Lecture CCNA Exploration 4.0 (Kỳ 2) - Chapter 8: The routing table - A closer look

The following will be discussed in this chapter: Describe the various route types found in the routing table structure, describe the routing table lookup process, describe routing behavior in routed networks.
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Lecture CCNA Exploration 4.0 (Kỳ 2) - Chapter 8: The routing table - A closer look Chapter 8: The Routing Table: A Closer Look CCNA Exploration version 4.0 1 Objectives • Describe the various route types found in the routing table structure • Describe the routing table lookup process. • Describe routing behavior in routed networks. Học viện mạng Bach Khoa - Website: www.bkacad.com 2 Routing Table Structure Học viện mạng Bach Khoa - Website: www.bkacad.com 3 Lab Topologies Học viện mạng Bach Khoa - Website: www.bkacad.com 4 Routing Table Structure • Routing table entries come from the following sources – Directly connected networks – Static routes – Dynamic routing protocols • The source of the route does not affect the structure of the routing table. • Although the routing table incorporates both classful and classless addressing, the overall structure is still built around this classful scheme. Học viện mạng Bach Khoa - Website: www.bkacad.com 5 Routing Table StructureRIP v1 Classful address RIP v2 Classful address RIP v2 Classless address Học viện mạng Bach Khoa - Website: www.bkacad.com 6 Routing Table Structure Level 1 Routes • As soon as the no shutdown command is issued the route is added to routing table Học viện mạng Bach Khoa - Website: www.bkacad.com 7 Routing Table Structure • Cisco IP routing table is a hierarchical structure – The reason for this is to speed up lookup process Học viện mạng Bach Khoa - Website: www.bkacad.com 8 Routing Table Structure • A level 1 route is a route with a subnet mask equal to or less than the classful mask of the network address. 192.168.1.0/24 is a level 1 network route, because the subnet mask is equal to the network's classful mask. /24 is the classful mask for class C networks, such as the 192.168.1.0 network. • A level 1 route can function as a: – Default route - A default route is a static route with the address 0.0.0.0/0. – Supernet route - A supernet route is a network address with a mask less than the classful mask. – Network route - A network route is a route that has a subnet mask equal to that of the classful mask. • A network route can also be a parent route. Học viện mạng Bach Khoa - Website: www.bkacad.com 9 Routing Table Structure Ultimate Route • The level 1 route 192.168.1.0/24 can be further defined as an ultimate route. • An ultimate route is a route that includes: – either a next-hop IP address (another path) – and/or an exit interface Học viện mạng Bach Khoa - Website: www.bkacad.com 10 Routing Table Structure • Parent and Child Routes – A parent route is a level 1 route – A parent route does not contain any next- hop IP address or exit interface information – The subnet is the level 2 child route of the parent route. Học viện mạng Bach Khoa - Website: www.bkacad.com 11 Parent and Child Routes: Classful Networks • A level 1 parent route is automatically created any time a subnet is added to the routing table. • A parent route is created whenever a route with a mask greater than the classful mask is entered into the routing table. • Child routes – Child routes are level 2 routes – Child routes are a subnet of a classful network address Học viện mạng Bach Khoa - Website: www.bkacad.com 12 Parent and Child Routes: Classful Networks • Level 2 child routes are also considered ultimate routes because they will contain the next-hop IP address and/or exit interface. Học viện mạng Bach Khoa - Website: www.bkacad.com 13 Parent and Child Routes: Classful Networks • Both child routes have the same subnet mask – This means the parent route maintains the /24 mask Học viện mạng Bach Khoa - Website: www.bkacad.com 14 Parent and Child Routes: Classless Networks • In classless networks, child routes do not have to share the same subnet mask. • Regardless of the addressing scheme used by the network (classless or classful), the routing table will use a classful scheme. Học viện mạng Bach Khoa - Website: www.bkacad.com 15 Parent and Child Routes: Classless Networks Học viện mạng Bach Khoa - Website: www.bkacad.com 16 Routing Table Structure Term variably Subnet mask Includes the # Parent route’s subnetted is ...