Routing Pt 1 Flashcards
What is Cisco Express Forwarding (CEF)?
The most recent and default Cisco IOS packet-forwarding mechanism that builds a Forwarding Information Base (FIB) and an adjacency table
CEF entries are changed based on network topology changes, not packet-triggered.
What does Fast Switching use to store next-hop information?
A fast-switching cache
Fast switching is an older packet forwarding mechanism that utilizes the CPU for unmatched packets.
What is Process Switching?
An older packet forwarding mechanism where each packet is processed individually by the CPU
This method matches the destination address with the routing table for every packet.
What are the three packet forwarding mechanisms supported by routers?
- Process switching
- Fast switching
- Cisco Express Forwarding (CEF)
What is the primary responsibility of packet forwarding?
To encapsulate packets in the appropriate data link frame type for the outgoing interface.
For example, the data link
frame format for a serial link could be Point-to-Point (PPP) protocol, High-Level Data Link
Control (HDLC) protocol, or some other Layer 2 protocol.
What command is used to enter configuration mode on a router?
configure terminal
What command is used to display the IP interface status?
show ip interface brief
What does the letter ‘L’ signify in a routing table?
Identifies the address assigned to a router interface.
What are static routes commonly used for?
- As a default route forwarding packets to a service provider
- For routes outside the routing domain
- Explicitly defining the path for a specific network
- Routing between stub networks
What filtering command parameter displays the entire section that starts with the filtering expression?
section
What happens if there is no match in the routing table for a packet?
The packet will be dropped.
What is meant by ‘the longest match’ in routing?
The route in the routing table with the greatest number of far-left matching bits with the destination IP address.
Fill in the blank: The routing table contains a list of routes to known networks derived from directly connected networks, static routes, and _______.
dynamic routing protocols
True or False: Every router makes its forwarding decision based on the information in its routing table.
True
What does the code ‘C’ indicate in a routing table?
Identifies a directly connected network. Stands for Connected
What is the command to encrypt passwords in router configuration?
service password-encryption
What is the function of the command ‘ping’ in router verification?
To test connectivity to another device.
What does the command ‘show ip route’ display?
The contents of the IP routing table.
What are the two primary functions of a router?
- Determine the best path to forward packets
- Forward packets toward their destination
What is the significance of prefix length in routing?
It determines the number of far-left bits that must match for a successful route match.
In IPv4 longest match, which route entry would be chosen for the destination address 172.16.0.10?
172.16.0.0/26
In IPv6, which route entry matches the destination address 2001:db8:c000::99?
2001:db8:c000::/48 (longest match)
What command is used to copy the running configuration to the startup configuration?
copy running-config startup-config
What is the purpose of the command ‘banner motd’?
To display a message of the day upon login.
What does the command ‘no shutdown’ do in interface configuration?
Enables the interface.
What are the steps of the packet forwarding decision process?
- A data link frame with an encapsulated IP packet arrives on the ingress interface.
- The router examines the destination ip address in the packet header and consults the routing table
- Router finds the longest matching prefix in the routing table
- Router encapsulates the packet in a data link frame and forwards it out the egress interface. Destination could be a device connected to the network or a next hop router
- If there is no matching route entry, the packet is dropped
How does a router determine the next hop for a packet?
The router examines the destination IP address in the packet header and consults its IP routing table.
What does the longest matching prefix in the routing table signify?
It identifies the best matching route for the destination IP address.
What happens if there is no matching route entry in the routing table?
The packet is dropped.
What are directly connected networks in the context of routing?
Networks added to the routing table when a local interface is configured with an IP address and is active.
What are the two ways routers learn about remote networks?
- Static routes
- Dynamic routing protocols
What is a default route?
Specifies a next-hop router when the routing table does not contain a specific route matching the destination IP address.
What prefix length does a default route have?
/0
What is the purpose of the administrative distance in a routing table?
It identifies the trustworthiness of the route source.