[v4] alfred: IPv4 multicast distribution support.

Message ID 1484884864-7315-1-git-send-email-jhaws@sdl.usu.edu
State Superseded, archived
Delegated to: Simon Wunderlich
Headers

Commit Message

Jonathan Haws Jan. 20, 2017, 4:01 a.m. UTC
  Enabled via -4 expert option where multicast group address is specified.
This option will disable IPv6 communication and is intended for use in
networks which do not support IPv6 addressing.

When this option is enabled, all IPv6 communication is disabled. Combining
IPv4 and IPv6 alfred nodes is unsupported.

Hardware address handling done by submitting queries to the local ARP
cache rather than forcing an ARP request.

Signed-off-by: Jonathan Haws <jhaws@sdl.usu.edu>
---
 README         |   4 +-
 alfred.h       |  23 ++++++---
 batadv_query.c |  50 +++++++++++-------
 batadv_query.h |   6 ++-
 client.c       |   2 +-
 main.c         |  14 ++++--
 man/alfred.8   |   5 ++
 netsock.c      | 156 +++++++++++++++++++++++++++++++++++++++++++++++++++++----
 recv.c         |  63 ++++++++++++++++-------
 send.c         |  48 +++++++++++-------
 server.c       |   8 +--
 unix_sock.c    |   2 +-
 util.c         |  30 +++++++++++
 13 files changed, 328 insertions(+), 83 deletions(-)
  

Comments

Jonathan Haws Jan. 20, 2017, 4:04 a.m. UTC | #1
Fixes per Sven's review (good catch on the MAC! I just missed the
return check...).

Thanks!

-- 
Jonathan R. Haws
Embedded Engineer
Space Dynamics Laboratory
jhaws@sdl.usu.edu
  
Simon Wunderlich Jan. 24, 2017, 11:44 a.m. UTC | #2
On Thursday, January 19, 2017 9:01:04 PM CET Jonathan Haws wrote:
> Enabled via -4 expert option where multicast group address is specified.
> This option will disable IPv6 communication and is intended for use in
> networks which do not support IPv6 addressing.
> 
> When this option is enabled, all IPv6 communication is disabled. Combining
> IPv4 and IPv6 alfred nodes is unsupported.
> 
> Hardware address handling done by submitting queries to the local ARP
> cache rather than forcing an ARP request.

Thanks Jonathan for your patch! I've just looked through the patch and 
discussed the matter with Sven yesterday. We are both not too big fans of 
supporting IPv4, but since it helps your scenario and you supplied a well 
written patch which properly abstracts the address mode and has separate IPv4/
IPv6 functions, I think we can adopt it.

Just two general questions/remarks:

 * I do not want to give support for IPv4-related questions of users. Would 
you be available to maintain and answer questions regarding the IPv4 support?
 * Do you plan to provide OpenWRT support as well? (This is more out of 
curiosity)

Thank you,
     Simon
  
Sven Eckelmann Jan. 24, 2017, 1:05 p.m. UTC | #3
On Donnerstag, 19. Januar 2017 21:01:04 CET Jonathan Haws wrote:
> @@ -273,10 +276,15 @@ static struct globals *alfred_init(int argc, char *argv[])
>  			return NULL;
>  		case 'p':
>  			sync_period = strtod(optarg, NULL);
> -			globals->sync_period.tv_sec = (int) sync_period;
> -			globals->sync_period.tv_nsec = (double) (sync_period - (int) sync_period) * 1e9;
> +			globals->sync_period.tv_sec = (int)sync_period;
> +			globals->sync_period.tv_nsec = (double)(sync_period - (int)sync_period) * 1e9;
>  			printf(" ** Setting sync interval to: %.9f seconds (%ld.%09ld)\n", sync_period, globals->sync_period.tv_sec, globals->sync_period.tv_nsec);
>  			break;

This doesn't seem to belong in this patch.

> +static int netsock_open4(struct interface *interface)
> +{
> +	int sock;
> +	int sock_mc;
> +	struct sockaddr_in sin4, sin_mc;
> +	struct ip_mreq mreq;
> +	struct ifreq ifr;
> +	int ret;
> +
> +	interface->netsock = -1;
> +	interface->netsock_mcast = -1;
> +
> +	sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
> +	if (sock  < 0) {
> +		perror("ipv4: can't open socket");
> +		return -1;
> +	}
> +
> +	sock_mc = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
> +	if (sock_mc  < 0) {
> +		perror("ipv4: can't open mc socket");
> +		return -1;
> +	}

You don't sock in this situation (on errors)?

> +	memset(&ifr, 0, sizeof(ifr));
> +	strncpy(ifr.ifr_name, interface->interface, IFNAMSIZ);
> +	ifr.ifr_name[IFNAMSIZ - 1] = '\0';
> +	if (ioctl(sock_mc, SIOCGIFHWADDR, &ifr) == -1) {
> +		perror("ipv4: can't get MAC address");
> +		goto err4;

And now (see err4) you only close sock_mc? This applies to basically the rest
of the function. So I will skip it and not mention every place which looks
suspicious.

[....]
> +
> +	interface->netsock = sock;
> +	interface->netsock_mcast = sock_mc;
> +
> +	return 0;
> +err4:
> +	close(sock_mc);
> +	return -1;
> +}
> +

You only close sock_mc on errors but not sock?

And please chose something better [1] than err4.

Kind regards,
	Sven

[1] https://static.lwn.net/kerneldoc/process/coding-style.html#centralized-exiting-of-functions
  
Jonathan Haws Jan. 24, 2017, 3:35 p.m. UTC | #4
> > @@ -273,10 +276,15 @@ static struct globals *alfred_init(int argc,

> > char *argv[])

> >  			return NULL;

> >  		case 'p':

> >  			sync_period = strtod(optarg, NULL);

> > -			globals->sync_period.tv_sec = (int)

> > sync_period;

> > -			globals->sync_period.tv_nsec = (double)

> > (sync_period - (int) sync_period) * 1e9;

> > +			globals->sync_period.tv_sec =

> > (int)sync_period;

> > +			globals->sync_period.tv_nsec =

> > (double)(sync_period - (int)sync_period) * 1e9;

> >  			printf(" ** Setting sync interval to: %.9f

> > seconds (%ld.%09ld)\n", sync_period, globals->sync_period.tv_sec,

> > globals->sync_period.tv_nsec);

> >  			break;

> This doesn't seem to belong in this patch.


Yes, that is correct.  I must have fixed that formatting when I was
going through everything else.  Would you like me to take it out of
this patch?

