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ROUTED(8)										ROUTED(8)

       routed - network routing daemon

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

       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 ker-
       nel  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  net-

       In  normal  operation  routed listens on the udp(4) socket for the route service (see ser-
       vices(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

       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
       ``infinite'').  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 ta-
	      ble entry.  That is, updated information is being received from the very	internet-
	      work 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 networks.  The response is sent to the broad-
       cast 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 reception of responses on  each  net-
       work 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'' des-
	      tination.  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

       -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  gateways are maintained in the routing tables forever and information
       regarding their existence is included in  any  routing  information  transmitted.   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  asso-
       ciated  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  configu-
       rations should contact the Computer Systems Research Group at Berkeley.

       /etc/gateways  for distant gateways

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

       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 fail-
       ures in network interfaces (e.g., when the output side fails).

4.2 Berkeley Distribution		November 17, 1996				ROUTED(8)
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