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net: Choose IP corresponding to the same network #102036

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Merged
henrikbrixandersen merged 1 commit into from
Jan 13, 2026
Merged

net: Choose IP corresponding to the same network #102036

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32 changes: 25 additions & 7 deletions subsys/net/l2/ethernet/arp.c
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Original file line number Diff line number Diff line change
Expand Up @@ -228,10 +228,19 @@ static void arp_request_timeout(struct k_work *work)
k_mutex_unlock(&arp_mutex);
}

static inline bool is_same_subnet(uint32_t addr1,
uint32_t addr2,
uint32_t netmask)
{
return ((addr1 & netmask) == (addr2 & netmask));
}

static inline struct net_in_addr *if_get_addr(struct net_if *iface,
const uint8_t *addr)
const uint8_t *own_addr,
const struct net_in_addr *dst_addr)
{
struct net_if_ipv4 *ipv4 = iface->config.ip.ipv4;
struct net_in_addr *fall_back = NULL;

if (!ipv4) {
return NULL;
Expand All @@ -241,14 +250,23 @@ static inline struct net_in_addr *if_get_addr(struct net_if *iface,
if (ipv4->unicast[i].ipv4.is_used &&
ipv4->unicast[i].ipv4.address.family == NET_AF_INET &&
ipv4->unicast[i].ipv4.addr_state == NET_ADDR_PREFERRED &&
(!addr ||
((own_addr == NULL) ||
net_ipv4_addr_cmp_raw(
addr, ipv4->unicast[i].ipv4.address.in_addr.s4_addr))) {
return &ipv4->unicast[i].ipv4.address.in_addr;
own_addr, ipv4->unicast[i].ipv4.address.in_addr.s4_addr))) {
if ((dst_addr == NULL) ||
is_same_subnet(dst_addr->s_addr,
ipv4->unicast[i].ipv4.address.in_addr.s_addr,
ipv4->unicast[i].netmask.s_addr)) {
/* Use preferred address on the same subnet as destination */
return &ipv4->unicast[i].ipv4.address.in_addr;
} else if (fall_back == NULL) {
/* Use address as fallback, if no match for subnet is found */
fall_back = &ipv4->unicast[i].ipv4.address.in_addr;
}
}
}

return NULL;
return fall_back;
}

static inline struct net_pkt *arp_prepare(struct net_if *iface,
Expand Down Expand Up @@ -339,7 +357,7 @@ static inline struct net_pkt *arp_prepare(struct net_if *iface,
} else if (!entry) {
my_addr = (struct net_in_addr *)NET_IPV4_HDR(pending)->src;
} else {
my_addr = if_get_addr(entry->iface, (const uint8_t *)current_ip);
my_addr = if_get_addr(entry->iface, (const uint8_t *)current_ip, next_addr);
}

if (my_addr) {
Expand Down Expand Up @@ -852,7 +870,7 @@ enum net_verdict net_arp_input(struct net_pkt *pkt,
}

/* Someone wants to know our ll address */
addr = if_get_addr(net_pkt_iface(pkt), arp_hdr->dst_ipaddr);
addr = if_get_addr(net_pkt_iface(pkt), arp_hdr->dst_ipaddr, NULL);
if (!addr) {
/* Not for us so drop the packet silently */
return NET_DROP;
Expand Down