path: root/eigrpd/eigrp_hello.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * EIGRP Sending and Receiving EIGRP Hello Packets.
 * Copyright (C) 2013-2016
 * Authors:
 *   Donnie Savage
 *   Jan Janovic
 *   Matej Perina
 *   Peter Orsag
 *   Peter Paluch
 *   Frantisek Gazo
 *   Tomas Hvorkovy
 *   Martin Kontsek
 *   Lukas Koribsky
 */

#include <zebra.h>

#include "frrevent.h"
#include "memory.h"
#include "linklist.h"
#include "prefix.h"
#include "if.h"
#include "table.h"
#include "sockunion.h"
#include "stream.h"
#include "log.h"
#include "sockopt.h"
#include "checksum.h"
#include "vty.h"
#include "md5.h"

#include "eigrpd/eigrp_structs.h"
#include "eigrpd/eigrpd.h"
#include "eigrpd/eigrp_interface.h"
#include "eigrpd/eigrp_neighbor.h"
#include "eigrpd/eigrp_packet.h"
#include "eigrpd/eigrp_zebra.h"
#include "eigrpd/eigrp_vty.h"
#include "eigrpd/eigrp_dump.h"
#include "eigrpd/eigrp_macros.h"
#include "eigrpd/eigrp_errors.h"

/* Packet Type String. */
static const struct message eigrp_general_tlv_type_str[] = {
	{EIGRP_TLV_PARAMETER, "PARAMETER"},
	{EIGRP_TLV_AUTH, "AUTH"},
	{EIGRP_TLV_SEQ, "SEQ"},
	{EIGRP_TLV_SW_VERSION, "SW_VERSION"},
	{EIGRP_TLV_NEXT_MCAST_SEQ, "NEXT_MCAST_SEQ"},
	{EIGRP_TLV_PEER_TERMINATION, "PEER_TERMINATION"},
	{EIGRP_TLV_PEER_MTRLIST, "PEER_MTRLIST"},
	{EIGRP_TLV_PEER_TIDLIST, "PEER_TIDLIST"},
	{0}};


/*
 * @fn eigrp_hello_timer
 *
 * @param[in]   thread  current execution thread timer is associated with
 *
 * @return void
 *
 * @par
 * Called once per "hello" time interval, default 5 seconds
 * Sends hello packet via multicast for all interfaces eigrp
 * is configured for
 */
void eigrp_hello_timer(struct event *thread)
{
	struct eigrp_interface *ei;

	ei = EVENT_ARG(thread);

	if (IS_DEBUG_EIGRP(0, TIMERS))
		zlog_debug("Start Hello Timer (%s) Expire [%u]", IF_NAME(ei),
			   ei->params.v_hello);

	/* Sending hello packet. */
	eigrp_hello_send(ei, EIGRP_HELLO_NORMAL, NULL);

	/* Hello timer set. */
	event_add_timer(master, eigrp_hello_timer, ei, ei->params.v_hello,
			&ei->t_hello);
}

/**
 * @fn eigrp_hello_parameter_decode
 *
 * @param[in]		nbr	neighbor the ACK should be sent to
 * @param[in]		param	pointer packet TLV is stored to
 *
 * @return uint16_t	number of bytes added to packet stream
 *
 * @par
 * Encode Parameter TLV, used to convey metric weights and the hold time.
 *
 * @usage
 * Note the addition of K6 for the new extended metrics, and does not apply to
 * older TLV packet formats.
 */
static struct eigrp_neighbor *
eigrp_hello_parameter_decode(struct eigrp_neighbor *nbr,
			     struct eigrp_tlv_hdr_type *tlv)
{
	struct eigrp *eigrp = nbr->ei->eigrp;
	struct TLV_Parameter_Type *param = (struct TLV_Parameter_Type *)tlv;

	/* First validate TLV length */
	if (tlv->length < sizeof(struct TLV_Parameter_Type))
		return NULL;

