So my home router is connected to the Internet and can forward traffic onto the Internet even though
it doesn't know all the routes in the Internet.
Internet routing tables are growing all the time.
So there are more than 500,000 routes on the Internet and a small router wouldn't be able to handle that
number of routes in its routing table.
Now it's possible to telnet to live BGP routers on the Internet.
So in this example, I'm gonna telnet to route-server.ip.att.net.
I'm told that I can log in with this username which gives me read-only access to the router and I'm
gonna type show route summary. As you can see here there are 8.5 million odd routes in the
routing table with 567,000 destinations.
BGP summary will show me the BGP routing table BGP is the routing protocol used on the Internet.
So total paths is 8.5 million, active paths is 567,000.
As you can imagine a small router is not going to be able to handle this number of routes in this routing
table.
Here you can see examples of routes in the BGP routing table on this router and how long those routes
have been in the routing table.
Small routers aren't going to handle that number of routes.
So you would typically use a default route pointing your router to a gateway of last resort.
So a default route is a special type of static route pointing your device or router to a gateway of
last resort.
This is similar to the concept of a default gateway on a PC or a device such as an iPhone or iPad when
the router doesn't know where to send the traffic
it simply sends it to the gateway of last resort.
In other words, it will send it to this IP address as configured with the static default route. Another
advantage of static routes is that you as the administrator determine explicitly where traffic flows.
So rather than a routing protocol making the decision for you you decide and have control over where
traffic goes or where packets are routed.
But on the flip side, the burden of management and keeping things up to date also fall on your shoulders.
So you have to administer the routing table.
Keep it up to date.
Make sure that routes are not pointing to non-existent devices where networks go down.
You would have to update the routing table and that's simply not scalable in large topologies.
So hence dynamic routing protocols such as OSPF or EIGRP are used to dynamically add or remove routes
from a routing table.
BGP is mentioned is the routing protocol used on the internet for very large-scale implementations.
The major advantage of dynamic routing protocols is that there is the dynamic or automatic adjustment of
the routing table based on topology changes in your network.
So rather than you having to manually adjust to a topology change the routing protocols update, insert
or remove routes from the routing table based on changing conditions in the network.
As soon as you enable a routing protocol such as OSPF or EIGRP the routers will form a neighbor or peer
relationships with each other and exchange routes with one another.
The routers will thus automatically learn about the networks available in the topology. Routers exchange
information about routes using different methods.
But as an example, OSPF uses link-state updates to advertise information about routes that are available
in the network topology.
This puts overhead on the network because additional traffic is sent and received by routers as they communicate
with one another.
However, as the network grows there is an exponential increase in the amount of work that would be required
if static routes were used and thus because of the advantage that dynamic routing protocols put less
overhead and workload on administrators to maintain routing tables.
They are used in most networks today especially larger networks with the largest being the Internet which
runs on BGP or border gateway protocol
and once again dynamic routing protocols can adjust to changes in the topology automatically and without
administrative intervention.