Chapter 3 - Routing Protocol Characteristics, EIGRP, and IS-IS Flashcards
What is the default metric for any interface for the IS-IS routing protocol?
- 5
- 10
- 70
- 100
B.
The default metric for interfaces for IS-IS is 10.
Which type of routers are used to interconnect areas in IS-IS?
- Level 1 routers
- Level 2 routers
- Level 1/2 routers
- Level 2 routers and Level 1/2 routers
D.
Both Level 2 and Level 1/2 routers are used to interconnect IS-IS areas.
Which routing protocol is a distance-vector and classless protocol?
- RIPv2
- EIGRP
- OSPF
- IS-IS
A.
RIPv2 is a classless distance-vector routing protocol.
Which type of routing protocol sends periodic routing updates?
- Static
- Distance-vector
- Link-state
- Hierarchical
B.
Distance-vector routing protocols send periodic updates.
Which routing protocol has a default metric of 10?
- OSPFv2
- IS-IS
- EIGRP
- BGPv4
B.
In IS-IS, every interface has a default metric of 10.
Which of the following is true regarding routing metrics?
- If the metric is bandwidth, the path with the lowest bandwidth is selected.
- If the metric is bandwidth, the path with the highest bandwidth is selected.
- If the metric is bandwidth, the highest sum of the bandwidth is used to calculate the highest cost.
- If the metric is cost, the path with the highest cost is selected.
B.
If bandwidth is used, the path with the highest bandwidth is selected. If cost is used, the path with the lowest cost is selected.
Both OSPF and EIGRP are enabled on a router with default values. Both protocols have a route to a destination network in their databases. Which route is entered into the routing table?
- The OSPF route is entered.
- The EIGRP route is entered.
- Both routes are entered with load balancing.
- Neither route is entered; an error has occurred.
B.
OSPF has an administrative distance of 110. EIGRP has an administrative distance of 90. The route with the lower administrative distance is selected: EIGRP.
Which is a route that satisfies the feasibility condition and is installed as a backup route?
- The successor
- The feasible successor
- The reported successor
- The backup successor
B.
The feasible successor satisfies the feasibility condition and is maintained as a backup route.
Which parameters are included in the computation of the EIGRP composite metric that is used by default?
- Bandwidth and load
- Bandwidth and delay
- Bandwidth and reliability
- Bandwidth and maximum transmission unit (MTU)
B.
The default metrics for EIGRP are bandwidth and delay.
Which routing protocol implements the Diffusing Update Algorithm (DUAL)?
- IS-IS
- IGRP
- EIGRP
- OSPF
C.
EIGRP implements DUAL.
What is ES and IS in IS-IS?
ES = Endpoint System (hosts)
IS = Intermediate System (Routers - switches - etc)
What are the following communication levels?
L0
L1
L2
L3
L0 - L0 (host) to L1 device communication
L1 - L1 to L1 intra-area communication within a single entity
L2 - L1 to L1 inter-area communication (different areas within same entity)
L3 - comms between different entities, beyond inter-area comms in a single entity.
Note: Cisco devices only operate on L1 and L2.
Which area is mandatory in IS-IS? (Like Area 0 in OSPF)
none.
There are not mandatory areas in IS-IS. There is no need for a ‘backbone’ area in IS-IS.
However it is a best practice to use a ‘transit fabric’ or ‘transit area’ to move that traffic from area to area. This area needs to be a L2 area.
The commands:
router isis
is-type level 1
Will allow adjacencies to form provide which two conditions are met?
The two conditions that must be met for an adjacency to form are: L1 to L1 routers and in the same area.
What does the ‘net’ command stand for and what does it do in IS-IS?
The net command defines the NET = Network Entity Title
There is a lot of info in the net. These are 8-20 bytes long.
49.0001.0000.0000.0001.00
AFI.area-id.some-unique-identifier-like-MAC.00
AFI = first byte = Address Family Identifier, (49 => ISIS)
area-id = 0001
unique identifier = 1 (ususally this is the MAC address, but can be anything)
00 = NSEL or N-Selector, always zero for ISIS.
T/F: IS-IS can form router adjacencies at layer 2, without IP addresses.
True.
What is an LSP?
Link State packet.
