Descripción del contenido del informe

At the inter-domain level, there are two major contributions: Hybrid Link-State Protocol[SCE+_05] and New Inter-domain Routing Architecture[YCB07]. Both aim to solve scalability and

convergence problems based on the hypothesis that the Internet follows a hierarchical structure.

Hybrid Link-State Protocol (HLP)

HLP assumes a hierarchical structure of Provider to Customer relationships rooted at each tier-1 provider. Each provider forms its own hierarchy, thus a multi-homed AS be- longs to multiple hierarchies.

The protocol routes packets based on AS identifiers, improving routing table scalability. It also differs from BGP since policy relationships are explicitly published and forms a hierarchy. Topological changes inside a hierarchy are reported using link-state messages and between peers of different hierarchies it uses Fragmented Path-Vector (FPV) mes- sages to report them.

FPV messages contain the following doublet (Pi, Ci), with Pi being the path and Ci the cost to reach destination i. Pi shows an ordered list of hierarchical border nodes that

2.4. ACADEMICAL SOLUTIONS 21

reach the destination AS. Upon the reception of a FPV message, its content is updated and a new message is flooded at each node of the hierarchy.

The system also uses another mechanism for better convergence: cost-hiding. Cost-hiding suppresses route announcements whose cost does not surpass a default value of ∆.

Despite complying scalability and convergence requirements to hierarchies, it fails to cope with the current Internet’s business model. Section 2.2.2 revolved on this issue with recent studies showing that the Internet presents a scale-free nature opposed to the idea of a hierarchy.

Besides the previous facts, multi-homed ASes have to process the link-state algorithm for each hierarchy, putting pressure on the protocol’s scalability.

New Inter-domain Routing Architecture (NIRA)

The NIRA protocol, just as HLP, assumes a hierarchical routing structure. Each hierar- chy has a tier-1 provider that belongs to the Core region. Each of these providers assigns recursively IPv6 prefixes to their customers. This hierarchy is labeled as a customer’s access network, or simply an up-graph. Opposite to the Core, P2P relationships can have non-core visible addresses and assign them recursively to their customers.

To disseminate routing information, NIRA uses a routing protocol named Topology In- formation Propagation Protocol (TIPP). TIPP has two components : A path-vector component that diffuses provider-level routes and a link-state component used to control topological changes inside a hierarchy.

For scalability and convergence sake a domain may configure TIPP to prohibit the dissem- ination of routing messages between domains, and the protocol only forwards link-state messages between transit domains.

So far NIRA’s concept is similar to HLP. However it allows a user to choose the traversed routes for its packets, constricting the user to his set of providers. This way if a user sends packets to a destination, these will be forwarded based on the user’s and destination’s address in a hierarchical sense: first upwards on the user’s up-graph and then downwards

on the destination’s up-graph.

NIRA supports multipath. When a user that wishes to use alternative routes, he can query a Name-to-Route Lookup Service (NRLS) server that works similarly to a DNS server, thus retrieving the remaining destination’s addresses. Despite letting a user choose its own providers, NIRA fails to address the current Internet’s Business Model, in the same manner as HLP. Taking into account the multi-homing reality of the Internet, the NIRA model is more capable of handling hierarchies than HLP, since it allows a user to choose its own set of hierarchies.

2.5

Summary

Table 2.5 summarizes the pros and cons of the previously discussed protocols. Based on the findings from recent studies of the Internet and the latest trends of the studied pro- tocols, it is possible to draw some insights on what should be the future of Inter-domain routing.

First it is essential to build a system that scales well, HLP and NIRA took a first step on this direction creating separate regions, though the assumption of the Internet structured as a hierarchy is not absolutely true.

G-ISP on the other hand tries something similar to a concept close to an overlay network to reduce the network’s convergence time. However, it still relies on BGP that features other issues besides this one.

Routing correctness is also an important matter. FCP brought the idea of distributing a network map to all nodes of a network ensuring routing correctness at the inter-domain level. Despite this advantage not all domains might want to publish their relationships.

Another incisive matter is the current address system that does not discern the identity of a node from its location. A service like ID-Mapping (from the LISP architecture) should be valuable for the future since its idea allows a protocol to locate a node based on its identification (Routing vs. Reachability).

2.5. SUMMARY 23

To end this summary some of the previous proposals suppress routing announcements based on a route’s cost, thereby improving the network’s convergence time. Although they don’t ensure routing correctness.

This thesis intends to merge some of these views and improve the current state of the art, which move us further to the next chapter.

Protocol Pros Cons Class

DV • Scalable • Count-to-Infinity prob-

lem

Intra-domain

Link-State • Small convergence time • Not Scalable Intra-domain

BGP • Policies Expression

through the use of at- tributes • Flexibility • Uncoordinated policies • Great convergence time • Not Scalable1 • Lack of QOS Inter-domain

LISP • Improves Internet Scal-

ability

• Non negligible traffic • Storage and Distribu- tion

Independent

G-ISP • Improves convergence

time • End-to-end QoS • Routing correctness of BGP Inter-domain and Indepen- dent XL • Improves convergence time • Usage of suboptimal routes Intra-domain

FCP • Suppresses the conver-

gence time

• Usage of suboptimal routes

Intra-domain

HLP • Improves convergence

time and scalability • Explicit use of policies

• Based on the assump- tion of a hierarchical structure

• More than one short- est path tree for multi- homed ASes

Inter-domain

NIRA • Improves convergence

time and scalability

• Based on the assump- tion of a hierarchical structure

Inter-domain

Table 2.2: Protocols Summary

1_{Under the following circumstances: multihomed ASes, multipath routing and without Classless Inter}

Chapter 3

An approach to multi-region routing