route - manually manipulate the routing tables
The utility supports a limited number of general options, but a rich command language, enabling the user to specify any arbitrary request that could be delivered via the programmatic interface discussed in route(4).
The following options are available:
The utility provides the following commands:
The monitor command has the syntax:
[-n ] monitor
The flush command has the syntax:
[-n ] flush [family ]
If the flush command is specified, will ``flush'' the routing tables of all gateway entries. When the address family may is specified by any of the -osi -xns -atalk -inet6 or -inet modifiers, only routes having destinations with addresses in the delineated family will be deleted.
The other commands have the following syntax:
[-n ] command [-net | -host ] destination gateway [netmask ]
where destination is the destination host or network, gateway is the next-hop intermediary via which packets should be routed. Routes to a particular host may be distinguished from those to a network by interpreting the Internet address specified as the destination argument. The optional modifiers -net and -host force the destination to be interpreted as a network or a host, respectively. Otherwise, if the destination has a ``local address part'' of INADDR_ANY (0.0.0.0 ) or if the destination is the symbolic name of a network, then the route is assumed to be to a network; otherwise, it is presumed to be a route to a host. Optionally, the destination could also be specified in the net / bits format.
For example, 128.32 is interpreted as -host 18.104.22.168 128.32.130 is interpreted as -host 22.214.171.124 -net 128.32 is interpreted as 126.96.36.199; -net 128.32.130 is interpreted as 188.8.131.52; and 192.168.64/20 is interpreted as -net 192.168.64 -netmask 255.255.240.0
A destination of default is a synonym for -net 0.0.0.0 which is the default route.
If the destination is directly reachable via an interface requiring no intermediary system to act as a gateway, the -interface modifier should be specified; the gateway given is the address of this host on the common network, indicating the interface to be used for transmission. Alternately, if the interface is point to point the name of the interface itself may be given, in which case the route remains valid even if the local or remote addresses change.
The optional modifiers -xns -osi -atalk and -link specify that all subsequent addresses are in the XNS OSI or AppleTalk address families, or are specified as link-level addresses, and the names must be numeric specifications rather than symbolic names.
The optional -netmask modifier is intended to achieve the effect of an OSI ESIS redirect with the netmask option, or to manually add subnet routes with netmasks different from that of the implied network interface (as would otherwise be communicated using the OSPF or ISIS routing protocols). One specifies an additional ensuing address parameter (to be interpreted as a network mask). The implicit network mask generated in the AF_INET case can be overridden by making sure this option follows the destination parameter.
For AF_INET6 the -prefixlen qualifier is available instead of the -mask qualifier because non-continuous masks are not allowed in IPv6. For example, -prefixlen 32 specifies network mask of ffff:ffff:0000:0000:0000:0000:0000:0000 to be used. The default value of prefixlen is 64 to get along with the aggregatable address. But 0 is assumed if default is specified. Note that the qualifier works only for AF_INET6 address family.
Routes have associated flags which influence operation of the protocols when sending to destinations matched by the routes. These flags may be set (or sometimes cleared) by indicating the following corresponding modifiers:
-cloning RTF_CLONING - generates a new route on use -xresolve RTF_XRESOLVE - emit mesg on use (for external lookup) -iface ~RTF_GATEWAY - destination is directly reachable -static RTF_STATIC - manually added route -nostatic ~RTF_STATIC - pretend route added by kernel or daemon -reject RTF_REJECT - emit an ICMP unreachable when matched -blackhole RTF_BLACKHOLE - silently discard pkts (during updates) -proto1 RTF_PROTO1 - set protocol specific routing flag #1 -proto2 RTF_PROTO2 - set protocol specific routing flag #2 -llinfo RTF_LLINFO - validly translates proto addr to link addr
The optional modifiers -rtt -rttvar -sendpipe -recvpipe -mtu -hopcount -expire and -ssthresh provide initial values to quantities maintained in the routing entry by transport level protocols, such as TCP or TP4. These may be individually locked by preceding each such modifier to be locked by the -lock meta-modifier, or one can specify that all ensuing metrics may be locked by the -lockrest meta-modifier.
change or add command where the destination and gateway are not sufficient to specify the route (as in the ISO case where several interfaces may have the same address), the -ifp or -ifa modifiers may be used to determine the interface or interface address.
The optional -proxy modifier specifies that the RTF_LLINFO routing table entry is the ``published (proxy-only)'' ARP entry, as reported by arp(8).
The optional -genmask modifier specifies that a cloning mask is present. This specifies the mask applied when determining if a child route should be created. It is only applicable to network routes with the RTF_CLONING flag set.
All symbolic names specified for a destination or gateway are looked up first as a host name using gethostbyname(3). If this lookup fails, getnetbyname(3) is then used to interpret the name as that of a network.
The utility uses a routing socket and the new message types RTM_ADD , RTM_DELETE , RTM_GET and RTM_CHANGE As such, only the super-user may modify the routing tables.
Currently, routes with the RTF_BLACKHOLE flag set need to have the gateway set to an instance of the lo(4) driver, using the -iface option, for the flag to have any effect; unless IP fast forwarding is enabled, in which case the meaning of the flag will always be honored.
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Created 1996-2022 by Maxim Chirkov
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