CCNA Flashes I.07 (Routing)
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- Define routing.
- Routing is the act of finding a path to a destination and moving information across an internetwork from the source to the destination.
- What are the two key functions a router performs?
- The two key functions a router performs are routing and switching. The routing mechanism is responsible for learning and maintaining awareness of the network topology. The switching function is the process of moving packets from an inbound interface to an outbound interface.
- What is a routing metric?
- A routing metric is a factor used to determine a route's desirability. A router uses the metric to determine the best or most optimal path on which network traffic should be forwarded.
- What are the 7 most common routing metrics used in routing algorithms?
- The most common routing metrics used in routing algorithms are: a) Bandwidth: A link's data capacity. b) Delay: The amount of time required to move a packet from source to destination. c) Load: The amount of activity on the link or network resource. d) Reliability: A reference to the error rate on each network link. e) Hop count: The number of routers a packet must take to reach its destination. f) Ticks: The delay on a data link using IBM PC clock ticks. 1 tick is 1/18 of a second. g) Cost: A value assigned by the network administrator, usually based on bandwidth or monetary expense on the link.
- What is the difference between a routed protocol and a routing protocol? Give examples.
- A routed protocol is a protocol suite that provides the information in its network layer to allow a packet to direct traffic. It also defines the use of fields in a packet. Examples of routed protocols are IP, IPX, and DECnet. A routing protocol is used to find routes in an internetwork, exchange routing tables, and maintain route awareness. Routing protocols determine how routed protocols are routed. RIP, EIGRP, IS-IS, OSPF, and BGP are examples of routing protocols.
- What 6 types of information are stored in routing tables?
- The types of information stored in routing tables are: a) Destination network address b) Next-hop address c) Exiting interface d) Metric e) Administrative distance f) Routing protocol used
- How do routing protocols maintain their routing tables with each other?
- Routing protocols maintain their routing tables through the transmission of routing update messages. Routing update messages are exchanged between routers at periodic intervals or when there is a change in the network topology. The information contained in the routing update messages and how and when updates are sent varies from routing protocol to routing protocol.
- What is administrative distance? What is its range? When is it important?
- Administrative distance (AD) is an integer from 0 to 255 that rates the trustworthiness of the source of the IP routing information. It is important only when a router learns about a destination route from more than one source. The path with the lower AD is the one given priority.
- What is the AD for each of the following? - Directly connected interface - Static route - EBGP - EIGRP - IGRP - OSPF - IS-IS - RIP - External EIGRP - IBGP - Unknown
- The ADs are as follows: - Directly connected interface 0 - Static route 1 - EBGP: 20 - EIGRP: 90 - IGRP: 100 - OSPF: 110 - IS-IS: 115 - RIP: 120 - External EIGRP: 170 - IBGP: 200 - Unknown: 255
- What is the AD for a directly connected interface?
- 0
- What is the AD for a static route?
- 1
- What is the AD for EBGP?
- 20
- What is the AD for EIGRP?
- 90
- What is the AD for IGRP?
- 100
- What is the AD for OSPF?
- 110
- What is the AD for IS-IS?
- 115
- What is the AD for RIP?
- 120
- What is the AD for External EIGRP?
- 170
- What is the AD for IBGP?
- 200
- What is the AD for an unknown routing?
- 255
- What is an autonomous system (AS)?
- An AS is a collection of networks under common administrative control sharing a common routing strategy.
- What is the difference between Interior Gateway Protocol (IGP) and Exterior Gateway Protocol (EGP)? Give examples.
- IGP routes data within an autonomous system. EGP routes data between autonomous systems. Examples of IGPs are RIP, EIGRP, IS-IS, and OSPF. BGP is an example of an EGP.
- How do distance vector routing protocols function?
- Also known as Bellman-Ford algorithms, distance vector routing protocols pass complete routing tables to neighboring routers. Neighboring routers then combine the received routing table with their own routing table. Each router receives a routing table from its directly connected neighbor. RIP and IGRP are the two most common distance vector protocols used in today's internetworks.
- How do distance vector routing protocols keep track of any changes to the internetwork?
- Distance vector routing protocols keep track of an internetwork by periodically broadcasting updates out all active interfaces. This broadcast contains the entire routing table. This method is often called "routing by rumor."
- Slow convergence of distance vector routing protocols can cause inconsistent routing tables and routing loops. What are 5 mechanisms that distance vector protocols implement to prevent routing loops and inconsistent routing tables?
- Here are some of the ways distance vector routing protocols prevent routing loops and inconsistent routing tables: a) Maximum hop count (count to infinity) b) Split horizon c) Route poisoning d) Holddowns e) TTL
- What are link-state protocols? How do they work? List two common link-state protocols.
- Designed to overcome the limitations of distance vector protocols, link-state protocols respond quickly to network changes and send triggered and periodic updates. Link-state protocols create a picture of the internetwork by determining the status of each interface (link) in the internetwork. When the interface goes down, link-state protocols send updates out all the other interfaces, informing other routers of the downed link. OSPF and IS-IS are the most common link-state protocols.
- Which of the following is a hybrid routing protocol? - RIPv2 - IGRP - DECnet - EIGRP?
- EIGRP is the only hybrid routing protocol listed. EIGRP was developed by Cisco and is considered a hybrid routing protocol because it combines the aspects of distance vector and link-state routing protocols.
- If a router with RIP enabled has two paths to the same destination, one path being four routers away and the other path ten routers away, which path does the router choose?
- The router chooses the path that is four routers away from the destination. RIP bases its metric on the number of hops (routers) to a destination. The route with the smallest number of hops is considered the best path and is the one used.
- If a router running RIP has a path to a network that is 16 hops away, what does the router do to any packets destined for that network?
- The router drops all packets. RIP has a hop count limit of 15, so any routes with a hop count of 16 and greater are considered unreachable, and the packet is dropped. RIP has this limitation to prevent a packet from looping infinitely.
- What version of RIP supports variable-length subnet masks? Which are classful or classless?
- RIP version 2 (RIPv2) supports variable-length subnet masks. RIPv1 is considered a classful protocol because it does not include subnet information with the routing update. RIPv2 is considered a classless protocol because it includes the subnet information with the routing update.
- What is Interior Gateway Routing Protocol (IGRP)? What is default hop count? What are its default metrics? Which others can it use?
- IGRP is a Cisco-proprietary distance vector routing protocol. IGRP has a default hop count of 100 hops, with a maximum hop count of 255. IGRP uses bandwidth and delay as its default metric, but it can also use reliability, load, and MTU.
- What four components does EIGRP include that are not included in IGRP?
- EIGRP is an improvement over IGRP and is considered a hybrid protocol. The four components of EIGRP that are not included in IGRP are: a) Dynamic neighbor discovery b) Reliable transport protocol guarantees delivery of EIGRP updates c) DUAL finite-state machine ensures a loop-free internetwork d) Protocol-dependent modules let EIGRP work with IP, IPX, and AppleTalk
- Which of the following are link-state protocols? - IS-IS - BGP - VLSM - RIP - OSPF
- IS-IS and OSPF are link-state protocols. Both protocols support fast convergence and variable-length subnet masks.
- What type of protocol is BGP?
- BGP is considered an exterior gateway protocol (EGP).
- What port number are BGP updates carried on?
- BGP uses TCP port 179 to carry all its routing updates.
- If a routing protocol has multiple paths within the same routing protocol to the same destination, what is used as a tiebreaker?
- The metric, specifically the lowest one.
- If a router running RIP has 2 equal paths (same # of hops) to a destination, what will RIP do?
- Load-balance