> > +static int netsock_open4(struct interface *interface)

> > +{

> > +	int sock;

> > +	int sock_mc;

> > +	struct sockaddr_in sin4, sin_mc;

> > +	struct ip_mreq mreq;

> > +	struct ifreq ifr;

> > +	int ret;

> > +

> > +	interface->netsock = -1;

> > +	interface->netsock_mcast = -1;

> > +

> > +	sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);

> > +	if (sock  < 0) {

> > +		perror("ipv4: can't open socket");

> > +		return -1;

> > +	}

> > +

> > +	sock_mc = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);

> > +	if (sock_mc  < 0) {

> > +		perror("ipv4: can't open mc socket");

> > +		return -1;

> > +	}

> You don't sock in this situation (on errors)?


Huh, I had saw that as well and thought I had it fixed.  I'll make sure
I didn't just miss a commit.

> > 

> > +	memset(&ifr, 0, sizeof(ifr));

> > +	strncpy(ifr.ifr_name, interface->interface, IFNAMSIZ);

> > +	ifr.ifr_name[IFNAMSIZ - 1] = '\0';

> > +	if (ioctl(sock_mc, SIOCGIFHWADDR, &ifr) == -1) {

> > +		perror("ipv4: can't get MAC address");

> > +		goto err4;

> And now (see err4) you only close sock_mc? This applies to basically

> the rest

> of the function. So I will skip it and not mention every place which

> looks

> suspicious.


Same comment as above.

> > 

> > +

> > +	interface->netsock = sock;

> > +	interface->netsock_mcast = sock_mc;

> > +

> > +	return 0;

> > +err4:

> > +	close(sock_mc);

> > +	return -1;

> > +}

> > +

> You only close sock_mc on errors but not sock?

> 

> And please chose something better [1] than err4.


I see why you'd want me to rename the goto - however it was chosen to
differentiate between the err goto in netsock_open.  I called it err4
since it is for the netsock_open4() function dealing with IPv4.  Would
err_ipv4 be better?
  
Jonathan Haws Jan. 24, 2017, 3:45 p.m. UTC | #5
> 

> > 

> > Enabled via -4 expert option where multicast group address is

> > specified.

> > This option will disable IPv6 communication and is intended for use

> > in

> > networks which do not support IPv6 addressing.

> > 

> > When this option is enabled, all IPv6 communication is disabled.

> > Combining

> > IPv4 and IPv6 alfred nodes is unsupported.

> > 

> > Hardware address handling done by submitting queries to the local

> > ARP

> > cache rather than forcing an ARP request.

> Thanks Jonathan for your patch! I've just looked through the patch

> and 

> discussed the matter with Sven yesterday. We are both not too big

> fans of 

> supporting IPv4, but since it helps your scenario and you supplied a

> well 

> written patch which properly abstracts the address mode and has

> separate IPv4/

> IPv6 functions, I think we can adopt it.

> 

> Just two general questions/remarks:

> 

>  * I do not want to give support for IPv4-related questions of users.

> Would 

> you be available to maintain and answer questions regarding the IPv4

> support?

I'd be happy to answer questions, but it would be best if those
questions are directed to the list and my address is in the CC field.
 That way I'll definitely see it and can answer.  If it just goes to
the list in general I'll very likely miss the message.  Is that
someting that could be added to the Wiki?


> 

>  * Do you plan to provide OpenWRT support as well? (This is more out

> of 

> curiosity)

I wasn't planning on OpenWRT support. What would be entailed? When I
hear OpenWRT, I think of the firmware I can load onto my old Linksys
WRT54G AP.  Would it simply be testing these changes on that device?

-- 
Jonathan R. Haws
Embedded Engineer
Space Dynamics Laboratory
jhaws@sdl.usu.edu
(435) 713-3489
  
Simon Wunderlich Jan. 24, 2017, 4:05 p.m. UTC | #6
Hey Jonathan,

On Tuesday, January 24, 2017 3:45:31 PM CET Jonathan Haws wrote:
> > 
> > 
> > > 
> > > Enabled via -4 expert option where multicast group address is
> > > specified.
> > > This option will disable IPv6 communication and is intended for use
> > > in
> > > networks which do not support IPv6 addressing.
> > > 
> > > When this option is enabled, all IPv6 communication is disabled.
> > > Combining
> > > IPv4 and IPv6 alfred nodes is unsupported.
> > > 
> > > Hardware address handling done by submitting queries to the local
> > > ARP
> > > cache rather than forcing an ARP request.
> > 
> > Thanks Jonathan for your patch! I've just looked through the patch
> > and 
> > discussed the matter with Sven yesterday. We are both not too big
> > fans of 
> > supporting IPv4, but since it helps your scenario and you supplied a
> > well 
> > written patch which properly abstracts the address mode and has
> > separate IPv4/
> > IPv6 functions, I think we can adopt it.
> > 
> > Just two general questions/remarks:
> > 
> >  * I do not want to give support for IPv4-related questions of users.
> > Would 
> > you be available to maintain and answer questions regarding the IPv4
> > support?
> 
> I'd be happy to answer questions, but it would be best if those
> questions are directed to the list and my address is in the CC field.
>  That way I'll definitely see it and can answer.  If it just goes to
> the list in general I'll very likely miss the message.  Is that
> someting that could be added to the Wiki?

Hmm, you can add anything you want in the wiki, but it's unlikely someone will 
read it before asking here on the mailing list, at least to my personal 
experience. ;)

But if you commit to look into these issues, just try to catch the mails sent 
here to this mailing list - if you don't i'll try to forward them to you. :)

> > 
> >  * Do you plan to provide OpenWRT support as well? (This is more out
> > of 
> > curiosity)
> 
> I wasn't planning on OpenWRT support. What would be entailed? When I
> hear OpenWRT, I think of the firmware I can load onto my old Linksys
> WRT54G AP.  Would it simply be testing these changes on that device?

Basically we already have an OpenWRT/LEDE integration [1] which provides 
configuration options in a config file, which are parsed and applied etc.

Not sure if the ancient WRT54G is still even properly supported, but there are 
dozens of cheap and more moderns APs you can use it. But if you are not 
familiar with OpenWRT, don't worry, someone else can provide the integration 
if they need it. :)

Cheers,
     Simon

[1] https://github.com/openwrt-routing/packages/tree/master/alfred
  
Jonathan Haws Jan. 24, 2017, 4:07 p.m. UTC | #7
> > >  * I do not want to give support for IPv4-related questions of

> > > users.

