Comments on "Interdomain Routing"

“Internet is not free” and it has been since the transition of the NSFNET Backbone service to the current commercial structure [1]. Although there are a lot of critiques of the privatization of the Internet, it certainly brought the Internet not only to our homes but practically everywhere including our pockets. With the sheer size of the Internet, one can’t imagine how a message from a computer can reach another computer with different ISPs. The paper gave a picture on how one’s message is routed through different autonomous systems that make up the Internet today; and how money affects all of this.

Admittedly, I needed further reading in order to understand the topic wholly. One of the questions that arose after reading the paper is: Where do BGP and IGP meet?

The paper gave hints that iBGP runs over IGP and the NEXT HOP attribute of the BGP is changed to the loopback address when disseminating learned routes between iBGP speakers. Further reading from other sources said that an AS employs an intradomain routing protocol (IGP) to determine how to reach each customer prefix, and employs an interdomain routing protocol (BGP) to advertise the reachability of these prefixes to neighboring ASes [2]. In contradictory in what the paper says regarding next hops, an article from Cisco says that:



“Router C advertises network 172.16.1.0 with a next hop of 10.1.1.1. When Router A propagates this route within its own AS, the EBGP next-hop information is preserved. If Router B does not have routing information regarding the next hop, the route will be discarded. Therefore, it is important to have an IGP running in the AS to propagate next-hop routing information.”[5]

Next is: What are the IP addresses of those in a peering relationship? Will they setup a LAN or will one sacrifice one of its precious IP address?

“A pair of ASs interconnect via dedicated links and/or public network access points, and routing between ASs is determined by the interdomain routing protocol such as Border Gateway Protocol (BGP)”[2]

Network Access Points are data communication facilities at which ASes would exchange traffic, in replacement of the publicly-financed NSFNET Internet backbone [3]. There were four original network access points located at New York, Washington D.C., Chicago, and San Francisco [4]. These data communication facilities were later replaced by Internet Exchange Points which serves the same purpose [3].

Curiously, I tried searching for my ISP’s AS (Smart Bro Wireless); and I got this result from a search at Robotex.com: http://www.robtex.com/as/as10139.html#graph.

References:
[1] http://en.wikipedia.org/wiki/National_Science_Foundation_Network
[2] Gao, Lixin, “On Inferring Autonomous System Relationships in the Internet”, IEEE/ACM Transactions on Networking, Vol. 9 No. 6,December 2001
[3] http://en.wikipedia.org/wiki/Network_access_point
[4] http://searchsoa.techtarget.com/sDefinition/0,,sid26_gci214106,00.html
[5] http://www.cisco.com/en/US/docs/internetworking/technology/handbook/bgp.html
[6] Balakrishnan, Hari and Feamster, Nick, “Interdomain Internet Routing”, 2001-2005