Internet Routing II Flashcards
What is routing?
- Routing is the process of populating the forwarding tables
Routers exchange messages about nets they can reach
Goal: find optimal route for every destination
… or maybe good route, or just any route (depending on scale)
What is forwarding?
It’s the act of moving packets between ports.
- We look up the destination address in a forwarding table
- Find out-port or (out-port, MAC addr) pair
Why are stable routes preferred over rapidly changing ones?
They aid in effective network management.
Higher level optimizations such as TCP RTT estimation, rely on stable routes.
What is the difference between global and decentralized routing algorithms?
In global routing algorithms, all routers have the complete topology.
In decentralized, the routers only know their neighbors.
What is the difference between intra-domain and inter-domain routing?
Intra-domain routing occurs within a single administrative domain, managing networks under the same control. It scales to around 100 networks, like a campus setup.
In contrast, inter-domain routing is decentralized and scales to the vastness of the Internet.
What are the two classes of intra-domain routing algorithms?
Link State & Distance Vector
What type of view does the Link State algorithm have? (which nodes can it use?)
Global view, it sees all nodes in the network.
What is contained in a Link State Packet?
The Link State Packet (LSP) contains key elements:
- ID of the node that generated the LSP.
- Cost of links to each directly connected neighbor.
- Sequence number (SEQNO) for versioning and avoiding outdated information.
- Time-to-live (TTL) for managing packet lifespan.
Is distance vector a distributed or globalized routing algorithm?
Distributed
Which equation do you use for calculating the best path in distance-vector algorithms?
Bellman-Ford equation
What can distance vector algorithms suffer from? What becomes the implication?
Loops.
infinite converge time.
What happens with malfunctioning routers with Link State?
Node can advertise incorrect link cost
What happens with malfunctioning routers with Link State?
Node can advertise incorrect path cost
Costs used by others, errors propagate through net
What are the two intra-domain routing protocols that has been mentioned in this course?
Routing information protocol (RIP) based on Link-state
Open Shortest Path First (OSPF), based on Distance Vector
What algorithm does Routing information protocol (RIP) use?
Distance Vector
What’s the difference between a RIPv2 Entry and a RIPv2 Packet?
A “RIPv2 entry” refers to a specific routing record within a route update packet. These entries carry crucial information about available routes within a network.
A packet includes information about routers in a network.
Packet Structure:
Command: Indicates the purpose of the packet, whether it’s a route update, request, or response.
Version: Specifies the RIP version being used (RIPv2 in this case).
Zeroes: Reserved field filled with zeroes for future use.
What is the purpose of the Route Tag Field in the context of Routing information protocol (RIP)?
It is used to distinguish between internal and external routes.
What the heell is “Next Hop Field”
Indicates the address of the next router or gateway that a data packet should be forwarded to in order to reach its destination.
What routing algorithm does Open Shortest Path First (OSPF) use?
Link State
What are Open Shortest Path First (OSPF) Areas?
OSPF Areas are subdivisions within an OSPF autonomous system. They provide hierarchy, reduce routing table size, and limit the scope of link-state updates, thereby improving routing efficiency and stability. Area 0 (zero) is the backbone area to which all other areas must connect.
What is included in a OSPF Packet header?
Version: This field indicates the OSPF version being used, such as OSPFv2 or OSPFv3.
Type: Specifies the type of OSPF packet (e.g., Hello, Link State Update, Link State Request, Link State Acknowledgment).
Packet Length: Indicates the total length of the OSPF packet, including the header and data.
Router ID: The Router ID of the sender, which is used to identify the source router.
Area ID: Identifies the OSPF area to which the packet belongs.
Checksum: A checksum for error detection in the packet.
Authentication: Contains information related to authentication, such as a password or authentication type.
What types of Open Shortest Path First (OSPF) exist?
OSPFv2 and OSPFv3
What are pros and cons of Link State and the Distance Vector algorithms
Link State:
Simpler to debug
Require global state (OSPF reduces this through areas)
Distance vector
Harder to debug
Can suffer from loops
How do you prevent loops in a distance vector algorithm?
Split horizon
Or Split horizion with poison reverse
