Network RIP and router discovery routing daemon
routed [-Adghmqstv] [-F net [/mask[,metric]]] [-P parms] [-T tracefile]
It's equivalent to -F 0/0,1 and exists for historical reasons. Because a metric of 1 is used, it's very likely that you'll create chaos with a routing loop rather than solve your problem. We recommend that you use -P pm_rdisc on the command line, or add pm_rdisc to your /etc/gateways file. Because a larger metric is used, the likelihood of spreading a potentially dangerous default route is reduced.
Any other argument supplied is interpreted as the name of a file in which the actions of routed should be logged. It's better to use -T instead of appending the name of the trace file to the command.
The routed daemon is invoked at boot time to manage the network routing tables. It uses Routing Information Protocol (RIP), 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 socket for the route service 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 advertise 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 hasn't 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 metric.
If more than one interface is present (not counting the loopback interface), it is assumed that the host should forward packets among the connected 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 generated contains a list of known routes, each marked with a “hop count” metric (a count of 16 or greater is considered “infinite”). Advertised metrics reflect the metric associated with interface (see ifconfig), so setting the metric on an interface is an effective way to steer traffic.
Responses don't include routes with a first hop on the requesting network to implement in part split-horizon. Requests from query programs such as rtquery 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 provided 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 isn't 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 hasn't 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 infinite metric to insure 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 default routes.
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 support 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), then the cable or some other part of the interface is assumed to be disconnected or broken, and routes are adjusted appropriately.
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 Advertisements. If it receives a good Advertisement and it's not multihomed, it stops listening for broadcast or multicast RIP responses. It tracks several 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 multihomed 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:
on the command line, or:
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 redirected 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 interfaces. Thus, multi-homed hosts running with -q might need no_rdisc described below.
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 PPP with the IFF_POINTOPOINT flag) is used by routed to infer the netmask used by the remote system when RIPv1 is used.
The routed daemon supports the notion of “distant” passive or active gateways. When routed is started, it reads /etc/gateways to:
For more information, see the /etc/gateways file.
ICMP and UDP protocols
gated (an unsupported version is available on the QDN), /etc/gateways file, rtquery
Internet Transport Protocols, XSIS 028112, Xerox System Integration Standard.