	/* copy over the values passed in by the neighbor */
	nbr->K1 = param->K1;
	nbr->K2 = param->K2;
	nbr->K3 = param->K3;
	nbr->K4 = param->K4;
	nbr->K5 = param->K5;
	nbr->K6 = param->K6;
	nbr->v_holddown = ntohs(param->hold_time);

	/*
	 * Check K1-K5 have the correct values to be able to become neighbors
	 * K6 does not have to match
	 */
	if ((eigrp->k_values[0] == nbr->K1) && (eigrp->k_values[1] == nbr->K2)
	    && (eigrp->k_values[2] == nbr->K3)
	    && (eigrp->k_values[3] == nbr->K4)
	    && (eigrp->k_values[4] == nbr->K5)) {

		if (eigrp_nbr_state_get(nbr) == EIGRP_NEIGHBOR_DOWN) {
			zlog_info(
				"Neighbor %pI4 (%s) is pending: new adjacency",
				&nbr->src,
				ifindex2ifname(nbr->ei->ifp->ifindex,
					       eigrp->vrf_id));

			/* Expedited hello sent */
			eigrp_hello_send(nbr->ei, EIGRP_HELLO_NORMAL, NULL);

			//     if(ntohl(nbr->ei->address->u.prefix4.s_addr) >
			//     ntohl(nbr->src.s_addr))
			eigrp_update_send_init(nbr);

			eigrp_nbr_state_set(nbr, EIGRP_NEIGHBOR_PENDING);
		}
	} else {
		if (eigrp_nbr_state_get(nbr) != EIGRP_NEIGHBOR_DOWN) {
			if ((param->K1 & param->K2 & param->K3 & param->K4
			     & param->K5)
			    == 255) {
				zlog_info(
					"Neighbor %pI4 (%s) is down: Interface PEER-TERMINATION received",
					&nbr->src,
					ifindex2ifname(nbr->ei->ifp->ifindex,
						       eigrp->vrf_id));
				eigrp_nbr_delete(nbr);
				return NULL;
			} else {
				zlog_info(
					"Neighbor %pI4 (%s) going down: Kvalue mismatch",
					&nbr->src,
					ifindex2ifname(nbr->ei->ifp->ifindex,
						       eigrp->vrf_id));
				eigrp_nbr_state_set(nbr, EIGRP_NEIGHBOR_DOWN);
			}
		}
	}

	return nbr;
}

static uint8_t
eigrp_hello_authentication_decode(struct stream *s,
				  struct eigrp_tlv_hdr_type *tlv_header,
				  struct eigrp_neighbor *nbr)
{
	struct TLV_MD5_Authentication_Type *md5;

	md5 = (struct TLV_MD5_Authentication_Type *)tlv_header;

	if (md5->auth_type == EIGRP_AUTH_TYPE_MD5) {
		/* Validate tlv length */
		if (md5->length < sizeof(struct TLV_MD5_Authentication_Type))
			return 0;

		return eigrp_check_md5_digest(s, md5, nbr,
					      EIGRP_AUTH_BASIC_HELLO_FLAG);
	} else if (md5->auth_type == EIGRP_AUTH_TYPE_SHA256) {
		/* Validate tlv length */
		if (md5->length < sizeof(struct TLV_SHA256_Authentication_Type))
			return 0;

		return eigrp_check_sha256_digest(
			s, (struct TLV_SHA256_Authentication_Type *)tlv_header,
			nbr, EIGRP_AUTH_BASIC_HELLO_FLAG);
	}

	return 0;
}

/**
 * @fn eigrp_sw_version_decode
 *
 * @param[in]		nbr	neighbor the ACK shoudl be sent to
 * @param[in]		param	pointer to TLV software version information
 *
 * @return void
 *
 * @par
 * Read the software version in the specified location.
 * This consists of two bytes of OS version, and two bytes of EIGRP
 * revision number.
 */
static void eigrp_sw_version_decode(struct eigrp_neighbor *nbr,
				    struct eigrp_tlv_hdr_type *tlv)
{
	struct TLV_Software_Type *version = (struct TLV_Software_Type *)tlv;

