Dynamic Routing Flashcards
(26 cards)
Distance Vector protocols
Routers with these dynamic routing protocols send info to their nearest neighbours about their known destination networks and metric for reaching them. Also known as “routing by rumour”
Link State Protocol
Each router forms their own map of the network. Information is advertised from routers and passed to others.
Metric
The total cost of each link based on the bandwidth (determines which route to use)
Administrative Distance
If two different routing protocols are used, the route created with that protocol with the lower AD is chosen (more trusted, ie static > ospf)
Floating static route
static route created with a high AD so its used if proper route goes down
How does EIGRP calculate the best route?
Bandwidth of the slowest link in the path + delay value of all links
What are loopback interfaces and why are they useful?
virtual interfaces on the router, useful because its independent of a physical interface and will always be up/up
How does OSPF work?
LSAs are created on the router and flooded to each router which are used to build a LSDB and SPF algorithm is used to calculate route
what are OSPF areas?
Used to break down a larger network into chunks so that routers don’t need to build up an LSDB of the entire network
all must have a connection to area 0 (backbone)
Internal routers
routers that are in a single areaA
Area Border Routers
routers between areas that contain their own LSDB
Backbone Router
Connected to area 0
Intra-area router
route to a destination inside the same OSPF area
inter area router
route to a destination in another OSPF area
Autonomous system boundary router
OSPF router that connects to a OSPF network on external network
How do you calculate the metric cost for OSPF?
cost = ref bandwidth (default 100) / interface bandwidth
sum up all of the links needed to be crossed for metric
What the requirements for OSPF routers to be considered neighbours?
1) area number must match
2) interfaces must be in the same subnet
3) OSPF process must not be shutdown
4) Router ID must be unique
5) timers must match
6) auth settings must match
What are the roles of hello timer and dead timers?
OSPF routers send hello packets every 10 seconds but if its not received by a neighbour, it will be removed after the dead timer expires (40 secs)
What are the three roles in OSPF?
- DR (Designated Router)
- BDR (Backup Designated Router)
- DRother
How are DR/BDR chosen?
election priority
1. Interface priority
2. Router ID
What happens if DR goes down?
BDR becomes DR and a new BDR is elected
Who can form full adjacencies? and with who?
DR and BDR will form full adjacencies with all routers but DRothers will only for adjacencies with DR/BDR
What is a point to point connection? (Routing Protocol)
Direct connection between two routers, DR/BDR not needed
LSA type 1
Router LSA, generated by OSPF routers and identifies routers and lists networks on its interfaces
