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Network+ > Lesson 7: Configuring and Troubleshooting Routers > Flashcards

Lesson 7: Configuring and Troubleshooting Routers Flashcards

1
Q

Define a Router

A

An intermediate system with links and network topology information to facilitate forwarding packets

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2
Q

Where is routing information stored in a router?

A

In the routing table

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3
Q

What does a protocol define?

A

The source of the route

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4
Q

What are the four types of routing table entries?

A
  1. Direct Network Routes
  2. Remote Network Routes
  3. Host Routes
  4. Default Routes
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5
Q

Define a direct network route

A

A routing table entry for an active router interface or subnet that is automatically added to the routing table

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6
Q

Define a static route

A

Manually added to the routing table

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7
Q

Define a default route

A

Entry in the routing table to represent the forwarding path that will be used if no other entries are matched, also known as default gateway

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8
Q

How does a router forward packets?

A

After receiving a packet, it reads the destination address and looks up a matching destination network address and prefix, if there is a match, the router will forward the packet out of one of its interfaces by encapsulating the packet in a new frame

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9
Q

How does a router forward packets in a LAN/subnet?

A

The router uses arp (IPV4) or neighbor discover (IPV6) to determine the interface address of the destination host

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10
Q

How does a router forward packets to an external network?

A

It inserts the next hop router’s MAC address into the new frame during encapsulation

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11
Q

Define hop count

A

The amount of hops it takes a packet to transverse the internet; each time a packet passes through a router, the hop count increases by one

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12
Q

Define TTL

A

Counter field in the IP header that records number of hops a packet can make before being dropped; the number of seconds a packet can stay on the network before being discarded; when TTL hits 0, the packet is discarded

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13
Q

Define Dynamic Routing

A

Routing entries learned from another router via a dynamic routing protocol

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14
Q

How does dynamic routing determine routing information?

A

By using one of two protocols, distance vector or link state to select the best route

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15
Q

Define the distance vector protocol

A

Distance vector protocols send their entire routing table to directly connected neighbors to determine the path with the least amount of hops

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16
Q

Define a link state protocol

A

Dynamic Routing algorigthm/protocol allows a router to store the complete network topology and assess the least-cost paths in the topology database.

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17
Q

Define Convergence

A

Process where routers agree on routes through the network to establish the same network topology in their routing tables

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18
Q

What is steady state?

A

A network where all the routers have the same topology

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19
Q

What is an autonomous system (AS)?

A

A network under the administrative control of a single owner

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20
Q

What is an Interior Gateway Protocol (IGP)?

A

A dynamic routing protocol used to share forwarding paths between routers in the same autonomous system (AS)

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21
Q

What is an Exterior Gateway Protocol (EGP)?

A

A dynamic routing protocol that can advertise routes between autonomous systems (AS) in the internetwork

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22
Q

What type of routing protocol is RIP (Routing Information Protocol)?

A

A distance vector routing protocol that only considers one metric to select the optimal path which is the route with the least amount of hops

23
Q

How does RIP (Routing Information Protocol) work?

A

RIP sends its routing database to neighboring routers every 30 seconds, and will send triggered updates whenever changes occur; When a router receives an update from a neighbor it adds the unknown route and increases the hop count by 1

24
Q

What are the downsides to RIP (Routing Information Protocol)?

A
  1. Suited for smaller networks because distance vector algorithms require that routers periodically update their routing table and is unsuitable for larger networks
  2. Distance vector algorithms provide slower convergence than link state algorithms
25
Q

Define EIGRP (Enhanced Interior Gateway Routing Protocol)

A

An advanced distance vector/hybrid routing protocol that uses two metrics to determine the best route

26
Q

What metrics are used in EIGRP (Enhanced Interior Gateway Routing Protocol) to determine the best route?

