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53 Cards in this Set
- Front
- Back
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Why is EIGRP classed as a Hybrid Routing Protocol?
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Because it advertises routes to directly attached neighbors just like a distance vector protocol, while using a series of tables similar to a link-state protocol.
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What are the 3 data structure types in EIGRP? The data structure injects the best route into the IP routing table.
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Interface Table = Has list of all interfaces configured to participate in EIGRP. Neighbor Table = List of routers whose hellos have been received from neighbors. Topology Table = Routes learned by the EIGRP routing process with their FD and AD.
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What is the Feasible Distance?
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It is the Advertised Distance (distance from neighbor to the dst network) plus the metric to reach the neighbor advertising the AD.
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What's the formula for EIGRP metric?
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Bandwidth + Delay, where b/w is 10,000,000,000 divided by minimum b/w in kbs x 256, and delay is sum of delays of all interfaces in path in tens of millisecs x 256
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To start the EIGRP routing process. All routers that exchange EIGRP routing information must use the same Autonomous System number.
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R1(config)# router eigrp [as num]
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To specify a network whose interface will participate in the EIGRP routing process.
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R1(config-router)# network [network IP] [wildcard mask]
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To turn off Route summarization in EIGRP or RIP, which is on by default.
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R1(config-router)# no auto-summary
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To configure unequal load balancing, which is set for whole router. By default is set to 1 which means equal load balancing. All Feasible Successor routes (have an AD lower than successors AD) within the variance are injected into the routing table.
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R1(config-router)# variance [number]
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To show a list of all the interfaces configured to take part in the EIGRP routing process (with exception of passive interfaces). Also tells if each has any peers.
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R1# show ip eigrp interfaces
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To show a routers EIGRP neighbors, their IP address and off which interface they are.
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R1# show ip eigrp neighbors
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To display the topology table, which displays the routes known to a router`s EIGRP routing process. It shows the AD, FD, route states (e.g. passive, active, etc), and all the successors and feasible successors. The "all-links" keyword shows also shows routes that aren't Successors or Feasible successors.
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R1# show ip eigrp topology [all-links]
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To display the updates that are occurring in the routers IP routing table in real time. For example, when routes are added or deleted from the table as an interfaces comes up or goes down.
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R1# debug ip routing
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To display the different packet types being exchanged with an EIGRP neighbor. Displays a lot of information, so can use keywords to specify specific packet types. Terse displays all EIGRP packets except hellos.
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R1# debug eigrp packets [SIAquery | SIAreply | ack | hello | reply | request | stub | terse | update | verbose]
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To show info contained within EIGRP packets and reveal how an EIGRP routing process responds to that information. Rather than packet types, it focuses more on what the EIGRP process is doing in response to the messages.
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R1# debug eigrp
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How is the metric of cost calculated in OSPF?
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100,000,000 divided by b/w
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What are the 4 data structure types in OSPF?
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Interface Table = Has list of all interfaces configured to participate in OSPF. Neighbor Table = List of routers who hellos have been received from (neighbors). Link-state Database = Topology info for all areas in which router participates and info about how to route traffic to networks in other areas or ASs. Routing Information Base (RIB) = Stores results of the OSPF SPF calculations.
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What are the states an OSPF interface goes through?
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Down = No hellos. Attempt = sends hello but not received one. 2-way = 2 routers received hellos from each other but no RID known yet. Exstart = DR and nonDR routers begin to exchange info. Exchange = 2 routers form an adjacency and send one another DBD packets containing linkstate database info. Loading = Load missing entries identified in Exchange state. Full = Successfully exchange link-state info and adjacency been formed.
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Where are OSPF timers (Hello & Dead) and network types (Broadcast, NBMA, P-t-P, etc ) configured? Use "no" to reset back to default times or network types.
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In interface config mode. For example R1(config-if)# [no] ip ospf [hello-interval | dead-interval] [time in secs]
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What needs to match for an OSPF adjacency to form?
