Instrumentation, measurement and control of bio process parameters ( Temperat...
Connected, Static & Dynamic Routes
1.
2. Subnets directly connected to a router interface are added to
the router's routing table.
Interface has to have an IP address configured and both
interface status codes must be in the "up and up" state.
A router will be able to route all packets destined for all
hosts in subnets directly connected to its active interfaces.
Consider the following example.
The router has two active interfaces, Fe0/0 and Fe0/1. Each
interface has been configured with an IP address and is
currently in the up-up state, so the router adds these subnets
to its routing table.
3.
4. As you can see from the output above, the router has two
directly connected routes to the subnets 10.0.0.0/8 and
192.168.0.0/24.
The character „C“ in the routing table indicates that a route
is a directly connected route.
TIP - you can see only connected routes in a router's routing table
by typing the show ip route connected command.
5. By adding static routes, a router can learn a route to a
remote network that is not directly connected to one of its
interfaces.
Static routes are configured manually by typing the global
configuration mode command ip route
DESTINATION_NETWORK SUBNET_MASK
NEXT_HOP_IP_ADDRESS.
This type of configuration is usually used in smaller
networks because of scalability reasons (you have to
configure each route on each router).
6. Router A is directly connected to router B.
Router B is directly connected to the subnet 10.0.1.0/24. Since
that subnet is not directly connected to Router A, the router
doesn't know how to route packets destined for that subnet.
You have to configure that route manually.
7.
8.
9. TIP - Another version of the ip route command exists.
You don't have to specify the next-hop IP address.
You can rather specify the exit interface of the local router.
In the example above you could have typed the ip route
DEST_NETWORK NEXT_HOP_INTERFACE command
to instruct router A to send all traffic destined for the subnet
out the right interface.
10. A router can learn dynamic routes if a routing protocol is enabled.
A routing protocol is used by routers to exchange routing
information with each other.
Every router in a network can then use information to build its
routing table.
A routing protocol can dynamically choose a different route if a
link goes down, so this type of routing is fault-tolerant.
Also, unlike with static routing, there is no need to manually
configure every route on every router, which greatly reduces the
administrative overhead.
You only need to define which routes will be advertised on a
router that connect directly to the corresponding subnets, routing
protocols take care of the rest.
One of the disadvantages of dynamic routing is that it increases
memory and CPU usage on a router, because every router has to
process received routing information and calculate its routing
table.
11. Both routers are running a routing protocol, namely EIGRP.
There is no static routes on Router A, so R1 doesn't know
how to reach the subnet 10.0.0.0/24 that is directly
connected to Router B. Router B then advertises the subnet
to Router A using EIGRP. Now Router A has the route to
reach the subnet. This can be verified by typing the show ip
route command:
12. You can see that Router A has learned the subnet from EIGRP. The
letter „D“ in front of the route indicates that the route has been
learned through EIGRP. If the subnet 10.0.0.0/24 fails, Router B can
immediately inform Router A that the subnet is no longer reachable.