ROUTED(8) BSD System Manager's Manual ROUTED(8)NAME
routed, rdisc — network RIP and router discovery routing daemon
SYNOPSISrouted [-sqdghmpAtv] [-T tracefile] [-F net[/mask[,metric]]] [-P parms]
The routed utility is a daemon invoked at boot time to manage the network
routing tables. It uses Routing Information Protocol, RIPv1 (RFC 1058),
RIPv2 (RFC 1723), and Internet Router Discovery Protocol (RFC 1256) to
maintain the kernel routing table. The RIPv1 protocol is based on the
reference 4.3BSD daemon.
It listens on the udp(4) socket for the route(8) service (see
services(5)) for Routing Information Protocol packets. It also sends and
receives multicast Router Discovery ICMP messages. If the host is a
router, routed periodically supplies copies of its routing tables to any
directly connected hosts and networks. It also advertises or solicits
default routes using Router Discovery ICMP messages.
When started (or when a network interface is later turned on), routed
uses an AF_ROUTE address family facility to find those directly connected
interfaces configured into the system and marked "up". It adds necessary
routes for the interfaces to the kernel routing table. Soon after being
first started, and provided there is at least one interface on which RIP
has not been disabled, routed deletes all pre-existing non-static routes
in kernel table. Static routes in the kernel table are preserved and
included in RIP responses if they have a valid RIP -hopcount (see
If more than one interface is present (not counting the loopback inter‐
face), it is assumed that the host should forward packets among the con‐
nected networks. After transmitting a RIP request and Router Discovery
Advertisements or Solicitations on a new interface, the daemon enters a
loop, listening for RIP request and response and Router Discovery 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 adver‐
tised metric for a route reflects the metrics associated with interfaces
(see ifconfig(8)) though which it is received and sent, so setting the
metric on an interface is an effective way to steer traffic. See also
adj_inmetric and adj_outmetric parameters below.
Responses do not include routes with a first hop on the requesting net‐
work to implement in part split-horizon. Requests from query programs
such as rtquery(8) are answered with the complete table.
The routing table maintained by the daemon includes space for several
gateways for each destination to speed recovery from a failing router.
RIP response packets received are used to update the routing tables pro‐
vided they are from one of the several currently recognized gateways or
advertise a better metric than at least one of the existing gateways.
When an update is applied, routed records the change in its own tables
and updates the kernel routing table if the best route to the destination
changes. The change in the kernel routing table is reflected in the next
batch of response packets sent. If the next response is not scheduled
for a while, a flash update response containing only recently changed
routes is 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 until the route has been advertised with an infi‐
nite metric to ensure the invalidation is propagated throughout the local
internet. This is a form of poison reverse.
Routes in the kernel table that are added or changed as a result of ICMP
Redirect messages are deleted after a while to minimize black-holes.
When a TCP connection suffers a timeout, the kernel tells routed, which
deletes all redirected routes through the gateway involved, advances the
age of all RIP routes through the gateway to allow an alternate to be
chosen, and advances of the age of any relevant Router Discovery Protocol
Hosts acting as internetwork routers gratuitously supply their routing
tables every 30 seconds to all directly connected hosts and networks.
These RIP responses are sent to the broadcast address on nets that sup‐
port broadcasting, to the destination address on point-to-point links,
and to the router's own address on other networks. If RIPv2 is enabled,
multicast packets are sent on interfaces that support multicasting.
If no response is received on a remote interface, if there are errors
while sending responses, or if there are more errors than input or output
(see netstat(1)), then the cable or some other part of the interface is
assumed to be disconnected or broken, and routes are adjusted appropri‐
The Internet Router Discovery Protocol is handled similarly. When the
daemon is supplying RIP routes, it also listens for Router Discovery
Solicitations and sends Advertisements. When it is quiet and listening
to other RIP routers, it sends Solicitations and listens for Advertise‐
ments. If it receives a good Advertisement and it is not multi-homed, it
stops listening for broadcast or multicast RIP responses. It tracks sev‐
eral advertising routers to speed recovery when the currently chosen
router dies. If all discovered routers disappear, the daemon resumes
listening to RIP responses. It continues listening to RIP while using
Router Discovery if multi-homed to ensure all interfaces are used.
