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[lik]

By default linux distributions (not only) expect that default gateway IP address belongs to configured subnetwork on the interface and is not a broadcast address.
As a result we will receive the following error trying to define gateway outside of configured network:

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# ifconfig eth0
eth0      Link encap:Ethernet  HWaddr 00:16:3E:29:5A:82 
          inet addr:10.10.10.10  Bcast:10.10.10.15  Mask:255.255.255.248
          inet6 addr: fe80::216:3eff:fe29:5a82/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:2522216 errors:0 dropped:0 overruns:0 frame:0
          TX packets:61813 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:185056341 (176.4 MiB)  TX bytes:122461673 (116.7 MiB)
          Interrupt:77


# route add default gw 11.11.11.11
SIOCADDRT: No such process

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To resolve it we can use the following way:

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route add 11.11.11.11/32 dev eth0
route add default gw 11.11.11.11

If we want to make above routes persistent we should define them in network init script:
Debian/Ubuntu case:
Add the following rules in /etc/network/interfaces :

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post-up route add 11.11.11.11/32 dev eth0
post-up route add default gw 11.11.11.11


RedHat/Centos case:
Add the following rule in /etc/sysconfig/network-scripts/ifcfg-eth0

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SCOPE="peer 11.11.11.11"

[lik]

FreeBSD case:

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/sbin/route add -host 11.11.11.11 -iface rl0
/sbin/route add default 11.11.11.11

To make these routes persistent define them in /etc/rc.conf :

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ifconfig_em0="inet 10.10.10.10 netmask 255.255.255.248"
static_routes="net1 net2"
route_net1="-net 11.11.11.11/32 -iface em0"
route_net2="default 11.11.11.11"

or even:

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ifconfig_em0="inet 10.10.10.10 netmask 255.255.255.248"
static_routes="net1"
route_net1="-net 0.0.0.0/0 -iface em0"