Chapter 7: Routing

Default Route

Entry on a router table that tells the router exactly what to do with every incoming packet unless another line in the routing table gives another route

(T/F) While BGP is capable of implementing route aggregation, it does not readily support it

False: BGP both implements and supports route aggregation

(T/F) Distance vector routing protocols works fine on large networks, but isn't recommended for networks with few connections

False: Distance vector routing protocols is not recommended for large networks because of the need to constantly send updated routing tables to every single router

(T/F) Path vector routing protocols were the first to appear in the TCP/IP routing world

False: Distance vector routing protocols were the first to appear

(T/F) RIPv1 dates back to the 1970s

False: Even though its predecessors date back to the 1960s, RIPv1 dates back to the 1980s

(T/F) Fragmentation is good because it allows packets to be more easily dispersed across the network

False: Fragmentation is bad because it slows down the movement of IP packets

(T/F) OSPF is the de facto standard for ISPs

False: IS-IS is the de facto standard

(T/F) IS-IS is a link state static routing protocol

False: It is a link state dynamic routing protocol

(T/F) The cornerstone of all distance vector routing protocols is the sum total of hops a route takes

False: It is some form of total cost of the route, not just hop count

(T/F) A router uses a combination of destination LAN IP & MAC address to see if a packet matches a route

False: It uses the destination LAN IP & a subnet mask

(T/F) Even if a router advertises a new, unreliable route BGP routers will accept it

False: Most BGP routers are smart enough to ignore unreliable routes

(T/F) Most routers still support RIPv1

False: Most routers still support RIPv2

(T/F) NAT manifests itself by a NAT program that runs exclusively on routers

False: NAT programs can be ran on systems as well, not just routers

(T/F) Only isolated internetworks, where every router knows about every single network, do not have default routes on their router tables

False: Neither isolated internetworks or "Tier One" backbone routers do not have default routes on their router tables

(T/F) Both EGP & IGP are dynamic routing protocols

False: Neither of these are dynamic routing protocols

(T/F) Route redistribution happens on omniprotocol routers

False: Route redistribution occurs on multiprotocol routers

(T/F) When a route on a network goes down, it sends out a down signal to inform the routers to switch to a different route

False: Routers detect downs themselves and switch traffic to different routes automatically

(T/F) A router uses packet origin information in order to process it

False: Routers do not care where a packet originated

(T/F) If an outgoing packet is for a network ID that is directly connected to the router, the Gateway column of its routing table tells the router the IP address of the endpoint to send the packet to

False: The Gateway column is used for packets going to network IDs not directly connected to the router. When a packet doesn't have a destination directly connected, then the Gateway column tells the router the next router's IP address to send them to

(T/F) The mapping of internal IP address and port numbers to translated IP address and port number does not enable perfect tracking of packets out & in

False: The PAT tracing of packets does enable perfect packet tracing

(T/F) The hop occurs when the packet leaves a router en route to the next router

False: The hop occurs when the packet is handed off to each subsequent router

(T/F) The NAT program takes packets from the router bound for client machines and translates their MAC address into an internal IP address, enabling systems to have multiple IP addresses

False: The program takes packets bound for the larger network and translates their internal private IP address into its own public IP address, enabling many systems to share a single IP address

(T/F) When a packet arrives at the router, the router examines the Layer 2 information for processing

False: The router immediately strips off any Layer 2 information and drops it into the queue

(T/F) The system running NAT software has two interfaces: an input & an output interface

False: The two interfaces are one that connects to the intranet & the other that connects to the larger internet

(T/F) There are three link state routing protocols: OSPF, IS-IS, & TY-VM

False: There are only two link state protocols: OSPF & IS-IS

(T/F) An MLS that handles routing is often called a "Layer 4 switch"

False: They are often called a "Layer 3 switch" because it handles IP traffic

(T/F) BGP routers advertise information passed to them from RIP routers

False: They pass on info from AS edge routers

(T/F) ASNs were originally 32 bit numbers, but now they are 64 bit numbers

False: They were originally 16 bit numbers, now they are 32 bit numbers

(T/F) By setting the optimal MTU size before IP packets are sent, administrators increase fragmentation

False: This helps avoid or at least reduce fragmentation

(T/F) A metric is a relative value that routers use when they have more than one route to get to another network

True

(T/F) BGP is a hybrid routing protocol

True

(T/F) Convergence is also known as "Steady State"

True

(T/F) If a routing table has two or more valid routes for a particular IP address destination, it always chooses the route with the lowest metric

True

(T/F) OSPF Version 2 is used for IPv4 networks & OSPF Version 3 includes updates to support IPv6

True

(T/F) OSPF is also known as "Link state algorithm"

True

(T/F) OSPF routers individually decide their own optimal routes once all the routers have communicated

True

(T/F) RIPv2 was adopted in 1994

True

(T/F) Relying exclusively on PAT for network address translation only allows for outgoing communication, not incoming communication

True

(T/F) Routers using a distance vector routing protocol transfer their entire routing table to other routers in the WAN