	/* Validate TLV length */
	if (tlv->length < sizeof(struct TLV_Software_Type))
		return;

	nbr->os_rel_major = version->vender_major;
	nbr->os_rel_minor = version->vender_minor;
	nbr->tlv_rel_major = version->eigrp_major;
	nbr->tlv_rel_minor = version->eigrp_minor;
	return;
}

/**
 * @fn eigrp_peer_termination_decode
 *
 * @param[in]		nbr	neighbor the ACK shoudl be sent to
 * @param[in]		tlv	pointer to TLV software version information
 *
 * @return void
 *
 * @par
 * Read the address in the TLV and match to out address. If
 * a match is found, move the sending neighbor to the down state. If
 * out address is not in the TLV, then ignore the peer termination
 */
static void eigrp_peer_termination_decode(struct eigrp_neighbor *nbr,
					  struct eigrp_tlv_hdr_type *tlv)
{
	struct eigrp *eigrp = nbr->ei->eigrp;
	struct TLV_Peer_Termination_type *param =
		(struct TLV_Peer_Termination_type *)tlv;

	/* Validate TLV length */
	if (tlv->length < sizeof(struct TLV_Peer_Termination_type))
		return;

	uint32_t my_ip = nbr->ei->address.u.prefix4.s_addr;
	uint32_t received_ip = param->neighbor_ip;

	if (my_ip == received_ip) {
		zlog_info(
			"Neighbor %pI4 (%s) is down: Peer Termination received",
			&nbr->src,
			ifindex2ifname(nbr->ei->ifp->ifindex, eigrp->vrf_id));
		/* set neighbor to DOWN */
		nbr->state = EIGRP_NEIGHBOR_DOWN;
		/* delete neighbor */
		eigrp_nbr_delete(nbr);
	}
}

/**
 * @fn eigrp_peer_termination_encode
 *
 * @param[in,out]   s      	  packet stream TLV is stored to
 * @param[in]		nbr_addr  pointer to neighbor address for Peer
 * Termination TLV
 *
 * @return uint16_t    number of bytes added to packet stream
 *
 * @par
 * Function used to encode Peer Termination TLV to Hello packet.
 */
static uint16_t eigrp_peer_termination_encode(struct stream *s,
					      struct in_addr *nbr_addr)
{
	uint16_t length = EIGRP_TLV_PEER_TERMINATION_LEN;

	/* fill in type and length */
	stream_putw(s, EIGRP_TLV_PEER_TERMINATION);
	stream_putw(s, length);

	/* fill in unknown field 0x04 */
	stream_putc(s, 0x04);

	/* finally neighbor IP address */
	stream_put_ipv4(s, nbr_addr->s_addr);

	return (length);
}

/*
 * @fn eigrp_hello_receive
 *
 * @param[in]   eigrp           eigrp routing process
 * @param[in]   iph             pointer to ip header
 * @param[in]   eigrph          pointer to eigrp header
 * @param[in]   s               input ip stream
 * @param[in]   ei              eigrp interface packet arrived on
 * @param[in]   size            size of eigrp packet
 *
 * @return void
 *
 * @par
 * This is the main worker function for processing hello packets. It
 * will validate the peer associated with the src ip address of the ip
 * header, and then decode each of the general TLVs which the packet
 * may contain.
 *
 * @usage
 * Not all TLVs are current decoder.  This is a work in progress..
 */
void eigrp_hello_receive(struct eigrp *eigrp, struct ip *iph,
			 struct eigrp_header *eigrph, struct stream *s,
			 struct eigrp_interface *ei, int size)
{
	struct eigrp_tlv_hdr_type *tlv_header;
	struct eigrp_neighbor *nbr;
	uint16_t type;
	uint16_t length;

