Chapter 8: Routing Flashcards
Router
Any piece of hardware or software that forwards packets based on their destination IP address.
Routing Table
A list of paths to various networks required by routers.
What two fields of a routing table are used to determine the route needed?
Destination LAN IP and Subnet Mask
What two fields of a routing table tell the router what to do with the packet?
Gateway (for IP of next hop)
and
Interface (for port to use)
If the network ID is directly connected, then the gateway field of the routing table gets set to _________
0.0.0.0
or
IP address of port you’re sending to
Command to see your routing table in Linux/OSX
netstat -r
Metric
A relative value that defines the cost of using this route. (Lowest routes win)
Network Address Translation (NAT)
A means of translating a system’s IP address into another IP address before sending it out to a larger network.
Gives individual systems private IPs, and hides them behind the public IP
Port Address Translation (PAT)
Form of NAT that uses port numbers to map traffic from specific machines in the network.
NAT Translation Table
Special database in a NAT router that stores destination IP addresses and ephemeral source ports from outgoing packets and compares them against returning packets.
Static NAT (SNAT)
Maps a single routable (public) IP address to a single machine, allowing you to access that machine from outside the network.
Port Forwarding
Preventing the passage of any IP packets through any ports other than the ones prescribed by the system administrator.
Dynamic NAT (DNAT)
Type of NAT in which many computers can share a pool of routable IP addresses that number fewer than the computers.
Static Route
An entry in a router’s routing table that is not updated by any automatic route discovery protocols.
Hop
Each time a packet goes through a router
Possible Criteria for Determining a Metric
1) Hop
2) Bandwidth
3) Latency
4) Cost
5) Maximum Transmission Unit (MTU)
6) Shortest Path Bridging (SPB)
7) Administrative Distance
Fragmentation
When a packet is too big and it’s broken into pieces.
Distance Vector
Routing protocols that calculate the total cost to get to a particular network ID and compare that cost to the total cost of all other routes to get to that same network. It chooses the route with the lowest cost.
Convergence
When routers using distance vector protocols continue sending their routing tables to each other, but the routing tables don’t change.
What size of network is distance vector good for?
Smaller networks with less than 10 routers or so.
Routing Information Protocol (RIP)
Distance vector routing protocol that dates from the 1980s
Autonomous System (AS)
One or more networks that are governed by a single dynamic routing protocol, which provides routing for the Internet backbone.