> > > Would 

> > > you be available to maintain and answer questions regarding the

> > > IPv4

> > > support?

> > I'd be happy to answer questions, but it would be best if those

> > questions are directed to the list and my address is in the CC

> > field.

> >  That way I'll definitely see it and can answer.  If it just goes

> > to

> > the list in general I'll very likely miss the message.  Is that

> > someting that could be added to the Wiki?

> Hmm, you can add anything you want in the wiki, but it's unlikely

> someone will 

> read it before asking here on the mailing list, at least to my

> personal 

> experience. ;)

> 

> But if you commit to look into these issues, just try to catch the

> mails sent 

> here to this mailing list - if you don't i'll try to forward them to

> you. :)


I'll do my best to keep an eye on things.  If you see something and I
don't respond, I'd appreciate the forward.

> > 

> > > 

> > > 

> > >  * Do you plan to provide OpenWRT support as well? (This is more

> > > out

> > > of 

> > > curiosity)

> > I wasn't planning on OpenWRT support. What would be entailed? When

> > I

> > hear OpenWRT, I think of the firmware I can load onto my old

> > Linksys

> > WRT54G AP.  Would it simply be testing these changes on that

> > device?

> Basically we already have an OpenWRT/LEDE integration [1] which

> provides 

> configuration options in a config file, which are parsed and applied

> etc.

> 

> Not sure if the ancient WRT54G is still even properly supported, but

> there are 

> dozens of cheap and more moderns APs you can use it. But if you are

> not 

> familiar with OpenWRT, don't worry, someone else can provide the

> integration 

> if they need it. :)


I think that sounds great.  Thanks!
  
Simon Wunderlich Jan. 24, 2017, 4:09 p.m. UTC | #8
On Tuesday, January 24, 2017 3:35:33 PM CET Jonathan Haws wrote:
> > > @@ -273,10 +276,15 @@ static struct globals *alfred_init(int argc,
> > > char *argv[])
> > >  			return NULL;
> > >  		case 'p':
> > >  			sync_period = strtod(optarg, NULL);
> > > -			globals->sync_period.tv_sec = (int)
> > > sync_period;
> > > -			globals->sync_period.tv_nsec = (double)
> > > (sync_period - (int) sync_period) * 1e9;
> > > +			globals->sync_period.tv_sec =
> > > (int)sync_period;
> > > +			globals->sync_period.tv_nsec =
> > > (double)(sync_period - (int)sync_period) * 1e9;
> > >  			printf(" ** Setting sync interval to: %.9f
> > > seconds (%ld.%09ld)\n", sync_period, globals->sync_period.tv_sec,
> > > globals->sync_period.tv_nsec);
> > >  			break;
> > 
> > This doesn't seem to belong in this patch.
> 
> 
> Yes, that is correct.  I must have fixed that formatting when I was
> going through everything else.  Would you like me to take it out of
> this patch?

Yes, format fixes should go into format fix patches preferably, not into 
patches adding functions. :)

>[...]
> > > 
> > > +
> > > +	interface->netsock = sock;
> > > +	interface->netsock_mcast = sock_mc;
> > > +
> > > +	return 0;
> > > +err4:
> > > +	close(sock_mc);
> > > +	return -1;
> > > +}
> > > +
> > 
> > You only close sock_mc on errors but not sock?
> > 
> > And please chose something better [1] than err4.
> 
> 
> I see why you'd want me to rename the goto - however it was chosen to
> differentiate between the err goto in netsock_open.  I called it err4
> since it is for the netsock_open4() function dealing with IPv4.  Would
> err_ipv4 be better?

Why not just using err? Since its a different function, I don't see why not 
re-using the label. Actually I would prefer that ...

Cheers,
     Simon
  
Sven Eckelmann Jan. 24, 2017, 4:19 p.m. UTC | #9
On Dienstag, 24. Januar 2017 15:35:33 CET Jonathan Haws wrote:
[...]
> > This doesn't seem to belong in this patch.
> 
> Yes, that is correct.  I must have fixed that formatting when I was
> going through everything else.  Would you like me to take it out of
> this patch?

Yes

[...]
> > > 
> > > +
> > > +	interface->netsock = sock;
> > > +	interface->netsock_mcast = sock_mc;
> > > +
> > > +	return 0;
> > > +err4:
> > > +	close(sock_mc);
> > > +	return -1;
> > > +}
> > > +
> > You only close sock_mc on errors but not sock?
> > 
> > And please chose something better [1] than err4.
> 
> I see why you'd want me to rename the goto - however it was chosen to
> differentiate between the err goto in netsock_open.  I called it err4
> since it is for the netsock_open4() function dealing with IPv4.  Would
> err_ipv4 be better?

How about "err_close_sock" and "err_close_sockmc" or something like that?
You will need two different ones and these describe what will be done
on errors.

Kind regards,
	Sven
  

Patch

diff --git a/README b/README
index bc1c3bc..28f3dc9 100644
--- a/README
+++ b/README
@@ -20,7 +20,9 @@  programs to communicate with alfred (done via unix sockets). alfred then takes
 care of distributing the local information to other alfred servers on other
 nodes. This is done via IPv6 link-local multicast, and does not require any
 configuration. A user can request data from alfred, and will receive the
-information available from all alfred servers in the network.
+information available from all alfred servers in the network. Alternatively,
+alfred can be configured to distribute the local information via IPv4 multicast.
+This is configured by setting the IPv4 multicast group address in the -4 option.
 
 Compilation
 -----------
diff --git a/alfred.h b/alfred.h
index 2e8db1e..6bdaac7 100644
--- a/alfred.h
+++ b/alfred.h
@@ -48,6 +48,11 @@  enum data_source {
 	SOURCE_SYNCED = 2,
 };
 
+typedef union {
+	struct in_addr ipv4;
+	struct in6_addr ipv6;
+} alfred_addr;
+
 struct dataset {
 	struct alfred_data data;
 	unsigned char *buf;
@@ -80,7 +85,7 @@  struct transaction_head {
 
 struct server {
 	struct ether_addr hwaddr;
-	struct in6_addr address;
+	alfred_addr address;
 	struct timespec last_seen;
 	uint8_t tq;
 };
@@ -100,11 +105,12 @@  enum clientmode {
 
 struct interface {
 	struct ether_addr hwaddr;
-	struct in6_addr address;
+	alfred_addr address;
 	uint32_t scope_id;
 	char *interface;
 	int netsock;
 	int netsock_mcast;
+	int netsock_arp;
 
 	struct hashtable_t *server_hash;
 
