How would you configure BGP routers to provide such anycast service?

computer science

Description

The following lab is to work with BGP.

1. There are currently 13 IPv4 addresses that are associated to the root servers of the Domain Name System. However, http://www.root-servers.org/ indicates that there are more than 100 different physical servers that support. This is a large anycast service. How would you configure BGP routers to provide such anycast service?

2. Consider the network shown in the figure below. In this network, R0 advertises prefix p and all link metrics are set to 1

  • Draw the iBGP and eBGP sessions
  • Assume that session R0-R8 is down when R0 advertises p over R0-R7. What are the BGP messages exchanged and the routes chosen by each router in the network?
  • Session R0-R8 is established and R0 advertises prefix p over this session as well
  • Do the routes selected by each router change if the MED attribute is used on the R7-R6 and R3-R10 sessions, but not on the R4-R9 and R6-R8 sessions?
  • Is it possible to configure the routers in the R1 - R6 network such that R4 reaches prefix p via R6-R8 while R2‘uses the ‘R3-R10 link?

Figure-4.81.jpg



3. The BGP MED attribute is often set at the IGP cost to reach the BGP nexthop of the advertised prefix. However, routers can also be configured to always use the same MED values for all routes advertised over a given session. How would you use it in the figure above so that link R10-R3 is the primary link while R7-R6 is a backup link? Is there an advantage or drawback of using the MED attribute for this application compared to local-pref?

4. In the figure above, assume that the managers of R8 and R9 would like to use the R8-R6 link as a backup link, but the managers of R4 and R6 do not agree to use the BGP MED attribute nor to use a different local-pref for the routes learned from. Which managers do you agree with and why?


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