Lesson 7: Configuring and Troubleshooting Routers Flashcards
Define a Router
An intermediate system with links and network topology information to facilitate forwarding packets
Where is routing information stored in a router?
In the routing table
What does a protocol define?
The source of the route
What are the four types of routing table entries?
- Direct Network Routes
- Remote Network Routes
- Host Routes
- Default Routes
Define a direct network route
A routing table entry for an active router interface or subnet that is automatically added to the routing table
Define a static route
Manually added to the routing table
Define a default route
Entry in the routing table to represent the forwarding path that will be used if no other entries are matched, also known as default gateway
How does a router forward packets?
After receiving a packet, it reads the destination address and looks up a matching destination network address and prefix, if there is a match, the router will forward the packet out of one of its interfaces by encapsulating the packet in a new frame
How does a router forward packets in a LAN/subnet?
The router uses arp (IPV4) or neighbor discover (IPV6) to determine the interface address of the destination host
How does a router forward packets to an external network?
It inserts the next hop router’s MAC address into the new frame during encapsulation
Define hop count
The amount of hops it takes a packet to transverse the internet; each time a packet passes through a router, the hop count increases by one
Define TTL
Counter field in the IP header that records number of hops a packet can make before being dropped; the number of seconds a packet can stay on the network before being discarded; when TTL hits 0, the packet is discarded
Define Dynamic Routing
Routing entries learned from another router via a dynamic routing protocol
How does dynamic routing determine routing information?
By using one of two protocols, distance vector or link state to select the best route
Define the distance vector protocol
Distance vector protocols send their entire routing table to directly connected neighbors to determine the path with the least amount of hops
Define a link state protocol
Dynamic Routing algorigthm/protocol allows a router to store the complete network topology and assess the least-cost paths in the topology database.
Define Convergence
Process where routers agree on routes through the network to establish the same network topology in their routing tables
What is steady state?
A network where all the routers have the same topology
What is an autonomous system (AS)?
A network under the administrative control of a single owner
What is an Interior Gateway Protocol (IGP)?
A dynamic routing protocol used to share forwarding paths between routers in the same autonomous system (AS)
What is an Exterior Gateway Protocol (EGP)?
A dynamic routing protocol that can advertise routes between autonomous systems (AS) in the internetwork
What type of routing protocol is RIP (Routing Information Protocol)?
A distance vector routing protocol that only considers one metric to select the optimal path which is the route with the least amount of hops
How does RIP (Routing Information Protocol) work?
RIP sends its routing database to neighboring routers every 30 seconds, and will send triggered updates whenever changes occur; When a router receives an update from a neighbor it adds the unknown route and increases the hop count by 1
What are the downsides to RIP (Routing Information Protocol)?
- Suited for smaller networks because distance vector algorithms require that routers periodically update their routing table and is unsuitable for larger networks
- Distance vector algorithms provide slower convergence than link state algorithms
