ROUTED(8)						      System Manager's Manual							 ROUTED(8)

NAME

       routed - network routing daemon

SYNOPSIS

       routed [ -d ] [ -g ] [ -s ] [ -q ] [ -t ] [ logfile ]

DESCRIPTION

       Routed is invoked at boot time to manage the network routing tables.  The routing daemon uses a variant of the Xerox NS Routing Information
       Protocol in maintaining up to date kernel routing table entries.  It used a generalized protocol  capable  of  use  with  multiple  address
       types, but is currently used only for Internet routing within a cluster of networks.

       In  normal  operation  routed listens on the udp(4) socket for the route service (see services(5)) for routing information packets.  If the
       host is an internetwork router, it periodically supplies copies of its routing tables to any directly connected hosts and networks.

       When routed is started, it uses the SIOCGIFCONF ioctl to find those directly connected interfaces configured into  the  system  and  marked
       ``up''  (the software loopback interface is ignored).  If multiple interfaces are present, it is assumed that the host will forward packets
       between networks.  Routed then transmits a request packet on each interface (using a broadcast packet if the  interface	supports  it)  and
       enters a loop, listening for request and response packets from other hosts.

       When  a	request  packet  is  received, routed formulates a reply based on the information maintained in its internal tables.  The response
       packet generated contains a list of known routes, each marked with a ``hop count'' metric (a count of 16, or greater, is considered ``infi-
       nite'').  The metric associated with each route returned provides a metric relative to the sender.

       Response packets received by routed are used to update the routing tables if one of the following conditions is satisfied:

       (1)    No  routing  table entry exists for the destination network or host, and the metric indicates the destination is ``reachable'' (i.e.
	      the hop count is not infinite).

       (2)    The source host of the packet is the same as the router in the existing routing table entry.  That is, updated information is  being
	      received from the very internetwork router through which packets for the destination are being routed.

       (3)    The  existing  entry in the routing table has not been updated for some time (defined to be 90 seconds) and the route is at least as
	      cost effective as the current route.

       (4)    The new route describes a shorter route to the destination than the one currently stored in the routing tables; the  metric  of  the
	      new route is compared against the one stored in the table to decide this.

       When  an update is applied, routed records the change in its internal tables and updates the kernel routing table.  The change is reflected
       in the next response packet sent.

       In addition to processing incoming packets, routed also periodically checks the routing table entries.  If an entry has	not  been  updated
       for 3 minutes, the entry's metric is set to infinity and marked for deletion.  Deletions are delayed an additional 60 seconds to insure the
       invalidation is propagated throughout the local internet.

       Hosts acting as internetwork routers gratuitously supply their routing tables every 30 seconds to all directly  connected  hosts  and  net-
       works.  The response is sent to the broadcast address on nets capable of that function, to the destination address on point-to-point links,
       and to the router's own address on other networks.  The normal routing tables are bypassed when sending gratuitous responses.   The  recep-
       tion  of  responses  on	each  network  is  used  to determine that the network and interface are functioning correctly.  If no response is
       received on an interface, another route may be chosen to route around the interface, or the route may  be  dropped  if  no  alternative	is
       available.

       Routed supports several options:

       -d     Enable additional debugging information to be logged, such as bad packets received.

       -g     This  flag  is used on internetwork routers to offer a route to the ``default'' destination.  This is typically used on a gateway to
	      the Internet, or on a gateway that uses another routing protocol whose routes are not reported to other local routers.

       -s     Supplying this option forces routed to supply routing information whether it is acting as an internetwork router or  not.   This	is
	      the default if multiple network interfaces are present, or if a point-to-point link is in use.

       -q     This is the opposite of the -s option.

       -t     If  the  -t  option  is  specified,  all	packets sent or received are printed on the standard output.  In addition, routed will not
	      divorce itself from the controlling terminal so that interrupts from the keyboard will kill the process.

       Any other argument supplied is interpreted as the name of file in which routed's actions should be logged.  This log  contains  information
       about  any  changes to the routing tables and, if not tracing all packets, a history of recent messages sent and received which are related
       to the changed route.

       In addition to the facilities described above, routed supports the notion of ``distant'' passive  and  active  gateways.   When	routed	is
       started	up,  it  reads	the file /etc/gateways to find gateways which may not be located using only information from the SIOGIFCONF ioctl.
       Gateways specified in this manner should be marked passive if they are not expected to exchange routing information, while gateways  marked
       active  should  be willing to exchange routing information (i.e.  they should have a routed process running on the machine).  Passive gate-
       ways are maintained in the routing tables forever and information regarding their existence is included in any routing  information  trans-
       mitted.	 Active  gateways  are treated equally to network interfaces.  Routing information is distributed to the gateway and if no routing
       information is received for a period of the time, the associated route is deleted.  External gateways are also passive, but are not  placed
       in  the	kernel	routing table nor are they included in routing updates.  The function of external entries is to inform routed that another
       routing process will install such a route, and that alternate routes to that destination should not be installed.  Such	entries  are  only
       required when both routers may learn of routes to the same destination.

       The /etc/gateways is comprised of a series of lines, each in the following format:

       < net | host > name1 gateway name2 metric value < passive | active | external >

       The net or host keyword indicates if the route is to a network or specific host.

       Name1  is  the name of the destination network or host.	This may be a symbolic name located in /etc/networks or /etc/hosts (or, if started
       after named(8), known to the name server), or an Internet address specified in ``dot'' notation; see inet(3).

       Name2 is the name or address of the gateway to which messages should be forwarded.

       Value is a metric indicating the hop count to the destination host or network.

       One of the keywords passive, active or external indicates if the gateway should be treated as passive or active (as  described  above),	or
       whether the gateway is external to the scope of the routed protocol.

       Internetwork  routers  that are directly attached to the Arpanet or Milnet should use the Exterior Gateway Protocol (EGP) to gather routing
       information rather then using a static routing table of passive gateways.  EGP is required in order to provide routes for local networks to
       the  rest  of the Internet system.  Sites needing assistance with such configurations should contact the Computer Systems Research Group at
       Berkeley.

FILES

       /etc/gateways  for distant gateways

SEE ALSO

       ``Internet Transport Protocols'', XSIS 028112, Xerox System Integration Standard.
       udp(4), XNSrouted(8), htable(8)

BUGS

       The kernel's routing tables may not correspond to those of routed when redirects change or add routes.  The only  remedy  for  this  is	to
       place the routing process in the kernel.

       Routed  should  incorporate  other  routing protocols, such as Xerox NS (XNSrouted(8)) and EGP.	Using separate processes for each requires
       configuration options to avoid redundant or competing routes.

       Routed should listen to intelligent interfaces, such as an IMP, and to error protocols, such as ICMP, to gather more information.  It  does
       not always detect unidirectional failures in network interfaces (e.g., when the output side fails).

4.2 Berkeley Distribution					 November 17, 1996							 ROUTED(8)