The Router Discovery standard requires that advertisements have a default
"lifetime" of 30 minutes. That means should something happen, a client
can be without a good route for 30 minutes. It is a good idea to reduce
the default to 45 seconds using -P rdisc_interval=45 on the command line
or rdisc_interval=45 in the /etc/gateways file.
While using Router Discovery (which happens by default when the system
has a single network interface and a Router Discover Advertisement is
received), there is a single default route and a variable number of redi‐
rected host routes in the kernel table. On a host with more than one
network interface, this default route will be via only one of the inter‐
faces. Thus, multi-homed hosts running with -q might need no_rdisc
See the pm_rdisc facility described below to support "legacy" systems
that can handle neither RIPv2 nor Router Discovery.
By default, neither Router Discovery advertisements nor solicitations are
sent over point to point links (e.g. PPP). The netmask associated with
point-to-point links (such as SLIP or PPP, with the IFF_POINTOPOINT flag)
is used by routed to infer the netmask used by the remote system when
RIPv1 is used.
The following options are available:
-s force routed to supply routing information. This is the default
if multiple network interfaces are present on which RIP or Router
Discovery have not been disabled, and if the kernel switch ipfor‐
-q is the opposite of the -s option. This is the default when only
one interface is present. With this explicit option, the daemon
is always in "quiet-mode" for RIP and does not supply routing
information to other computers.
-d do not run in the background. This option is meant for interac‐
-g used on internetwork routers to offer a route to the "default"
destination. It is equivalent to -F 0/0,1 and is present mostly
for historical reasons. A better choice is -P pm_rdisc on the
command line or pm_rdisc in the /etc/gateways file, since a
larger metric will be used, reducing the spread of the poten‐
tially dangerous default route. This is typically used on a
gateway to the Internet, or on a gateway that uses another rout‐
ing protocol whose routes are not reported to other local
routers. Notice that because a metric of 1 is used, this feature
is dangerous. It is more commonly accidentally used to create
chaos with a routing loop than to solve problems.
-h cause host or point-to-point routes to not be advertised, pro‐
vided there is a network route going the same direction. That is
a limited kind of aggregation. This option is useful on gateways
to Ethernets that have other gateway machines connected with
point-to-point links such as SLIP.
-m cause the machine to advertise a host or point-to-point route to
its primary interface. It is useful on multi-homed machines such
as NFS servers. This option should not be used except when the
cost of the host routes it generates is justified by the popular‐
ity of the server. It is effective only when the machine is sup‐
plying routing information, because there is more than one inter‐
face. The -m option overrides the -q option to the limited
extent of advertising the host route.
-A do not ignore RIPv2 authentication if we do not care about RIPv2
authentication. This option is required for conformance with RFC
1723. However, it makes no sense and breaks using RIP as a dis‐
covery protocol to ignore all RIPv2 packets that carry authenti‐
cation when this machine does not care about authentication.
-t increase the debugging level, which causes more information to be
logged on the tracefile specified with -T or standard out. The
debugging level can be increased or decreased with the SIGUSR1 or
SIGUSR2 signals or with the rtquery(8) command.
increases the debugging level to at least 1 and causes debugging
information to be appended to the trace file. Note that because
of security concerns, it is wisest to not run routed routinely
with tracing directed to a file.
-v display and logs the version of daemon.
minimize routes in transmissions via interfaces with addresses
that match net/mask, and synthesizes a default route to this
machine with the metric. The intent is to reduce RIP traffic on
slow, point-to-point links such as PPP links by replacing many
large UDP packets of RIP information with a single, small packet
containing a "fake" default route. If metric is absent, a value
of 14 is assumed to limit the spread of the "fake" default route.
