4.3BSD - /usr/man/cat8/routed.0

ROUTED(8C)                                                          ROUTED(8C)


NAME
       routed - network routing daemon

SYNOPSIS
       /etc/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(4P) 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 rout‐
       ing 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  pack‐
       ets  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  rela���
       tive 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  dele‐
       tion.   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.

       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 gate‐
              way 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 informa‐
              tion 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.  Gate‐
       ways  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 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 destina‐
       tion 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 fol‐
       lowing 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
       symbolic name located in /etc/networks or /etc/hosts  (or,  if  started
       after named(8), known to the name server), or an Internet address spec‐
       ified in ‘‘dot’’ notation; see inet(3N).

       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  gate‐
       way  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  Mil‐
       net  should  use  the Exterior Gateway Protocol (EGP) to gather routing
       information rather then using a static routing table of  passive  gate‐
       ways.  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(4P), XNSrouted(8C), 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(8C)) 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        May 24, 1986                       ROUTED(8C)