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--- ubuntu:network:routing:create_a_persistent_static_route [2020/08/19 15:18] – created 192.168.1.1
+++ ubuntu:network:routing:create_a_persistent_static_route [2021/01/07 10:46] (current) – removed peter
@@ Line 1: / Line 1: @@
-====== Ubuntu - Network - Routing - Create a persistent static route ======
-To create a persistent static route to a remote network via a gateway.
-----
-===== Scenario =====
-Suppose that a host is connected via eth0 to the subnet 192.168.0.0/24 with the address 192.168.0.7.
-The default gateway for this subnet is 192.168.0.1, but to reach the subnet 10.0.0.0/8 it is necessary to use a different gateway at 192.168.0.2.
-----
-===== Method =====
-Ideally the route should be added immediately after the relevant interface has been brought up, and removed immediately before it is taken down.
-This can be achieved using up and down commands in **/etc/network/interfaces**.
-First ensure that the relevant interface is down (if it is not already):
-<file bash /etc/network/interfaces>
-ifdown eth0
-</file>
-Next add suitable up and down commands to the relevant interface definition within the interfaces file.
-If an interface definition does not already exist then you will need to add one:
-<file bash /etc/network/interfaces>
-auto eth0
-iface eth0 inet static
-  address 192.168.0.7
-  netmask 255.255.255.0
-  gateway 192.168.0.1
-  up /sbin/route add -net 10.0.0.0 netmask 255.0.0.0 gw 192.168.0.2
-  down /sbin/route del -net 10.0.0.0 netmask 255.0.0.0
-</file>
-If there is more than one route to be created then this can be done using multiple up and down commands.
-Once the interfaces file has been modified, bring the interface back up:
-<code bash>
-ifup eth0
-</code>
-----
-===== Testing =====
-Print the routing table using the route command:
-<code bash>
-route -n
-</code>
-When the interface is up you should be able to see the new route (the line with a destination of 10.0.0.0):
-<code bash>
-Kernel IP routing table
-Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
-.168.0.0     0.0.0.0         255.255.255.0   U     0      0        0 eth0
-.0.0.0        192.168.0.2     255.0.0.0       UG    0      0        0 eth0
-.0.0.0         192.168.0.1     0.0.0.0         UG    0      0        0 eth0
-</code>
-If you take the interface down again then all three of these routes should disappear.
-----
-===== Troubleshooting =====
-==== Network is unreachable ====
-If ifup gives an error of the form:
-<code bash>
-SIOCADDRT: Network is unreachable
-Failed to bring up eth0.
-</code>
-then the likely cause is that the specified gateway is not directly reachable via any local interface.  Gateways must be reachable in a single hop: having a route to them is not sufficient.
-----
-==== No such process ====
-In place of 'Network is unreachable', recent versions of the Kernel may return the rather less helpful message:
-<code bash>
-SIOCDELRT: No such process
-Failed to bring up eth0.
-</code>
-----
-==== File exists ====
-An error of the form:
-<code bash>
-SIOCADDRT: File exists
-Failed to bring up eth0.
-</code>
-indicates that there is already a route to the specified destination via the specified gateway.
-One way this could happen is by bringing the interface up manually (using ifconfig and route) and then attempting to bring it up using ifup.
-If you suspect that something like this has happened then you should manually restore the interface and routing table (using ifconfig and route) to the state expected by ifup and ifdown.