Key Concepts in Network Routing and Load Balancing
Non-Routable Addresses
What are the addresses that are not routable? Broadcast addresses.
Router Behavior with Unroutable Packets
How does a router behave if it is unable to route an IP data packet? It drops the packet and sends a Destination Unreachable ICMP message.
Conditions for Static Route Entry
What are the conditions to be satisfied before a static route is written into a routing table?
- IP routing must be enabled.
- The next-hop interface must be reachable.
- The exit interface must have an IP address configured and must be up.
Summary Route Definition
What is a summary route? A summary route is an address that encompasses several more specific addresses in a route table. It is the address mask used with a route entry to create a single summary route for several destination addresses.
Equal-Cost vs. Unequal-Cost Load Sharing
What is the difference between equal-cost and unequal-cost load sharing? Equal-cost load sharing distributes traffic equally among multiple paths with equal metrics. However, unequal-cost load sharing distributes traffic among multiple paths with different metrics. Paths with lower costs are assigned more traffic.
Default Load Sharing in Cisco
What is the default type of load sharing used by Cisco?
Cisco Express Forwarding (CEF) – traffic is distributed according to the destination. Two sources can go through two different paths.
CEF Status Check Command
What does this command return: show ipv6 cef? It determines whether CEF is enabled on the router or not.
Per-Packet vs. Per-Destination Load Sharing
What are the differences between per-packet load sharing and per-destination load sharing?
- Per-destination load sharing: Uses fast switching. All packets to a specific destination use the same interface, decreasing time and CPU utilization.
- Per-packet load sharing: The router makes a route table lookup and selects the interface for each packet.
Reliability Metric Definition
What is the reliability metric? It measures the likelihood that a link will fail. This could be based on the number of times it has failed or the number of errors received within a certain time period.
Route Convergence Explained
What is route convergence? It is the process of bringing routing tables to a state of consistency, without route loops. Convergence time should be short, even when the topology changes.
Main Load Balancing Policies
What are the main load balancing policies? Load balancing can be equal-cost or unequal-cost, and per-packet or per-destination.
Disadvantage of Distance Vector Routing
What is the main disadvantage of a distance vector routing protocol? The router periodically has to broadcast its entire routing table.
Reverse Route and Prevention
What is a reverse route, and how can it be avoided? A reverse route points back to the route from which packets were received. Split horizon is a technique to prevent this.
Common Routing Protocol Issues
What are the common issues to any routing protocol? The issues common to any routing protocol are best path determination, network metrics, convergence time, and efficient load balancing.
Distance Vector vs. Link State Protocols
What are the differences between distance vector and link-state routing protocols? A distance vector router broadcasts its entire routing table to all its directly connected neighbors. However, a link-state router sends only information about its directly connected links but floods this information throughout the network area.
IGP vs. EGP
What is the difference between an Interior Gateway Protocol and an Exterior Gateway Protocol? An Interior Gateway Protocol (IGP) is a routing protocol that routes within an autonomous system. An Exterior Gateway Protocol (EGP) is a routing protocol that routes between autonomous systems.
Autonomous System Definition
What is an autonomous system? Depending on the usage, an autonomous system can be defined as a network under a common administrative domain or a single routing domain.