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+.NC "The Design of the ARGO Network Layer"
+.sh 1 "End System to Intermediate System Routing Protocol"
+.pp
+The following sections describe the design of the End System to Intermediate
+System (ES-IS) Routing Exchange Protocol.
+.sh 2 "Overview"
+.nf
+- protocol involves sending/receiving hello pdus.
+- timers determine
+	- when to send information
+	- when to discard information
+- want to keep as much of the work outside of kernel
+- only put functions and tables in kernel when necessary
+.sh 2 "Supported Features (brief overview of each)"
+- report configuration (both ES and IS)
+- record configuration (both ES and IS)
+- flush configuration (both ES and IS)
+- query configuration (ES only)
+- configuration response (ES only)
+- request redirect (IS only)
+- record redirect (ES only)
+- flush old redirect (ES only)
+- multicast vs. broadcast (using broadcast only)
+.sh 2 "Kernel Resident Features"
+.sh 3 "Support for PDU Transmission"
+- need mechanism to send/receive PDUs
+- utilize ES-IS socket (like raw socket)
+- socket(AF_ISO, SOCK_DGRAM, ISOPROTO_ESIS)
+.sh 4 "Sending PDUs"
+- sendmsg() used for transmitting PDUS
+- data will be pre-formed ES-IS PDU
+- no checks will be made on the pdu format
+- addr_snpa is the destination (to)
+- before sending, socket must be associated with a particular interface
+	this is done via setsockopt():
+		ESISOPT_SETIF - option
+		buffer is name of interface, ie. "un0"
+.sh 4 "Receiving PDUs"
+- recvmsg() used for receiving PDUs
+- data will be:
+	#define	ESIS_PDU
+	#define ESIS_CONFIG_RESP
+	#define ESIS_REDIR_REQ
+	struct esis_indication {
+		short	ei_type;		/* type of indication */
+		union {
+			struct ? config_resp
+			struct ? redir_req
+			char	 pdu[0]
+		} ei_u;
+	}
+- no checks will be made on the pdu format
+- addr_snpa is the source (from)
+.sh 4 "Addressing"
+- ES-IS PDUs are sent to SNPA.
+- addresses used are SN addresses, not NSAP addresses
+- format of msg_name (part of msghdr) struct sockaddr_iso
+	afi = 0	/* means special snpa address */
+	isoa_u is struct addr_snpa
+		struct addr_snpa {
+			char	sn_addr[7];	/* snpa addr */
+		}
+	isoa_len is number of bytes of sn_addr that are valid
+
+- sn_addr may be a unicast or multicast address
+- multicast addresses will be faked via broadcast addresses
+.sh 3 "NSAP to SNPA translation"
+- translation from NSAP to SNAP required for every CLNP PDU sent
+- function provided by iso_nsap_to_snpa
+
+	iso_nsap_to_snpa(ifp, m, nsap, snpa)
+	struct ifnet		*ifp;	/* outgoing interface */
+	struct mbuf			*m;		/* pkt */
+	struct sockaddr_iso	*nsap;	/* destination address */
+	char				*snpa;	/* RESULT: snpa address */
+	{
+		if (nsap.afi == AFI_SNPAADDR) {
+			copy snpa addr from nsap into snpa
+			return SUCCESS
+		} else {
+			scan RIB for (RIB.nsap == nsap)
+			if (found) {
+				copy RIB.snpa into snpa
+				return SUCCESS
+			}
+			scan RIB for (RIB.type == IS) && (RIB.ifp = ifp)
+			if (found) {
+				copy RIB.snpa into snpa
+				return SUCCESS
+			}
+			if (ifp allows multicast) {
+				/* invoke query configuration function */
+				copy ifp.ifaddr.ifa_all_es into snpa
+				return SUCCESS
+			}
+
+			return FAILURE
+		}
+	}
+
+- NSAP to SNPA table resides in kernel so CLNP has quick access
+- entries added/timed-out of table via user level ES-IS daemon
+.sh 3 "Query Configuration Functon"
+- invoked when iso_nsap_to_snpa
+	- requires snpa, but
+	- does not find a match for dest nsap, and
+	- does not find a match for Any IS.
+- clnp packet is sent to address "all ES" as specified in ifnet structure
+	(for now, this is just the broadcast address)
+.sh 3 "Configuration Response Function"
+- invoked by clnp_input(), after determining that the packet received is
+	destined for one of its NSAPs
+- checks if sn_dst == "all ES" (for now, this is all hex ffs)
+- if true, a copy of packet is made, and passed up to esis_input()