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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 route(8)).
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"). The advertised 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 network 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 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 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 infinite 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 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(1)), 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 is not multi-homed, 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 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
It is a good idea to reduce the default to 45
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
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:
to accept a RIP request from non-router node.
When specified once,
replies to a route information query from neighbor nodes.
When specified twice,
it replies to a query from remote nodes in addition.
utility can be used to send a request.
This feature is disabled by default because of a risk of reflection attack though it is useful for debugging purpose.
|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 ipforwarding=1.|
is the opposite of the
|do not run in the background. This option is meant for interactive use.|
used on internetwork routers to offer a route
to the "default" destination.
It is equivalent to
|cause host or point-to-point routes to not be advertised, provided 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.|
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 popularity of
It is effective only when the machine is supplying
routing information, because there is more than one interface.
|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 discovery protocol to ignore all RIPv2 packets that carry authentication when this machine does not care about authentication.|
increase the debugging level, which causes more information to be logged
on the tracefile specified with
|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.|
|display and logs the version of daemon.|
minimize routes in transmissions via interfaces with addresses that match
and synthesizes a default route to this machine with the
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.
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
Notice also that more than one interface can match the specified network
number and mask.
|is equivalent to adding the parameter line parms to the /etc/gateways file.|
Any other argument supplied is interpreted as the name
of a file in which the actions of
should be logged.
It is better to use
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 information 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 kernel 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 destination 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" notation (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 routed.)
Mask is an optional number between 1 and 32 indicating the netmask associated with Nname.
Gname is the name or address of the gateway to which RIP responses should be forwarded.
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 indicate whether the gateway should be treated as passive or active (as described above), or whether the gateway is external to the scope of the RIP protocol.
As can be seen when debugging is turned on with
|indicates that the other parameters on the line apply to the interface name ifname.|
advertises a route to network
and the supplied 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 \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 timestamps 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 settings 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 responses.|
|marks the interface to not be advertised in updates sent via other interfaces, and turns off all RIP and router discovery through the interface.|
disables all RIP processing on the specified interface.
If no interfaces are allowed to process RIP packets,
acts purely as a router discovery daemon.
Note that turning off RIP without explicitly turning on router
discovery advertisements with
|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 multicast when possible.|
|ripv2||is equivalent to no_ripv1_in and no_ripv1_out. This enables RIPv2.|
|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 preferred by clients.|
|sets the nominal interval with which Router Discovery Advertisements are transmitted to N seconds and their lifetime to 3*N.|
has an identical effect to
|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" protocol.|
|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 ifconfig(8).|
|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 metric. 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 system is acting as a router and forwarding packets. Otherwise, ICMP Redirect messages are overridden and deleted when the system is acting as a router.|
|for distant gateways|
|ROUTED (8)||August 26, 2014|
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|“||The most horrifying thing about Unix is that, no matter how many times you hit yourself over the head with it, you never quite manage to lose consciousness. It just goes on and on.||”|
|— Patrick Sobalvarro|