NT1 Finals

static routes

are manually configured by network administrators, have low system requirements, and apply to simple, stable, and small networks

they cannot automatically adapt to network changes and so require manual intervention

what is the disadvantage of static routes?

true

(T/F) in the case where a router’s IP routing table has only one direct route that doesn’t match its destination address, a static route needs to be manually configured so that the packers can be forwarded to the next hop

it manually sets up the optimal paths between the source and the destination computers

what else does static routing do?

nexthop-address

to specify a next-hop IP address for a static route, the huawei router configuration is:

[Huawei] ip route-static ip-address { mask /mask-length } ___

interface-type interface-number

to specify an outbound interface for a static route, the huawei router configuration is:

[Huawei] ip route-static ip-address { mask /mask-length } ___

interface-type interface-number [ nexthop-address ]

to specify both the outbound interface and next hop for a static route, the huawei router configuration is:

[Huawei] ip route-static ip-address { mask /mask-length } ___

true

(T/F) packets are forwarded hop by hop. therefore, all the routers along the path from the source to the destination must have pre-determined routes

true

(T/F) forward and background routes must also be available when forwarding packets

default routes

are used only when packets to be forwarded do not match any routing entry in an IP routing table

0.0.0.0 with mask 0.0.0.0, namely 0.0.0.0/0

in an IP routing table, a default route is the route to network ___

true

(T/F) a packet that matches no routing entry other than the default route is forwarded to an address mapped to the default route

yes. if no default route is available, IP packets with no matching routing entry will be silently discarded

can routers/computers have/have no default route stored in their IP routing table?

dynamic routes

these routing protocols provide different routing algorithms to adapt to network topology changes

static routes

(static or dynamic) when a network scale expands, it becomes increasingly complex to manually configure static routes. when the topology changes, they cannot adapt to these changes in a timely and flexible manner

dynamic routes

(static or dynamic) automatically discover and generate routes, and update routes when the topology changes. these reduce the workload of network administrators and are used on large networks

autonomous systems (AS or domains)

on the internet, routers need to exchange routing information in the interconnection of networks called ___, a collection of networks and subnetworks

true

(T/F) one AS is independent of another AS. an AS can have its own routing algorithm and can be managed independently

interior gateway

within AS, one network is connected to another network by an ___

core network (backbone)

the autonomous systems are connected together in the form of a network called the ___

exterior gateways

the gateways that connect all the autonomous systems to the core network are called ___

• interior gateway protocol (IGP)

• exterior gateway protocol (BGP)

routing protocols are classified into two, which are?

interior gateway protocol

is meant to dynamically route data across a network that you fully control and maintain

RIP, OSPF, IS-IS

these are examples under interior gateway protocol

exterior gateway protocol

used to exchange routes between distinctly separate networks that you have no administrative control over

true

(T/F) external gateway protocol is the routing protocol used on the internet. therefore, the most common enterprise use is to run it on your internet edge when connecting to your ISP

border gateway protocol

this is an example under exterior gateway protocol

routing algorithms

determine good paths (routes) from senders to receivers through the network of routers

least cost path

finds a path between the source and destination with the least cost

shortest path

the path with the smallest number of links between the source and the destination

distance vector routing protocol

in this type of routing, all the routers send their routing tables to only their neighboring routers

true

(T/F) the routers use the received information to determine any changes that need to be made to their own routing table

it is iterative in that this process continues on until no more information is exchanged between neighbors

route exchange

a router running the distance vector routing protocol periodically floods routes. through ___, each router learns routes from neighboring routers and installs the routes into its routing table

routing information protocol (RIP)

a commonly used distance vector routing that uses its routing metric to determine the best route or shortest path a packet has to traverse from the source to a destination over a network

100

RIP is a distance-vector IGP and has a preference of ___

hop count

RIP uses a ___ as the route cost. it is the number of routers through which a packet passes to

• network of 250 routes

• maximum of 15 hops

RIP was designed for exchanging information within a limited size network, such as?

