1ROUTED(8) System Manager's Manual ROUTED(8)
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6 routed - network routing daemon
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9 routed [ -d ] [ -g ] [ -s ] [ -q ] [ -t ] [ logfile ]
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12 Routed is invoked at boot time to manage the network routing tables.
13 The routing daemon uses a variant of the Xerox NS Routing Information
14 Protocol in maintaining up to date kernel routing table entries. It
15 used a generalized protocol capable of use with multiple address types,
16 but is currently used only for Internet routing within a cluster of
17 networks.
18 In normal operation routed listens on the udp(4) socket for the route
20 service (see services(5)) for routing information packets. If the host
21 is an internetwork router, it periodically supplies copies of its rout‐
22 ing tables to any directly connected hosts and networks.
23 When routed is started, it uses the SIOCGIFCONF ioctl to find those
25 directly connected interfaces configured into the system and marked
26 ``up'' (the software loopback interface is ignored). If multiple
27 interfaces are present, it is assumed that the host will forward pack‐
28 ets between networks. Routed then transmits a request packet on each
29 interface (using a broadcast packet if the interface supports it) and
30 enters a loop, listening for request and response packets from other
31 hosts.
32 When a request packet is received, routed formulates a reply based on
34 the information maintained in its internal tables. The response packet
35 generated contains a list of known routes, each marked with a ``hop
36 count'' metric (a count of 16, or greater, is considered ``infinite'').
37 The metric associated with each route returned provides a metric rela‐
38 tive to the sender.
39 Response packets received by routed are used to update the routing
41 tables if one of the following conditions is satisfied:
42 (1) No routing table entry exists for the destination network or
44 host, and the metric indicates the destination is ``reachable''
45 (i.e. the hop count is not infinite).
46 (2) The source host of the packet is the same as the router in the
48 existing routing table entry. That is, updated information is
49 being received from the very internetwork router through which
50 packets for the destination are being routed.
51 (3) The existing entry in the routing table has not been updated for
53 some time (defined to be 90 seconds) and the route is at least
54 as cost effective as the current route.
55 (4) The new route describes a shorter route to the destination than
57 the one currently stored in the routing tables; the metric of
58 the new route is compared against the one stored in the table to
59 decide this.
60 When an update is applied, routed records the change in its internal
62 tables and updates the kernel routing table. The change is reflected
63 in the next response packet sent.
64 In addition to processing incoming packets, routed also periodically
66 checks the routing table entries. If an entry has not been updated for
67 3 minutes, the entry's metric is set to infinity and marked for dele‐
68 tion. Deletions are delayed an additional 60 seconds to insure the
69 invalidation is propagated throughout the local internet.
70 Hosts acting as internetwork routers gratuitously supply their routing
72 tables every 30 seconds to all directly connected hosts and networks.
73 The response is sent to the broadcast address on nets capable of that
74 function, to the destination address on point-to-point links, and to
75 the router's own address on other networks. The normal routing tables
76 are bypassed when sending gratuitous responses. The reception of
77 responses on each network is used to determine that the network and
78 interface are functioning correctly. If no response is received on an
79 interface, another route may be chosen to route around the interface,
80 or the route may be dropped if no alternative is available.
81 Routed supports several options:
83 -d Enable additional debugging information to be logged, such as
85 bad packets received.
86 -g This flag is used on internetwork routers to offer a route to
88 the ``default'' destination. This is typically used on a gate‐
89 way to the Internet, or on a gateway that uses another routing
90 protocol whose routes are not reported to other local routers.
91 -s Supplying this option forces routed to supply routing informa‐
93 tion whether it is acting as an internetwork router or not.
94 This is the default if multiple network interfaces are present,
95 or if a point-to-point link is in use.
96 -q This is the opposite of the -s option.
98 -t If the -t option is specified, all packets sent or received are
100 printed on the standard output. In addition, routed will not
101 divorce itself from the controlling terminal so that interrupts
102 from the keyboard will kill the process.
103 Any other argument supplied is interpreted as the name of file in which
105 routed's actions should be logged. This log contains information about
106 any changes to the routing tables and, if not tracing all packets, a
107 history of recent messages sent and received which are related to the
108 changed route.
109 In addition to the facilities described above, routed supports the
111 notion of ``distant'' passive and active gateways. When routed is
112 started up, it reads the file /etc/gateways to find gateways which may
113 not be located using only information from the SIOGIFCONF ioctl. Gate‐
114 ways specified in this manner should be marked passive if they are not
115 expected to exchange routing information, while gateways marked active
116 should be willing to exchange routing information (i.e. they should
117 have a routed process running on the machine). Passive gateways are
118 maintained in the routing tables forever and information regarding
119 their existence is included in any routing information transmitted.
120 Active gateways are treated equally to network interfaces. Routing
121 information is distributed to the gateway and if no routing information
122 is received for a period of the time, the associated route is deleted.
123 External gateways are also passive, but are not placed in the kernel
124 routing table nor are they included in routing updates. The function
125 of external entries is to inform routed that another routing process
126 will install such a route, and that alternate routes to that destina‐
127 tion should not be installed. Such entries are only required when both
128 routers may learn of routes to the same destination.
129 The /etc/gateways is comprised of a series of lines, each in the fol‐
131 lowing format:
132 < net | host > name1 gateway name2 metric value < passive | active | external >
134 The net or host keyword indicates if the route is to a network or spe‐
136 cific host.
137 Name1 is the name of the destination network or host. This may be a
139 symbolic name located in /etc/networks or /etc/hosts (or, if started
140 after named(8), known to the name server), or an Internet address spec‐
141 ified in ``dot'' notation; see inet(3).
142 Name2 is the name or address of the gateway to which messages should be
144 forwarded.
145 Value is a metric indicating the hop count to the destination host or
147 network.
148 One of the keywords passive, active or external indicates if the gate‐
150 way should be treated as passive or active (as described above), or
151 whether the gateway is external to the scope of the routed protocol.
152 Internetwork routers that are directly attached to the Arpanet or Mil‐
154 net should use the Exterior Gateway Protocol (EGP) to gather routing
155 information rather then using a static routing table of passive gate‐
156 ways. EGP is required in order to provide routes for local networks to
157 the rest of the Internet system. Sites needing assistance with such
158 configurations should contact the Computer Systems Research Group at
159 Berkeley.
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162 /etc/gateways for distant gateways
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165 ``Internet Transport Protocols'', XSIS 028112, Xerox System Integration
166 Standard.
167 udp(4), XNSrouted(8), htable(8)
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170 The kernel's routing tables may not correspond to those of routed when
171 redirects change or add routes. The only remedy for this is to place
172 the routing process in the kernel.
173 Routed should incorporate other routing protocols, such as Xerox NS
175 (XNSrouted(8)) and EGP. Using separate processes for each requires
176 configuration options to avoid redundant or competing routes.
177 Routed should listen to intelligent interfaces, such as an IMP, and to
179 error protocols, such as ICMP, to gather more information. It does not
180 always detect unidirectional failures in network interfaces (e.g., when
181 the output side fails).
1824.2 Berkeley Distribution November 17, 1996 ROUTED(8)