The internet is based on the integration of separated administrative networks, named autonomous systems. In the introduction of this thesis we shortly describe what is necessary in order to establish successful communication between devices that are connected to the internet or between devices within an organization. This includes information about routing protocols and internet addressing. The thesis mostly deals with how internet providers and large organizations connect with each other and exchange information. The protocol that serves this purpose, and is the main object of interest of the thesis, is called the border gateway protocol (BGP).
The core part of the thesis includes the basic functions and ways of connecting with the protocol. Providers and large organizations keep multiple mutual links for this purpose. In order to balance and distribute the traffic load between them, they use the BGP protocol. The basic theory about the protocol includes its terminology and concepts, the focus being on how the routers – devices that forward data packets along networks – connect to each other using this protocol, as well as which messages they exchange and how they, on the basis of these messages, build the routing table. The theory features some of the following concepts: autonomous system, iBGP/eBGP sessions and attributes of BGP protocol.
This is followed up with more advanced applications of the protocol. There are some demanding questions, namely about how to influence the selection of paths, how to reduce the number of networks in the routing tables and so on. There is a lot of filtering going on throughout the web; so it is necessary to know its tools. We describe the following tools: route maps, regular expressions, prefix lists and BGP communities.
The next part deals with how service providers exchange internet traffic between/among their autonomous systems through physical infrastructure, called internet exchange points. We have taken a closer look at the Slovenian IX and another larger one located in Amsterdam. We also describe the benefits of such connections, compared to direct connections.
The final part of the thesis gives a practical example of how two operators can interconnect through the internet exchange, and how they – if necessary – can build a routing policy. But since in this case, the operators connect through a route server, we have to start by describing the function and usage of this server first. The results show that the main benefits of route servers are the following - a smaller number of eBGP sessions, separated functions of routing and forwarding and more stages of filtering of the internet traffic. Further on, we take a look at some practical implementations of the route servers on offer.
In the practical part of the thesis we explain the list of commands on routers provided by the American firm Cisco Systems. Our conclusion is that the basic setting is a simple one, but complexity rises as we receive more infromation, meaning we have to filter some out. To conclude, some results from practical part are presented and they confirm the theory accrued during this thesis. We then compare the commercial solution with the open-source one, as well as listing all pros and cons regarding one and the other.
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