- [Instructor] The routing table is the heart
of every router, and it's filled
via a few different methods.
One is connected routes.
As an IP address is added to a router's interface
via the IP address command and then the interface
is in the up/up state, an entry is placed
into the routing table for this subnet.
When I've referred to a directly connected subnet,
this is precisely what I'm referring to.
Another is static routes.
A static route is one that is manually configured
by an administrator using the IP route command.
Last is via routing protocols.
When routing protocols are configured
on multiple connected routers,
they will dynamically inform each other of routes
from their routing tables, as well as those
taught to them from other routers
participating in the protocol.
The local routing table is viewed
via the show ip route command.
The command outputs stats by giving
all of the codes that will be associated
with routing entries.
These codes will show up to the left
of each routing entry, and generally display
where the route was learned.
Notice the classful network shown here that's 10.0.0./8.
To the right of it is how many subnets exists
that fit inside that larger classful network.
To the right of that is the number of different
subnet masks used within this network.
Now look at the individual routes themselves.
To the very left is the legend codes.
In this example I see a C connected
listed to each connected route.
Again, these are the subnets of IP addresses
configured on the router's interfaces.
Any static routes will show up with an S as seen here.
Note also that each entry shows the prefix
or subnet ID as well as the subnet mask in slash notation.
Moving to the right is the prefix or subnet ID
for this specific route.
After that is the subnet mask assigned to this route.
Again, to the right is the administrative distance.
This is the value assigned to a route
based on the source it learned the route from.
It's possible to learn the same route
from multiple sources, and among identical routes,
the one with the lowest AD is used.
To the right of that is the metric for this specific route.
Next on the right is the next hop router
IP address that packets will be sent to
if they utilize this routing entry.
Provided that this route was learned via EIGRP
or OSPF, the timer value to determine how long it's been
since this route was first learned will be listed next.
Last is the outgoing interface the packet will be sent via
when using this route.
Understanding how to interpret the routing table
will be key to success on the test
and your career in networking.