Term
| How does EIGRP differ from other routing protocols when it comes to sending updates? |
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Definition
| EIGRP sends triggered updates instead of periodic ones. These contian only paths that have changed,and are automatically bounded so that only those routers that require the information is updated. |
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Term
| How does EIGRP need to be configured when using different L2 protocols? |
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Definition
| EIGRP does not require special configuration to work across any L2 protocols. |
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Term
| How many bits represent the metric calculation of EIGRP? |
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Definition
EIGRP uses the same algorithm for metric calculation as IGRP, but represents values in a 32-bit format, rather than IGRP's 24-bit format. |
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Term
| What is the multicast address used by EIGRP to communicate between routers? |
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Definition
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Term
| At what layer does EIGRP operate? |
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Definition
| The EIGRP routing process is a transport layer function of the OSI model. |
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Term
| What's the protocol number that is carried in IP packets when EIGRP is used? |
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Definition
| IP packets carrying EIGRP information have protocol number 88 in their IP header. |
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Term
| How is EIGRP able to guarantee ordered delivery of EIGRP packets to all of its neighbors? |
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Definition
| EIGRP uses Reliable Transport Protocol (RTP) to guarantee packet delivery. RTP supports intermixed transmission of multicast and unicast packets. |
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Term
| How does EIGRP work with other network layer protocols? |
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Definition
| EIGRP supports IP, Appletalk, and IPX, each having its own EIGRP module and operates independently from any of the others that might be running. |
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Term
| What are the different types of packets that are sent out by EIGRP? |
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Definition
| EIGRP sends out 5 different types of packets- hello, update, query, reply, and acknowledge (ACK)- that are used to establish the initial adjacency between neighbors and to keep the topology and routing tables current. |
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Term
| What information is contained in an EIGRP neighbor table? |
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Definition
| The EIGRP neighbor table contains adjacencies formed with its neighbors, including the neighbor's address and the interface through which it can be reached. |
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Term
| What information is contained in an EIGRP topology table? |
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Definition
| The topology tables contains all destinations advertised by neighboring routers, so each router stores its neighbor's routing table in its EIGRP topology table. |
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Term
| What's the different between an advertised distance and feasible distance? |
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Definition
| The advertised distance is the cost the next-hop router and the destination network. The sum of these costs from the local router to the next-hop and the advertised distance is referred to as the feasible distance. |
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Term
| What is a successor in regards to EIGRP? |
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Definition
| A successor is a neighboring router that has a least-cost path to a destination. |
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Term
| How does EIGRP determine and use feasible successors? |
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Definition
| A feasible successor is a back-up path to another next-hop router. To qualify as a feasible successor, a next-hop router must have an AD less than the FD of the current successor route. So the FS is a neighbor that is closer to the destination, but it is not the least-cost path. If a successor becomes invalid, a router will use its FS to avoid a recomputation for a new route. |
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Term
| What are the 3 different tables that are maintained by EIGRP? |
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Definition
- Neighbor table - lists adjacent routers - Topology table - lists all the learned routes to each destination - Routing table - contains the best route (the successor route) to each destination |
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Term
| What command can be used to display the successor and feasible successor for IP routes? |
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Definition
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Term
| What command can be used to view all the IP entries in an EIGRP topology table? |
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Definition
show ip eigrp topology all-links
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Term
| When does a router update its EIGRP topology table? |
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Definition
| The topology table is updated when a directly connected route or interface changes or when a neighboring router reports a change to a route. |
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Term
| What are the 2 different states that an EIGRP topology entry can exist in? |
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Definition
| A route is considered passive when the router is not performing recomputation on that route. A route is active when it is undergoing recomputation (looking for another successor). |
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Term
| What does a router do if it does not have a successor or feasible successor router? |
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Definition
| The router sends out a query packet to each of its neighbors. If they have a route, then they reply with a reply packet. If not, that router will send out its own query packet. The information in the routing table is not changed until a reply is received. |
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Term
| What are the 5 different packets that are used by EIGRP? |
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Definition
- Hello - Update - Query - Reply - ACK |
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Term
| What are EIGRP hello packets used for? |
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Definition
| Hello packets are used for neighbor discovery. They are sent as mulitcast and do not require an acknowledgment. |
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Term
| What are EIGRP update packets used for? |
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Definition
| Update packets contain route change information. These updates are sent as multicasts when a new route is discovered, and when convergence is complete (when the route becomes active). |
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Term
| What are EIGRP query packets used for? |
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Definition
| EIGRP query packets are used when a router is performing route computation and does not have a feasible successor. |
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Term
| What are EIGRP reply packets used for? |
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Definition
| EIGRP reply packets is sent in response to a query packet. Replies are unicast to the originator of the query. |
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Term
| What are EIGRP ACK packets used for? |
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Definition
| The ACK packet is used to acknownledge updates, queries and replies. |
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Term
| How often are hello packets sent when using EIGRP? |
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Definition
| Hello packets are sent every 5 seconds on serial interfaces and on LANs. But they are sent out every 60 seconds on T1 or slower multipoint interfaces and WAN links. |
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Term
| What command can be used to adjust the interval that hello packets are sent? |
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Definition
| ip hello-interval eigrp as-number seconds |
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Term
| What is the default hold-time interval when using EIGRP? |
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Definition
| The hold-time interval is set to 3 times the hello interval. |
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Term
| What command is used to adjust the hold time when using EIGRP? |
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Definition
| ip hold-time eigrp as-number seconds |
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