Routing Flashcards
What is a router?
A router relays packets among interconnected networks. It has links to 2 or more networks at the same time.
In which layers does a router operate.
Network, Datalink and Physical
Explain least cost routing?
A value is assigned to each link called a cost.
The cost of a route is the sum of the link costs.
The best route is the one with the lowest cost.
What two categories of routing algorithms exist?
Non-adaptive (Virtual circuit) Routing decisions pre-determined.
Adaptive (Datagram) Traffic load can change route.
Explain distance-vector routing algorithm.
each router exchanges information about the entire network with
neighbouring routers at regular intervals.
Explain link state.
Each router exchanges information about its neighbourhood with all
routers in the network when there is a change.
Advantage of link state.
Converges faster.
What is convergence?
Process of determining optimal routes.
Explain distributed Bellman-Ford algorithm.
-Add 1 to cost of each incoming route.
-New destination learned, add to routing table
-Existing destination,
* if Next Hop field is the same, replace existing entry with the new
information always
* if Next Hop field is not the same, only replace existing entry with the new information if the cost is lower
What do the following stand for?
ARPANET
RIP
BGP
IS-IS
Advanced Research Projects Agency Network
Routing Information Protocol
Border Gateway Protocol
Intermediate System to Intermediate System
What are the problems with distance-vector routing?
Count-to-infinity problem/slow convergence
Slow to react to router failure
Explain Dijkstra’s algorithm.
Starting at root, we get from link-state database, the cumulative cost of each arc out of the root.
We select lowest cost arc, and make that node the new root.
Explain transparent bridge.
Essentially bridge floods network, sending frame to every router in particular section, and each router can then check if it was the destination.
Distinguish between Transparent bridge and source routing bridge.
TB: Bridges co-operate to perform function.
SR: The route to be followed is inserted in the frame.
TB: Suboptimal flooding.
SR: Optimum route selected.
TB: Will not use full bandwidth.
SR: Will use full bandwidth.
What is a repeater?
Operates in physical layer is an electronic device which regenerates incoming signals. Allows the physical reach of a network to be extended.
In which layer do bridges operate?
Datalink, physical
In which layer are link-state routing or distance-vector routing used.
Network, datalink, physical
Distinguish between broadcast and point to point.
Broadcast: star - single communication channel shared by all network nodes.
Point to point: mesh - many possible connection paths between a pair of nodes.
What happens if a frame arrives at a bridge with a destination 37 and the forwarding database says destination 37 is port 2?
If frame arrived on any port except port 2 we forward it to port 2 otherwise we drop the frame.
If a frame arrives at a bridge with a destination number not in the forwarding database what happens?
The bridge forwards the frame to every port apart from the one it arrived on.
T or F. If the control field in a HDLC frame starts with 11 then this is a U-Frame.
True
T or F. Only one station in a token ring network needs to be able to manage the ring.
False.
T or F. Optimising the total throughput in a network will not give a fair usage to all flows.
True.
T or F. Distance Vector shares their view of the whole network with it’s neighbouring routers.
True.
T or F. A router operates only at the Network layer.
False.
T or F. A neighbouring router is where both routers share a network.
True.
T or F. A router is a device that is connected to a single network.
False.
T or F. The cost of a route is the sum of all the link costs.
False.
T or F. Transparent bridges form a spanning tree for frame delivery.
True.
T or F. Source Routing bridge finds all possible routes.
True.
T or F. A ring network with N nodes has N links.
True.
T or F. Link State routing suffers from slow convergence called “count to infinity”.
False.
T or F. Link state routing sends information about its own neighbours to all other routers.
True.
T or F. Distance Vector routing replaces information only when it is lower when the next hop field is the same.
False.
T or F. A bridge operates in the physical layer.
True.
T or F. Source routing bridges can use all available links.
True.
T or F. A transparent bridge has to be configured in advance of any frames being sent.
False.
