Routing Flashcards
Generalize the Routing Proccess
Routers receive the frame Checks for FCS error If error, drop frame If no error de-encapsulate into packet Read destination IP Check IP Routing Table for route Re-encapsulate packet into frame Send off frame
What first happens when a router receives a frame?
The router checks for any FCS errors. If there are any errors the frame is dropped. If there are no errors the Router will confirm that the MAC address was destined for the router
What happens after a router confirms that a frame was sent to it?
The packet is de-encapsulated.
The data-link header and trailer are discarded leaving only the IP packet.
What does a router do after a frame has been de-encapsulated?
The destination IP address of the packet will checked against the IP Routing Table.
Depending on the “Routing Protocol”, a destination will be set for the packet to be forwarded.
Extra info will be sent with the packet in order to tell the next router where to send the packet.
What happens after the a received packet is given a destination for routing?
The packet is encapsulated into a frame.
B/c it is being forwarded a data-link header and trailer is attached to the packet.
In HDLC and PPP encapsulation is simple.
What are connected routes?
Added by the use of the configuration of the “ip address int # “ subcommand.
Given to interfaces.
What are static routes?
Added by the use of the “ip route” global command.
What are routing protocols?
Added as a function by configuration on all routers
Resulting in a process by which routers “dynamically” tell each other about the network so that they all learn routes.
What are local routes?
Defines a route for the one specific IP address configured on the router interface.
Briefly describe Routed Protocols. What are some examples?
Carries user data
Each router making independent decisions in determining paths
EX: IPv4, IPv6
Briefly describe Routing Protocols. What are some examples?
Communicate info about networks
determine the best route b/t networks
EX: EIGRP (bandwidth and delay), OSPF (bandwidth), RIP (hop-count)
Briefly describe Static Routes. What are the advantages and disadvantages?
Routes are manually entered
Default routes or Gateway of last resort => tells router where to go if no specific route to send packet
Advantages:
No overhead on network
Disadvantages:
Manual update required when topology changes
Briefly describe Dynamic Routes.
Uses a routing protocols
Automatically adjusts based on topology changes or traffic changes
Learns and maintains routes by exchanging network updates w/ each other
can enable be enabled w/ less commands
What is AS? Describe AS. What is IGPs? What is EGPs?
AS = Automated Systems
AS is a grouping of networks in a single administrative domain
IGPs = Interior (or internal) Gateway Protocols => w/n AS
EGPs = Exterior (or external) Gateway Protocols => outside AS
What is an AS number?
W/n an AS no need to register or apply for an AS number
When communicating onto the internet apply for an AS number
What are the three types of Routing Protocols?
Distance Vector
Link State
Advanced Distance Vector
Describe Distance Vector Routing Protocols
“Routing by rumor”
Determines the direction (vector) and distance (next hop-count) to destination
Easy to configure
very LIMITED visibility (only knows what neighbors know)
Describe Link State Routing Protocols
“Visibility of entire network”
Can make more informed decision about how to get to the dest. network
All routers share same info. that they have learned
Difficult to conf. (hierarchical network topology)
Requires more memory and processing power
What algorithm is used in Link State Routing Protocols? Distance Vector Routing Protocols?
Link State Routing Protocols => Uses shortest path First alg.
Distance Vector Routing Protocols => Uses the Belmant-Ford alg.
Describe Advanced Distance Vector Routing Protocols
“Takes the best of both Routing Protocols”
Forms neighbor relationships
Cisco proprietary (only Cisco products)
List examples for the routing protocols
Distance Vector => RIP
Link State => OSPF and IS-IS
Advanced Distance Vector => EIGRP
What is AD? Describe AD.
AD = Administrative Distance
Factor that chooses route
“Tie breaker” when multiple routing protocols disagree (ONLY WHEN THERE IS NO GREATEST MATCH)
Low administrative distance means higher “trust factor”
What is the AD for a connected interface? Static route? OSPF? Internal EIGRP? Unknown routes? RIP?
Connected interfaces => 0 Static route => 1 (routers trust your decision) OSPF => 110 Internal EIGRP => 90 Unknown routes => 0 RIP => 120
What are Class-full Routing Protocols?
Does NOT advertisement subnet mask
consistency of subnet mask assumed (routers assume that all others use the same mask)
summarize routes across class-full boundaries
Class A to class B
What are Classless Routing Protocols? What are some examples.
Does advertise subnet mask Supports VLSM Summary routes can be manually conf AD is used during this EX: OSPF, EIGRP, RIP v2
What are LSAs?
LSA = Link state Advertisements. These contain info. like, are the links up or down
What is the OSPF Hierarchy
Allows for smaller routing tables
Less areas flooded w/ LSAs
more efficient use of resources
AS routers, Internal routers, Area Border routers, Backbone routers
What are the advantages of the OSPF Hierarchy?
Faster convergence
robustness against routing loops
Link state packets are sequenced and acknowledged
Hierarchical design enables optimization of resources
Can scale to much larger envir. than distance vector protocols
What are the disadvantages of the OSPF Hierarchy?
Significant demands for resources
Memory => topology, forwarding tables
CPU => alg
Requires strict design
Conf. and design can be complexWhat are AS routers? Internal routers? ABRs? Backbone Routers?
Automated System routers connect the the RIP router to the Internal routers
Internal routers are routers that are in the network
ABR = Area Border Routers => connects Internal routers to backbone routers
Backbone routers are the centralized routers in the network
