[lwip-devel] [patch #6683] Customizable AUTOIP "seed" address

[Luca Ceresoli]

Follow-up Comment #4, patch #6683 (project lwip):

You are 100% right.

I sketched out a tentative improvement:


// 169.254.0.0
#define AUTOIP_NET 0xA9FE0000
...
static void
autoip_create_addr(struct netif *netif, struct ip_addr *IPAddr)
{
  /* Here we create an IP-Address out of range 169.254.1.0 to
169.254.254.255
   * compliant to RFC 3927 Section 2.1
   * We have 254 * 256 possibilities
   */
  u32_t addr = ntohl(LWIP_AUTOIP_CREATE_SEED_ADDR(netif));
  addr += netif->autoip->tried_llipaddr;
  addr = AUTOIP_NET | (addr & 0xffff);
  /* Now, 169.254.0.0 <= addr <= 169.254.255.255 */ 

  if (addr < AUTOIP_RANGE_START) {
    addr += AUTOIP_RANGE_END - AUTOIP_RANGE_START + 1;
  }
  if (addr > AUTOIP_RANGE_END) {
    addr -= AUTOIP_RANGE_END - AUTOIP_RANGE_START + 1;
  }
  IPAddr->addr = htonl(addr);
  
  LWIP_DEBUGF(AUTOIP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE | 1,
    ("autoip_create_addr(): tried_llipaddr=%"U16_F", 0x%08"X32_F"n",
    (u16_t)(netif->autoip->tried_llipaddr), (u32_t)(IPAddr->addr)));
}


Pros:
* The seed is a complete IP address (in ip_addr byte order).
* It is safe (no risk to go out of range).


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