Читать книгу Communication Networks and Service Management in the Era of Artificial Intelligence and Machine Learning - Группа авторов - Страница 23

Routing protocols are among the most successful deployed solutions to manage a network. A routing protocol specifies how routers communicate each other to exchange information that allows them to get the current network topology and compute the paths to reach possible destinations. Routing protocols give the Internet the ability to dynamically adjust to changing conditions such as topology changes, links and node failures, and congestion situations. There are two main classes of routing protocols in use on IP networks. Interior gateway protocols based distance‐vector routing protocols, such as Routing Information Protocol (RIP) [15], Enhanced Interior Gateway Routing Protocol (EIGRP) [16], or based on link‐state routing protocols, such as Open Shortest Path First (OSPF) [17], Intermediate System to Intermediate System IS‐IS [18], are used in networks that belong to the same administrator domain, i.e. within the same Autonomous System (AS). Interior gateways protocols base their decision on the minimization of the path costs, defined as the sum of link costs. As such, they aim at minimizing the cost of routing the traffic, i.e. maximizing the performance. Exterior gateway protocols aim instead at exchanging routing information between Autonomous Systems and finding the most convenient path – in terms of Autonomous Systems – to reach the destination. Here, Border Gateway Protocol (BGP) [19] is the de facto only choice. It is a path‐vector routing protocol and it makes routing decisions based on network policies and rules and not based on cost functions. BGP allows network operators to define routing policies that reflects administrative costs and political decisions in terms of agreements between Autonomous Systems.

Given the importance of optimizing exterior routing policies and the partial view that each network operator can get of the global Autonomous System (AS) level topology, several mechanisms are in place to gain visibility on the current Internet routing. Among those, the University of Oregon Route Views Project [20] leverages information provided by collectors, vantage points that expose their partial view of the BGP data, to create interactive maps, which are historized and made browsable via an ecosystem of tools and software that simplify the management and query of the information [21]. Thanks to Routeviews and the information exposed by BGP, it is possible to observe Internet‐wide outages [22, 23], routing hijacking [24], routing anomalies [25], or check the IPv4 address space utilization [26].

All the above‐mentioned routing protocols implement closed loop mechanisms – from monitoring to actions. Another category of routing protocols enable traffic engineering and network management opportunities. Among those, Multiprotocol Label Switching (MPLS) [27] is a routing technique based on the label swapping principle. Each node along the path reads the incoming packets' label and uses it to quickly route the packets to the next hop. Before the forwarding operation, the packet label is replaced with a new label that indicates the next forwarding operation to be done at the next node. Via a concatenation of labels, packets follow a pre‐computed path (a so called MPLS tunnel), which is distributed to all the nodes along the path prior the actual transmission. This on the one hand avoids complex look‐ups in the routing table, and on the other hand it enables the definition of explicit and well‐controlled paths that traffic flows will follow. By computing explicit tunnels is then possible to implement complex traffic engineering policies [28], setup end‐to‐end virtual private networks (VPNs) [29], and design specific protection mechanisms that quickly recover connectivity in case of failures [30].