Routing Flashcards
In what type of routing algorithm does each router sends all or some portion of its routing table only to directly connected devices?
Distance vector
What does an advanced distance vector algorithm provide that a traditional distance vector does not?
Advanced distance vector algorithms rapid convergence, use of hello mechanisms, formation of neighborships, and the ability to balance traffic over equal- and unequal-metric paths.
In what routing algorithm does each router build a picture of the network and calculates the shortest path to each known destination?
Link state
What routing algorithm is similar to distance vector protocols, but instead of looking at the distance to figure out the best loop-free path, it looks at various BGP path attributes?
Path vector
What is the purpose of a floating static route?
A floating static route is a static route that a router uses as a backup to a primary or dynamic route.
What is the default AD (administrative distance) that OSPF uses?
110
What does the EIGRP topology table contain?
The EIGRP topology table contains all of the prefixes that are advertised in that particular EIGRP autonomous system.
What is the hello timer interval that EIGRP uses on a slow interface?
60 seconds
What is the main purpose of a virtual link in an OSPF implementation?
A virtual link in OSPF provides a disconnected area with a logical path to the backbone (Area 0).
In OSPFv3, the AllDRouters designated router (DR) is represented by what address?
FF02::06
What is the administrative distance of a connect interface?
0
What is the administrative distance of a static route?
1
What is the administrative distance of EIGRP summary route?
5
What is the administrative distance of BGP?
20
What is the administrative distance of Internal EIGRP?
90
What is the administrative distance of OSPF?
110
What is the administrative distance of IS-IS?
115
What is the administrative distance of RIP?
120
What is the administrative distance of EIGRP external route?
170
What is the administrative distance of Internal and Local BGP?
200
What are the three main components of path selection?
Prefix length, administrative distance, and metric
What type of static routes can reference the outbound interface of a router?
Directly attached static routes
ip route network subnet-mask next-hop-interface-id.
What type of static route is a route whose next hop and the destination network are covered by another learned route in the RIB?
Recursive static routes
ip route network subnet-mask next-hop-ip.
What type of static route is a fully specified static route is a route that specifies both an interface and a next-hop IP address?
Fully specified static routes
ip route network subnet-mask interface-id next-hop-ip
What is a floating static route?
A static route that the router uses as a backup to a primary or dynamic route
ip route network subnet-mask next-hop-interface-id 205
What is a successor route in EIGRP?
The successor route is the route with the lowest-metric path to reach the destination network.
What is the first next-hop router for the successor route?
Successor
What is the EIGRP metric value for the lowest-metric path to reach a destination network?
Feasible distance (FD)
In EIGRP, what is the distance reported by a router to reach a particular network prefix?
Reported distance (RD)
What states that for a route to be considered a backup route, the RD received for that route must be less than the FD that is calculated locally?
Feasibility condition
What is not the current best route but a backup route that can be used if the successor route is lost?
Feasible successor
T/F: EIGRP relies on the periodic advertisement of all network prefixes, which is done with other routing protocols, such as RIP and OSPF
False
T/F: EIGRP relies on the periodic advertisement of all network prefixes, which is done with other routing protocols, such as RIP and OSPF
False
What EIGRP packet type is used for discovering EIGRP neighbors and for detecting when a neighbor is lost?
Hello
What is the EIGRP default hello timer?
5 seconds
60 sec for slower interfaces
What is the amount of time EIGRP deems the router as still reachable and functioning?
Hold time
What is the EIGRP default hold timer?
The default hold time is three times the hello time interval. So, the default is 15 seconds, and it is 180 seconds on slower links.
What EIGRP packet type is used to get specific information from a neighbor?
Request
What EIGRP packet type is used to transmit routing and reachability information with EIGRP neighbors?
Update
What EIGRP packet type is used to search for other paths during convergence?
Query
What EIGRP packet type is sent in response to a query packet?
Reply
EIGRP uses which protocol number and multicast address for communication?
IP protocol number 88. Communication happens using the multicast group address 224.0.0.10.
What contains all of the prefixes that are advertised in a particular EIGRP autonomous system?
Topology Table
What does the K1 value represent?
The minimum bandwidth of the route, in Kbps
What does the K2 value represent?
The effective load of the route, expressed as a number from 0 to 255, where 255 is 100% loading.
What does the K3 value represent?
The route delay, in tens of microseconds: Scaled delay = Delay/10.
What does the K4 value represent?
Reliability: The likelihood of successful packet transmission, expressed as a number between 0 and 255, where 255 means 100% reliability and 0 means no reliability.
What does the K5 value represent?
The minimum maximum transmission unit (MTU) size of the route, in bytes. It can be 0 or any positive integer.
How would you configure manual EIGRP route summarization in classic mode?
ip summary-address eigrp command in interface configuration mode
How would configure manual EIGRP route summarization in named mode?
summary-address command
How does OSPF calculate cost?
The cost is inversely proportional to the bandwidth of that interface, and the higher the bandwidth of an interface, the lower the cost.
Cost = 100 Mbps/Bandwidth of the Interface, in Mbps
What needs to parameters need to match for OSPF routers to from an adjacency?
