Chapter 7: Routing Flashcards
Define: Layer 3 Capable Switch
A multilayer switch (MLS) that can understand and route IP traffic.
What tells a router exactly where to send the packets it receives?
Its routing table
Is there a one-to-one correlation of routes to ports shown in a routing table?
No
What is in the “Destination” column in a routing table?
A defined network ID (IP address).
Every network ID directly connected to one of the router’s ports is always listed here. The default gateway is also here.
What is in the “Gateway” column in a routing table?
The IP address for the next hop router.
If the outgoing packet is for a network ID that’s not directly connected to the router, the Gateway column tells the router the IP address of a router to which to send this packet (default gateway).
What is in the “Genmask” column in a routing table?
A subnet mask
What is in the “Flags” column in a routing table?
The code that describes the destination.
U: Means the route is up and working.
H: Means this route is a host (host IP address).
G: Means this is the route to the gateway.
What is in the “Metric, Ref, and Use” columns in a routing table?
Numerical values used for picking the best route to a destination.
What is in the “Type and Iface” columns in a routing table?
They tell the router which of its ports to use and what type of port it is.
How does a router decide where to send a packet?
It compares the destination IP address on a packet to every route listed in the routing table and then sends the packet out.
What is the “default route” on a routing table?
It tells the router what to do with every incoming packet unless another line in the routing table gives another route.
What command do you type in a terminal on Linux to view a computer’s routing table?
ip route
What command do you type in both macOS and Windows to view a computer’s routing table?
netstat -r
What is a routing metric?
A relative value that defines the desirability of a route.
It helps routers choose between multiple known routes to get a packet to its destination. The route with the lowest metric always wins.
What does Network Address Translation (NAT) do?
NAT replaces the source IP address of a computer with the source IP address from the outside router interface on outgoing packets. NAT is performed by NAT-capable routers.
Routers running some form of NAT hide the IP addresses of computers on the LAN but still enable Internet access.
What does Port Address Translation (PAT) do?
The router running PAT records the source and destination IP addresses and port numbers for the TCP segment or UDP datagram and translates the private IP address for a public IP address and the source port number for a unique port number.
How does Port Forwarding work?
Specific local addresses are designated for various network services (ports).
Computers outside the network can request a service using the public IP address of the router and the port number of the desired service. The router would examine the packet, look at the list of services mapped to local addresses, and then send that packet to the proper recipient.
What does Static NAT (SNAT) do?
SNAT maps a single public IP address to a single machine, enabling you to access that machine from outside the network and vice versa.
What does Dynamic NAT (DNAT) do?
Allows many computers to share a pool of routable IP addresses that number fewer than the computers.
The process that routers use to update routes to accommodate conditions is called ____.
dynamic routing
Define: Hop
Each network/router a packet passes through.
What are the three distinct groups of dynamic routing protocols?
Distance Vector
Link State
Hybrid
What are the four common criteria for determining a routing metric?
Hop count
Bandwidth
Delay
Cost
Which dynamic routing protocol type calculates the metric number to get to a particular network ID and compares that metric to the metrics of all the other routes to get to that same network ID, and then deletes all but the route with the lowest metric?
Distance vector routing protocols
How do routers using distance vector routing protocols communicate with each other?
They transfer their entire routing table to other routers in the WAN.
Each distance vector routing protocol has a maximum number of hops that a router will send its routing table.
When are routers in convergence or a steady state?
When the updating of the routing tables for all the routers has completed.
What are the two distance vector routing protocols?
Routing Information Protocol: RIPv1 and RIPv2
Define: Autonomous System (AS)
One or more networks that share a unified policy regarding how they exchange traffic with other Autonomous Systems.
Define: Autonomous System Number (ASN)
A globally unique number assigned by IANA to each Autonomous System that is 32 bits and displayed as two 16-bit numbers separated by a dot.
The routers that comprise the AS have to be configured to use the ASN.
When routers in one Autonomous System (AS) need to communicate with routers in another AS, they use a/an ____ protocol.
Exterior Gateway Protocol (EGP)
Who uses Interior Gateway Protocols (IGPs)?
The network or networks within an AS communicate with IGPs.
Enterprise networks also use IGPs for communication.
What is the one EGP that the Internet uses for AS-to-AS communication?