	/* get neighbor struct */
	nbr = eigrp_nbr_get(ei, eigrph, iph);

	/* neighbor must be valid, eigrp_nbr_get creates if none existed */
	assert(nbr);

	if (IS_DEBUG_EIGRP_PACKET(eigrph->opcode - 1, RECV))
		zlog_debug("Processing Hello size[%u] int(%s) nbr(%pI4)", size,
			   ifindex2ifname(nbr->ei->ifp->ifindex, eigrp->vrf_id),
			   &nbr->src);

	size -= EIGRP_HEADER_LEN;
	if (size < 0)
		return;

	tlv_header = (struct eigrp_tlv_hdr_type *)eigrph->tlv;

	do {
		type = ntohs(tlv_header->type);
		length = ntohs(tlv_header->length);

		/* Validate length against packet size */
		if (length > size)
			return;

		if ((length > 0) && (length <= size)) {
			if (IS_DEBUG_EIGRP_PACKET(0, RECV))
				zlog_debug(
					"  General TLV(%s)",
					lookup_msg(eigrp_general_tlv_type_str,
						   type, NULL));

			// determine what General TLV is being processed
			switch (type) {
			case EIGRP_TLV_PARAMETER:
				nbr = eigrp_hello_parameter_decode(nbr,
								   tlv_header);
				if (!nbr)
					return;
				break;
			case EIGRP_TLV_AUTH: {
				if (eigrp_hello_authentication_decode(
					    s, tlv_header, nbr)
				    == 0)
					return;
				else
					break;
				break;
			}
			case EIGRP_TLV_SEQ:
				break;
			case EIGRP_TLV_SW_VERSION:
				eigrp_sw_version_decode(nbr, tlv_header);
				break;
			case EIGRP_TLV_NEXT_MCAST_SEQ:
				break;
			case EIGRP_TLV_PEER_TERMINATION:
				eigrp_peer_termination_decode(nbr, tlv_header);
				return;
				break;
			case EIGRP_TLV_PEER_MTRLIST:
			case EIGRP_TLV_PEER_TIDLIST:
				break;
			default:
				break;
			}
		}

		tlv_header = (struct eigrp_tlv_hdr_type *)(((char *)tlv_header)
							   + length);
		size -= length;

	} while (size > 0);


	/*If received packet is hello with Parameter TLV*/
	if (ntohl(eigrph->ack) == 0) {
		/* increment statistics. */
		ei->hello_in++;
		if (nbr)
			eigrp_nbr_state_update(nbr);
	}

	if (IS_DEBUG_EIGRP_PACKET(0, RECV))
		zlog_debug("Hello Packet received from %pI4", &nbr->src);
}

uint32_t FRR_MAJOR;
uint32_t FRR_MINOR;

void eigrp_sw_version_initialize(void)
{
	char ver_string[] = VERSION;
	char *dash = strstr(ver_string, "-");
	int ret;

	if (dash)
		dash[0] = '\0';

	ret = sscanf(ver_string, "%" SCNu32 ".%" SCNu32, &FRR_MAJOR,
		     &FRR_MINOR);
	if (ret != 2)
		flog_err(EC_EIGRP_PACKET,
			 "Did not Properly parse %s, please fix VERSION string",
			 VERSION);
}

/**
 * @fn eigrp_sw_version_encode
 *
 * @param[in,out]	s	packet stream TLV is stored to
 *
 * @return uint16_t	number of bytes added to packet stream
 *
 * @par
 * Store the software version in the specified location.
 * This consists of two bytes of OS version, and two bytes of EIGRP
 * revision number.
 */
static uint16_t eigrp_sw_version_encode(struct stream *s)
{
	uint16_t length = EIGRP_TLV_SW_VERSION_LEN;

	// setup the tlv fields
	stream_putw(s, EIGRP_TLV_SW_VERSION);
	stream_putw(s, length);

	stream_putc(s, FRR_MAJOR); //!< major os version
	stream_putc(s, FRR_MINOR); //!< minor os version

