prefix_len(), called inany_prefix_len6()
>      which always returns the prefix in IPv6 or mapped IPv4 format.
>      The name of the function isn't great, but any alternative I came up
>      with became too long to be practical.
> ---
>  arp.c    |  12 ++++-
>  conf.c   | 143 ++++++++++++++++++++++++++++++-------------------------
>  dhcp.c   |  14 ++++--
>  dhcpv6.c |  15 ++++--
>  fwd.c    | 109 ++++++++++++++++++++++++++++++++++--------
>  fwd.h    |   4 ++
>  inany.h  |  41 ++++++++++++++++
>  ip.h     |   2 +
>  ndp.c    |  16 +++++--
>  passt.h  |  67 ++++++++++++++++++++++----
>  pasta.c  |  25 ++++++----
>  tap.c    |   7 ++-
>  12 files changed, 340 insertions(+), 115 deletions(-)
> 
> diff --git a/arp.c b/arp.c
> index bb042e9..a7fd82f 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;
> +
>  	if (ah->ar_hrd != htons(ARPHRD_ETHER)	||
>  	    ah->ar_pro != htons(ETH_P_IP)	||
>  	    ah->ar_hln != ETH_ALEN		||
> @@ -54,7 +56,8 @@ 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)))
> +	a = fwd_get_addr(c, AF_INET, 0, 0);

I guess it's not strictly needed right now to avoid breaking things,
but, eventually, if we support multiple assigned / configured /
observed addresses for the guest, we should make sure we don't resolve
any of them. That is, we should eventually pass am->tip to a lookup
function. It might be in scope for this series but not necessarily.

A further remark: while it's absolutely canonical and expected that "no
flags" is 0, fwd_*() functions change prototypes so frequently these
days that I would consider something perhaps unconventional but
probably helpful for readability: define CONF_ADDR_PICK_ANY as
UINT8_MAX (I'm not sure if there's a nicer macro denoting "all bits
set"), CONF_ADDR_EXCLUDE_NONE as 0, and then pass them here instead of
0, 0. Maybe it's ugly. I'm not sure.

> +	if (a && !memcmp(am->tip, inany_v4(&a->addr), sizeof(am->tip)))
>  		return true;
>  
>  	return false;
> @@ -123,12 +126,17 @@ int arp(const struct ctx *c, struct iov_tail *data)
>   */
>  void arp_send_init_req(const struct ctx *c)
>  {
> +	const struct guest_addr *a;
>  	struct {
>  		struct ethhdr eh;
>  		struct arphdr ah;
>  		struct arpmsg am;
>  	} __attribute__((__packed__)) req;
>  
> +	a = fwd_get_addr(c, AF_INET, 0, 0);

Same comment as above.