Border Gateway Protocol (BGP)
Current version BGP-4
What type of routing protocol is BGP classified as (besides as an EGP)?
A path vector routing protocol technically, but also considered a hybrid routing protocol.
What are the AS-to-AS routers called?
Edge Routers
What is route aggregation?
A way to simplify routing tables into manageable sizes. The Internet backbone routers track the shortest common network ID(s) of all the routes managed by each AS.
BGP uses and supports route aggregation.
What is the main difference between Link State dynamic routing protocols and Distance Vector routing protocols when it comes to routing table updates?
Link State routing protocols announce and forward individual route changes as they appear.
Distance Vector routing protocols forward their whole routing table at specified time intervals.
What are the two Link State dynamic routing protocols?
Open Shortest Path First (OSPF)
Intermediate System to Intermediate System (IS-IS)
After OSPF-capable routers send out Hello packets and establish a neighborship with adjacent routers, what type of packets do they send to exchange information about routers and networks?
Link State Advertisement (LSA) packets
Who creates Link State Advertisement (LSA) packets and how do they propagate?
LSAs are created by each router and are flooded from router to router through each OSPF area.
How long does it take for OSPF-capable router convergence?
Almost immediately after all the routers communicate with LSAs.
How do OSPF routers deal with link failures?
They correct them by quickly computing a new route with stored LSAs.
What is the Open Shortest Path First (OSPF) metric?
Cost, which is a function of bandwidth.
The lowest cost route is always chosen and could go through more routers (hops) than if RIP was used.
What is an OSPF area?
Administrative groupings of interconnected routers that are used to help control how routers reroute traffic if a link goes down.
What is OSPF’s Area ID 0 (0.0.0.0)?
The central area (backbone) when you interconnect multiple areas. All traffic between areas has to go through the backbone.
A single area also gets Area ID 0 in small networks.
Who uses the IS-IS link state dynamic routing protocol?
Internet Service Providers (ISPs)
Define: Variable-Length Subnet Masking (VLSM)
Where networks that are connected through the router use different subnet masks.
What type of dynamic routing protocol is Enhanced Interior Gateway Routing Protocol (EIGRP) and who developed it?
Hybrid
It has aspects of both distance vector and link state protocols.
Cisco developed it.
What is route redistribution?
When a router takes routes it has learned by one method and announces those routes over another protocol.
Routers can speak multiple routing protocols simultaneously.
A feature used by multilingual routers to determine which route is the most reliable when they have two or more protocol choices to connect to the same destination is called ____.
administrative distance or route preference
What are the four Interior Gateway Protocols (IGPs)?
RIP
OSPF
IS-IS
EIGRP
What do you call (three common names) the serial cable used to connect to and communicate with a router?
Console cable
Rollover cable
Yost cable
What software do you use to connect to and configure routers once you have connected physically to the router?
A terminal emulation program that enables your PC to pretend to be a dumb terminal.
What is Cisco’s proprietary operating system?
Cisco IOS
What are the four ways you can access a router?
Serial cable
Web access
Network management software
Terminal emulation protocols
When should you plug in a new router to an existing network?
After it has been fully configured.
What can Network Management Software (NMS) do?
It can describe, visualize, and configure a network. NMS also communicates with routers, switches, and computers.
What are the two terminal emulation protocols that allow you to connect to routers?
Telnet (older, not secure)
Secure Shell (SSH)
These allow you to use the network instead of a serial cable.
What are the five general steps to configure a router?
- Set up the WAN side
- Set up the LAN side
- Establish Routes
- Configure a Dynamic Protocol (optional)
- Document and Backup
Define: Maximum Transmission Unit (MTU)
The maximum size of a single protocol data unit (PDU) that a given networking technology can transmit.
The largest packet size transmissible without fragmentation through all the hops in a route is called ____.
path MTU
What is Path MTU Discovery?
How devices determine the path MTU.
What command do you type in the Windows command prompt to record the route between any two hosts and the information of every router between them?
tracert
What command do you type in a terminal for macOS/UNIX/Linux to record the route between any two hosts and the information of every router between them?
traceroute
What Windows command line tool pings each node on a route and computes the performance over a set time and then shows you the summary after it has finished?
pathping
What Linux tool is dynamic and continually updates the route you have selected?
My traceroute (mtr)