@@ -122,6 +128,7 @@  struct globals {
 	int clientmode_arg;
 	int clientmode_version;
 	int verbose;
+	int ipv4mode;
 
 	int unix_sock;
 	const char *unix_path;
@@ -142,7 +149,7 @@  struct globals {
 
 #define MAX_PAYLOAD ((1 << 16) - 1 - sizeof(struct udphdr))
 
-extern const struct in6_addr in6addr_localmcast;
+extern alfred_addr alfred_mcast;
 
 /* server.c */
 int alfred_server(struct globals *globals);
@@ -169,13 +176,13 @@  static inline bool transaction_finished(struct transaction_head *head)
 
 /* send.c */
 int push_data(struct globals *globals, struct interface *interface,
-	      struct in6_addr *destination, enum data_source max_source_level,
+	      alfred_addr *destination, enum data_source max_source_level,
 	      int type_filter, uint16_t tx_id);
 int announce_master(struct globals *globals);
 int push_local_data(struct globals *globals);
 int sync_data(struct globals *globals);
-ssize_t send_alfred_packet(struct interface *interface,
-			   const struct in6_addr *dest, void *buf, int length);
+ssize_t send_alfred_packet(struct globals *globals, struct interface *interface,
+			   const alfred_addr *dest, void *buf, int length);
 /* unix_sock.c */
 int unix_sock_read(struct globals *globals);
 int unix_sock_open_daemon(struct globals *globals);
@@ -195,10 +202,12 @@  int netsock_prepare_select(struct globals *globals, fd_set *fds, int maxsock);
 void netsock_check_error(struct globals *globals, fd_set *errfds);
 int netsock_receive_packet(struct globals *globals, fd_set *fds);
 int netsock_own_address(const struct globals *globals,
-			const struct in6_addr *address);
+			const alfred_addr *address);
 /* util.c */
 int time_diff(struct timespec *tv1, struct timespec *tv2,
 	      struct timespec *tvdiff);
 void time_random_seed(void);
 uint16_t get_random_id(void);
 bool is_valid_ether_addr(uint8_t *addr);
+int ipv4_arp_request(struct interface *interface, const alfred_addr *addr,
+		     struct ether_addr *mac);
diff --git a/batadv_query.c b/batadv_query.c
index ac45b9b..6ec086b 100644
--- a/batadv_query.c
+++ b/batadv_query.c
@@ -80,22 +80,22 @@  out:
 	return ret;
 }
 
-int mac_to_ipv6(const struct ether_addr *mac, struct in6_addr *addr)
+int mac_to_ipv6(const struct ether_addr *mac, alfred_addr *addr)
 {
 	memset(addr, 0, sizeof(*addr));
-	addr->s6_addr[0] = 0xfe;
-	addr->s6_addr[1] = 0x80;
+	addr->ipv6.s6_addr[0] = 0xfe;
+	addr->ipv6.s6_addr[1] = 0x80;
 
-	addr->s6_addr[8] = mac->ether_addr_octet[0] ^ 0x02;
-	addr->s6_addr[9] = mac->ether_addr_octet[1];
-	addr->s6_addr[10] = mac->ether_addr_octet[2];
+	addr->ipv6.s6_addr[8] = mac->ether_addr_octet[0] ^ 0x02;
+	addr->ipv6.s6_addr[9] = mac->ether_addr_octet[1];
+	addr->ipv6.s6_addr[10] = mac->ether_addr_octet[2];
 
-	addr->s6_addr[11] = 0xff;
-	addr->s6_addr[12] = 0xfe;
+	addr->ipv6.s6_addr[11] = 0xff;
+	addr->ipv6.s6_addr[12] = 0xfe;
 
-	addr->s6_addr[13] = mac->ether_addr_octet[3];
-	addr->s6_addr[14] = mac->ether_addr_octet[4];
-	addr->s6_addr[15] = mac->ether_addr_octet[5];
+	addr->ipv6.s6_addr[13] = mac->ether_addr_octet[3];
+	addr->ipv6.s6_addr[14] = mac->ether_addr_octet[4];
+	addr->ipv6.s6_addr[15] = mac->ether_addr_octet[5];
 
 	return 0;
 }
@@ -118,17 +118,29 @@  int is_ipv6_eui64(const struct in6_addr *addr)
 	return 1;
 }
 
-int ipv6_to_mac(const struct in6_addr *addr, struct ether_addr *mac)
+int ipv6_to_mac(const alfred_addr *addr, struct ether_addr *mac)
 {
-	if (!is_ipv6_eui64(addr))
+	if (!is_ipv6_eui64(&addr->ipv6))
 		return -EINVAL;
 
-	mac->ether_addr_octet[0] = addr->s6_addr[8] ^ 0x02;
-	mac->ether_addr_octet[1] = addr->s6_addr[9];
-	mac->ether_addr_octet[2] = addr->s6_addr[10];
-	mac->ether_addr_octet[3] = addr->s6_addr[13];
-	mac->ether_addr_octet[4] = addr->s6_addr[14];
-	mac->ether_addr_octet[5] = addr->s6_addr[15];
+	mac->ether_addr_octet[0] = addr->ipv6.s6_addr[8] ^ 0x02;
+	mac->ether_addr_octet[1] = addr->ipv6.s6_addr[9];
+	mac->ether_addr_octet[2] = addr->ipv6.s6_addr[10];
+	mac->ether_addr_octet[3] = addr->ipv6.s6_addr[13];
+	mac->ether_addr_octet[4] = addr->ipv6.s6_addr[14];
+	mac->ether_addr_octet[5] = addr->ipv6.s6_addr[15];
+
+	if (!is_valid_ether_addr(mac->ether_addr_octet))
+		return -EINVAL;
+
+	return 0;
+}
+
+int ipv4_to_mac(struct interface *interface,
+		const alfred_addr *addr, struct ether_addr *mac)
+{
+	if (ipv4_arp_request(interface, addr, mac) < 0)
+		return -EINVAL;
 
 	if (!is_valid_ether_addr(mac->ether_addr_octet))
 		return -EINVAL;
diff --git a/batadv_query.h b/batadv_query.h
index 0df8a35..9aa4f0e 100644
--- a/batadv_query.h
+++ b/batadv_query.h
@@ -28,8 +28,10 @@  struct ether_addr *translate_mac(const char *mesh_iface,
 				 const struct ether_addr *mac);
 uint8_t get_tq(const char *mesh_iface, struct ether_addr *mac);
 int batadv_interface_check(const char *mesh_iface);
-int mac_to_ipv6(const struct ether_addr *mac, struct in6_addr *addr);
-int ipv6_to_mac(const struct in6_addr *addr, struct ether_addr *mac);
+int mac_to_ipv6(const struct ether_addr *mac, alfred_addr *addr);
+int ipv6_to_mac(const alfred_addr *addr, struct ether_addr *mac);
+int ipv4_to_mac(struct interface *interface,
+		const alfred_addr *addr, struct ether_addr *mac);
 int is_ipv6_eui64(const struct in6_addr *addr);
 
