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routed [ -n ] status
It listens on the udp socket for the route service for Routing Information Protocol packets. It also solicits multicast 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.
Normally routed acts as a silent router and never broadcasts its routing table. This is similar to the -q option on UNIX systems. However, routed will respond to requests from query programs such as rtquery by answering with the complete table. In addition, the -m option, described below, will cause RIP response messages to be generated.
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.
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 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.
If no response is received on a remote interface, or if there are more errors than input or output (see na_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. If routed 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 listen 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 30 minutes. It is a good idea to reduce the default to 45 seconds using -P rdisc_interval=45 on the command line or rdisc_interval=45 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 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, Router Discovery advertisements are not sent over point-to-point links (for example 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:
Routed 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 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 comprises a series of lines, each in one of the following two formats or consists of parameters described later. Blank lines and lines starting with `#' are comments.
net <Nname[/mask]> gateway <Gname> metric <value> < passive No | active No | extern >
host <Hname> gateway <Gname> metric <value> < passive No active No | 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. (If it is a name, then it must either be defined in /etc/networks or /etc/hosts, or DNS and/or NIS, 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 -t, such lines create psuedo-interfaces. To set parameters for remote or external interfaces, a line starting with if=alias(Hname), if=remote(Hname), and so on should be used.
Lines that start with neither "net" nor "host" must consist of one or more of the following parameter settings, separated by commas or blanks:
if = <ifname>
indicates that the other parameters on the line apply to the interface name <ifname>.
subnet = <nname[/mask][,metric]>
advertises a route to network <nname> with mask <mask> 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.
ripv1_mask = <nname/mask1,mask2>
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.
passwd = <XXX[|KeyID[start|stop]]>
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 \n, \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 24 hours, or that was valid within 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.
md5_passwd = <XXX|KeyID[start|stop]>
specifies a RIPv2 MD5 password. Except that a KeyID is required, this keyword is similar to passwd.
passive marks the interface to not be advertised in updates sent via other interfaces, and turns off all RIP and router discovery through the interface.
causes RIPv2 packets to be broadcast instead of multicast.
causes RIPv1 received responses to be ignored.
causes RIPv2 received responses to be ignored.
ripv2_out turns off RIPv1 output and causes RIPv2 advertisements to be multicast when possible.
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.
rdisc_adv 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.
rdisc_pref = <N>
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.
rdisc_interval = <N>
sets the nominal interval with which Router Discovery Advertisements are transmitted to N seconds and their lifetime to 3*N.
fake_default = <metric>
has an identical effect to -F <net[/mask][=metric]> with the network and mask coming from the specified interface.
pm_rdisc 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.
trust_gateway = <rname[|net1/mask1|net2/mask2|...]> causes RIP packets from that router 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.
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