> +	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 +153,7 @@ 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 f13fef6..591f561 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);
> +		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_GENERATED | CONF_ADDR_LINKLOCAL,
> +		     IP4_LL_PREFIX_LEN);
>  }
>  
>  /**
>   * 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)
>  {
> +	struct ip6_ctx *ip6 = &c->ip6;
> +	const struct guest_addr *a;
> +	union inany_addr addr;
>  	int prefix_len = 0;
>  	int rc;
>  
> @@ -827,21 +826,28 @@ 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;
> +	a = fwd_get_addr(c, AF_INET6, 0, 0);
> +	if (!a) {
> +		if (IN6_IS_ADDR_UNSPECIFIED(&addr))
> +			return 0;
> +
> +		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 +855,13 @@ 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 +1143,7 @@ enum passt_modes conf_mode(int argc, char *argv[])
>  static void conf_print(const struct ctx *c)
>  {
>  	char buf[INANY_ADDRSTRLEN];
> +	const struct guest_addr *a;
>  	int i;
>  
>  	if (c->ifi4 > 0 || c->ifi6 > 0) {
> @@ -1181,16 +1188,18 @@ 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->addr,
> +							 a->prefix_len));
>  
>  			info("DHCP:");
>  			info("    assign: %s",
> -			     inet_ntop(AF_INET, &c->ip4.addr, buf, sizeof(buf)));
> +			     inany_ntop(&a->addr, buf, sizeof(buf)));
>  			info("    mask: %s",
> -			     inet_ntop(AF_INET, &mask,        buf, sizeof(buf)));
> +			     inet_ntop(AF_INET, &mask, buf, sizeof(buf)));
>  			info("    router: %s",
>  			     inet_ntop(AF_INET, &c->ip4.guest_gw,
>  				       buf, sizeof(buf)));
> @@ -1201,8 +1210,8 @@ static void conf_print(const struct ctx *c)
>  				break;
>  			if (!i)
>  				info("DNS:");
> -			inet_ntop(AF_INET, &c->ip4.dns[i], buf, sizeof(buf));
> -			info("    %s", buf);
> +			info("    %s", inet_ntop(AF_INET, &c->ip4.dns[i],
> +						 buf, sizeof(buf)));
>  		}
>  
>  		for (i = 0; *c->dns_search[i].n; i++) {
> @@ -1227,13 +1236,14 @@ static void conf_print(const struct ctx *c)
>  		else
>  			goto dns6;
>  
> -		info("    assign: %s",
> -		     inet_ntop(AF_INET6, &c->ip6.addr, buf, sizeof(buf)));
> +		a = fwd_get_addr(c, AF_INET6, 0, CONF_ADDR_LINKLOCAL);
> +		if (a)
> +			info("    assign: %s",
> +			     inany_ntop(&a->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)));
> +		     inet_ntop(AF_INET6, &c->ip6.our_tap_ll, buf, sizeof(buf)));
>  
>  dns6:
>  		for (i = 0; i < ARRAY_SIZE(c->ip6.dns); i++) {
> @@ -1241,8 +1251,10 @@ dns6:
>  			    break;
>  			if (!i)
>  				info("DNS:");
> -			inet_ntop(AF_INET6, &c->ip6.dns[i], buf, sizeof(buf));
> -			info("    %s", buf);
> +			info("    %s",
> +			     inet_ntop(AF_INET6, &c->ip6.dns[i],
> +				       buf, sizeof(buf)));
> +
>  		}
>  
>  		for (i = 0; *c->dns_search[i].n; i++) {
> @@ -1886,19 +1898,16 @@ 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': {
> +			struct guest_addr *a;
>  			int plen;
>  
>  			if (addr_has_prefix_len)
> @@ -1908,8 +1917,12 @@ void conf(struct ctx *c, int argc, char **argv)
>  			if (plen < 0)
>  				die("Invalid prefix length: %s", optarg);
>  
> -			prefix_len_from_opt = plen + 96;
> -			c->ip4.prefix_len = plen;
> +			prefix_len_from_opt = plen;
> +
> +			for_each_addr(a, c->addrs, c->addr_count, AF_INET) {
> +				a->prefix_len = inany_prefix_len(&a->addr, plen);
> +				break;
> +			}
>  			break;
>  		}
>  		case 'M':
> @@ -2103,9 +2116,9 @@ 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)",
> @@ -2128,7 +2141,7 @@ 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;
>  	}
> @@ -2136,7 +2149,7 @@ 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;
>  	}
> @@ -2201,7 +2214,7 @@ 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..f0fa212 100644
> --- a/dhcp.c
> +++ b/dhcp.c
> @@ -303,6 +303,7 @@ static void opt_set_dns_search(const struct ctx *c, size_t max_len)
>  int dhcp(const struct ctx *c, struct iov_tail *data)
>  {
>  	char macstr[ETH_ADDRSTRLEN];
> +	const struct guest_addr *a;
>  	size_t mlen, dlen, opt_len;
>  	struct in_addr mask, dst;
>  	struct ethhdr eh_storage;
> @@ -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 +346,10 @@ int dhcp(const struct ctx *c, struct iov_tail *data)
>  	    m->op != BOOTREQUEST)
>  		return -1;
>  
> +	a = fwd_get_addr(c, AF_INET, 0, 0);
> +	assert(a);
> +	addr = *inany_v4(&a->addr);
> +
>  	reply.op		= BOOTREPLY;
>  	reply.htype		= m->htype;
>  	reply.hlen		= m->hlen;
> @@ -352,7 +358,7 @@ 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;

This implies a strict preference ordering in fwd_get_addr(), because if
we store multiple addresses, we don't want to override an explicitly
configured address (-a) with anything else, for example.

At this point of this series we should still have a single address in
the array, but maybe it would be good to clarify this aspect of
fwd_get_addr() already at this point (and introduce an explicit
selection order)?

Yes, you add a flag for DHCP eligibility later in the series, but
that's not equivalent to a preference mechanism.