This is a dangerous feature that when used carelessly can cause
routing loops. Notice also that more than one interface can
match the specified network number and mask. See also -g.
is equivalent to adding the parameter line parms to the
Any other argument supplied is interpreted as the name of a file in which
the actions of routed should be logged. It is better to use -T instead
of appending the name of the trace file to the command.
The routed utility also supports the notion of "distant" passive or
active gateways. When routed is started, it reads the file /etc/gateways
to find such distant gateways which may not be located using only infor‐
mation from a routing socket, to discover if some of the local gateways
are passive, and to obtain other parameters. 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 RIP packets. Routes through passive gateways are installed in
the kernel's routing tables once upon startup and are not included in
transmitted RIP responses.
Distant active gateways are treated like network interfaces. RIP
responses are sent to the distant active gateway. If no responses are
received, the associated route is deleted from the kernel table and RIP
responses advertised via other interfaces. If the distant gateway
resumes sending RIP responses, the associated route is restored.
Such gateways can be useful on media that do not support broadcasts or
multicasts but otherwise act like classic shared media like Ethernets
such as some ATM networks. One can list all RIP routers reachable on the
HIPPI or ATM network in /etc/gateways with a series of "host" lines.
Note that it is usually desirable to use RIPv2 in such situations to
avoid generating lists of inferred host routes.
Gateways marked external are also passive, but are not placed in the ker‐
nel routing table nor are they included in routing updates. The function
of external entries is to indicate that another routing process will
install such a route if necessary, and that other routes to that destina‐
tion should not be installed by routed. Such entries are only required
when both routers may learn of routes to the same destination.
The /etc/gateways file is comprised of a series of lines, each in one of
the following two formats or consist of parameters described later.
Blank lines and lines starting with '#' are comments.
net Nname[/mask] gateway Gname metric value <passive | active | extern>
host Hname gateway Gname metric value <passive | active | extern>
Nname or Hname is the name of the destination network or host. It may be
a symbolic network name or an Internet address specified in "dot" nota‐
tion (see inet(3)). (If it is a name, then it must either be defined in
/etc/networks or /etc/hosts, or named(8), must have been started before
Mask is an optional number between 1 and 32 indicating the netmask asso‐
ciated with Nname.
Gname is the name or address of the gateway to which RIP responses should
Value is the hop count to the destination host or network.
Host hname is equivalent to net nname/32.
One of the keywords passive, active or external must be present to indi‐
cate whether the gateway should be treated as passive or active (as
described above), or whether the gateway is external to the scope of the
As can be seen when debugging is turned on with -t, such lines create
pseudo-interfaces. To set parameters for remote or external interfaces,
a line starting with if=alias(Hname), if=remote(Hname), etc. should be
Lines that start with neither "net" nor "host" must consist of one or
more of the following parameter settings, separated by commas or blanks:
indicates that the other parameters on the line apply to the
interface name ifname.
advertises a route to network nname with mask mask and the sup‐
plied metric (default 1). This is useful for filling "holes" in
CIDR allocations. This parameter must appear by itself on a
line. The network number must specify a full, 32-bit value, as
in 192.0.2.0 instead of 192.0.2.
Do not use this feature unless necessary. It is dangerous.
specifies that netmask of the network of which nname/mask1 is a
subnet should be mask2. For example,
“ripv1_mask=192.0.2.16/28,27” marks 192.0.2.16/28 as a subnet of
192.0.2.0/27 instead of 192.0.2.0/24. It is better to turn on
RIPv2 instead of using this facility, for example with ripv2_out.
specifies a RIPv2 cleartext password that will be included on all
RIPv2 responses sent, and checked on all RIPv2 responses
received. Any blanks, tab characters, commas, or '#', '|', or
NULL characters in the password must be escaped with a backslash
(\). The common escape sequences \n, \r, \t, \b, and \xxx have
their usual meanings. The KeyID must be unique but is ignored
for cleartext passwords. If present, start and stop are time‐
stamps in the form year/month/day@hour:minute. They specify when
the password is valid. The valid password with the most future
is used on output packets, unless all passwords have expired, in
which case the password that expired most recently is used, or
unless no passwords are valid yet, in which case no password is
output. Incoming packets can carry any password that is valid,
will be valid within the next 24 hours, or that was valid within
the preceding 24 hours. To protect the secrets, the passwd set‐
tings are valid only in the /etc/gateways file and only when that
file is readable only by UID 0.
