ROUTED(1M) ROUTED(1M)
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(4)) 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 ``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 table entry. That is, updated
information is being received from the very
internetwork router through which packets for the
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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.
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.
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-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 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(1M), known to the
name server), or an Internet address specified in ``dot''
notation; see inet(3N).
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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(4P), htable(1M)
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).
ORIGIN
U.C. Berkeley, with changes from Silicon Graphics, Inc.
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