Area ID, authentication, hello/ dead timers, stub area flag, and MTU
What determines which router will be the DR on a broadcast segment?
Highest OSPF priority. In the event of a tie, the router with the highest router ID wins.
What is the multicast address routers running OSPF should be able to receive these packets?
224.0.0.5
What is the multicast address for only DR OSPF routers?
224.0.0.6
In which OSPF state no hellos have been received from any router on the segment, but hellos are being sent?
Down
On non-broadcast multi-access links, which OSPF state indicates that no recent hello has been received from the neighbor?
Attempt
Which OSPF state hello packet was detected on the interface, but bidirectional communication has not yet been established?
Init
In which OSPF state bidirectional communication with the neighbor has occurred, and the router saw its own router ID in the neighbor field of the hello packet coming from the neighbor?
Two-way
In which OSPF state do routers establish the initial sequence number that is to be used for information exchange?
Exstart
In which OSPF state do routers send database descriptor packets describing their LSDB?
Exchange
In which OSPF state do routers finalize the information exchange?
Loading
In which OSPF state is the adjacency is completed?
Full
Which OSPF packet type is used for discovering and maintaining neighbors?
Hello
Which OSPF packet type is used for summarizing link-state database contents?
Database descriptor (DBD)
Which OSPF packet type is used to request link-state database updates?
Link-state request (LSR)
Which OSPF packet type is used to send link-state database updates?
Link-state update (LSU)
Which OSPF packet type is used to ensure reliable transmission of LSAs?
Link-state ack (LSACK)
How would you configure OSPF via the interface method?
int g1/1
ip ospf 1 area 0
What command allows you to verify OSPF interface info?
show ip ospf interface and show ip ospf interface brief commands
If not specified, how does OSPF dynamically assign the RID?
The router ID (RID) is dynamically allocated and is the highest IP address of any loopback interface in the up state. If there are no loopback interfaces in the up state, then the highest IP address of any active physical interface in the up state is used when the OSPF process initializes.
What does a passive interface mean in OSPF?
A passive interface in OSPF prevents the sending of OSPF hellos and prevents the processing of any received OSPF packets.
How would advertise a default route in OSPF?
You advertise the default route by using the command default-information originate [always] [metric metric value] metric-type type-value] in the OSPF process. The always option installs a default route even if one does not exist in the RIB.
How can you influence OSPF DR placement on a router?
You can raise the priority above the default value (which is 1) to make an interface more favorable than other interfaces that have the default value. You change the priority by using the interface configuration command ip ospf priority 0-255.
What type of LSA advertises the network prefixes that have originated from a different area?
Type 3 (summary LSA)
What type of LSA advertises the multi-access network segment that is attached to a DR within an area?
Type 2 (network LSA)
What type of LSA advertises the LSAs that are originated within an area?
Type 1 (router LSA)
What type of LSA advertises the ID of the ABR that needs to be used to reach an ASBR if the ASBR is not in the area where the type 5 LSA is being seen?
Type 4 (ASBR summary)
What type of LSA advertises LSAs for routes that were redistributed and therefore external to the OSPF routing domain?
Type 5 (AS external LSA)
What type of LSA advertises redistributed routes in not-so-stubby areas (NSSAs) and is therefore external to the OSPF routing domain?
Type 7 (NSSA external LSA)
What type of routes are most preferred in the OSPF path selection process?
Intra-area. The routes advertised through a type 1 LSA are always preferred over type 3 and type 5 LSAs. When multiple intra-area routes exist, the path with the lowest total path metric is installed in the RIB.
After Intra-area routes, what is preferred next?
Interarea. These routes are flagged as O IA in the routing table.
After Interarea routes, what is preferred next?
External type 1. External type 1 LSAs use the redistribution metric in addition to the lowest path metric to get to the ASBR that advertises the route.
After External type 1 routes, what is preferred next?
External type 2.
How can you configure interarea summarization?
Using the command area area-id range network subnet-mask [advertise | not-advertise] [cost metric] under the OSPF process.
How can you configure external summarization?
summary-address network subnet-mask
Do you enable OSPFv3 via network command or on the interface?
OSPFv3 specifies that each interface must be enabled using commands in interface configuration mode.
Can multiple instances of OSPFv3 can run on a link?
Yes
In OSPFv3, routers communicate with each other using the local interface’s ______ address as the source.
IPv6 link-local address
What are the OSPFv3 multicast link-local scoped addresses?
FF02::05: OSPFv3 AllSPFRouters
OSPFv3 AllDRouters designated router (DR) router
Do you need to configure a separate OSPFv3 process from regular IPv4 OSPF?
Yes by using the command router ospfv3 [process-id].
What are the four required steps to configure OSPFv3?
Enable IPv6 unicast routing by using the command ipv6 unicast-routing.
Configure the OSPFv3 process by using the command router ospfv3 [process-id].
Define the router ID by using the command router-id router-id.
Enable OSPFv3 on an interface and assign the interface to an area by using the command ospfv3 process-id ipv6 area area-id.
How many packet types does OSPF use for communication?
Five
With OSPF, which factor is used for calculating the cost of an interface?
