Routing Protocols Flashcards
Routing Protocol
A set of rules and processes that routers use to learn routes.
Interior Gateway Protocol
A protocol used by routers to share information within a single autonomous network
Exterior Gateway Protocol
A protocol used by routers to share information between autonomous networks.
Autonomous Network
A network or collection of networks that fall under the control of a single organization.
Routing Table
The list of routes that is used to make a decision on where to forward IP packets based on destination IP address.
Frame Rewrite
The process of reconstructing a packet to be forwarded to the next hop where the router strips the layer 2 information packet, discards the old frame and encapsulates the packet with a new destination MAC address.
Route Sources
Connected Routes
Static Routes
Dynamic Routes
Default Route
The route used to forward a packet if a destination IP is unknown.
What would occur if the routing table contains more than one route with the same destination?
The most specific route is chosen (longest prefix)
or load balance if the routes have equal subnet lengths.
Advantages of Dynamic Routes
Greatly reduces administrative overhead by eliminating the need to create many manual routes.
Fault Tolerant as it can automatically choose an alternative route if a link faills.
Distance Vector Protocol
A Dynamic Routing Protocl where route tables are shared with direct neighbors and uses hop count to determine routes.
Link State Routing Protocol
A Dynamic Routing Protocol where routers share detailed information about the topology via Link State Adveritisements to create a connectivity map in a Link State Database.
Metric
The value used to determine which protocol’s route is preferred.
RIP
An old Distance Vector protocol that determined routes via hop count. Has been largely replaced by OSPF.
Multicast: 224.0.0.9
AD: 120
EIGRP
A Cisco Proprietary Avanced/Hybrid Distance Vector Protocol. Determined routes via Hop Count but has no Hop Limit and can perform Unequal Cost Load Balancing
OSPF
Open Shortest Path First.
A Link State Routing Protocol that determines routes via Dijkstra’s algorithm.
Multicast: 224.0.0.5
AD 110
OSPF Area Design Rules
OSPF Areas Must start with Area 0 (Backbone Area)
Must be contiguous (able to reach the backbone via ABRs)
Interfaces must be in the same subnet
3 Main Phases of OSPF
1) Establish neighbor relationships with other routers
2) Exchange Database information with neighbors
3) Choose routes via LSDB
OSPF RID selection Process
1) Manual RID
2) Highest UP loopback IP
3) Highest UP interface IP
Neighbor States
1) Down
2) Init
3) 2Way
4) Exstart
5) Exchange
6) Loading
7) Full
Down State
Routers send multicast hello packet hoping to learn about neighbors
Init State
Router receives hello response and routers check Neighbor Adjacency requirements
2way
Routers become neighbors
Exstart
Routers select Master and Slave router based on Highest RID