specifies a RIPv2 MD5 password. Except that a KeyID is required,
this keyword is similar to passwd.
no_ag turns off aggregation of subnets in RIPv1 and RIPv2 responses.
turns off aggregation of networks into supernets in RIPv2
marks the interface to not be advertised in updates sent via
other interfaces, and turns off all RIP and router discovery
through the interface.
no_rip disables all RIP processing on the specified interface. If no
interfaces are allowed to process RIP packets, routed acts purely
as a router discovery daemon.
Note that turning off RIP without explicitly turning on router
discovery advertisements with rdisc_adv or -s causes routed to
act as a client router discovery daemon, not advertising.
causes RIPv2 packets to be broadcast instead of multicast.
causes no RIP updates to be sent.
causes RIPv1 received responses to be ignored.
causes RIPv2 received responses to be ignored.
turns on RIPv2 output and causes RIPv2 advertisements to be mul‐
ticast when possible.
ripv2 is equivalent to no_ripv1_in and no_ripv1_out. This enables
disables the Internet Router Discovery Protocol.
disables the transmission of Router Discovery Solicitations.
specifies that Router Discovery solicitations should be sent,
even on point-to-point links, which by default only listen to
Router Discovery messages.
disables the transmission of Router Discovery Advertisements.
specifies that Router Discovery Advertisements should be sent,
even on point-to-point links, which by default only listen to
Router Discovery messages.
specifies that Router Discovery packets should be broadcast
instead of multicast.
sets the preference in Router Discovery Advertisements to the
optionally signed integer N. The default preference is 0.
Default routes with smaller or more negative preferences are pre‐
ferred by clients.
sets the nominal interval with which Router Discovery Advertise‐
ments are transmitted to N seconds and their lifetime to 3*N.
has an identical effect to -F net[/mask][=metric] with the net‐
work and mask coming from the specified interface.
is similar to fake_default. When RIPv2 routes are multicast, so
that RIPv1 listeners cannot receive them, this feature causes a
RIPv1 default route to be broadcast to RIPv1 listeners. Unless
modified with fake_default, the default route is broadcast with a
metric of 14. That serves as a "poor man's router discovery"
adjusts the hop count or metric of received RIP routes by delta.
The metric of every received RIP route is increased by the sum of
two values associated with the interface. One is the
adj_inmetric value and the other is the interface metric set with
adjusts the hop count or metric of advertised RIP routes by
delta. The metric of every received RIP route is increased by
the metric associated with the interface by which it was
received, or by 1 if the interface does not have a non-zero met‐
ric. The metric of the received route is then increased by the
adj_outmetric associated with the interface. Every advertised
route is increased by a total of four values, the metric set for
the interface by which it was received with ifconfig(8), the
adj_inmetric delta of the receiving interface, the metric set for
the interface by which it is transmitted with ifconfig(8), and
the adj_outmetric delta of the transmitting interface.
causes RIP packets from router rname and other routers named in
other trust_gateway keywords to be accepted, and packets from
other routers to be ignored. If networks are specified, then
routes to other networks will be ignored from that router.
allows the kernel to listen ICMP Redirect messages when the sys‐
tem is acting as a router and forwarding packets. Otherwise,
ICMP Redirect messages are overridden and deleted when the system
is acting as a router.
/etc/gateways for distant gateways
SEE ALSOicmp(4), udp(4), rtquery(8)
Internet Transport Protocols, XSIS 028112, Xerox System Integration
The routed utility appeared in 4.2BSD.
It does not always detect unidirectional failures in network interfaces,
for example, when the output side fails.
BSD June 1, 1996 BSD