True

(T/F) Routers using distance vector routing protocols have two protocol options: RIPv1 or RIPv2

True

(T/F) The RIP protocol is an IGP

True

(T/F) The current version of BGP is BGP-4

True

(T/F) When routing packets, the route with the lowest metric always wins

True

Pillars of Troubleshooting Basic Router Problems

1) Consider issues other than the router first 2) Keep in mind what the router is supposed to do 3) Know how to use a few basic tools that can help check the router

Steps of Basic Router Configuration

1) Set up the WAN side 2) Set up the LAN side 3) Establish routes 4) Configure a Dynamic Protocol (optional) 5) Document & back up

EGP (Abbr)

Exterior Gateway Protocol

(T/F) Bandwidth does not include the measurement of capacity of a network to transmit a given amount of data during a given period

False

(T/F) RIPv2 is no longer the current version of RIP

False

(T/F) With port forwarding you cannot designate a specific address for various network services

False

What is the maximum hop count for the RIPv1 protocol?

15 hops

Hop Count

A fundamental metric value for the number of routers a packet will pass through on the way to its destination network

Routing Table

A list of paths to various networks required by routers

NAT (Definition)

A means of translating a system's IP address into another IP address before sending it out to a larger network

Latency

A measure of a signal's delay

Cost

A network measurement tool used by some routing protocols to determine the desirability of a particular route

Cisco Console Cable

A proprietary cable from Cisco for configuring their managed devices

Dynamic Routing Protocols

A protocol that supports the building of automatic routing tables

Gateway Router

A router that acts as a default gateway in a TCP/IP network

(Definition) MLS

A switch that works at more than one layer of the OSI model

Route Aggregation

A technique for simplifying routing tables into manageable levels where rather than trying to keep track of every other router on the Internet, backbone routers track the location of routers that connect to subsets of locations

BGP (Definition)

An exterior gateway routing protocol that enables groups of routers to share routing information so that efficient, loop-free routes can be established

OSPF (Definition)

An interior gateway routing protocol developed for IP networks based on the shortest path first

ATM (Abbr.)

Asynchronous Transfer Mode

AS (Abbr)

Autonomous System

ASN (Abbr)

Autonomous System Number

BGP (Abbr)

Border Gateway Protocol

EIGRP (Definition)

Cisco's proprietary hybrid protocol that has elements of both distance vector & link state routing

Cisco IOS

Cisco's proprietary operating system used on most of its networking devices

netstat -r

Command to view the contents of a device's routing table

DOCSIS (Abbr.)

Data-Over-Cable Service Interface Specification

DNAT(Abbr)

Dynamic Network Address Translation

EIGRP (Abbr)

Enhanced Interior Gateway Routing Protocol

(T/F) The "route print" command is an alternative to "netstat -r" command on Linux machines

False: "route print" works on Windows machines. "netstat -r" works on all operating system architectures

(T/F) ASNs are assigned by the IETF

False: ASNs are assigned by IANA

(T/F) All packets are dropped into a router's queue based on its validation flags

False: Any packet is dropped into the queue based on the time it arrived

What are the most common criteria for determining a metric?

Hop Count Bandwidth Delay Cost

IGP (Abbr)

Interior Gateway Protocol

IS-IS (Abbr.)

Intermediate System to Intermediate System

IANA (Abbr)

Internet Assigned Numbers Authority

IETF (Abbr)

Internet Engineering Task Force

ISOC (Abbr.)

Internet Society

IOS (Abbr)

Internetwork Operating System

____ are sourced by each OSPF router & flooded from router to router through each OSPF area

LSAs

LSA (Abbr.)

Link State Advertisement

mtr (Definition)

Linux command tool that acts like traceroute, but dynamically updates information between the two connections

SNAT (Definition)

Mapping protocol that allows for the mapping of a single routable IP address to a single machine, enabling access to that machine from outside the network

MTU (Abbr)

Maximum Transmission Unit

MTU (Definition)

Metric that determines the largest frame a particular technology can handle

(Abbr.) MLS

Multilayer Switch

mtr (Abbr)

My traceroute

NAT (Abbr.)

Network Address Translation

NMS (Abbr)

Network Management Software

Managed Device

Networking devices, such as routers and advanced switches, that must be configured to use

____ corrects link failures & creates convergence almost immediately

OSPF

AS (Definition)

One or more networks that are governed by a single dynamic routing protocol within it

OSPF (Abbr.)

Open Shortest Path First

OEM (Abbr)

Original Equipment Manufacturer

Hello Packets

Packets sent out when an OSPF-capable router connects to a network to discover other OSPF-capable routers

LSA (Definition)

Packets used by OSPF routers to exchange information about the other routers & network information

Bandwidth

Piece of the spectrum occupied by some form of signal, such as television, voice, or fax data

PAT (Abbr.)

Port Address Translation

Port Forwarding

Preventing the passage of any IP packets through any ports other than the ones prescribed by the system administrator

IS-IS (Definition)

Protocol similar to OSPF, but with support for IPv6 since inception

Edge Router

Router that connects one (AS) to another.