A
  1. Bandwidth - applies a cost based on the lowest bandwidth link in the path
  2. Delay/Latency - Applies a cost based on the time it takes for a packet to traverse the link; most important if route is used to carry time sensitive data
27
Q

How do routers using EIGRP (Enhanced Interior Gateway Routing Protocol) communicate with their neighbors?

A
  1. EIGRP sends a full update of its routing database when it first establishes contact with a neighbor, and thereafter only sends updates when there is a topology change
  2. Sends hello messages to confirm connectivity with neighbors
28
Q

How do EIGRP (Enhanced Interior Gateway Routing Protocol) routers leverage topology tables

A

Topology tables are used to prevent loops while support a greater number of max hops (up to 255)

29
Q

What protocol number does EIGRP (Enhanced Interior Gateway Routing Protocol) use?

30
Q

Define Open Shortest Path First (OSPF) routing protocol

A

A link-state protocol that uses a hierarchical topology of its connected networks

31
Q

What is a Link State Advertisement (LSA)?

A

How OSPF routers communicate link state within the AS

32
Q

How do routers using Open Shortest Path First (OSPF) communicate?

A

Routers distribute information about its local state (usable interfaces, reachable neighbors, and cost of each interface) to other routers using LSA advertisements and stores the information in the link state database (LSDB)

33
Q

What is area routing?

A

An AS can be divided into areas, which are connected to each other by routers. An area consists of groups of contiguous networks and attached hosts. The topology of an area is invisible to entities outside the area.

34
Q

What is a border router?

A

A router that is located on the border of OSPF areas and connects these areas to the backbone and maintains separate link-state databases for each area

35
Q

Define Area 0 in an OSPF topology

A

Also known as a backbone, is created by the collection of border routers and is only visible to the border routers

36
Q

How are messages in OSPF sent?

A

They’re sent as multicasts and tagged with the protocol number 89 that supports cryptographic authentication

37
Q

How is BGP (Border Gateway Protocol) used?

A

Designated routing protocol used between ISPs

38
Q

Does BGP (Border Gateway Protocol) use classless or classful IP addressing?

A

Classes network addressing called Network Layer Reachability Information (NLRI)

39
Q

How does BGP (Border Gateway Protocol) select the best path/route?

A

Based on hop count, weight, local preference, origin, and community

40
Q

What port does BGP (Border Gateway Protocol) use?

A

TCP port 179

41
Q

Define the “longest prefix match”

A

Presented with a packet to route, a router will route the packet to the the network with the largest prefix

42
Q

What is Administrative Distance (AD)?

A

The first criteria a router uses to determine which routing protocol to use if two protocols have the same destination in their routing table

43
Q

List routing protocols by Administrative Distance (AD) from lowest to highest

A
  1. Local interface/directly connected
  2. Static route
  3. BGP
  4. EIGRP
  5. OSPF
    5.RIP
44
Q

What is an Anatonoumous System Number (ASN)?

A

Identifies a group of network prefixes under the control of a single entity

45
Q

Define an edge router

A

A perimeter router that physically links remote networks and subdivides autonomous IP networks into multiple subnets

46
Q

Define an internal router

A

Positioned to implement internal routing topologies and to create VLANS

47
Q

What command is used to list the routing table in Linux and windows?

48
Q

If you can ping a host’s default gateway but not the host, what is most likely the issue?

A

A routing issue

49
Q

What command is used to check for a route to a specific network?

A

show up route x.x.x.x

50
Q

What is a routing loop?

A

Occurs when two routers use each other as the path to a network and causes a packet to be forwarded in a loop until its TTL expires

51
Q

What mechanisms are implemented to stop routing loops?

A

Distance vector protocols use max hop count, holddown timer, and split horizon

52
Q

What is the holddown timer metric?

A

Routers in an AS start a holddown timer for a route if a node declares a network is unreachable to allow all routers in the AS to converge routing tables

53
Q

Define asymmetric routing

A

a packet traverses from a source to a destination in one path and takes a different path when it returns to the source

Network+ (19 decks)

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