| Jon Crowcroft | |
| University of Cambridge in London… | |
| IP routing currently is hierarchical | ||
| ISPs are “tiered” with core, transit and access ISPs | ||
| Intra-as, typically Dijkstra SPF (OSPF or ISIS) single destination, opportunistic (“greedy”), non pinned & symmetric | ||
| Inter-AS is path vector policy constrained, single destination, greedy, non pinned and asymmetric | ||
| IntraAS multipath exists (c.f OSPF-SMP), mainly for load balancing traffic on disaster recovery paths (rather than leaving them idle/”hot standby”) | |
| InterAS multipath does not currently exist in the routing infrastructure, although | |
| However: Multi-homing does, at both layers |
Background: Multi-metric Routing
| Intra-AS exists, sort of QOSPF | |
| Its quite hard – (NP hard for more than additive + 1 non additive parameter | |
| throughput and jitter are all non-additive metrics and loss and delay may be | |
| Inter-AS we have zilch (except hacks based on multi-homing) | |
| In theory could do shortest widest or widest shortest, but user still needs to see ful MESH of BGP path data! | |
| Creative incentive to rationalise inter-AS routes by allowing users choice | |
| Just as with congestion pricing, its not pricing congestion, it’s the threat of pricing that creates pressure/evolutionary trend – similarly, threat of user route alternates creases same | |
| Requires routing system to export alternatives so user can exercise choice |
| Policy = Router Information Filter | ||
| Ingress, transit or egress | ||
| Applied to who we advertise to, and | ||
| Who we accept advertisements from | ||
| Unilateral | ||
| Followed by Path Vector Computation | ||
| There are some global fields (AS registration, and community attributes) | ||
| Can use global attr and create a “long haul provider selection” overlay | ||
| Implement 3 ways: | ||
| Loose source route | ||
| Dynamic Address allocation (draw address from space of desired) next hop provider | ||
| Address Translation (whether IPv4 NAT, or IPv6 GSE like) | ||
| Need to offer users possibility of path choice | |
| Ingress selection not sufficient | |
| May (just may) also need information brokering about conditions | |
| Problem of thrashing of address/route tables if we use hacks (already known/seen in BGP _ c.f. Huston et al) | |
| Problem of traffic engineering thrashing if user dynamics are bad… | |
| Research needed… |