IS-IS uses these L2 packets to exchange info to form adjacencies.
What is the metric for every Cisco interface with respect to IS-IS?
10.
Every link has a metric of 10.
What is the command ‘metric-style wide’ used for?
This allows the IS-IS system to bypass the default limit of hops.
This is best-practice.
T/F: Security in IS-IS at three different levels.
True.
INTERFACE LEVEL:
At the interface level use this command:
R1(config)# router isis
R1(config-router)# isis password your_secret_password
and on the neighbor router, do the same.
AREA LEVEL:
This can be done at the area level as well, with this command:
R1(config)# router isis
R1(config-router)# area-password password
DOMAIN LEVEL:
This can be done at the domain level under the ‘router isis’ config.
R1(config)# router isis
R1(config-router)#domain-password password
T/F: Adjacencies can be password protected, as in the neighborship will not form unless the password is used.
True.
INTERFACE LEVEL:
At the interface level use this command:
R1(config)# router isis
R1(config-router)# isis password your_secret_password
and on the neighbor router, do the same.
AREA LEVEL:
This can be done at the area level as well, with this command:
R1(config)# router isis
R1(config-router)# area-password password
DOMAIN LEVEL:
This can be done at the domain level under the ‘router isis’ config.
R1(config)# router isis
R1(config-router)#domain-password password
What does the ATT bit advertise to the the routers that receive it from an IS-IS router?
This comes from a L1-L2 router and says “ I am your exit point.” , like a default route.
What does RTP stand for with respect to EIGRP?
Reliable Transport Protocol
224.0.0.10 is the multicast address that EIGRP sends updates to using RTP, Hellos use this address for instance.
Sequence numbers are used by RTP to track what has been sent and received.
How often does EIGRP send hello packets?
every 5 seconds for LAN links
every 60 seconds for WAN or really slow links
What is “dead interval” or “hold timer” in EIGRP?
Three times the hello period is the time it take for a route to be removed if the hellos have not been seen. The route is considered to be non-functional.
How many metrics are used in EIGRP? What are they?
The K values are:
- Bandwidth
- Delay
- Load
- Reliablity
- MTU
Bandwidth and Delay are the most important, by far.
Lowest Bandwidth and sum of delays are used on a path to calculate the metric.
T/F: When EIGRP advertises a metric it includes the delay of the egress interface.
False. It sends a delay from it’s perspective, as in looking out from the router towards the destination. This does not include the egress interface delay.
T/F: The command “sh eigrp topology” will show the FD.
true.
FD, Active and Passive routes, successor routes too.
What is the FD in EIGRP?
The Feasible Distance is the lowest cost, the metric itself, of the best route to get to a destination.
What is a sucessor?
The advertising router for the best route, the route with the best FD, is the sucessor.
T/F: When EIGRP receives two equal RD, Reported Distances, then it will install both routes into the table and perform equal cost load balancing.
True EIGRP does this by default.
Note: The RD is also known as the AD, Advertised Distance.
Note: The FD is the best RD.
What is the best metric to change in EIGRP to influence a route manually?
delay.
What is the feasibility condition used for?
This is a route loop prevention mechanism.
- The lowest FD is selected as the successor router. This router has the route that has the best metric, and definitely closer than we are.
- The second lowest FD is the “feasible successor”, or backup router. This backup router has the route that is still closer to the destination than we are.
T/F: AS boundaries are query domain boundaries.
True.
When a route goes down, queries are sent out to every other router asking how to get to the missing route. The limits of these messages is bounded by the AS.
What is the AD of internal and external routes in EIGRP?
90 and 170.
Administrative distance is much greater for an external AS, or routes that are redistributed from other routing protocols.
T/F: Stub routers do not participate in queries for alternative routes.
True.
This is one of the main advantages of stub domains.
For instance, a branch office participates in sending and receiving routes, of course. But when a route goes down in the main network we do not want the branch office to be queried for alternative routes. That could lead to circuitous routes that are not efficient, routing tons of traffic through a little branch router. Bad things follow…
T/F: A stub router will not advertise a route that it has learned from another EIGRP router.
True!
This is very important. Stubs should not advertise routes they have learned, they will never be the optimal path.
