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.