ROUTED(8)

NAME
routed - network routing daemon

SYNOPSIS
routed [-d] [-g] [-s] [-q] [-t] [-p] [-i device] [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(4) socket for the route(8) service (see services(5)) 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(2) 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 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.

Options supported by routed:

-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 that it is acting as an internetwork router. 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.

-p  this option forces routed to ignore existence of all point-to-point network interfaces. Routed wont send nor receive routing updates through these interfaces and also wont propagate corresponding routes to remote endpoints directly reachable through them. Sometimes it is not desirable to send/receive routing information about routes through such interfaces, for example when point-to-point link with proxy-arp is in use.

-i dev
    this option forces routed to ignore existence of a specified network interface dev. Similarly to -p flag, routed wont send nor receive routing updates through dev, nor it will advertise direct routes via such interface.

Any other argument supplied is interpreted as the full path to and 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. With first event to be logged, routed will create log file in "/var/log/routed" directory (which has to exist and be readable/writeable only by root). For security reasons, this argument has to begin with "/var/log/routed", as routed itself does not perform other security checks towards validity of the remote traceon/traceoff requests it may receive. Unless for debugging purposes, it is strongly recommended that the logging path itself does not exist nor is specified as routed parameter at all.

In addition to the facilities described above, routed supports the notion of ``distant'' passive , active , external and announced gateway types. 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(2). 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).

Routes through passive gateways are installed in the kernel's routing tables by routed once upon its startup. Such routes are not included in any routing information transmitted.

Active gateways are treated equally to network interfaces. Routing information is distributed to the gateway and routed listens for updates on the interface that the gateway is reachable through.

Gateways marked external 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, so that it should not install alternate routes to that destination. Such entries are only required when both routers may learn of routes to the same destination.

Routes to networks through gateways marked as announced will be included in each routing advertisement, but won't be installed in the kernel routing table. This kind of entries is only required for the gateways that are directly reachable, but are unable to announce their routes, so that the rest of the RIP1 protocol-equipped network will know about such routes too. Entries of announced type can also be used to announce direct routes for own interfaces, that didn't exist at the time when routed has been started, but can be expected to come up later (such as routes for point-to-point interfaces).

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 | announced>

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(8), known to the name server), or an Internet address specified in ``dot'' notation; see inet(3).

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, external or announced indicates if the gateway should be treated as passive or active (as described above), whether the gateway is external to the scope of the routed protocol, or whether the route reachable via such gateway should be included in the routing table announcements.

Internetwork routers that are directly attached to the Arpanet or Milnet should use the Exterior Gateway Protocol (EGP) to gather routing information rather than 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.

FILES
/etc/gateways
    for distant gateways

SEE ALSO
udp(7), icmp(7). Internet Transport Protocols, XSIS 028112, Xerox System Integration Standard.

BUGS

Routed is heavily 32bit architecture dependant. You should eventually consider using gated(8) or zebra(8).

The kernel's routing tables may not correspond to those of routed when redirects change or add routes. Routed should note any redirects received by reading the ICMP packets received via a raw socket.

Routed also doesn't notice of any new interface, that didn't exist prior to its start, but has newly appeared and come to ``up'' state after routed has been started, and won't announce route for such interface.

Routed should incorporate other routing protocols. Using separate processes for each requires configuration options to avoid redundant or competing routes.

Routed should listen to intelligent interfaces, such as an IMP, to gather more information. It does not always detect unidirectional failures in network interfaces (e.g., when the output side fails).

HISTORY
The routed command appeared in 4.2BSD.