By default a stub router can only advertise it’s directly connected routes or a summary of them.
The command “eigrp stub” will create a stub network.
T/F: Making an interface passive will still advertise the directly connected route but the interface will not form an adjancy with other routers.
True. Here is an example of why…
Above we have two routers, R1 and R2. On the left side there’s the 192.168.10.0 /24 network with a switch and some computers. R1 wants to advertise this network to R2 but since there are no other EIGRP routers in the 192.168.10.0 /24 network, it’s pointless to send EIGRP hello packets on the FastEthernet 0/1 interface.
It’s also a security risk, when someone connects a router in the 192.168.10.0 /24 network (or starts a virtual router on their computer) they will be able to become EIGRP neighbors with R1.
To prevent this from happening, we will use the passive-interface command. This will ensure that the network is advertised in EIGRP but it will disable hello packets on the interface.
What are the differences between configuring authentication for eigrp between classic and named mode?
Classic mode: (auth is set on interface and limited to md5)
int eth0/0
ip authentication mode eigrp 10 md5
Named mode:
R1(config)# router eigrp ENSLD
R1(config-router)# address-family ipv4 unicast autonomous-system 10
R1(config-router-af)# af-interface eth 0/0
R1(config-router-af-interface)# authentication mode hmac-sha-256
T/F: The command “upgrade-cli” under the eigrp context will change your classic instance to a named mode.
True.
T/F: Distance-vector algorithms call for each router to send its entire routing table to only its immediate neighbors.
True.
RIPng can send triggered updates—that is, full routing table updates sent before the update timer has expired.
True.
However, this means that a router can receive a routing table with 500 routes with only one route change, which creates serious overhead on the network ( drawback).
T/F: EIGRP does not send periodic updates as other distance-vector routing protocols do.
True.
EIGRP is a hybrid routing protocol. It is a distance-vector protocol that implements some link-state routing protocol characteristics. Although EIGRP uses distance-vector metrics, it sends partial updates and maintains neighbor state information just as link-state protocols do.
EIGRP does not send periodic updates as other distance-vector routing protocols do.
T/F: After the initial exchange of information, link-state updates are not sent unless a change in the topology occurs.
True.
After the initial exchange of information, link-state updates are not sent unless a change in the topology occurs. Routers do send small hello messages between neighbors to maintain neighbor relationships. If no updates have been sent, the link-state route database is refreshed after 30 minutes.
Which routing protocols use more network bandwidth? Which use more CPU and memory?
When choosing a routing protocol, consider that distance-vector routing protocols use more network bandwidth than link-state protocols. Distance-vector protocols generate more bandwidth overhead because of the large periodic routing updates.
Link-state routing protocols do not generate significant routing update overhead but do use more router CPU and memory resources than distance-vector protocols. This occurs because with link-state routing protocols (generally speaking), WAN bandwidth is a more expensive resource than router CPU and memory in modern devices.
Which routing protocol, DV or Link State,
- has better scalability?
- converges faster?
- has less routing overhead?
- is easier to implement?
- LS
- LS
- LS
- DV
T/F: OSPF and IS-IS are hierarchical routing protocols.
True.
What type of routing protocol is EIGRP by default? flat or hierarchical?
By default, EIGRP is a flat routing protocol, but it can be configured with manual summarization to support hierarchical designs.
Flat routing protocols do not allow a hierarchical network organization. They propagate all routing information throughout the network without dividing or summarizing large networks into smaller areas.
Carefully designing network addressing to naturally support aggregation within routing-protocol advertisements can provide many of the benefits offered by hierarchical routing protocols. Every router is a peer of every other router in flat routing protocols; no router has a special role in the internetwork. EIGRP, RIPv1, and RIPv2 are flat routing protocols.
T/F: Classful routing protocols do not advertise subnet masks in their routing updates.
True.
Classful routing protocols do not advertise subnet masks in their routing updates; therefore, the configured subnet mask for the IP network must be the same throughout the entire internetwork. Furthermore, the subnets must, for all practical purposes, be contiguous within the larger internetwork.