>  	reply.siaddr		= 0;
>  	reply.giaddr		= m->giaddr;
>  	memcpy(&reply.chaddr,	m->chaddr,	sizeof(reply.chaddr));
> @@ -404,7 +410,7 @@ 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->addr, a->prefix_len));
>  	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 +418,7 @@ 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 +477,7 @@ 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 2db0944..0a064a9 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;
> @@ -567,6 +567,7 @@ 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;
> @@ -574,6 +575,8 @@ 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;
> @@ -627,7 +630,7 @@ 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, saddr, data, &client_id_base,
>  						 ntohs(client_id->l), mh->xid);
> @@ -680,7 +683,8 @@ int dhcpv6(struct ctx *c, struct iov_tail *data,
>  	resp.hdr.xid = mh->xid;
>  
>  	tap_udp6_send(c, src, 547, saddr, 546, mh->xid, &resp, n);
> -	c->ip6.addr_seen = c->ip6.addr;
> +	if (a)
> +		c->ip6.addr_seen = a->addr.a6;
>  
>  	return 1;
>  }
> @@ -691,6 +695,7 @@ 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;
>  
> @@ -704,5 +709,7 @@ 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..14ce0a7 100644
> --- a/fwd.c
> +++ b/fwd.c
> @@ -249,6 +249,61 @@ 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 or IPv4 format
> + *
> + * 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_each_addr(a, c->addrs, c->addr_count, inany_af(addr)) {
> +		goto found;
> +	}

Nit: curly brackets not needed.

> +
> +	if (c->addr_count >= MAX_GUEST_ADDRS)
> +		return;
> +
> +	a = &c->addrs[c->addr_count++];
> +
> +found:
> +	a->addr = *addr;
> +	a->prefix_len = inany_prefix_len6(addr, 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)

I think AF_UNSPEC (that you seem to use later?) is more common to denote
"any". Not a strong preference, 0 might have some advantages as well.

> + * @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->addrs, c->addr_count, af) {
> +		if (incl && !(a->flags & incl))

Regardless of my CONF_ADDR_PICK_ANY suggestion above, it might be a bit
surprising that 0 matches all flags (but so does 0xff). If it needs to
be like that for whatever reason, I think that deserves a mention in
the comment to @incl ("0 means any").

> +			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 +996,10 @@ 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;
> +
>  	if (IN4_IS_ADDR_LOOPBACK(addr))
>  		return false;
>  
> @@ -957,7 +1014,8 @@ 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) ||
> +	a = fwd_get_addr(c, AF_INET, 0, 0);
> +	if ((a && IN4_ARE_ADDR_EQUAL(addr, inany_v4(&a->addr))) ||
>  	    IN4_ARE_ADDR_EQUAL(addr, &c->ip4.addr_seen))
>  		return false;
>  
> @@ -975,10 +1033,13 @@ 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;
> +
>  	if (IN6_IS_ADDR_LOOPBACK(addr))
>  		return false;
>  
> -	if (IN6_ARE_ADDR_EQUAL(addr, &c->ip6.addr))
> +	a = fwd_get_addr(c, AF_INET6, 0, 0);
> +	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
> @@ -1023,16 +1084,21 @@ 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)
>  {
> -	if (inany_equals4(addr, &c->ip4.map_host_loopback))
> +	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))
> +	} 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
> +	} 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 +1203,21 @@ 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/inany.h b/inany.h
> index 9891ed6..0450c45 100644
> --- a/inany.h
> +++ b/inany.h
> @@ -102,6 +102,16 @@ static inline struct in_addr *inany_v4(const union inany_addr *addr)
>  	return (struct in_addr *)&addr->v4mapped.a4;
>  }
>  
> +/** inany_af - Get address family of IPv[46] address
> + * @addr:	IPv4 or IPv6 address
> + *
> + * Return: AF_INET for IPv4, AF_INET6 for IPv6
> + */
> +static inline sa_family_t inany_af(const union inany_addr *addr)
> +{
> +	return inany_v4(addr) ? AF_INET : AF_INET6;
> +}
> +
>  /** inany_default_prefix_len() - Get default prefix length for address
>   * @addr:	IPv4 or iPv6 address
>   *
> @@ -115,6 +125,37 @@ static inline int inany_default_prefix_len(const union inany_addr *addr)
>  	return v4 ? ip4_class_prefix_len(v4) + 96 : 64;
>  }
>  
> +
> +/** inany_prefix_len() - Convert prefix length to native format
> + * @addr:	IPv4 or IPv6 address
> + * @prefix_len:	prefix length (any format, auto-detected)
> + *
> + * Return: prefix length in native format (0-32 for IPv4, 0-128 for IPv6)
> + */
> +static inline int inany_prefix_len(const union inany_addr *addr,
> +				   int prefix_len)
> +{
> +	if (inany_v4(addr) && prefix_len >= 96)
> +		return prefix_len - 96;
> +
> +	return prefix_len;
> +}
> +
> +/** inany_prefix_len6() - Convert prefix length to generic format
> + * @addr:	IPv4 or IPv6 address
> + * @prefix_len:	prefix length (any format, auto-detected)
> + *
> + * Return: prefix length in generic format (96-128 for IPv4, 0-128 for IPv6)
> + */
> +static inline int inany_prefix_len6(const union inany_addr *addr,
> +				    int prefix_len)
> +{
> +	if (inany_v4(addr) && prefix_len && prefix_len <= 32)
> +		return prefix_len + 96;
> +
> +	return prefix_len;
> +}
> +
>  /** inany_equals - Compare two IPv[46] addresses
>   * @a, @b:	IPv[46] addresses
>   *
> 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);

