Function carp6_input

freebsd/netinet/ip_carp.c:538–596

#ifdef INET6
int
carp6_input(struct mbuf **mp, int *offp, int proto)
{
	struct mbuf *m = *mp;
	struct ip6_hdr *ip6 = mtod(m, struct ip6_hdr *);
	struct carp_header *ch;
	u_int len;

	CARPSTATS_INC(carps_ipackets6);

	if (!V_carp_allow) {
		m_freem(m);
		return (IPPROTO_DONE);
	}

	/* check if received on a valid carp interface */
	if (m->m_pkthdr.rcvif->if_carp == NULL) {
		CARPSTATS_INC(carps_badif);
		CARP_DEBUG("%s: packet received on non-carp interface: %s\n",
		    __func__, m->m_pkthdr.rcvif->if_xname);
		m_freem(m);
		return (IPPROTO_DONE);
	}

	/* verify that the IP TTL is 255 */
	if (ip6->ip6_hlim != CARP_DFLTTL) {
		CARPSTATS_INC(carps_badttl);
		CARP_DEBUG("%s: received ttl %d != 255 on %s\n", __func__,
		    ip6->ip6_hlim, m->m_pkthdr.rcvif->if_xname);
		m_freem(m);
		return (IPPROTO_DONE);
	}

	/* verify that we have a complete carp packet */
	if (m->m_len < *offp + sizeof(*ch)) {
		len = m->m_len;
		m = m_pullup(m, *offp + sizeof(*ch));
		if (m == NULL) {
			CARPSTATS_INC(carps_badlen);
			CARP_DEBUG("%s: packet size %u too small\n", __func__, len);
			return (IPPROTO_DONE);
		}
	}
	ch = (struct carp_header *)(mtod(m, char *) + *offp);

	/* verify the CARP checksum */
	m->m_data += *offp;
	if (in_cksum(m, sizeof(*ch))) {
		CARPSTATS_INC(carps_badsum);
		CARP_DEBUG("%s: checksum failed, on %s\n", __func__,
		    m->m_pkthdr.rcvif->if_xname);
		m_freem(m);
		return (IPPROTO_DONE);
	}
	m->m_data -= *offp;

	carp_input_c(m, ch, AF_INET6);
	return (IPPROTO_DONE);