For example, if you use a classful routing protocol for network 200.170.0.0, you must use the chosen mask (such as 255.255.255.0) on all router interfaces using the 200.170.0.0 network. You must configure serial links with only two hosts and LANs with tens or hundreds of devices with the same mask, 255.255.255.0. The big disadvantage of classful routing protocols is that the network designer cannot take advantage of address summarization across networks (CIDR) or allocation of smaller or larger subnets within an IP network (VLSM).
T/F: None of the IPv4 routing protocols support IPv6 networks, and none of the IPv6 routing protocols are backward compatible with IPv4 networks.
True.
But both protocols can coexist on the same network, each with its own routing protocol. Devices with dual stacks recognize which protocol is being used by the IP Version field in the IP header.
T/F: If two or more routing protocols offer the same route (with the same prefix length) for inclusion in the routing table, the Cisco IOS router selects the route with the lowest administrative distance.
True.
See attached table of AD values.
T/F:
Cost is the metric used by OSPF and IS-IS.
True.
T/F: In OSPF on a Cisco router, a link’s default cost is derived from the interface’s bandwidth.
True.
The formula to calculate cost in OSPF is:
10^8/BW where BW is the interface’s default or configured bandwidth.
For 10 Mbps Ethernet, cost is calculated as follows: BW = 10 Mbps = 10 × 10^6 = 10,000,000 = 10^7
cost (10M Ethernet) = 10^8/10^7 = 10
Cisco’s implementation of IS-IS assigns a default cost of ____ to all interfaces.
10
In OSPF, the sum of all the _______ to reach a destination is the metric for that route.
The sum of all the costs to reach a destination is the metric for that route.
The lowest cost is the preferred path.
The _____ parameter refers to the degree to which the interface link is busy.
The load parameter refers to the degree to which the interface link is busy.
A router keeps track of interface utilization; routing protocols can use this metric when calculating the best route. Load is one of the five parameters included in the definition of the EIGRP metric.
By default, ______ is not used to calculate the composite metric
By default, load is not used to calculate the composite metric.
If you have 512 kbps and 256 kbps links to reach a destination, but the 512 kbps circuit is 99% busy and the 256 kbps circuit is only 5% busy, the 256 kbps link is the preferred path. On Cisco routers, the percentage of load is shown as a fraction over 255.
What does ‘load 255/255” on an interface indicate?
Utilization at 100% is shown as 255/255, and utilization at 0% is shown as 0/255.
The _____ parameter refers to how long it takes to move a packet to the destination.
The delay parameter refers to how long it takes to move a packet to the destination.
Delay depends on many factors, such as link bandwidth, utilization, port queues, and physical distance traveled.
T/F: Total delay is one of the five parameters included in the definition of the EIGRP composite metric.
True.
Total delay is one of the five parameters included in the definition of the EIGRP composite metric. By default, it is used to calculate the composite metric.
You can configure an interface’s delay with the delay tens-of-microseconds command, where tens-of-microseconds specifies the delay, in tens of microseconds, for an interface or network segment.
The interface delay can be checked with the show interface command. In Example 3-2, the interface’s delay is 20,000 microseconds.
What parameter measures the dependability of a network link?
The reliability parameter is the dependability of a network link.
Some WAN links tend to go up and down throughout the day. These links get a small reliability rating. Reliability is measured by factors such as a link’s expected received keepalives and the number of packet drops and interface resets.
If the ratio is high, the line is reliable. The best rating is 255/255, which is 100% reliability. Reliability is one of the five parameters included in the definition of the EIGRP metric. By default, it is not used to calculate the composite metric.
T/F: The MTU parameter is the maximum size of bits a unit can have on an interface.
False.
The MTU parameter is the maximum size of bytes a unit can have on an interface.
If the outgoing packet is larger than the MTU, the IP protocol might need to fragment it. If a packet larger than the MTU has the Do Not Fragment flag set, the packet is dropped.
As shown in Example 3-4, you can verify an interface’s MTU by using the show interface command.
What is Split Horizon?
Split horizon is a technique used by distance-vector routing protocols to prevent routing loops. Routes that are learned from a neighboring router are not sent back to that neighboring router, thus suppressing the route. If the neighbor is already closer to the destination, it already has a better path.
