routed(8) CLIX routed(8)
NAME
routed - Runs a network routing daemon
SYNOPSIS
/etc/routed [-d] [-g] [-s] [-q] [-t] [logfile]
FLAGS
The routed command supports the following flags:
-d Enables additional debugging information to be logged (such as bad
packets received).
-g Offers a route to the default destination on internetwork routers.
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 Forces the routed command to supply routing information, despite
whether or not it is acting as an internetwork router. This is the
default flag if multiple network interfaces are present, or if a
point-to-point link is in use.
-q Causes the opposite effect of the -s flag.
-t Displays all sent or received packets on stdout. In addition, when
this flag is set, keyboard interrupts can still kill displaying
processes.
DESCRIPTION
The routed command is invoked during system boot to manage the network
routing tables. The routed command uses a variant of the Xerox Network
System (XNS) Routing Information Protocol (RIP) in maintaining up-to-date
kernel routing table entries. It uses a generalized protocol capable of
use with multiple address types, however, it is currently used only for
Internet routing within a cluster of networks.
In normal operation, the routed command listens to the udp socket for the
route service and for routing information packets. (See services(4)). If
the host is an internetwork router, it periodically supplies copies of its
routing tables to any hosts and networks which may be directly connected.
When routed is started, it uses the I_IFGETCONF ioctl() to find directly
connected interfaces configured into the system and marked up. If
multiple interfaces are present, it is assumed that the host will forward
packets between networks. The routed command then transmits a request
packet on each interface (using a broadcast packet if the interface
supports it) and enters a loop, listening for the request and response
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packets from other hosts.
When a request packet is received, the routed command formulates a reply
based on the information maintained in its internal tables. The generated
response packet contains a list of known routes, each marked with a hop
count metric. (A count of 16 or greater is 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:
⊕ No routing table entry exists for the destination network or host, and
the metric indicates the destination is reachable. (The hop count is
not infinite.)
⊕ 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 internetwork router through which packets for the destination
are being routed.
⊕ 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 short as
the current route.
⊕ The new route describes a route to the destination shorter than the one
currently stored in the routing tables (the metric length of the new
route is compared to the one stored in the table).
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
three minutes, the entry's metric is set to infinity and marked for
deletion. Deletions are delayed an additional 60 seconds to ensure that
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 networks capable of handling that function
⊕ The destination address on point-to-point links
⊕ The router's own address on other networks.
The normal routing tables are bypassed when gratuitous responses are sent.
The reception of responses on each network is used to determine if the
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network and interface are functioning correctly. If no response is
received for an interface, another route may be chosen to route around the
interface, or the route may be dropped if no alternative is available.
The logfile variable is interpreted as the name of a file in which the
routed command actions are logged. This log contains information about
any changes to the routing tables and, a history of recent messages sent
and received that are related to the changed route.
In addition to the facilities described above, the routed command supports
the concept of distant, passive, and active gateways. When routed is
started, it reads the file /etc/gateways to find gateways that may not be
located using only information from the I_IFGETCONF ioctl(). Gateways
specified in this manner should be marked as passive if they are not
expected to exchange routing information, while gateways marked as active
should be willing to exchange routing information. (They should have a
routed command 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 as 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 or included in routing updates. External entries inform
routed that another routing process will install such a route and
therefore alternate routes to that destination should not be installed.
This type of entry is required only when there is a chance that both
routers may learn of routes to the same destination.
The /etc/gateways file is composed of a series of lines, each in the
following format:
net name1 gateway name2 metric value [passive|active|externa]
The net keyword indicates that the route is to a network.
The name1 variable is the name of the destination network. This may be a
symbolic name located in the /etc/networks, the Domain Name System (DNS)
database, or an Internet address specified in dot notation. (See inet(3)).
The name2 variable represents the name or address of the gateway to which
messages should be forwarded.
The value variable is a metric indicating the hop count to the destination
host or network. If value is 0, name1 is a logically equivalent network
for the interface with address name2.
Either the passive, active, or external keyword indicates whether the
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gateway should be treated as passive or active (as described above) or if
the gateway is external to the scope of the routed daemon.
Internetwork routers that are directly attached to the Advanced Research
Project Agency Network (ARPANET) or Military Network (MILNET) should use
the Exterior Gateway Protocol (EGP) to gather routing information rather
than using a static routing table of passive gateways. The EGP is
required to provide routes for local networks to the rest of the Internet
system.
EXAMPLES
1. To run the routing daemon, enter:
/etc/routed
2. To run the routing daemon and permit the user to see diagnostic
messages, enter:
/etc/routed -d
3. To run the routing daemon and advertise the distant destination,
enter:
/etc/routed -g
4. To run the routing daemon and supply routing information, enter:
/etc/routed -s
5. To suppress transmission of routing information, enter:
/etc/routed -q
6. To display incoming and outgoing routing packets, enter:
/etc/routed -t
7. To log diagnostics to the file /usr/log/routed.log, enter:
/etc/routed /usr/log/routed.log
FILES
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/etc/gateways Distant gateways.
CAUTIONS
Kernel routing tables may not correspond to routed routing tables when
these tables have been redirected, changed, or have had routes added.
DIAGNOSTICS
routed: Cannot open udp device
The routed command is unable to open the network device.
Other diagnostics messages are displayed if system errors are encountered.
EXIT VALUES
Exit values are not valid for this command.
RELATED INFORMATION
Commands: gated(1)
Files: udp(7)
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