Section 8: Routing

Question 1

Split Horizon

Answer 1

Prevents a route learned on one interface from being advertised on the same interface.

Question 2

Poison Reverse

Answer 2

Causes a route received on one interface to be advertised back out the same interface with a metric considered infinite. (High cost.)

Question 3

IGP

Answer 3

▪ Interior Gateway Protocol - Operate within an autonomous system.
▪ Specifies how routers within an autonomous system (AS) exchange routing information with other routers within the same autonomous system.
Examples: RIP, OSPF, EIGRP

Question 4

EGP

Answer 4

▪ Exterior Gateway Protocols - Operate between autonomous systems.
▪ A type of routing protocol used to distribute routing information between different autonomous systems in large internetworks (the internet) based on the TCP/IP protocol.
Examples: BGP (Border Gateway Protocol)

Question 5

Distance Vector

Answer 5

▪ Uses hop count as a metric (Number of routers from source to destination) does not consider speed.
▪ Sends full copy of routing table to its directly connected neighbors at regular intervals
▪ Slow convergence time - Time it takes for all routers to update their routing tables in response to a topology change
▪ Holding-down timers speeds up convergence
- Prevents updates for a specific period of time

Question 6

Link State

Answer 6

Information passed between nodes (routers) is connectivity related.
Examples: OSPF (Open Shortest Path First) and IS-IS (Intermediate System to Intermediate System)
▪ All routers know about the paths all other routers can reach in the network
▪ Information is flooded throughout the link-state domain (OSPF or IS-IS) to ensure routers have synchronized information
▪ Faster convergence time than distance vectors and uses cost or other factors as a metric
▪ Each router constructs its own relative shortest-path tree with itself as the root for all known routes in the network

Question 7

RIP

Answer 7

Routing Information Protocol
▪ Classful Interior Gateway Protocol
(RIPv2 and greater are classless)
▪ Is a distance-vector protocol (uses hop count)
▪ Maximum hops of 15, 16 is considered infinite (dead)
▪ Provides updates every 30 seconds
▪ Easy to configure and runs over UDP

Question 8

OSPF

Answer 8

Open Shortest Path First
▪ Classless, Link-State, Interior Gateway Protocol
- Classless (supports VLSM-Variable Length Subnet Mask)
- Link-state protocol (using cost based on link speed between routers)

Question 9

IS-IS

Answer 9

Intermediate System to Intermediate System
▪ Interior Gateway Protocol
▪ Link-state protocol
(Functions like OSPF protocol, but not as popular or widely utilized)

Question 10

EIGRP

Answer 10

Enhanced Interior Gateway Routing Protocol (Classless)
▪ Interior Gateway Protocol
▪ Advanced distance-vector protocol.
(A hybrid of distance-vector and link-state)
▪ Proprietary Cisco protocol

Question 11

BGP

Answer 11

Border Gateway Protocol
▪ External Gateway Protocol (The only one.)
▪ Path vector

▪ This protocol runs the backbone of the Internet
▪ Does not converge quickly, though, when the topology changes

Question 12

Route Believability

Answer 12

Administrative Distance (AD) - If a router is using multiple protocols the protocol with the lowest AD is used to make routing decisions.
Protocol believability Most to Least:
a) Direct Connect; b) Static Connected; c) EIGRP; d) OSPF; e) RIP; f) External EIGRP

Question 13

NAT

Answer 13

Network Address Translation
Translates private IP address to public IP address

Question 14

PAT

Answer 14

Port Address Translation -
Sharing one public IP with multiple private IP addresses which gives a many-to-one translation

Question 15

DNAT

Answer 15

Dynamic Network Address Translation -
Automatically assigns an IP address from a pool and gives a one-to-one translation.

Question 16

SNAT

Answer 16

Static Network Address Translation -
Manually Assigns an IP Address

Question 17

NAT IP Address Names to know for exam

Answer 17

▪ Inside local
- Private IP address referencing an inside device
▪ Inside global
- Public IP address referencing an inside device
▪ Outside local
- Private IP address referencing an outside device
▪ Outside global
- Public IP address referencing an outside device

Question 18

Multicast Routing

Answer 18

Sends traffic to a Class D IP Address, known as a multicast group
▪ Goal
- Send the traffic only to the devices that want it
▪ Two primary protocols
- Internet Group Management Protocol (IGMP)
- Protocol Independent Multicast (PIM)

Question 19

IGMP (3 Variants)

Answer 19

Internet Group Management Protocol (IGMP)
Used by hosts and adjacent routers on IPv4 networks to establish multicast group memberships.
▪ IGMPv1: Client requests to join the group and is asked every 60 seconds if it wants to remain in the group
▪ IGMPv2: Client can send a leave message to exit multicast group
▪ IGMPv3: Client can request multicast from only specific server
- IGMPv3 is a requirement for Source-Specific Multicast (SSM)
- Allows multiple video streams to single multicast

Question 20

PIM

Answer 20

Protocol Independent Multicast
▪ Routes multicast traffic between multicast-enabled routers
▪ Multicast routing protocol forms a multicast distribution tree
● PIM Dense Mode (PIM-DM)
o Uses periodic flood and prune behavior to form optimal distribution tree
o Causes a negative performance impact on the network
o Rarely used in modern networks

● PIM Sparse Mode (PIM-SM)
o Initially uses a shared distribution tree, which may be suboptimal, but…
o Eventually creates an optimal distribution tree through shortest path tree (SPT) switchover

Question 21

IGRP

Answer 21

Interior Gateway Routing Protocol (IGRP) - Classful
A Classful distance vector interior gateway protocol (IGP) developed by Cisco.

Question 22

Classful Versus Classless Routing Protocols

Answer 22

Classful routing protocols do not carry subnet masks; classless routing protocols do.
Classful Protocols: RIP and IGRP
Classless Protocols: RIP-2, EIGRP, and OSPF