 #endif
diff --git a/client.c b/client.c
index 357fdb9..4102046 100644
--- a/client.c
+++ b/client.c
@@ -239,7 +239,7 @@  static int check_interface(const char *iface)
 		return -1;
 	}
 
-	sock = socket(PF_INET6, SOCK_DGRAM, 0);
+	sock = socket(PF_INET, SOCK_DGRAM, 0);
 	if (sock < 0) {
 		perror("can't open socket");
 		return -1;
diff --git a/main.c b/main.c
index 0d30ea4..446eecf 100644
--- a/main.c
+++ b/main.c
@@ -19,6 +19,7 @@ 
  *
  */
 
+#include <arpa/inet.h>
 #include <getopt.h>
 #include <signal.h>
 #include <stdio.h>
@@ -61,6 +62,7 @@  static void alfred_usage(void)
 	printf("                                      other masters\n");
 	printf("  -p, --sync-period [period]          set synchronization period, in seconds\n");
 	printf("                                      fractional seconds are supported (i.e. 0.2 = 5 Hz)\n");
+	printf("  -4 [group-address]                  specify IPv4 multicast address and operate in IPv4 mode");
 	printf("\n");
 	printf("  -u, --unix-path [path]              path to unix socket used for client-server\n");
 	printf("                                      communication (default: \""ALFRED_SOCK_PATH_DEFAULT"\")\n");
@@ -196,6 +198,7 @@  static struct globals *alfred_init(int argc, char *argv[])
 	globals->mesh_iface = "bat0";
 	globals->unix_path = ALFRED_SOCK_PATH_DEFAULT;
 	globals->verbose = 0;
+	globals->ipv4mode = 0;
 	globals->update_command = NULL;
 	globals->sync_period.tv_sec = ALFRED_INTERVAL;
 	globals->sync_period.tv_nsec = 0;
@@ -204,7 +207,7 @@  static struct globals *alfred_init(int argc, char *argv[])
 
 	time_random_seed();
 
-	while ((opt = getopt_long(argc, argv, "ms:r:hi:b:vV:M:I:u:dc:p:", long_options,
+	while ((opt = getopt_long(argc, argv, "ms:r:hi:b:vV:M:I:u:dc:p:4:", long_options,
 				  &opt_ind)) != -1) {
 		switch (opt) {
 		case 'r':
@@ -273,10 +276,15 @@  static struct globals *alfred_init(int argc, char *argv[])
 			return NULL;
 		case 'p':
 			sync_period = strtod(optarg, NULL);
-			globals->sync_period.tv_sec = (int) sync_period;
-			globals->sync_period.tv_nsec = (double) (sync_period - (int) sync_period) * 1e9;
+			globals->sync_period.tv_sec = (int)sync_period;
+			globals->sync_period.tv_nsec = (double)(sync_period - (int)sync_period) * 1e9;
 			printf(" ** Setting sync interval to: %.9f seconds (%ld.%09ld)\n", sync_period, globals->sync_period.tv_sec, globals->sync_period.tv_nsec);
 			break;
+		case '4':
+			globals->ipv4mode = 1;
+			inet_pton(AF_INET, optarg, &alfred_mcast.ipv4);
+			printf(" ** IPv4 Multicast Mode: %x\n", alfred_mcast.ipv4.s_addr);
+			break;
 		case 'h':
 		default:
 			alfred_usage();
diff --git a/man/alfred.8 b/man/alfred.8
index 5936e64..a2c3d4c 100644
--- a/man/alfred.8
+++ b/man/alfred.8
@@ -123,6 +123,11 @@  as arguments.
 Specify alfred synchronization period, in seconds. If not specified, the default
 ALFRED_INTERVAL setting of 10 seconds will be used. Fractional seconds are
 supported.
+.TP
+\fB\-4 \fIgroup-address\fP \fP
+Specify the IPv4 multicast group address and enable IPv4 data-sharing (disabling
+IPv6 communication). This option is required on systems that do not support IPv6
+addressing.
 .
 .SH EXAMPLES
 Start an alfred server listening on bridge br0 (assuming that this bridge
diff --git a/netsock.c b/netsock.c
index 86db8a6..3ddde69 100644
--- a/netsock.c
+++ b/netsock.c
@@ -43,10 +43,12 @@ 
 #include "list.h"
 #include "hash.h"
 
-const struct in6_addr in6addr_localmcast = {{{ 0xff, 0x02, 0x00, 0x00,
-					       0x00, 0x00, 0x00, 0x00,
-					       0x00, 0x00, 0x00, 0x00,
-					       0x00, 0x00, 0x00, 0x01 } } };
+alfred_addr alfred_mcast = {
+		.ipv6 = {{{ 0xff, 0x02, 0x00, 0x00,
+			    0x00, 0x00, 0x00, 0x00,
+			    0x00, 0x00, 0x00, 0x00,
+			    0x00, 0x00, 0x00, 0x01 } } }
+};
 
 static int server_compare(void *d1, void *d2)
 {
@@ -262,7 +264,7 @@  static int netsock_open(struct interface *interface)
 	memset(&sin6_mc, 0, sizeof(sin6_mc));
 	sin6_mc.sin6_port = htons(ALFRED_PORT);
 	sin6_mc.sin6_family = AF_INET6;
-	memcpy(&sin6_mc.sin6_addr, &in6addr_localmcast,
+	memcpy(&sin6_mc.sin6_addr, &alfred_mcast,
 	       sizeof(sin6_mc.sin6_addr));
 	sin6_mc.sin6_scope_id = interface->scope_id;
 
@@ -291,7 +293,7 @@  static int netsock_open(struct interface *interface)
 		goto err;
 	}
 
-	memcpy(&mreq.ipv6mr_multiaddr, &in6addr_localmcast,
+	memcpy(&mreq.ipv6mr_multiaddr, &alfred_mcast,
 	       sizeof(mreq.ipv6mr_multiaddr));
 	mreq.ipv6mr_interface = interface->scope_id;
 
