30 Questions
What is the primary function of a routing algorithm in a router?
To select the best route between the source and the destination
What is the key difference between static and dynamic routing?
Static routes are configured before any network interactions, whereas dynamic routing requires routers to communicate with each other to learn about network paths.
What is stored in a routing table?
Path data
What is the primary advantage of static routing in terms of network security?
The network administrator conducts the necessary routing activities, making the network more secure
What is the characteristic of routing decisions in static routing?
Routing decisions do not depend on factors like network traffic or topology
What is the economic benefit of static routing?
The overall cost of static routing is less
What does a router do when it finds a matching network in the routing table?
The router encapsulates the packet into the data link frame of the outgoing exit interface and then forwards the packet out that interface to its destination.
What are the primary functions of a router?
To determine the best path to send packets and to forward packets toward their destination.
What does a router examine when it receives a packet?
The destination address of the packet.
What does a router do when it receives a frame from its Ethernet interface?
It de-encapsulates the packet to search the routing table for a matching network.
What is a key characteristic of a router's ability to handle different data link layer frame encapsulations?
The router can receive a frame from one interface (e.g. Ethernet) and encapsulate it into a different frame type (e.g. PPP) for the outgoing interface.
What happens to a packet after a router finds a match in the routing table?
The router encapsulates the packet into the data link frame of the outgoing exit interface and then forwards the packet out that interface to its destination.
What action does R2 take after determining that the destination IP address is on a different network?
R2 searches the routing table to find a corresponding route for the destination IPv4 address.
Why does R2 not have to resolve the next-hop IP address with a destination MAC address?
Because the exit interface is not Ethernet.
What type of data link frame is used by the exit interface of R2?
A new data link frame used by the Serial 0/0/0 interface.
What is the destination address set to by R2 on the serial interface?
An equivalent of a broadcast.
What action does R3 take after receiving the packet from R2?
R3 de-encapsulates the data link PPP frame and searches the routing table for the destination IPv4 address.
What happens to the Ethernet frame when R1 forwards it out of the FastEthernet 0/1 interface?
R2 examines the destination MAC address and copies the frame into its buffer.
What is the primary function of a router in a network?
To determine the best path to send packets.
What happens to the Layer 3 IP addresses as a packet travels from the source device to the destination device?
They do not change.
What is the purpose of de-encapsulating the packet in the switching function of a router?
To expose the Layer 3 packet.
What happens to the Layer 2 data link addresses as a packet travels from the source device to the destination device?
They change at every hop.
What is the result of a routing table search in a router?
One of three path determinations: directly connected network, or one of two other possibilities.
What is the final step in the switching function of a router?
The router encapsulates the Layer 3 packet into a new Layer 2 frame and forwards the frame out the exit interface.
What information does a routing table entry contain?
The destination network and the outgoing interface to use when forwarding packets to the destination network.
What happens to interfaces when they are configured with an IP address, subnet mask, and activated with the no shutdown command?
They are automatically added to the routing table with connected („C‟) and local („L‟) entries.
What command is used to verify that IPv6 networks and interface addresses have been installed in the IPv6 routing table?
The show ipv6 route command.
What does an 'L' indicate in an IPv6 routing table entry?
It is a local route, but with a /128 prefix.
What type of routes are manually configured and define an explicit path between two networking devices?
Static routes.
What is a limitation of static routes?
They must be manually reconfigured if the network topology changes.
Study Notes
Routing Concepts
- Routing is the technique of determining the optimal path to transmit data from one location to another.
- Routers operate on the network layer of the OSI model and the internet layer of the TCP/IP model.
- Routing algorithms enable routers to select the best route between the source and destination.
- Routing tables store path data.
Types of Routing
- Static routing: configured before network interactions, also known as "non-adaptive routing".
- Dynamic routing: requires routers to communicate with other routers to learn about network paths.
Static Routing
- Network administrators configure routes in the routing table.
- Routers transfer data from source to destination using the administrator-defined route.
- Routing decisions do not depend on network traffic or topology.
- Static routing does not require much bandwidth between routers.
- The network is more secure because the network administrator conducts the necessary routing activities.
- The overall cost of static routing is less.
Packet Forwarding Mechanisms
- Routers determine the best path to send packets and forward packets toward their destination.
- When a router receives a packet, it examines the destination address and uses the routing table to look for the best path.
- Routers can handle different data link layer frame encapsulations.
Packet Routing
- Routers de-encapsulate packets to search the routing table for a matching network.
- When a match is found, the router encapsulates the packet into the data link frame of the outgoing exit interface and forwards the packet out that interface to its destination.
Reach the Destination
- Routers use a switching function to accept a packet on one interface and forward it out of another interface.
- This process involves de-encapsulating the Layer 2 frame header and trailer, examining the destination IP address, and encapsulating the packet into a new Layer 2 frame.
Path Determination
- Routing decisions result in one of three path determinations: directly connected network, remote network, or no route.
- Directly connected networks are forwarded out of the interface connected to the destination network.
Directly Connected Networks
- Interfaces are configured with an appropriate IP address, subnet mask, and activated with the no shutdown command.
- Configured interfaces are automatically added to the routing table as directly connected networks.
- The routing table shows the destination network and the outgoing interface to use when forwarding packets to the destination network.
Learn about the basics of routing, including routing concepts and static routing. Understand how routers operate on the network layer of the OSI model and the internet layer of the TCP/IP model.
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