As David pointed out, this is unnecessarily fragile, but as I was
looking into what the behaviour should be, here, it just occurred to me
that RFC 4861 doesn't mandate the presence of any Prefix Option (3) in
a Router Advertisement message, and it looks like there is at least one
reported case:

  https://forum.mikrotik.com/t/how-to-send-router-advertisements-without-prefix/182496/5

of this kind of usage: advertise ourselves as router, but let the
address assignment work with DHCPv6 (or not even, just use link-local
address).

At the moment an early return looks sufficient, also because I'm not
sure if things would actually work if we don't advertise a prefix at
the moment, but that's something we should probably consider for the
future (or maybe even in this series).

> +
> +	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..f75656d 100644
> --- a/passt.h
> +++ b/passt.h
> @@ -64,11 +64,28 @@ enum passt_modes {
>  	MODE_VU,
>  };
>  
> +/* Maximum number of addresses in context address array */
> +#define MAX_GUEST_ADDRS		32
> +
> +/**
> + * 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;
> +#define CONF_ADDR_USER		BIT(0)		/* User set via -a */
> +#define CONF_ADDR_HOST		BIT(1)		/* From host interface */
> +#define CONF_ADDR_GENERATED	BIT(2)		/* Generated by PASST/PASTA */
> +#define CONF_ADDR_LINKLOCAL	BIT(3)		/* Link-local address */
> +};
> +
>  /**
>   * 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 +101,7 @@ 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 +121,6 @@ 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 +138,6 @@ 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 +192,8 @@ 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 +273,9 @@ 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 +317,41 @@ struct ctx {
>  	bool migrate_exit;
>  };
>  
> +/**
> + * next_addr_idx_() - Find next address index matching family filter
> + * @addrs:	Array of guest addresses
> + * @count:	Number of addresses in array
> + * @i:		Starting index
> + * @af:		Address family filter: AF_INET, AF_INET6, or 0 for all
> + *
> + * Return: next matching index, or count if none found
> + */
> +static inline int next_addr_idx_(const struct guest_addr *addrs, int count,
> +				 int i, sa_family_t af)
> +{
> +	for (; i < count; i++) {
> +		sa_family_t entry_af;
> +
> +		entry_af = inany_v4(&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 array
> + * @a:		Pointer variable for current entry (struct guest_addr *)
> + * @addrs:	Array of guest addresses (e.g., c->addrs)
> + * @count:	Number of addresses (e.g., c->addr_count)
> + * @af:		Address family filter: AF_INET, AF_INET6, or 0 for all
> + */
> +#define for_each_addr(a, addrs, count, af)				\
> +	for (int i_ = next_addr_idx_((addrs), (count), 0, (af));	\
> +	     i_ < (count) && ((a) = &(addrs)[i_], true);		\

Why do you need that ", true"? Isn't an extra () pair enough to silence
warnings about evaluating the assignment as a condition? I find it a
bit hard to read like that.

> +	     i_ = next_addr_idx_((addrs), (count), 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..c51e4cd 100644
> --- a/pasta.c
> +++ b/pasta.c
> @@ -330,6 +330,8 @@ void pasta_ns_conf(struct ctx *c)
>  
>  	if (c->pasta_conf_ns) {
>  		unsigned int flags = IFF_UP;
> +		const struct guest_addr *a;
> +		int plen;
>  
>  		if (c->mtu)
>  			nl_link_set_mtu(nl_sock_ns, c->pasta_ifi, c->mtu);
> @@ -341,10 +343,15 @@ 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) {
> +					plen = inany_prefix_len(&a->addr,
> +								a->prefix_len);
> +					rc = nl_addr_set(nl_sock_ns,
> +							 c->pasta_ifi, AF_INET,
> +							 inany_v4(&a->addr),
> +							 plen);
> +				}
>  			} else {
>  				rc = nl_addr_dup(nl_sock, c->ifi4,
>  						 nl_sock_ns, c->pasta_ifi,
> @@ -397,11 +404,13 @@ 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 59c45a3..eb93f74 100644
> --- a/tap.c
> +++ b/tap.c
> @@ -936,8 +936,11 @@ 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;
>  		}

-- 
Stefano