@@ -335,6 +337,132 @@  err:
 	return -1;
 }
 
+static int netsock_open4(struct interface *interface)
+{
+	int sock;
+	int sock_mc;
+	struct sockaddr_in sin4, sin_mc;
+	struct ip_mreq mreq;
+	struct ifreq ifr;
+	int ret;
+
+	interface->netsock = -1;
+	interface->netsock_mcast = -1;
+
+	sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
+	if (sock  < 0) {
+		perror("ipv4: can't open socket");
+		return -1;
+	}
+
+	sock_mc = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
+	if (sock_mc  < 0) {
+		perror("ipv4: can't open mc socket");
+		return -1;
+	}
+
+	memset(&ifr, 0, sizeof(ifr));
+	strncpy(ifr.ifr_name, interface->interface, IFNAMSIZ);
+	ifr.ifr_name[IFNAMSIZ - 1] = '\0';
+	if (ioctl(sock_mc, SIOCGIFHWADDR, &ifr) == -1) {
+		perror("ipv4: can't get MAC address");
+		goto err4;
+	}
+	memcpy(&interface->hwaddr, &ifr.ifr_hwaddr.sa_data, 6);
+
+	memset(&sin4, 0, sizeof(sin4));
+	sin4.sin_port = htons(ALFRED_PORT);
+	sin4.sin_family = AF_INET;
+	sin4.sin_addr.s_addr = INADDR_ANY;
+
+	memset(&sin_mc, 0, sizeof(sin_mc));
+	sin_mc.sin_port = htons(ALFRED_PORT);
+	sin_mc.sin_family = AF_INET;
+	memcpy(&sin_mc.sin_addr, &alfred_mcast, sizeof(sin_mc.sin_addr));
+
+	enable_raw_bind_capability(1);
+	if (setsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE, interface->interface,
+		       strlen(interface->interface) + 1)) {
+		perror("ipv4: can't bind to device");
+		goto err4;
+	}
+
+	if (setsockopt(sock_mc, SOL_SOCKET, SO_BINDTODEVICE,
+		       interface->interface, strlen(interface->interface) + 1)) {
+		perror("ipv4: can't bind to device");
+		goto err4;
+	}
+	enable_raw_bind_capability(0);
+
+	ret = 1;
+	if (setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &ret, sizeof(ret)) < 0) {
+		perror("ipv4: can't set reuse flag");
+		goto err4;
+	}
+	if (setsockopt(sock_mc, SOL_SOCKET, SO_REUSEADDR, &ret, sizeof(ret)) < 0) {
+		perror("ipv4: can't set mc reuse flag");
+		goto err4;
+	}
+
+	if (bind(sock, (struct sockaddr *)&sin4, sizeof(sin4)) < 0) {
+		perror("ipv4: can't bind");
+		goto err4;
+	}
+
+	if (bind(sock_mc, (struct sockaddr *)&sin_mc, sizeof(sin_mc)) < 0) {
+		perror("ipv4: can't bind mc");
+		goto err4;
+	}
+
+	memcpy(&mreq.imr_multiaddr, &alfred_mcast.ipv4, sizeof(mreq.imr_multiaddr));
+
+	if (ioctl(sock_mc, SIOCGIFADDR, &ifr) < 0) {
+		perror("ipv4: can't get IP address");
+		goto err4;
+	}
+	mreq.imr_interface = ((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr;
+	memcpy(&interface->address.ipv4,
+	       &((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr,
+	       sizeof(struct in_addr));
+
+	if (setsockopt(sock_mc, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq))) {
+		perror("ipv4: can't add multicast membership");
+		goto err4;
+	}
+
+	ret = fcntl(sock, F_GETFL, 0);
+	if (ret < 0) {
+		perror("failed to get file status flags");
+		goto err4;
+	}
+
+	ret = fcntl(sock, F_SETFL, ret | O_NONBLOCK);
+	if (ret < 0) {
+		perror("failed to set file status flags");
+		goto err4;
+	}
+
+	ret = fcntl(sock_mc, F_GETFL, 0);
+	if (ret < 0) {
+		perror("ipv4: failed to get file status flags");
+		goto err4;
+	}
+
+	ret = fcntl(sock_mc, F_SETFL, ret | O_NONBLOCK);
+	if (ret < 0) {
+		perror("ipv4: failed to set file status flags");
+		goto err4;
+	}
+
+	interface->netsock = sock;
+	interface->netsock_mcast = sock_mc;
+
+	return 0;
+err4:
+	close(sock_mc);
+	return -1;
+}
+
 int netsock_open_all(struct globals *globals)
 {
 	int num_socks = 0;
@@ -342,7 +470,11 @@  int netsock_open_all(struct globals *globals)
 	struct interface *interface;
 
 	list_for_each_entry(interface, &globals->interfaces, list) {
-		ret = netsock_open(interface);
+		if (globals->ipv4mode)
+			ret = netsock_open4(interface);
+		else
+			ret = netsock_open(interface);
+
 		if (ret >= 0)
 			num_socks++;
 	}
@@ -355,8 +487,12 @@  void netsock_reopen(struct globals *globals)
 	struct interface *interface;
 
 	list_for_each_entry(interface, &globals->interfaces, list) {
-		if (interface->netsock < 0)
-			netsock_open(interface);
+		if (interface->netsock < 0) {
+			if (globals->ipv4mode)
+				netsock_open4(interface);
+			else
+				netsock_open(interface);
+		}
 	}
 }
 
@@ -430,7 +566,7 @@  int netsock_receive_packet(struct globals *globals, fd_set *fds)
 }
 
 int netsock_own_address(const struct globals *globals,
-			const struct in6_addr *address)
+			const alfred_addr *address)
 {
 	struct interface *interface;
 
diff --git a/recv.c b/recv.c
index bb8cc05..3fd964d 100644
--- a/recv.c
+++ b/recv.c
@@ -190,7 +190,8 @@  static int finish_alfred_transaction(struct globals *globals,
 }
 
 static int process_alfred_push_data(struct globals *globals,
-				    struct in6_addr *source,
+				    struct interface *interface,
+				    alfred_addr *source,
 				    struct alfred_push_data_v0 *push)
 {
 	int len;
@@ -200,7 +201,10 @@  static int process_alfred_push_data(struct globals *globals,
 	struct transaction_packet *transaction_packet;
 	int found;
 
-	ret = ipv6_to_mac(source, &mac);
+	if (globals->ipv4mode)
+		ret = ipv4_to_mac(interface, source, &mac);
+	else
+		ret = ipv6_to_mac(source, &mac);
 	if (ret < 0)
 		goto err;
 
