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1.1 root 1: .\" Copyright (c) 1990 The Regents of the University of California.
2: .\" All rights reserved.
3: .\"
4: .\" Redistribution and use in source and binary forms are permitted
5: .\" provided that: (1) source distributions retain this entire copyright
6: .\" notice and comment, and (2) distributions including binaries display
7: .\" the following acknowledgement: ``This product includes software
8: .\" developed by the University of California, Berkeley and its contributors''
9: .\" in the documentation or other materials provided with the distribution
10: .\" and in all advertising materials mentioning features or use of this
11: .\" software. Neither the name of the University nor the names of its
12: .\" contributors may be used to endorse or promote products derived
13: .\" from this software without specific prior written permission.
14: .\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
15: .\" IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
16: .\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
17: .\"
18: .\" @(#)route.4 6.2 (Berkeley) 5/30/90
19: .\"
20: .TH ROUTE 4 "May 30, 1990"
21: .UC 5
22: .SH NAME
23: .UC 4
24: .SH NAME
25: ROUTE \- Kernel Packet Forwarding Database
26: .SH SYNOPSIS
27: .nf
28: \fB#include <sys/socket.h>\fR
29: \fB#include <net/if.h>\fR
30: \fB#include <net/route.h>\fR
31: .br
32: .B int family
33: .br
34: .B s = socket(PF_ROUTE, SOCK_RAW, family);
35: .SH DESCRIPTION
36: .PP
37: .UX
38: provides some packet routing facilities.
39: The kernel maintains a routing information database, which
40: is used in selecting the appropriate network interface when
41: transmitting packets.
42: .PP
43: A user process (or possibly multiple co-operating processes)
44: maintains this database by sending messages over a special kind
45: of socket.
46: This supplants fixed size
47: .IR ioctl 's
48: used in earlier releases.
49: Routing table changes may only be carried out by the super user.
50: .PP
51: The operating system may spontaneously emit routing messages in response
52: to external events, such as recipt of a re-direct, or failure to
53: locate a suitable route for a request.
54: The message types are described in greater detail below.
55: .PP
56: Routing database entries come in two flavors: for a specific
57: host, or for all hosts on a generic subnetwork (as specified
58: by a bit mask and value under the mask.
59: The effect of wildcard or default route may be achieved by using
60: a mask of all zeros, and there may be hierarchical routes.
61: .PP
62: When the system is booted and addresses are assigned
63: to the network interfaces, each protocol family
64: installs a routing table entry for each interface when it is ready for traffic.
65: Normally the protocol specifies the route
66: through each interface as a ``direct'' connection to the destination host
67: or network. If the route is direct, the transport layer of
68: a protocol family usually requests the packet be sent to the
69: same host specified in the packet. Otherwise, the interface
70: is requested to address the packet to the gateway listed in the routing entry
71: (i.e. the packet is forwarded).
72: .PP
73: When routing a packet,
74: the kernel will first attempt to find a route to the destination host.
75: Failing that, a search is made for a route to the network of the destination.
76: Finally, any route to a default (``wildcard'') gateway is chosen.
77: If no entry is found, the destination is declared to be unreachable,
78: and a routing\-miss message is generated if there are any
79: listers on the routing control socket described below.
80: .PP
81: A wildcard routing entry is specified with a zero
82: destination address value. Wildcard routes are used
83: only when the system fails to find a route to the
84: destination host and network. The combination of wildcard
85: routes and routing redirects can provide an economical
86: mechanism for routing traffic.
87: .PP
88: One opens the channel for passing routing control messasges
89: by using the socket call shown in the synopsis above:
90: .PP
91: The \fIfamily\fP paramter may be AF_UNSPEC which will provide
92: routing information for all address families, or can be restricted
93: to a specific address family by specifying which one is desired.
94: There can be more than one routing socket open per system.
95: .PP
96: Messages are formed by a header followed by a small
97: number of sockadders (now variable length particularly
98: in the ISO case), interpreted by position, and delimited
99: by the new length entry in the sockaddr.
100: An example of a message with four addresses might be an ISO redirect:
101: Destination, Netmask, Gateway, and Author of the redirect.
102: The interpretation of which address are present is given by a
103: bit mask within the header, and the sequence is least significant
104: to most significant bit within the vector.
105: .PP
106: Any messages sent to the kernel are returned, and copies are sent
107: to all interested listeners. The kernel will provide the process
108: id. for the sender, and the sender may use an additional sequence
109: field to distinguish between outstanding messages. However,
110: message replies may be lost when kernel buffers are exhausted.
111: .PP
112: The kernel may reject certain messages, and will indicate this
113: by filling in the rtm_errno field.
114: The routing code returns EEXIST if
115: requested to duplicate an existing entry, ESRCH if
116: requested to delete a non-existent entry,
117: or ENOBUFS if insufficient resources were available
118: to install a new route.
119: In the current implementation, all routing process run locally,
120: and the values for rtm_errno are available through the normal
121: errno mechanism, even if the routing reply message is lost.
122: .PP
123: A process may avoid the expense of reading replies to
124: its own messages by issuing a
125: .IR setsockopt ()
126: call indicating that the SO_USELOOPBACK option
127: at the SOL_SOCKET level is to be turned off.
128: A process may ignore all messages from the routing socket
129: by doing a
130: .IR shutdown (2)
131: system call for further input.
132: .PP
133: If a route is in use when it is deleted,
134: the routing entry will be marked down and removed from the routing table,
135: but the resources associated with it will not
136: be reclaimed until all references to it are released.
