Split horizon is a scheme for preventing routing loops. When split
horizon is active, routes are not regularly propagated back to the
@@ -3520,7 +3531,7 @@ default route to prevent routing loops).
packets to a neighboring router, multipath routes specifying several (possibly
weighted) neighboring routers, device routes specifying forwarding to hosts on a
directly connected network, recursive routes computing their nexthops by doing
-route table lookups for a given IP and special routes (sink, blackhole etc.)
+route table lookups for a given IP, and special routes (sink, blackhole etc.)
which specify a special action to be done instead of forwarding the packet.
When the particular destination is not available (the interface is down or
@@ -3528,8 +3539,26 @@ the next hop of the route is not a neighbor at the moment), Static just
uninstalls the route from the table it is connected to and adds it again as soon
as the destination becomes adjacent again.
-
The Static protocol does not have many configuration options. The definition
-of the protocol contains mainly a list of static routes:
+
There are three classes of definitions in Static protocol configuration --
+global options, static route definitions, and per-route options. Usually, the
+definition of the protocol contains mainly a list of static routes.
+
+
Global options:
+
+
+ check link
+ If set, hardware link states of network interfaces are taken into
+ consideration. When link disappears (e.g. ethernet cable is unplugged),
+ static routes directing to that interface are removed. It is possible
+ that some hardware drivers or platforms do not implement this feature.
+ Default: off.
+
+ igp table
+ Specifies a table that is used for route table lookups of recursive
+ routes. Default: the same table as the protocol is connected to.
+
+
+
Route definitions (each may also contain a block of per-route options):
route
@@ -3537,7 +3566,7 @@ of the protocol contains mainly a list of static routes:
interface can be specified as a part of the address (e.g.,
route
+ route
Static multipath route. Contains several nexthops (gateways), possibly
with their weights.
@@ -3553,17 +3582,33 @@ of the protocol contains mainly a list of static routes:
Special routes specifying to silently drop the packet, return it as
unreachable or return it as administratively prohibited. First two
targets are also known as
- check link
- If set, hardware link states of network interfaces are taken into
- consideration. When link disappears (e.g. ethernet cable is unplugged),
- static routes directing to that interface are removed. It is possible
- that some hardware drivers or platforms do not implement this feature.
- Default: off.
+Per-route options:
- igp table
- Specifies a table that is used for route table lookups of recursive
- routes. Default: the same table as the protocol is connected to.
+
+ bfd
+ The Static protocol could use BFD protocol for next hop liveness
+ detection. If enabled, a BFD session to the route next hop is created
+ and the static route is BFD-controlled -- the static route is announced
+ only if the next hop liveness is confirmed by BFD. If the BFD session
+ fails, the static route is removed. Note that this is a bit different
+ compared to other protocols, which may use BFD as an advisory mechanism
+ for fast failure detection but ignores it if a BFD session is not even
+ established.
+
+ This option can be used for static routes with a direct next hop, or
+ also for for individual next hops in a static multipath route (see
+ above). Note that BFD protocol also has to be configured, see
+ [ section for details. Default value is no.
+
+
+ This is a special option that allows filter expressions to be configured
+ on per-route basis. Can be used multiple times. These expressions are
+ evaluated when the route is originated, similarly to the import filter
+ of the static protocol. This is especially useful for configuring route
+ attributes, e.g.,
]Static routes have no specific attributes.
@@ -3572,14 +3617,23 @@ of the protocol contains mainly a list of static routes:
protocol static {
- table testable; # Connect to a non-default routing table
+ table testable; # Connect to a non-default routing table
+ check link; # Advertise routes only if link is up
route 0.0.0.0/0 via 198.51.100.130; # Default route
- route 10.0.0.0/8 multipath # Multipath route
+ route 10.0.0.0/8 multipath # Multipath route
via 198.51.100.10 weight 2
- via 198.51.100.20
+ via 198.51.100.20 bfd # BFD-controlled next hop
via 192.0.2.1;
route 203.0.113.0/24 unreachable; # Sink route
- route 10.2.0.0/24 via "arc0"; # Secondary network
+ route 10.2.0.0/24 via "arc0"; # Secondary network
+ route 192.168.10.0/24 via 198.51.100.100 {
+ ospf_metric1 = 20; # Set extended attribute
+ }
+ route 192.168.10.0/24 via 198.51.100.100 {
+ ospf_metric2 = 100; # Set extended attribute
+ ospf_tag = 2; # Set extended attribute
+ bfd; # BFD-controlled route
+ }
}