3.1.a Packet handling along the path through a network
3.1.b Forwarding decision based on route lookup
3.1.c Frame rewrite
It’s the 25th of December and happy holidays! We are now moving to routing. I wont dwell much with the explanation with this. I only have the figure below:
From R2 which has 192.168.50.2, let us ping 192.168.50.1
R2 pings 192.168.10.1
R3 pings 172.16.50.1
Alright so I wont paste all the possible ping outcomes but I just would like to highlight out goal as network Engineers. Our goal is to provide successful ping from one end to other end. You want to know why the ping on R2 with 192.168.50.2 has successful ping to 192.168.50.1? Because it is the nature of router to know those IP addresses which are directly connected with him. Just like you as part of neighborhood and you live on 43 Pittsborough Street, you might know 100 Pittsborough Street but you might know 44, 45, 46 and 47 Pitttsborough Street. Gets? hehe.
So without any routing configuration, it is predictable that the ping of 192.168.50.2 to 192.168.10.1 is a failing ping because logically R2 is not directly connected to the loopback of R1
The most powerful show commands:
show ip route
This show command is very handy because it gives us a guide on how router learned the network addresses. There are only three ways a router will learn the network.
1.) Directly connected- these network addresses are obviously directly connected to the router itself. These are interface network address and loopback address configured on the router itself and the interface of the neighbor router.
2.Static – Every time we encounter the word “static” in networking world, always be reminded that we manually configure it, so static means we intend the routing of the network.
3. Dynamic- for any changes on the network, let us say, link failure, these learned network addresses will adjust to the scenario.
The routing table above shows that R2 can only get a successful ping to networks:
C 10.0.10.0 is directly connected, Loopback0
C 10.0.20.0 is directly connected, Loopback1
C 10.0.30.0 is directly connected, Loopback2
C 192.168.50.0/24 is directly connected, Serial2/0
Note: In the event that we would like to be connected to the network that is not on the list, then we have to make a way to add that network on either static routing or dynamic routing. There are a lot of protocols to consider for dynamic routing namely:
1.) RIP ( Routing Information Protocol)
2.) OSPF (Open Shortest Path First)
3.) EIGRP ( Extended Interior Gateway Routing Protocol)
4.) BGP ( Border Gateway Protocol)
Those are protocols which are just highlights of the curriculum, but surely there are more protocols that are used in other vendors or on CCNP curriculum.
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