	/* and the core eigrp version */
	stream_putc(s, EIGRP_MAJOR_VERSION);
	stream_putc(s, EIGRP_MINOR_VERSION);

	return (length);
}

/**
 * @fn eigrp_tidlist_encode
 *
 * @param[in,out]	s	packet stream TLV is stored to
 *
 * @return void
 *
 * @par
 * If doing mutli-topology, then store the supported TID list.
 * This is currently a place holder function
 */
static uint16_t eigrp_tidlist_encode(struct stream *s)
{
	// uint16_t length = EIGRP_TLV_SW_VERSION_LEN;
	return 0;
}

/**
 * @fn eigrp_sequence_encode
 *
 * @param[in,out]       s       packet stream TLV is stored to
 *
 * @return uint16_t    number of bytes added to packet stream
 *
 * @par
 * Part of conditional receive process
 *
 */
static uint16_t eigrp_sequence_encode(struct eigrp *eigrp, struct stream *s)
{
	uint16_t length = EIGRP_TLV_SEQ_BASE_LEN;
	struct eigrp_interface *ei;
	struct listnode *node, *node2, *nnode2;
	struct eigrp_neighbor *nbr;
	size_t backup_end, size_end;
	int found;

	// add in the parameters TLV
	backup_end = stream_get_endp(s);
	stream_putw(s, EIGRP_TLV_SEQ);
	size_end = s->endp;
	stream_putw(s, 0x0000);
	stream_putc(s, IPV4_MAX_BYTELEN);

	found = 0;
	for (ALL_LIST_ELEMENTS_RO(eigrp->eiflist, node, ei)) {
		for (ALL_LIST_ELEMENTS(ei->nbrs, node2, nnode2, nbr)) {
			if (nbr->multicast_queue->count > 0) {
				length += (uint16_t)stream_put_ipv4(
					s, nbr->src.s_addr);
				found = 1;
			}
		}
	}

	if (found == 0) {
		stream_set_endp(s, backup_end);
		return 0;
	}

	backup_end = stream_get_endp(s);
	stream_set_endp(s, size_end);
	stream_putw(s, length);
	stream_set_endp(s, backup_end);

	return length;
}

/**
 * @fn eigrp_sequence_encode
 *
 * @param[in,out]       s       packet stream TLV is stored to
 *
 * @return uint16_t    number of bytes added to packet stream
 *
 * @par
 * Part of conditional receive process
 *
 */
static uint16_t eigrp_next_sequence_encode(struct eigrp *eigrp,
					   struct stream *s)
{
	uint16_t length = EIGRP_NEXT_SEQUENCE_TLV_SIZE;

	// add in the parameters TLV
	stream_putw(s, EIGRP_TLV_NEXT_MCAST_SEQ);
	stream_putw(s, EIGRP_NEXT_SEQUENCE_TLV_SIZE);
	stream_putl(s, eigrp->sequence_number + 1);

	return length;
}

/**
 * @fn eigrp_hello_parameter_encode
 *
 * @param[in]		ei	pointer to interface hello packet came in on
 * @param[in,out]	s	packet stream TLV is stored to
 *
 * @return uint16_t	number of bytes added to packet stream
 *
 * @par
 * Encode Parameter TLV, used to convey metric weights and the hold time.
 *
 * @usage
 * Note the addition of K6 for the new extended metrics, and does not apply to
 * older TLV packet formats.
 */
static uint16_t eigrp_hello_parameter_encode(struct eigrp_interface *ei,
					     struct stream *s, uint8_t flags)
{
	// add in the parameters TLV
	stream_putw(s, EIGRP_TLV_PARAMETER);
	stream_putw(s, EIGRP_TLV_PARAMETER_LEN);