@@ -260,7 +264,7 @@  err:
 static int
 process_alfred_announce_master(struct globals *globals,
 			       struct interface *interface,
-			       struct in6_addr *source,
+			       alfred_addr *source,
 			       struct alfred_announce_master_v0 *announce)
 {
 	struct server *server;
@@ -271,7 +275,10 @@  process_alfred_announce_master(struct globals *globals,
 
 	len = ntohs(announce->header.length);
 
-	ret = ipv6_to_mac(source, &mac);
+	if (globals->ipv4mode)
+		ret = ipv4_to_mac(interface, source, &mac);
+	else
+		ret = ipv6_to_mac(source, &mac);
 	if (ret < 0)
 		return -1;
 
@@ -316,7 +323,7 @@  process_alfred_announce_master(struct globals *globals,
 
 static int process_alfred_request(struct globals *globals,
 				  struct interface *interface,
-				  struct in6_addr *source,
+				  alfred_addr *source,
 				  struct alfred_request_v0 *request)
 {
 	int len;
@@ -336,7 +343,8 @@  static int process_alfred_request(struct globals *globals,
 }
 
 static int process_alfred_status_txend(struct globals *globals,
-				       struct in6_addr *source,
+				       struct interface *interface,
+				       alfred_addr *source,
 				       struct alfred_status_v0 *request)
 {
 	struct transaction_head search, *head;
@@ -351,7 +359,10 @@  static int process_alfred_status_txend(struct globals *globals,
 	if (len != (sizeof(*request) - sizeof(request->header)))
 		return -1;
 
-	ret = ipv6_to_mac(source, &mac);
+	if (globals->ipv4mode)
+		ret = ipv4_to_mac(interface, source, &mac);
+	else
+		ret = ipv6_to_mac(source, &mac);
 	if (ret < 0)
 		return -1;
 
@@ -389,15 +400,25 @@  int recv_alfred_packet(struct globals *globals, struct interface *interface,
 	uint8_t buf[MAX_PAYLOAD];
 	ssize_t length;
 	struct alfred_tlv *packet;
-	struct sockaddr_in6 source;
+	struct sockaddr_in *source;
+	struct sockaddr_in source4;
+	struct sockaddr_in6 source6;
 	socklen_t sourcelen;
+	alfred_addr alfred_source;
 
 	if (interface->netsock < 0)
 		return -1;
 
-	sourcelen = sizeof(source);
+	if (globals->ipv4mode) {
+		source = (struct sockaddr_in *)&source4;
+		sourcelen = sizeof(source4);
+	} else {
+		source = (struct sockaddr_in *)&source6;
+		sourcelen = sizeof(source6);
+	}
+
 	length = recvfrom(recv_sock, buf, sizeof(buf), 0,
-			  (struct sockaddr *)&source, &sourcelen);
+			  (struct sockaddr *)source, &sourcelen);
 	if (length <= 0) {
 		perror("read from network socket failed");
 		return -1;
@@ -405,12 +426,18 @@  int recv_alfred_packet(struct globals *globals, struct interface *interface,
 
 	packet = (struct alfred_tlv *)buf;
 
-	/* drop packets not sent over link-local ipv6 */
-	if (!is_ipv6_eui64(&source.sin6_addr))
-		return -1;
+	if (globals->ipv4mode) {
+		memcpy(&alfred_source, &source4.sin_addr, sizeof(source4.sin_addr));
+	} else {
+		memcpy(&alfred_source, &source6.sin6_addr, sizeof(source6.sin6_addr));
+
+		/* drop packets not sent over link-local ipv6 */
+		if (!is_ipv6_eui64(&alfred_source.ipv6))
+			return -1;
+	}
 
 	/* drop packets from ourselves */
-	if (netsock_own_address(globals, &source.sin6_addr))
+	if (netsock_own_address(globals, &alfred_source))
 		return -1;
 
 	/* drop truncated packets */
@@ -424,20 +451,20 @@  int recv_alfred_packet(struct globals *globals, struct interface *interface,
 
 	switch (packet->type) {
 	case ALFRED_PUSH_DATA:
-		process_alfred_push_data(globals, &source.sin6_addr,
+		process_alfred_push_data(globals, interface, &alfred_source,
 					 (struct alfred_push_data_v0 *)packet);
 		break;
 	case ALFRED_ANNOUNCE_MASTER:
 		process_alfred_announce_master(globals, interface,
-					       &source.sin6_addr,
+					       &alfred_source,
 					       (struct alfred_announce_master_v0 *)packet);
 		break;
 	case ALFRED_REQUEST:
-		process_alfred_request(globals, interface, &source.sin6_addr,
+		process_alfred_request(globals, interface, &alfred_source,
 				       (struct alfred_request_v0 *)packet);
 		break;
 	case ALFRED_STATUS_TXEND:
-		process_alfred_status_txend(globals, &source.sin6_addr,
+		process_alfred_status_txend(globals, interface, &alfred_source,
 					    (struct alfred_status_v0 *)packet);
 		break;
 	default:
diff --git a/send.c b/send.c
index c7a2af2..b566503 100644
--- a/send.c
+++ b/send.c
@@ -42,7 +42,7 @@  int announce_master(struct globals *globals)
 		announcement.header.version = ALFRED_VERSION;
 		announcement.header.length = htons(0);
 
-		send_alfred_packet(interface, &in6addr_localmcast,
+		send_alfred_packet(globals, interface, &alfred_mcast,
 				   &announcement, sizeof(announcement));
 	}
 
@@ -50,7 +50,7 @@  int announce_master(struct globals *globals)
 }
 
 int push_data(struct globals *globals, struct interface *interface,
-	      struct in6_addr *destination, enum data_source max_source_level,
+	      alfred_addr *destination, enum data_source max_source_level,
 	      int type_filter, uint16_t tx_id)
 {
 	struct hash_it_t *hashit = NULL;
@@ -90,7 +90,7 @@  int push_data(struct globals *globals, struct interface *interface,
 			tlv_length += sizeof(*push) - sizeof(push->header);
 			push->header.length = htons(tlv_length);
 			push->tx.seqno = htons(seqno++);
-			send_alfred_packet(interface, destination, push,
+			send_alfred_packet(globals, interface, destination, push,
 					   sizeof(*push) + total_length);
 			total_length = 0;
 		}
@@ -114,7 +114,7 @@  int push_data(struct globals *globals, struct interface *interface,
 		tlv_length += sizeof(*push) - sizeof(push->header);
 		push->header.length = htons(tlv_length);
 		push->tx.seqno = htons(seqno++);
-		send_alfred_packet(interface, destination, push,
+		send_alfred_packet(globals, interface, destination, push,
 				   sizeof(*push) + total_length);
 	}
 