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Hello timer (Default Bcast & P-t-P 10secs, NBMA & P-t-M 30secs), Dead timer (Default Bcast & P-t-P 40secs, NBMA & P-t-M 120secs), area number, area type, subnet and authentication.
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When trouble shooting OSPF, what is a good first few steps to make sure there is connectivity between routers at L2 and L3?
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You can try pinging to see if the neighbor is reachable, and the "show cdp neighbor" cmd can be used to confirm a L2 adjacency.
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To advertise a default route in OSPF. Unlike RIP and EIGRP, you cannot create a default route in OSPF by simply redistributing a static route. Even if there is a default route in the routing table, by default Cisco's OSPF implementation will not forward it to the rest of the network. So Cisco forces you to be sure that you really want to source a default route into OSPF by requiring you to specifically enable it with the default-information originate command. This cmd will not advertise a default route unless a static default route exist on the router you’ve issued this command on unless you add keyword “always”.
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R1(config-router)# default-information originate always
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To show a list of all the interfaces configured to take part in the OSPF routing process. Similar to show ip interface, but with info about ospf on the interface (e.g. timers, network type, area id). The "brief" keyword provides a more concise view in a table format with the PID, network associated with each interface, metric cost, state info and number of neighbors the interface has.
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R1# show ip ospf interfaces [brief]
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To show neighbors RID, interface & IP address and their state. For multi-access segment also shows if is DR and priority as well.
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R1# show ip ospf neighbors
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To show the LSA headers contained in the routers Link-state database. "Router Link States" come from type 1 LSAs and "Net Link States" from type 2 LSAs.
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R1# show ip ospf database
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To see how the SPF algorithm is meant to run. Shows how many times it has run (frequency) and when it last run.
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R1# show ip ospf statistics
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To see in real-time when the SPF is scheduled to run and when it does run.
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R1# debug ip ospf monitor
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To show the transmission and reception of OSPF packets in real-time between neighbors. Rather than packet info, it just shows the RID and interface involved.
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R1# debug ip ospf packet
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To display real time updates about the formation of an adjacency, so shows the states through which the adjacency transitions (e.g. init, exstart, exchange, etc)
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R1# debug ip ospf adjacency
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To display real-time info about OSPF events as they happen. So this would show the transmission of hellos and LSAs as they happen.
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R1# debug ip ospf events
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To show information on the status of OSPF virtual links and the configuration information for them. They are required for areas not physically adjacent to the backbone area. The router you configure it on becomes a ABR, since it is then theoretically connected to the backbone. This is reflected in the routing table with less "O IA" states.
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R1# show ip ospf virtual-links
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What are the 3 ways in a seed metric can be defined? If one isn't specified the default is used, which for OSPF is 20 (unless BGP route when is 1), yet for EIGRP is 0, which means the redistributed route will be unreachable.
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1. The "default metric" cmd, 2. The "metric" parameter in the "redistribute" cmd, 3. A route map configuration.
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What 2 prerequisites must be met for the routes of 1 IP routing protocol to be redistributed into another?
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1. A route needs to be installed in a routers IP routing table before it can be redistributed, 2. The dst IP routing protocol needs a reachable metric assigned to the redistributed route.
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What's the cmd to redistribute routes from a specified EIGRP AS into OSPF. If no metric specified, given default of 20. You must add the "subnets" keyword for all non-classfull networks to be redistributed into OSPF.
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R1(config-router)# redistribute eigrp [AS] subnets
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What's the cmd to redistribute routes from a specified OSPF process ID into EIGRP with the specified metric.
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R1(config-router)# redistribute ospf [process id) metric [b/w delay reliability load mtu]
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The router config mode cmd that specifies the metric used for routes redistributed into OSPF or EIGRP.
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R1(config-router)# default-metric [metric] or [b/w(in kbps) delay(in tens of microsecs) reliability(max of 255) load(min of 1) mtu(in bytes)]
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What's the cmd to use IP route profiling to troubleshoot route instability? It works by measuring the number and type of routing table updates every 5 secs, and ideally only numbers in the first row (that is, 0 row) should change in a stable network.