137: User processes can obtain information about the routing
138: entry to a specific destination by using a RTM_GET message,
139: or by reading the
140: .I /dev/kmem
141: device, or by issuing a
142: .I getkerninfo ()
143: system call.
144: .nf
145:
146: Messages include:
147:
148: .ta \w'#define 'u +\w'RTM_REDIRECT 'u +\w'0x7 'u
149: #define RTM_ADD 0x1 /* \fIAdd Route\fP */
150: #define RTM_DELETE 0x2 /* \fIDelete Route\fP */
151: #define RTM_CHANGE 0x3 /* \fIChange Metrics, Flags, or Gateway\fP */
152: #define RTM_GET 0x4 /* \fIReport Information\fP */
153: #define RTM_LOOSING 0x5 /* \fIKernel Suspects Partitioning\fP */
154: #define RTM_REDIRECT 0x6 /* \fITold to use different route\fP */
155: #define RTM_MISS 0x7 /* \fILookup failed on this address\fP */
156: #define RTM_RESOLVE 0xb /* \fIrequest to resolve dst to LL addr\fP */
157:
158: .ta \w'struct 'u +\w'u_short 'u +\w'rt_metrics rtm_rmx 'u
159: A message header consists of:
160: struct rt_msghdr {
161: u_short rmt_msglen; /* \fIto skip over non-understood messages\fP */
162: u_char rtm_version; /* \fIfuture binary compatability\fP */
163: u_char rtm_type; /* \fImessage type\fP */
164: u_short rmt_index; /* \fIindex for associated ifp \fP */
165: pid_t rmt_pid; /* \fIidentify sender\fP */
166: int rtm_addrs; /* \fIbitmask identifying sockaddrs in msg\fP */
167: int rtm_seq; /* \fIfor sender to identify action\fP */
168: int rtm_errno; /* \fIwhy failed\fP */
169: int rtm_flags; /* \fIflags, incl. kern & message, e.g. DONE\fP */
170: int rtm_use; /* \fIfrom rtentry\fP */
171: u_long rtm_inits; /* \fIwhich values we are initializing\fP */
172: struct rt_metrics rtm_rmx; /* \fImetrics themselves\fP */
173: };
174:
175: where
176:
177: .ta \w'struct 'u +\w'u_long 'u +\w'rmx_hopcount 'u
178: struct rt_metrics {
179: u_long rmx_locks; /* \fIKernel must leave these values alone\fP */
180: u_long rmx_mtu; /* \fIMTU for this path\fP */
181: u_long rmx_hopcount; /* \fImax hops expected\fP */
182: u_long rmx_expire; /* \fIlifetime for route, e.g. redirect\fP */
183: u_long rmx_recvpipe; /* \fIinbound delay-bandwith product\fP */
184: u_long rmx_sendpipe; /* \fIoutbound delay-bandwith product\fP */
185: u_long rmx_ssthresh; /* \fIoutbound gateway buffer limit\fP */
186: u_long rmx_rtt; /* \fIestimated round trip time\fP */
187: u_long rmx_rttvar; /* \fIestimated rtt variance\fP */
188: };
189:
190:
191: Flags include the values:
192:
193: .ta \w'#define 'u +\w'RTF_MODIFIED 'u +\w'0x80 'u
194: #define RTF_UP 0x1 /* \fIroute useable\fP */
195: #define RTF_GATEWAY 0x2 /* \fIdestination is a gateway\fP */
196: #define RTF_HOST 0x4 /* \fIhost entry (net otherwise)\fP */
197: #define RTF_NORMAL 0x8 /* \fIsubnet mask is cannonical\fP */
198: #define RTF_DYNAMIC 0x10 /* \fIcreated dynamically (by redirect)\fP */
199: #define RTF_MODIFIED 0x20 /* \fImodified dynamically (by redirect)\fP */
200: #define RTF_DONE 0x40 /* \fImessage confirmed\fP */
201: #define RTF_MASK 0x80 /* \fIsubnet mask present\fP */
202:
203: Specfiers for metric values in rmx_locks and rtm_inits are:
204:
205: .ta \w'#define 'u +\w'RTF_HOPCOUNT 'u +\w'0x80 'u
206: #define RTV_SSTHRESH 0x1 /* \fIinit or lock _ssthresh\fP */
207: #define RTV_RPIPE 0x2 /* \fIinit or lock _recvpipe\fP */
208: #define RTV_SPIPE 0x4 /* \fIinit or lock _sendpipe\fP */
209: #define RTV_HOPCOUNT 0x8 /* \fIinit or lock _hopcount\fP */
210: #define RTV_RTT 0x10 /* \fIinit or lock _rtt\fP */
211: #define RTV_RTTVAR 0x20 /* \fIinit or lock _rttvar\fP */
212: #define RTV_MTU 0x40 /* \fIinit or lock _mtu\fP */
213:
214: Specifiers for which addresses are present in the messages are:
215:
216: .ta \w'#define 'u +\w'RTA_GATEWAY 'u +\w'0x80 'u
217: #define RTA_DST 0x1 /* \fIdestination sockaddr present\fP */
218: #define RTA_GATEWAY 0x2 /* \fIgateway sockaddr present\fP */
219: #define RTA_NETMASK 0x4 /* \fInetmask sockaddr present\fP */
220: #define RTA_GENMASK 0x8 /* \fIcloning mask sockaddr present\fP */
221: #define RTA_IFP 0x10 /* \fIinterface name sockaddr present\fP */
222: #define RTA_IFA 0x20 /* \fIinterface addr sockaddr present\fP */
223: #define RTA_AUTHOR 0x40 /* \fIsockaddr for author of redirect\fP */
224:
225: .fi
226:
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