@@ -128,7 +128,7 @@  int push_data(struct globals *globals, struct interface *interface,
 		status_end.tx.id = tx_id;
 		status_end.tx.seqno = htons(seqno);
 
-		send_alfred_packet(interface, destination, &status_end,
+		send_alfred_packet(globals, interface, destination, &status_end,
 				   sizeof(status_end));
 	}
 
@@ -170,24 +170,38 @@  int push_local_data(struct globals *globals)
 	return 0;
 }
 
-ssize_t send_alfred_packet(struct interface *interface,
-			   const struct in6_addr *dest, void *buf, int length)
+ssize_t send_alfred_packet(struct globals *globals, struct interface *interface,
+			   const alfred_addr *dest, void *buf, int length)
 {
 	ssize_t ret;
-	struct sockaddr_in6 dest_addr;
-
-	memset(&dest_addr, 0, sizeof(dest_addr));
-	dest_addr.sin6_family = AF_INET6;
-	dest_addr.sin6_port = htons(ALFRED_PORT);
-	dest_addr.sin6_scope_id = interface->scope_id;
-	memcpy(&dest_addr.sin6_addr, dest, sizeof(*dest));
+	struct sockaddr *dest_addr;
+	struct sockaddr_in6 dest_addr6;
+	struct sockaddr_in dest_addr4;
+	socklen_t slen;
+
+	if (globals->ipv4mode) {
+		memset(&dest_addr4, 0, sizeof(dest_addr4));
+		dest_addr4.sin_family = AF_INET;
+		dest_addr4.sin_port = htons(ALFRED_PORT);
+		memcpy(&dest_addr4.sin_addr, &dest->ipv4, sizeof(dest->ipv4));
+
+		slen = sizeof(struct sockaddr_in);
+		dest_addr = (struct sockaddr *)&dest_addr4;
+	} else {
+		memset(&dest_addr6, 0, sizeof(dest_addr6));
+		dest_addr6.sin6_family = AF_INET6;
+		dest_addr6.sin6_port = htons(ALFRED_PORT);
+		dest_addr6.sin6_scope_id = interface->scope_id;
+		memcpy(&dest_addr6.sin6_addr, &dest->ipv6, sizeof(dest->ipv6));
+
+		slen = sizeof(struct sockaddr_in6);
+		dest_addr = (struct sockaddr *)&dest_addr6;
+	}
 
 	if (interface->netsock < 0)
 		return 0;
 
-	ret = sendto(interface->netsock, buf, length, 0,
-		     (struct sockaddr *)&dest_addr,
-		     sizeof(struct sockaddr_in6));
+	ret = sendto(interface->netsock, buf, length, 0, dest_addr, slen);
 	if (ret == -EPERM) {
 		perror("Error during sent");
 		close(interface->netsock);
diff --git a/server.c b/server.c
index f6e0c8a..2c4042a 100644
--- a/server.c
+++ b/server.c
@@ -218,7 +218,7 @@  static int purge_data(struct globals *globals)
 	return 0;
 }
 
-static void check_if_socket(struct interface *interface)
+static void check_if_socket(struct interface *interface, struct globals *globals)
 {
 	int sock;
 	struct ifreq ifr;
@@ -226,7 +226,7 @@  static void check_if_socket(struct interface *interface)
 	if (interface->netsock < 0)
 		return;
 
-	sock = socket(PF_INET6, SOCK_DGRAM, 0);
+	sock = socket(PF_INET, SOCK_DGRAM, 0);
 	if (sock < 0) {
 		perror("can't open socket");
 		return;
@@ -240,7 +240,7 @@  static void check_if_socket(struct interface *interface)
 		goto close;
 	}
 
-	if (interface->scope_id != (uint32_t)ifr.ifr_ifindex) {
+	if (!globals->ipv4mode && (interface->scope_id != (uint32_t)ifr.ifr_ifindex)) {
 		fprintf(stderr,
 			"iface index changed from %"PRIu32" to %d, closing netsock\n",
 			interface->scope_id, ifr.ifr_ifindex);
@@ -282,7 +282,7 @@  static void check_if_sockets(struct globals *globals)
 	globals->if_check = now;
 
 	list_for_each_entry(interface, &globals->interfaces, list)
-		check_if_socket(interface);
+		check_if_socket(interface, globals);
 }
 
 static void execute_update_command(struct globals *globals)
diff --git a/unix_sock.c b/unix_sock.c
index 0a819a2..4a8c6e0 100644
--- a/unix_sock.c
+++ b/unix_sock.c
@@ -258,7 +258,7 @@  static int unix_sock_req_data(struct globals *globals,
 	head->client_socket = client_sock;
 	head->requested_type = request->requested_type;
 
-	send_alfred_packet(interface, &globals->best_server->address,
+	send_alfred_packet(globals, interface, &globals->best_server->address,
 			   request, sizeof(*request));
 
 	return 0;
diff --git a/util.c b/util.c
index ea75643..84ab3af 100644
--- a/util.c
+++ b/util.c
@@ -23,7 +23,10 @@ 
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdint.h>
+#include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
 #include <sys/time.h>
 #include <time.h>
 #include "alfred.h"
@@ -75,3 +78,30 @@  bool is_valid_ether_addr(uint8_t addr[ETH_ALEN])
 
 	return true;
 }
+
+int ipv4_arp_request(struct interface *interface, const alfred_addr *addr,
+		     struct ether_addr *mac)
+{
+	struct arpreq arpreq;
+	struct sockaddr_in *sin;
+
+	memset(&arpreq, 0, sizeof(arpreq));
+	memset(mac, 0, ETH_ALEN);
+
+	sin = (struct sockaddr_in *)&arpreq.arp_pa;
+	sin->sin_family = AF_INET;
+	sin->sin_addr.s_addr = addr->ipv4.s_addr;
+
+	strcpy(arpreq.arp_dev, interface->interface);
+	if (ioctl(interface->netsock, SIOCGARP, &arpreq) < 0)
+		return -1;
+
+	if (arpreq.arp_flags & ATF_COM) {
+		memcpy(mac, arpreq.arp_ha.sa_data, sizeof(*mac));
+	} else {
+		perror("arp: incomplete");
+		return -1;
+	}
+
+	return 0;
+}