Routing protocols Flashcards
Families of routing protocols
- Interior Gateway protocol (IGP): Intra-domain routing
- Exterior gateway protocol (EGP): Inter-domain routing
IGP features, design criteria, objectives
Interior gateway protocol
- objectives: find the best route
- design criteria: choose routes based on topological information
- distribute topological information
Distance Vector:
- RIP
- IGRP and E-IGRP
Link State:
- OSPF
- Integrates IS-IS
EGO features, objectives, design criteria
Enhanced Geographic Opportunistic routing
- objective: find preferred route
- design criteria: decide based on policies
- distribute Autonomous system information
- Distribute administrative costs
Protocols:
- BPG: Border Gateway protocol
- IDRP: Inter Domain Routing protoocl
- Static routing is also viable
RIP
Routing Information Protocol
Originally developed for another architecture.
Implemented also in the Linux kernel.
Features:
- Hop count (at most 15)
- Periodic update messages (every 30s)
- Distance vectors
- Time-out based operation
- Convergence: 3min
IGRP
Cisco Systems proprietary.
Interior gateway routing protocol.
It overcomes some shortcomings of RIP, only alternative to RIP for a while.
It uses Distance Vector the other way around: when a routers suspects a topological change it requests DV from neighbors, generating much less traffic.
Features:
- Articulated metrics
- Delay
- Bandwidth
- Reliability
- load
- Maximum packet lenght
- Multipath routing: sending a packet to multiple networks in inverse proportion to the cost of the route (I.E. Send 1 packet every 10 to a 10Gb/s path and the others to 100Gb/s).
OSPF
Open shortest paths first
Hierarchical Routing:
- Routing domain divided in areas
- Routers know every detail of their area
- Limited knowledge about the outside
- Aggregation of information among areas
OSPF, Strictly Hierarchical Routing
Strictly Hierarchical Routing:
- No knowledge about the outside
- If destination is outside area, packet is forwarded to edge router.
- Maximum scale
- Limited routing capability
- Higher level routers have domain level view
- Paths are sub-optimal
- Loss of connectivity may occur
OSPF, Loosely Hierarchical Routing
Routers have high level knowledge of the outside:
- Less scalability
- Routers have to store and share more information
- Does not require strictly hierarchical addressing: all host in one domain do not need common prefix
- Possibile in IPv4
OSPF Broadcast (Multiple Access) Networks
N Routers -> N2 links
Dijkstra complexity is linear with number of links → N^2 log(N) → too complex, use star topology
Pseudo Node:
- Virtual node to transform full mesh into star (designated node)
- Role played by one of the routers by election, a back-up is also elected.
- Responsible for reliable delivery of link states of the Multiple access network
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