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R1# show ip route profile
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What are BGPs 2 data structures?
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Neighbor table = Contains a listing of all BGP neighbors configured for a router, including their IP, AS and state of neighborship. BGP table = Contains routes (prefixes) learned from BGP peers and routes injected into the BGP table of a router.
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What are the criteria that BGP uses to make routing decisions and their priorities?
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1.Highest Weight , 2.Highest Local Preference, 3.Originated by BGP on local router, 4.Shortest AS path, 5.Lowest Origin type (IGP), 6.Lowest MED, 7. Prefers eBGP over iBGP, 8.Lowest IGP metric to the BGP next-hop, 9.Neighbor with lowest BGP RID.
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What are 2 reasons why a BGP session may fail? When Sessions are established with configured neighbors, they use TCP port 179.
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1. AS numbers must match, if not the session is reset. 2.If the peer doesn't recognize the src IP of the BGP message. The src IP must match the IP configured for that router on its peer.
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Are BGP neighbors learned dynamically or need to be configured manually?
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Neighbors are always learned by manual configuration as opposed to dynamically, which makes sense since neighbors don't have to be physically adjacent.
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How does the BGP AS-path attribute work?
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Is the ASs that must be crossed to reach a dst, with less ASs being the most preferable route. So you can prepend ASs (can be multiple instances of the same AS) to the AS path attribute of a route advertised to a neighbor, thereby making that path appear less attractive to the neighbor, therefore influencing how the neighbor routes traffic to this router.
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How can you decide whether a route map should be applied to a BGP update coming in or going out to influence BGP routing decisions?
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Got to think logically about it. If you want the influence the route out on the router your working, you would add the map to the routing updates coming IN from the neighbor. Likewise, if you want traffic to come in on a certain route, you would add the route map OUT to routing updates being advertised to neighbors.
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To set the BGP weight metric on an interface.
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R1(config-router)# neighbor [IP add] weight [weight]
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To set the BGP local preference attribute for route matched by a route map. Is applied to routes coming into a router, causing the router to make its outbound routing decisions based on the local preference values.
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R1(config-route-map)# set local-preference [loc-prf]
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To create a route map. If you`re not going to use "match" and apply it to all routes, no need to also create an ACL.
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R1(config)# route-map [name] [permit | deny] [seq num]
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To define an AS path to prepend to an AS path known by the BGP forwarding table using route maps. These are the AS paths a BGP router thinks it must transcend to get to a dst.
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R1(config-route-map)# set as-path prepend [as num] [as num] [as num]etc.
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To apply a specific route map to routes received from or advertised to a specific BGP neighbor.
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R1(config-router)# neighbor [IP add] route-map [name] [in | out]
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To display a routers BGP RID, AS number, info about BGP memory usage and a summary table of neighbors and there info (e.g. AS, msgs rcvd & sent, up/down time)
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R1# show ip bgp summary
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To see detailed info about BGP neighbors, very detailed and in a list rather than table. Some of the info included is the BGP state and the local and foreign hosts TCP port numbers being used.
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R1# show ip bgp neighbors
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To see the network prefixes present in the BGP table, along with info such as next-hop IP, loc prf, weight and the AS paths crossed. ">" represents the selected best path.
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R1# show ip bgp
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To display real-time info about BGP events, such as the establishment of a peering relationship. So doesn't show contents of BGP updates, just the peer and state change
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R1# debug ip bgp
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To display real-time info about BGP updates sent and received, specifically the contents of the updates like the routes being added.
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R1# debug ip bgp updates
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To display table of how much memory is being consumed by the various BGP processes of a router. Be aware BGP runs multiple processes and can consume significant amounts of router memory. To reduce you can filter out unneeded BGP routes or upgrade memory of router.
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R1# show processes memory | include BGP
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