routed



ROUTED(8)                 BSD System Manager’s Manual                ROUTED(8)


NAME

     routed - network routing daemon


SYNOPSIS

     routed [-d] [-g] [-q] [-s] [-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 Proto-
     col 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(8)
     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(2) to find those
     directly connected interfaces configured into the system and marked
     ‘‘up’’ (the software loopback interface is ignored).  If multiple inter-
     faces are present, it is assumed that the host will forward packets
     between networks.  Routed then transmits a request packet on each inter-
     face (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 gen-
     erated contains a list of known routes, each marked with a ‘‘hop count’’
     metric (a count of 16, or greater, is considered ‘‘infinite’’).  The met-
     ric 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 networks.
     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 reception 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.

     Options supported by routed:

     -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 his-
     tory 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(2).  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).  Routes through passive gateways are
     installed in the kernel’s routing tables once upon startup.  Such routes
     are not included in any routing information transmitted.  Active gateways
     are treated equally to network interfaces.  Routing information is dis-
     tributed to the gateway and if no routing information is received for a
     period of time, the associated route is deleted.  Gateways marked
     external 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 follow-
     ing 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 spe-
     cific host.

     Name1 is the name of the destination network or host.  This may be a sym-
     bolic 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 informa-
     tion 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.


FILES

     /etc/gateways  for distant gateways


SEE ALSO

     udp(7), icmp(7)

     Internet Transport Protocols, XSIS 028112, Xerox System Integration
     Standard.


BUGS

     routed is of dubious value. Consider using gated(8) or zebra(8).

     The kernel’s routing tables may not correspond to those of routed when
     redirects change or add routes.  Routed should note any redirects
     received by reading the ICMP packets received via a raw socket.

     Routed should incorporate other routing protocols.  Using separate pro-
     cesses for each requires configuration options to avoid redundant or com-
     peting routes.

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


HISTORY

     The routed command appeared in 4.2BSD.

Linux NetKit (0.17)            December 11, 1993           Linux NetKit (0.17)

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