routed(8c)routed(8c)Namerouted - network routing daemon
Syntax
/etc/routed [ options ] [ logfile ]
Description
The program 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.
In normal operation the program listens on a socket for packets of
routing information. If the host is an internetwork router, it period‐
ically supplies copies of its routing tables to any directly connected
hosts and networks.
When 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 net‐
works. The command 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, 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".
The response packets received by 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. That is,
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 very 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
cost effective as the current route.
· 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, the command records the change in its inter‐
nal tables and generates a response packet to all directly connected
hosts and networks. The command waits a short period of time (no more
than 30 seconds) before modifying the kernel's routing tables to allow
possible unstable situations to settle.
In addition to processing incoming packets, the command 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 internet.
Hosts acting as internetwork routers 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 responses. The reception of responses on each network is
used to determine if that network and interface are functioning cor‐
rectly. 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.
The program supports the notion of distant passive and active gateways.
When is started up, it reads the file to find gateways which may not be
identified using the SIOGIFCONF ioctl. Gateways specified in this man‐
ner should be marked passive if they are not expected to exchange rout‐
ing information, while gateways marked active should be willing to
exchange routing information (that is, they should have a process run‐
ning on the machine). Passive gateways are maintained indefinitely in
routing tables. Note, however, that passive gateways are known only to
the local host that lists them in its file. Information about passive
gateways is not included in any routing information that is transmit‐
ted.
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 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 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 is 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 spe‐
cific host.
The name1 is the name of the destination network or host. This may be
a symbolic name located in or or an Internet address specified in dot
notation. For further information, see
The name2 is the name or address of the gateway to which messages
should be forwarded.
The value is a metric indicating the hop count to the destination host
or network.
The keywords passive, active, or external indicate if the gateway
should be treated as passive or active (as previously described), or
whether the gateway is external to the scope of the protocol.
Any other argument supplied is interpreted as the name of a file in
which the actions of should be logged. This log contains information
about any changes to the routing tables and a history of recent mes‐
sages sent and received which are related to the changed route.
Options-d Enables additional debugging information to be logged, such as bad
packets received.
-g Offers a route, on internetwork routers, to the default destina‐
tion. 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 to supply routing information whether it is acting as an
internetwork router or not.
-q Opposite of the option.
-t Prints all packets, sent or received, on the standard output. In
addition, continues to receive input from the controlling termi‐
nal, so that interrupts from the keyboard will kill the process.
Restrictions
The kernel's routing tables may not correspond to those of for short
periods of time while processes utilizing existing routes exit; the
only remedy for this is to place the routing process in the kernel.
The command should listen to intelligent interfaces, such as an IMP,
and to error protocols, such as ICMP, to gather more information. How‐
ever, it does not always detect unidirectional failures in network
interfaces, such as when the output side fails.
Files
For distant gateways
See Alsoudp(4p), htable(8)routed(8c)