	// if graceful shutdown is needed to be announced, send all 255 in K
	// values
	if (flags & EIGRP_HELLO_GRACEFUL_SHUTDOWN) {
		stream_putc(s, 0xff); /* K1 */
		stream_putc(s, 0xff); /* K2 */
		stream_putc(s, 0xff); /* K3 */
		stream_putc(s, 0xff); /* K4 */
		stream_putc(s, 0xff); /* K5 */
		stream_putc(s, 0xff); /* K6 */
	} else			      // set k values
	{
		stream_putc(s, ei->eigrp->k_values[0]); /* K1 */
		stream_putc(s, ei->eigrp->k_values[1]); /* K2 */
		stream_putc(s, ei->eigrp->k_values[2]); /* K3 */
		stream_putc(s, ei->eigrp->k_values[3]); /* K4 */
		stream_putc(s, ei->eigrp->k_values[4]); /* K5 */
		stream_putc(s, ei->eigrp->k_values[5]); /* K6 */
	}

	// and set hold time value..
	stream_putw(s, ei->params.v_wait);

	return EIGRP_TLV_PARAMETER_LEN;
}

/**
 * @fn eigrp_hello_encode
 *
 * @param[in]		ei	pointer to interface hello packet came in on
 * @param[in]		s	packet stream TLV is stored to
 * @param[in]		ack	 if non-zero, neigbors sequence packet to ack
 * @param[in]		flags  type of hello packet
 * @param[in]		nbr_addr  pointer to neighbor address for Peer
 * Termination TLV
 *
 * @return eigrp_packet		pointer initialize hello packet
 *
 * @par
 * Allocate an EIGRP hello packet, and add in the the approperate TLVs
 *
 */
static struct eigrp_packet *eigrp_hello_encode(struct eigrp_interface *ei,
					       in_addr_t addr, uint32_t ack,
					       uint8_t flags,
					       struct in_addr *nbr_addr)
{
	struct eigrp_packet *ep;
	uint16_t length = EIGRP_HEADER_LEN;

	// allocate a new packet to be sent
	ep = eigrp_packet_new(EIGRP_PACKET_MTU(ei->ifp->mtu), NULL);

	if (ep) {
		// encode common header feilds
		eigrp_packet_header_init(EIGRP_OPC_HELLO, ei->eigrp, ep->s, 0,
					 0, ack);

		// encode Authentication TLV
		if ((ei->params.auth_type == EIGRP_AUTH_TYPE_MD5)
		    && (ei->params.auth_keychain != NULL)) {
			length += eigrp_add_authTLV_MD5_to_stream(ep->s, ei);
		} else if ((ei->params.auth_type == EIGRP_AUTH_TYPE_SHA256)
			   && (ei->params.auth_keychain != NULL)) {
			length += eigrp_add_authTLV_SHA256_to_stream(ep->s, ei);
		}

		/* encode appropriate parameters to Hello packet */
		if (flags & EIGRP_HELLO_GRACEFUL_SHUTDOWN)
			length += eigrp_hello_parameter_encode(
				ei, ep->s, EIGRP_HELLO_GRACEFUL_SHUTDOWN);
		else
			length += eigrp_hello_parameter_encode(
				ei, ep->s, EIGRP_HELLO_NORMAL);

		// figure out the version of code we're running
		length += eigrp_sw_version_encode(ep->s);

		if (flags & EIGRP_HELLO_ADD_SEQUENCE) {
			length += eigrp_sequence_encode(ei->eigrp, ep->s);
			length += eigrp_next_sequence_encode(ei->eigrp, ep->s);
		}

		// add in the TID list if doing multi-topology
		length += eigrp_tidlist_encode(ep->s);

		/* encode Peer Termination TLV if needed */
		if (flags & EIGRP_HELLO_GRACEFUL_SHUTDOWN_NBR)
			length +=
				eigrp_peer_termination_encode(ep->s, nbr_addr);

		// Set packet length
		ep->length = length;