In Figure 3-6, Routers 1, 2, and 3 learn about Networks A, B, C, and D. Router 2 learns about Network A from Router 1 and also has Networks B and C in its routing table. Router 3 advertises Network D to Router 2. Now, Router 2 knows about all networks. Router 2 sends its routing table to Router 3 without the route for Network D because it learned that route from Router 3.
What is Poison Reverse?
Poison reverse is a route update sent out an interface with an infinite metric for routes learned (received) from the same interface. Poison reverse simply indicates that the learned route is unreachable. It is more reliable than split horizon alone.
Examine Figure 3-7. Instead of suppressing the route for Network D, Router 2 sends that route in the routing table marked as unreachable. In RIP, the poison-reverse route is marked with a metric of 16 (infinite) to prevent that path from being used.
What is counting to infinity?
Some routing protocols keep track of router hops as a packet travels through the network. In large networks where a routing loop might be present because of a network outage, routers might forward a packet without it reaching its destination. Counting to infinity is a loop-prevention technique in which the router discards a packet when it reaches a maximum limit. It assumes that the network diameter is smaller than the maximum allowed hops. RIP has a maximum of 16 hops, and EIGRP has a maximum of 100 hops by default. Maximum values are considered infinity.
T/F: EIGRP sends routing updates periodically, every 90 seconds.
EIGRP does not send routing updates periodically,
Where does EIGRP autosummarize networks, at what points in the network?
EIGRP autosummarizes networks at network borders.
T/F: EIGRP can load share over unequal-cost paths.
True. EIGRP can load share over unequal-cost paths.
What protocol number do EIGRP packets use?
Packets using EIGRP use IP number 88.
EIGRP uses five packet types. What are they?
- Hello: EIGRP uses hello packets in the discovery of neighbors.
- Acknowledgment: An acknowledgment packet acknowledges the receipt of an update packet.
- Update: Update packets contain routing information for destinations.
- Query: EIGRP sends query packets to find feasible successors to a destination.
- Reply: EIGRP sends reply packets to respond to query packets.
Figure 3-9 shows an example of EIGRP stub router operation. If the LAN 10.10.10.0/24 goes down, where are the query packets sent?
Normally the Hub1 router would send query packets everywhere; however, there is no need to send query packets to stub branches because there are no alternate routes there.
Once you configure the branch routers as EIGRP stub routers, the query is sent only to the Hub2 router.
An IS-IS NET consists of an AFI, area ID, system ID, and a SEL.
What is an AFI and a SEL?
An IS-IS NET consists of an authority and format identifier (AFI), area ID, system ID, and selector (SEL), as shown in Figure 3-10.
The system ID must be unique within the network.
See attached diagram for an example of a NET.
What type of IS-IS topology is depicted in the attached diagram?
The IS-IS flat design consists of a single area. As shown in Figure 3-12, all routers are on the same level. There is no summarization with this design. This design is recommended for a small network.
Which type of IS-IS topology is shown in the attached diagram?
An IS-IS hierarchical topology is recommended for large networks. A backbone area can be created, much as with OSPF, and can have other areas connected via L1/L2 routers, as shown in Figure 3-13. This design allows for network summarization.
Which IS-IS topology is shown in the attached diagram?
A hybrid IS-IS design is recommended for networks that might not be large enough for a backbone area. As shown in Figure 3-14, the IS-IS areas are connected using L1/L2 routers. This design allows for summarization between areas.
See attached diagram.
By default, if EIGRP is enabled on all routers, what path is taken?
- Path 1
- Path 2
- Unequal-cost load sharing Path 1 and Path 2
- Equal-cost load balancing with Path 1 and Path 2
B. Path 2 has greater bandwidth.
EIGRP is configured on the routers. If it is configured with the variance 2 command, what path is taken?
- Path 1
- Path 2
- Unequal-cost load sharing Path 1 and Path 2
- Equal-cost load balancing with Path 1 and Path 2
C. Load sharing is enabled with the variance command.
By default, if EIGRP for IPv6 is enabled on all routers and this is an IPv6 network, what path is taken?
- Path 1
- Path 2
- Unequal-cost load balancing with Path 1 and Path 2
- Equal-cost load balancing with Path 1 and Path 2
B. By default, Path 2 has higher bandwidth and thus has the better metric.
