From lwIP mailing list, Arpit Agarwal
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Hi Ivan,

I am testing Core Protocols Only.

For e.g. Core Protocols Section 1: (spec.p2) : In my test many of the test cases are failing due to improper neighbor cache cleanup. If I am not wrong, the reason might be non-handling of one of the transition of nd6 state machine (refer link: https://njetwork.files.wordpress.com/2014/01/msi_ipv6-nd-state-machine1.png). I am unable to find the State change from Reachable to Stale on receiving NA with LLADDR change anywhere in the nd6 code.

Similary as per RFC 4861 , DAD-NA might not contain lladdr_opt, but the stack in lwip seems to drop NA if there is not lladdr_opt.

Refer Below code from nd6.c:

/* Unsolicited NA?*/
    if (ip6_addr_ismulticast(ip6_current_dest_addr())) {
      /* This is an unsolicited NA.
       * link-layer changed?
       part of DAD mechanism? /

      /* Check that link-layer address option also fits in packet. */
      if (p->len < (sizeof(struct na_header) + 2)) {
        /* @todo debug message */
        pbuf_free(p);
        ND6_STATS_INC(nd6.lenerr);
        ND6_STATS_INC(nd6.drop);
        return;
      }

      lladdr_opt = (struct lladdr_option )((u8_t)p->payload + sizeof(struct na_header));

      if (p->len < (sizeof(struct na_header) + (lladdr_opt->length << 3))) {
        /* @todo debug message */
        pbuf_free(p);
        ND6_STATS_INC(nd6.lenerr);
        ND6_STATS_INC(nd6.drop);
        return;
      }