Dynamic Routing Protocols Flashcards
What are the three types of dynamic routing protocols (regarding how they actually function)? Give an example of each.
Distance Vector - RIP
Advanced Distance Vector - EIGRP
Link-State - OSPF, IS-IS
What is the purpose of dynamic routing protocols?
To allow routers to share network topology information. The routers use this information to choose what are, according to the routing protocol, the best routes to different destinations and populate their routing tables with these routes. Without dynamic routing protocols EVERY route would have to be input manually.
How does a distance vector routing protocol determine the best route? Why does this not always result in the best routing decisions?
Comparing the number of hops necessary for each route; the route with the fewest hops is chosen.
Because link speed is ignored.
What are the two types of routing protocols (regarding what portion of the network they cover)? Give an example of each.
Internal Gateway Protocols (EIGRP, OSPF, RIP) and External Gateway Protocols (BGP).
What three tables do link-state protocols create? What is the purpose of each?
Topology Table - stores the topology
of the network.
Routing Table - stores best routes
Neighbor Table - stores neighbors
that are participating
in the routing
protocol
What path-selection algorithm does EIGRP use? What does it stand for?
DUAL (Diffused Update Algorithm)
Describe the metric that DUAL uses. What things are taken into consideration by default? What additional factors can it be configured to consider?
It’s a composite metric - it takes multiple factors into consideration. By default it uses bandwidth and delay to choose the best path. Load and reliability are optional.
View information regarding neighboring devices participating in EIGRP:
show IP EIGRP neighbors
View information about interfaces that are configured for EIGRP on a device:
show IP EIGRP interfaces
What is the only dynamic routing protocol that offers unequal-cost load balancing?
EIGRP
What are the commands associated with configuring EIGRP?
router eigrp [AS #]
network [network address]
Show information regarding any routing protocols enabled on the device:
show IP protocols
Make EIGRP run classless:
Router(config)#router eigrp [AS#]
Router(config-router)#no auto-summary
How is EIGRP configuration different for IPv6?
IPv6 EIGRP must be turned on with the command (in global config):
ipv6 unicast-routing
then assigned an AS and turned on:
(config)#ipv6 unicast-routing
(config)#ipv6 router eigrp (AS#)
(config-router)#router-id [IP address]
(config-router)#no shutdown
Then turned on on a per-interface basis:
(config-if)#ipv6 enable*
(config-if)#ipv6 eigrp 1
(config-if)#no shutdown
*if IPv6 hasn’t already been enabled on the router/interface
In what DRP might a router be referred to as an internal router? What does this mean?
In OSPF, an internal router is a router that sits inside a particular area.
Set an interface’s cost in OSPF:
(config-if)# IP OSPF cost (cost#)
What are the benefits of using multiarea OSPF?
Each router has to store the topology of a smaller portion of the network (the portion inside its area). This can cut down on processing time when topology changes.
Command format for creating an OSPF area:
router OSPF 1
network (IP address) (wildcard mask) area(area#)
Turn off EIGRP on a router:
no router EIGRP (AS #)
In order for OSPF neighbors to create an adjacency, what criteria must be met?
The Area ID, Hello Timer and Dead Timer must be the same for both routers. Also, if you’ve configured authentication the neighboring routers must pass each other’s authentication checks.
Also, the MTUs apparently have to match.
Which DRP, EIGRP or OSPF, has a lower default administrative distance?
EIGRP - its default AD is 90, OSPF’s is 110
What algorithm does OSPF use to determine the best path to a destination network? (It can be called two different things)
- SPF (shortest path first) algorithm
* Dijkstra algorithm
What command would you use to change an interface’s priority in OSPF?
ip OSPF priority (1-255)
What is the default frequency of hello packet transmission in OSPF on a broadcast segment (Ethernet)?
10 seconds
What is the default frequency of hello packet transmission in OSPF on a non-broadcast segment (serial)?
30 seconds
What’s the destination ip of an OSPF hello packet?
224.0.0.5
What is split horizon route advertisement?
A method of preventing routing loops in distance vector routing protocols by prohibiting a router from advertising around back onto the interface from which it was learned (in the same way that of switch will not flood a frame with an unknown destination MAC address back out the interface from which it received the frame).
What type of dynamic routing protocols typically use the split horizon technique?
Distance-vector protocols
What address does EIGRP use for multicasts?
224.0.0.10
In EIGRP, what are the default hello and hold-time counters in a high-speed Ethernet network? In a low-speed NBMA?
High speed Ethernet:
Hello - 5s
Hold-time - 15s
Low speed NBMA:
Hello - 60s
Dead - 180s
In RIP, load balancing is performed over links with equal what?
Hop count, since RIP uses hop count as its metric.
Do OSPF neighbor MTUs need to be the same in order for them to create an adjacency?
Yes
What type of routing authentication is used in the packet?
Router1# debug ip ospf packet
OSPF: rcv. v:2 t:1 l:58 rid: 10.0.0.1 aid: 0.0.0.0 chk: 64ABC aut:2 keyid:1 seq: 0x0
MD5 encrypted
Configure EIGRP md5 authentication on R1’s serial 0/0 interface with a password of cisco.
R1(config)#key chain Chain
R1(config)#key 1
R1(config)#key-string cisco
R1(config)#int s0/0
R1(config-if)#ip authentication mode eigrp 1 md5
R1(config-if)#ip authentication key-chain eigrp 1 Chain