RIP (Abbr)

Routing Information Protocol

Interface Column

Routing table column that tells the router which port to use when handling traffic

Distance Vector

Set of routing protocols that calculates the total cost to get to a particular network ID and compares that cost to the total cost of all the other routes to get to that same network ID

SNAT (Abbr)

Static Network Address Table

Translation Table

Table that stores the IP address and port combinations from source machines when they are converted into external addresses to reach out to external machines.

EGP (Definition)

Term used to describe the communication between different AS

IGP (Definition)

Term used to describe the communication of networks within a particular AS

Fragmentation

The act of breaking up a packet when it is too large for a particular technology

Destination LAN IP

The defined network ID of every network ID that is directly connected to one of a router's ports

NMS (Definition)

Tools that enable you to describe, visualize, & configure an entire network

PAT (Definition)

The most commonly used form of NAT where the NAT uses the outgoing IP address and port numbers to map traffic from specific machines in the network

Next Hop

The next router a packet should go to at any given point

Hop

The passage of a packet through a router

Metric

The relative value that defines the "cost" of using a particular route

Convergence

The updating of the routing tables in a distance vector routing protocol network on all routers has been completed

(T/F) 1.33457 is a valid ASN

True: ASNs are displayed as two 16 bit numbers separated by a dot

(T/F) Even when routers using distance vector routing protocol have all the information about the network, they still continue to send their complete routing tables to each other

True: Because the information is the same, the routing tables don't change

(T/F) OSPF's metric is cost

True: Cost is a function of bandwidth

(T/F) CompTIA lists EIGRP as a distance vector protocol

True: If EIGRP is the only right answer as a distance vector protocol, take it

(T/F) A router compares the destination IP address on a packet to every route listed in the routing table & only then sends the packet out

True: If the router finds more than one route to send a packet, it will use the better of them

(T/F) OSPFs only recently started supporing IPv6 addresses

True: It initially did not support the IPv6 addressing standard

(T/F) When it comes to MTU, Ethernet uses 1500-byte frames

True: Other technologies use smaller or larger frames

(T/F) Most industry routers enable users to add interfaces

True: The user can buy interfaces based on their needs & snap them into the router

(T/F) The entire Internet is nothing more than a series of big, powerful routers connected to lots of other big, powerful routers

True: These routers make up the backbone of the Internet

(T/F) The higher the bandwidth, the faster the signal transmission

True: This allows for more complex signals such as audio or video

(T/F) When an internal machine initiates a session with an external machine the source and destination IP address and port numbers are recorded in the NAT table

True: This allows for the retranslation when the packet returns from the external machine

(T/F) A network using NAT provides the systems on the network with private IP addresses

True: This allows them to operate without a direct IP address from the ISP

(T/F) With port forwarding you can hide a service hosted inside your network

True: This can be done by changing the default port number for that service

(T/F) You should never plug a new router into an existing network

True: This can cause major issues to the network, because there is no telling what the new router may do

(T/F) A routing table can be built automatically or manually

True: This depends on the needs of the admins and the network

(T/F) The outgoing IP address and port number used by a NAT during PAT are collectively known as a "socket"

True: This helps when translating from the private IP to public IP & back

(T/F) When reading a routing table, a zero (0) means "anything"

True: This is an important trick that saves a lot of time

(T/F) All routers examine packets & then send the packets to the proper destination

True: This is the case regardless of if the router is large or small, plain or bundled with a switch.]

(T/F) The internet has settled on BGP as its protocol for communication between each AS

True: This is the protocol for connecting all of the AS

(T/F) Every node on a network has a routing table

True: This is true for every TCP/IP capable device connected

(T/F) RIPv1 routers had no authentication methods

True: This left them open to hackers sending false routing table information

(T/F) When two adjacent OSPF-capable routers interact they form a neighborship

True: This will happen after the sending of Hello packets

(T/F) Routers using RIPv1 would send their routing table updates out at the same time

True: This would cause massive network overloads

(T/F) NAT is not routing

True: While many routers offer NAT as a feature, it is in addition to the core capability of routing. NAT is a separate technology

DNAT (Definition)

Type of NAT in which many computers can share a pool of routable IP addresses that number fewer than the computers

Link State

Type of dynamic routing protocol that announces only changes to the routing table, as opposed to entire routing tables

What is the update time for the RIPv1 protocol?

Update sent out every 30 seconds

What two major ways was RIPv2 improved over RIPv1?

VSLM was added & authentication was built into the protocol

VLSM (Abbr)

Variable Length Subnet Masking

Route Redistribution

When a multiprotocol router learns route information using one routing protocol & disseminates that information using another routing protocol

VLSM (Definition)

Where networks that connected to a router used different subnet masks

tracert

Windows command that records the route between any two hosts on a network

pathping

Windows tool that pings each node on a route and computes the performance over a set time before showing results

traceroute

macOS/Unix/Linux tool that records the route between any two hosts on a network