Bandwidth
Which of the following is a pure distance vector routing protocol?
A. RIP
B. EIGRP
C. OSPF
D. BGP
RIP
What is the default hello timer that EIGRP uses on slower interfaces?
60 Seconds
In OSPF, what is the AllSPFRouters multicast destination?
A. 224.0.0.5
B. 224.0.0.6
C. 224.0.0.8
D. 224.0.0.10
224.0.0.5
What is the multicast destination address that OSPFv3 uses to communicate with the AllDRouters designated routers?
A. 224.0.0.5
B. 224.0.0.6
C. FF02::05
D. FF02::06
FF02::06
True or false: Unlike OSPFv2, OSPFv3 supports running multiple instances of OSPFv3 for each link
True
What are the two blocks of private ASNs that organizations can use as long as they are not exchanged publicly on the Internet?
64,512–65,535 within the 16-bit ASN range
4,200,000,000–4,294,967,294 within the 32-bit range
What are the three tables BGP uses to store information?
BGP neighbor table, BGP table, and the IP routing table
How many message types does BGP use for communication?
4
What are the four message types BGP uses for communication?
Open, update, notification, keepalive
Which BGP message type indicates error conditions to BGP neighbors?
Notification
Which BGP message type ensures the BGP neighbors are still alive?
Keepalive
What are the default keepalive and hold times on Cisco routers?
Cisco routers use a default hold time of 180 seconds, so the keepalive interval is 60 seconds
What type of BGP messages are responsible for setting up and establishing BGP adjacencies?
Open
What type of BGP messages are responsible for advertising, updating, and withdrawing previously advertised routes?
Update
What is the initial BGP state?
Idle. In this state, the router waits on a start event from the peering router, such as a peering confirmation from the remote peer.
What is the BGP state where the BGP process tries to establish a TCP session with a peer using the ConnectRetry timer?
Active
What is the state when the BGP routing process detects that a peer is trying to establish a TCP session with the local BGP speaker?
Connect
What BGP state indicates an open message is sent from the originating router, that router waits for an open message from the other router?
OpenSent
Which BGP state waits for a keepalive or notification message?
OpenConfirm
Which BGP state indicates session is established, and BGP neighbors begin exchanging routes with update messages?
Established
Which BGP attributes must be included with every prefix advertisement?
Well-known mandatory
What are the well-known mandatory attributes?
Origin, AS_PATH, Next_Hop
What type of attributes may or may not be included with the advertised prefix?
Well-known discretionary
What are the two Well-known discretionary attributes?
Local Preference and atomic aggregate
What type of attributes do not have to be recognized by all implementations and can be set so that they are transitive and stay with route advertisements from AS to AS?
Optional transitive
What type of attributes cannot be shared from AS to AS?
Optional nontransitive
What is the BGP best path selection sequence?
We Love Oranges As Oranges Mean Pure Refreshment” for Weight, LOCAL_PREF, Originated Locally, AS_PATH, ORIGIN Type, MED, Paths, and RID.
Prefer the path with the highest WEIGHT (local to a router).
Prefer the path with the highest LOCAL_PREF (global within AS).
Prefer the path that was locally originated via a network or aggregate BGP subcommand or through redistribution from an IGP.
Prefer the path with the shortest AS path (that is, the smallest number of autonomous systems in the AS_PATH attribute).
Prefer the path with the lowest Origin type.
Prefer the path with the lowest MED. (MEDs are compared only if the first AS in the AS sequence is the same for multiple paths.)
Prefer eBGP over iBGP paths.
Prefer the path with the lowest IGP metric to the BGP next hop.
If both paths are external, prefer the path that was received first (that is, the oldest route).
Prefer the route that comes from the BGP router with the lowest router ID (RID).
Prefer the path from the lowest neighbor address (which is the IP address used in the BGP neighbor configuration).
What command allows you to see bgp table?
show ip bgp
What command displays the status of bgp connections?
show ip bgp summary
What symbol indicates the best route for a prefix in the BGP table?
>
What symbol indicates the route is valid in the BGP table?
*
True or false: The network statement in BGP indicates to the local router which routes should be injected into the BGP table.
True
Which BGP verification command shows information about the TCP and BGP connection to BGP neighbors?
show ip bgp summary
show ip route bgp
show ip bgp
show ip bgp neighbors
show ip bgp neighbors
In which BGP state does the BGP process try to establish a TCP session with a peer by using the ConnectRetry timer?
Active
True or false: The version number of a BGP table changes when BGP updates the table with routing information changes.
True
Which of the following techniques is the third selection criterion when making the BGP best path determination?
Weight
Origin (originated)
AS path
MED
Origin
True or false: AS_PATH is a well-known discretionary attribute.
False. Well-known mandatory
In OSPFv3, what is a type 3 LSA?
interarea prefix LSAs
In OSPFv3, what is a type 4 LSA?
interarea router LSAs
In OSPFv3, what is a type 5 LSA?
AS external LSAs
In OSPFv3, what is a type 8 LSA?
link LSAs
In OSPFv3, what is a type 9 LSA?
intra-area prefix LSAs