30 seconds

a router running RIP sends the contents of its routing table to each of its adjacent routers every ___

180 seconds

when a route is removed from the routing table, it is flagged as unusable by the receiving routers after how many seconds?

120 seconds

after being flagged as unusable, the routes are removed from their tables after an additional of how many seconds?

request and response messages

RIP routers exchange two types of RIP messages, which are?

RIP request

when a RIP router starts up, it sends a RIP request to all of its neighbors to request routing information of the entire RIP network

RIP response

a running RIP router can also send a RIP request. upon receipt, a RIP router immediately replies with a ___ that contains the routing information

IP broadcast

RIPv1 uses ___ packets for its announcements

IP multicast

RIPv2 also allows ___ packets for its announcements

link-state routing protocol

in this type of routing, each of the routers sends the state of its own interfaces to all other routers only when there is a change to report

true

(T/F) in link-state routing protocol, each router uses the received information to recalculate the best path to each network and then saves this information in its routing table

link-state (LS)

the description of the router interface

• single IP interface address and interface mask

• output cost

• list of neighboring routers

these three are included in the link-state

output cost

the cost of sending data packets on the interface, expressed in the link state metric

list of neighboring routers

these are the other routers that are attached through the link state

link-state advertisement (LSA)

an OSPF data packet containing link-state and routing information that is shared with the other routers

link-state PDU

a unit of data describing the local state of router’s interfaces and adjacencies

true

(T/F) the collected ls advertisements of all routers and networks form the LDSB

link-state database (LSDB)

a collection of all LS PDUs originated from the area’s routers. each router advertises directly-connected networks via LS PDU

true

(T/F) each router will have a logically separated LSDB for each area the router is connected to

identical LSDBs for that area

two routers interfacing the same area must have what?

yes, it builds a topologic database

under LDSB, does every router have its own view of the network?

LSA flooding

step 1 in the link state process, routers that run a link-state routing protocol establish a neighbor relationship and then exchange LSA, which indicate the devices’ presence with every interface port of a router

LSDB creation

step 2 in the link state process, each router generates LSAs and adds the received LSAs to its own LSDB. routers learn the whole network topology through the LDSB

shortest path first (SPF)

step 3 of link state process, each router uses the ___ algorithm and LSDB information to calculate routes

true

(T/F) in SPF calculation, each router calculates a loop-free tree with itself as the root and the shortest path. with this three, a router determines the optimal path to each corner of a network

routing table calculation

step 4 of link state process, the router installs routes for the calculated preferred paths into its routing table

open shortest path first (OSPF)

this is a link-state routing protocol developed by the IETF in 1988 that is capable of quickly detecting topological changes within the autonomous system and establishing loop-free routes in a short period of time, with minimum additional communication overhead for negotiating topology changes between peering routers

area

considered a logical group, and each group is identified by an area ID

router ID

uniquely identifies a router in an OSPF area, can be manually specified or automatically assigned by the system

cost value

OSPF uses costs as route metrics. each OSPF-enabled interface maintains this

neighbor relationship and adjacency

important concepts about the relationship between OSPF routers are?

HELLO packet

is a special data packet (message) that is sent out periodically from a router to establish and confirm network adjacency relationships to other routers in the OSPF

true

(T/F) OSPF is enabled on interconnected interfaces. the routers start to send and listen to hello packets. after the two routers discover each other through hello packets, they establish a neighbor relationship

link status information

OSPF routers exchange ___, but not routes. this is key information for OSPF to perform topology and route escalation

true

(T/F) an OSPF router collects link status information on a network and stores the in

[R1] display ospf peer

in this command, the OSPF neighbor table describes the status of the neighbor relationship between OSPF routers

run the command to query LSDB

OSPF routing table

this contains information such as the destination IP address, cost, and next hop IP address, which guides packet forwarding

{R1

intermediate system-to-intermediate system (IS-IS)

this forms neighbor adjacencies, has areas, exchanges link-state packets, builds a link-state database, and runs the dijkstra’s (SPF) algorithm to find the best path to each destination, which is installed in the routing table

IS (