		// set soruce address for the hello packet
		ep->dst.s_addr = addr;

		if ((ei->params.auth_type == EIGRP_AUTH_TYPE_MD5)
		    && (ei->params.auth_keychain != NULL)) {
			eigrp_make_md5_digest(ei, ep->s,
					      EIGRP_AUTH_BASIC_HELLO_FLAG);
		} else if ((ei->params.auth_type == EIGRP_AUTH_TYPE_SHA256)
			   && (ei->params.auth_keychain != NULL)) {
			eigrp_make_sha256_digest(ei, ep->s,
						 EIGRP_AUTH_BASIC_HELLO_FLAG);
		}

		// EIGRP Checksum
		eigrp_packet_checksum(ei, ep->s, length);
	}

	return (ep);
}

/**
 * @fn eigrp_hello_send
 *
 * @param[in]		nbr	neighbor the ACK should be sent to
 *
 * @return void
 *
 * @par
 *  Send (unicast) a hello packet with the destination address
 *  associated with the neighbor.  The eigrp header ACK feild will be
 *  updated to the neighbor's sequence number to acknolodge any
 *  outstanding packets
 */
void eigrp_hello_send_ack(struct eigrp_neighbor *nbr)
{
	struct eigrp_packet *ep;

	/* if packet succesfully created, add it to the interface queue */
	ep = eigrp_hello_encode(nbr->ei, nbr->src.s_addr,
				nbr->recv_sequence_number, EIGRP_HELLO_NORMAL,
				NULL);

	if (ep) {
		if (IS_DEBUG_EIGRP_PACKET(0, SEND))
			zlog_debug("Queueing [Hello] Ack Seq [%u] nbr [%pI4]",
				   nbr->recv_sequence_number, &nbr->src);

		/* Add packet to the top of the interface output queue*/
		eigrp_fifo_push(nbr->ei->obuf, ep);

		/* Hook thread to write packet. */
		if (nbr->ei->on_write_q == 0) {
			listnode_add(nbr->ei->eigrp->oi_write_q, nbr->ei);
			nbr->ei->on_write_q = 1;
		}
		event_add_write(master, eigrp_write, nbr->ei->eigrp,
				nbr->ei->eigrp->fd, &nbr->ei->eigrp->t_write);
	}
}

/**
 * @fn eigrp_hello_send
 *
 * @param[in]		ei	pointer to interface hello should be sent
 * @param[in]		flags type of hello packet
 * @param[in]		nbr_addr  pointer to neighbor address for Peer
 * Termination TLV
 *
 * @return void
 *
 * @par
 * Build and enqueue a generic (multicast) periodic hello packet for
 * sending.  If no packets are currently queues, the packet will be
 * sent immadiatly
 */
void eigrp_hello_send(struct eigrp_interface *ei, uint8_t flags,
		      struct in_addr *nbr_addr)
{
	struct eigrp_packet *ep = NULL;

	if (IS_DEBUG_EIGRP_PACKET(0, SEND))
		zlog_debug("Queueing [Hello] Interface(%s)", IF_NAME(ei));

	/* if packet was succesfully created, then add it to the interface queue
	 */
	ep = eigrp_hello_encode(ei, htonl(EIGRP_MULTICAST_ADDRESS), 0, flags,
				nbr_addr);

	if (ep) {
		// Add packet to the top of the interface output queue
		eigrp_fifo_push(ei->obuf, ep);

		/* Hook thread to write packet. */
		if (ei->on_write_q == 0) {
			listnode_add(ei->eigrp->oi_write_q, ei);
			ei->on_write_q = 1;
		}

		if (ei->eigrp->t_write == NULL) {
			if (flags & EIGRP_HELLO_GRACEFUL_SHUTDOWN) {
				event_execute(master, eigrp_write, ei->eigrp,
					      ei->eigrp->fd, NULL);
			} else {
				event_add_write(master, eigrp_write, ei->eigrp,
						ei->eigrp->fd,
						&ei->eigrp->t_write);
			}
		}
	}
}