1ROUTE(8) Linux Programmer's Manual ROUTE(8)
2
6 route - show / manipulate the IP routing table
7
9 route [-CFvnee]
10 route [-v] [-A family] add [-net|-host] target [netmask Nm] [gw Gw]
12 [metric N] [mss M] [window W] [irtt I] [reject] [mod] [dyn]
13 [reinstate] [[dev] If]
14 route [-v] [-A family] del [-net|-host] target [gw Gw] [netmask Nm]
16 [metric N] [[dev] If]
17 route [-V] [--version] [-h] [--help]
19
21 Route manipulates the kernel's IP routing tables. Its primary use is
22 to set up static routes to specific hosts or networks via an interface
23 after it has been configured with the ifconfig(8) program.
24 When the add or del options are used, route modifies the routing
26 tables. Without these options, route displays the current contents of
27 the routing tables.
28
31 -A family
32 use the specified address family (eg `inet'; use `route --help'
33 for a full list).
34 -F operate on the kernel's FIB (Forwarding Information Base) rout‐
37 ing table. This is the default.
38 -C operate on the kernel's routing cache.
40 -v select verbose operation.
43 -n show numerical addresses instead of trying to determine symbolic
45 host names. This is useful if you are trying to determine why
46 the route to your nameserver has vanished.
47 -e use netstat(8)-format for displaying the routing table. -ee
49 will generate a very long line with all parameters from the
50 routing table.
51 del delete a route.
54 add add a new route.
56 target the destination network or host. You can provide IP addresses in
58 dotted decimal or host/network names.
59 -net the target is a network.
61 -host the target is a host.
63 netmask NM
65 when adding a network route, the netmask to be used.
66 gw GW route packets via a gateway. NOTE: The specified gateway must
68 be reachable first. This usually means that you have to set up a
69 static route to the gateway beforehand. If you specify the
70 address of one of your local interfaces, it will be used to
71 decide about the interface to which the packets should be routed
72 to. This is a BSDism compatibility hack.
73 metric M
75 set the metric field in the routing table (used by routing dae‐
76 mons) to M.
77 mss M set the TCP Maximum Segment Size (MSS) for connections over this
79 route to M bytes. The default is the device MTU minus headers,
80 or a lower MTU when path mtu discovery occured. This setting can
81 be used to force smaller TCP packets on the other end when path
82 mtu discovery does not work (usually because of misconfigured
83 firewalls that block ICMP Fragmentation Needed)
84 window W
86 set the TCP window size for connections over this route to W
87 bytes. This is typically only used on AX.25 networks and with
88 drivers unable to handle back to back frames.
89 irtt I set the initial round trip time (irtt) for TCP connections over
91 this route to I milliseconds (1-12000). This is typically only
92 used on AX.25 networks. If omitted the RFC 1122 default of 300ms
93 is used.
94 reject install a blocking route, which will force a route lookup to
96 fail. This is for example used to mask out networks before
97 using the default route. This is NOT for firewalling.
98 mod, dyn, reinstate
100 install a dynamic or modified route. These flags are for diag‐
101 nostic purposes, and are generally only set by routing daemons.
102 dev If force the route to be associated with the specified device, as
104 the kernel will otherwise try to determine the device on its own
105 (by checking already existing routes and device specifications,
106 and where the route is added to). In most normal networks you
107 won't need this.
108 If dev If is the last option on the command line, the word dev
110 may be omitted, as it's the default. Otherwise the order of the
111 route modifiers (metric - netmask - gw - dev) doesn't matter.
112
115 route add -net 127.0.0.0
116 adds the normal loopback entry, using netmask 255.0.0.0 (class A
117 net, determined from the destination address) and associated
118 with the "lo" device (assuming this device was prviously set up
119 correctly with ifconfig(8)).
120 route add -net 192.56.76.0 netmask 255.255.255.0 dev eth0
123 adds a route to the network 192.56.76.x via "eth0". The Class C
124 netmask modifier is not really necessary here because 192.* is a
125 Class C IP address. The word "dev" can be omitted here.
126 route add default gw mango-gw
129 adds a default route (which will be used if no other route
130 matches). All packets using this route will be gatewayed
131 through "mango-gw". The device which will actually be used for
132 that route depends on how we can reach "mango-gw" - the static
133 route to "mango-gw" will have to be set up before.
134 route add ipx4 sl0
137 Adds the route to the "ipx4" host via the SLIP interface (assum‐
138 ing that "ipx4" is the SLIP host).
139 route add -net 192.57.66.0 netmask 255.255.255.0 gw ipx4
142 This command adds the net "192.57.66.x" to be gatewayed through
143 the former route to the SLIP interface.
144 route add -net 224.0.0.0 netmask 240.0.0.0 dev eth0
147 This is an obscure one documented so people know how to do it.
148 This sets all of the class D (multicast) IP routes to go via
149 "eth0". This is the correct normal configuration line with a
150 multicasting kernel.
151 route add -net 10.0.0.0 netmask 255.0.0.0 reject
154 This installs a rejecting route for the private network
155 "10.x.x.x."
156
159 The output of the kernel routing table is organized in the following
160 columns
161 Destination
163 The destination network or destination host.
164 Gateway
166 The gateway address or '*' if none set.
167 Genmask
169 The netmask for the destination net; '255.255.255.255' for a
170 host destination and '0.0.0.0' for the default route.
171 Flags Possible flags include
173 U (route is up)
174 H (target is a host)
175 G (use gateway)
176 R (reinstate route for dynamic routing)
177 D (dynamically installed by daemon or redirect)
178 M (modified from routing daemon or redirect)
179 A (installed by addrconf)
180 C (cache entry)
181 ! (reject route)
182 Metric The 'distance' to the target (usually counted in hops). It is
184 not used by recent kernels, but may be needed by routing dae‐
185 mons.
186 Ref Number of references to this route. (Not used in the Linux ker‐
188 nel.)
189 Use Count of lookups for the route. Depending on the use of -F and
191 -C this will be either route cache misses (-F) or hits (-C).
192 Iface Interface to which packets for this route will be sent.
194 MSS Default maximum segement size for TCP connections over this
196 route.
197 Window Default window size for TCP connections over this route.
199 irtt Initial RTT (Round Trip Time). The kernel uses this to guess
201 about the best TCP protocol parameters without waiting on (pos‐
202 sibly slow) answers.
203 HH (cached only)
205 The number of ARP entries and cached routes that refer to the
206 hardware header cache for the cached route. This will be -1 if a
207 hardware address is not needed for the interface of the cached
208 route (e.g. lo).
209 Arp (cached only)
211 Whether or not the hardware address for the cached route is up
212 to date.
213
215 /proc/net/ipv6_route
216 /proc/net/route
217 /proc/net/rt_cache
218
220 ifconfig(8), netstat(8), arp(8), rarp(8)
221
223 Route for Linux was originally written by Fred N. van Kempen,
224 <waltje@uwalt.nl.mugnet.org> and then modified by Johannes Stille and
225 Linus Torvalds for pl15. Alan Cox added the mss and window options for
226 Linux 1.1.22. irtt support and merged with netstat from Bernd Ecken‐
227 fels.
228
230 Currently maintained by Phil Blundell <Philip.Blundell@pobox.com>.
231net-tools 2 January 2000 ROUTE(8)