Metarouting (SIGCOMM 2005) T. G. Griffin and J. L. Sobrinho

Background: What is in this paper: BGP is used as IGP? Why? Routing protocols are hard to develop and deploy. What is in this paper: A new approach to define and deploy new routing protocols by composing protocols from existing protocol elements. A clear separation between protocol mechanisms (how information is exchanged) and routing policies (how routes are described and compared). Use routing algebras (route preference is rigorously captured in algebraic structures) to describe the policy component. Use a language, RAML, to define more complex algebras from simpler ones. RAML allows the correctness property to be derived automatically.

Routing protocols Mechanisms Policy: How to exchange route information Route selection algorithm Rely on the policy component to determine route preferences Policy: Information describing the characteristics of routes The method to compare characteristics to determine route preference. The method to apply policies to routes This paper focuses on using routing algebra to describe policy.

Routing algebras: Signatures describe the characteristics of a route Signatures can be the path, path length, the path weight, etc. The route preference is determined only based on the route signatures Link weight is generalized as a policy label.

Routing algebra:

A routing protocol computes routes that have the form: Different routing protocols correspond to different operator (+), and thus, different algebras.

Convergence guarantees: The routing protocol must eventually determine the stable forwarding tables that implement loop-free paths between every pair of nodes In routing algebra, algebraic properties are identified for routing algebras: E,g for vectoring algorithms:strict monotonicity (SM) guarantees correctness:

Convergence guarantees: For link state algorithm: Associativity of + Isotonic: Left-SM and right SM

Base Algebras:

A Routing Algebra Metalanguage: Define a protocol RP as RP = (A, M, LM) Routing Algebra Meta-Language (RAML) defines A – make it easy by automatically derived monotonicity conditions.

Lexical Product

Scope Product:

Disjunction, An operation that allows the use of either A, or B, or both

Monptpnicity Preservation:

Routing algebra for a RIP-like protocol that supports complex policy routing:

Routing algebra for the RIP-like protocol for a three-level network(metropolitan area networks (MAN), regional area networks (RAN), and global networks (GN):

Modeling the policy component of BGP: