Consistency First Approach for Routing (BGP revision)

Consistency:


consistency-first approach (over availabiliy or performance)
1.necessary
2.feasible
3.powerful abstractions

scater: consisent storage manager??? (maybe some storage abstraction here????)

internet availability not high: 2.0-2.6%
because an available physical path doesn't imply a router path

90% of outages are less than 700 secs (due to tansiant failure of network maybe?)
so more robust routing prococols to avoid short-term outtage caused by dynamics of routing protocols

bgp protocol:
1.opaque local policies
2. distributed mechanism to update paths (with some delay, thus inconsistency)
so causes short network unavailability

so underlying cause of short -term outages is inconsistent global state

Consensus Routing:
consistency-first approach
decouple safety and liveness

safety: forwarding tables always consistent and police compliant:
apply route updates only after they have reached all dependent Ases
apply updaes synchronously accross Ases
mechanism:
1. run bgp but don't apply the updates
2. a distributed snapshot taken periodically
3. ases send list of incomplet consolidators
4. sonsolidators run a consensus algorithm to agree on the set of imcomplete updates
5. consolidators flood new routes, and forwarding table updated (Note: they are route states updates, not route updates! which route to take is still within choices of each as, and doesn't have to be exposed to outside world)
(in essense, a two-phase commit process)

liveness:routing system adapts to failures quickly
solution: use old path, but dynamically re-route around the failed link (use exissting techniques)


scatter (p2p consistent storage layer)

design patter for consistency-first approach:
1. separation of safety and liveness
2. consistency as a baseline guarantee: trade-off is then between performance and availability (more constraint design space)