The next example we'll look at is traffic engineering and CDNs, the content distribution networks. Now each CDN has its own configuration recommendations so these slides are only a guideline it is best to consult directly with the CDN in question about the operational and traffic engineering policies several CDNs do not wish for their peers the network operators to attempt to do traffic engineering because they have fairly sophisticated tools operating within this CDN itself to ensure that traffic flow is optimum for end user enjoyment the very CDN implementations deployed one example might be the CDN is present at the exchange point via the exchange point services infrastructure transit or backhaul Cash-fill is via one of the i-x members or a transit provider or via the CDN or an infrastructure other CDNs will peer directly at the exchange point they will take a port on the Ethernet switch and openly appear with the members of the i-x other CDNs will not be at the i-x but will be hosted by the i-x member who then makes the address space and therefore the content available to other members of the internet exchange part the diagram shows an example where the CDN is present as part of the exchange point services lab exchange point services is gateway Don to the exchange point through router a and the CDN provides the infrastructure servers and probably their own router to connect it into the ixb services LAN the CDN has its own transit connection for Cashville bgp configuration here would be that the ixb members peer with the ixp services router the router a in the diagram they will receive the routes originated by the CDN the ixb services will announce the routes to be served to the CDN and of course the CDN has its own transit arrangements either via the exchange plant member or separate infrastructure CDNs usually serve content to operators based on a combination of lowest round-trip time or latency because end-users expect instant access to all content they also pay attention to beech be announcements of the peer following more specific announcements in some cases sometimes they look at a s path length and quite often the BGP meed but operators need to talk to CDN operator about the CDNs actual BGP policy operators also need to watch the bandwidth to the CDN and pay close attention to the BGP announcements that they're making globally as well across the exchange point the next example is where the CDN is a member of the internet exchange point the CDN router will connect directly to the i-x and will peer with all members of the exchange the CDN will have its own separate transit connection for the cache fill so the BGP configuration is just like any other exchange point member the CDN will appear with all the ixb members the ixp members will receive the riots originated by the CDN and the CDN has its own transit arrangements via the IXP member or the separate infrastructure and the operations are the same as for the previous example the third example is where the CDN is hosted by a member this is more common in the cases of the smaller exchange points or where the members cannot work out how to host the CDN at the exchange quite often it might be the major telecom operator or the major transit provider that has enough traffic to justify the CDN so host it within their own network so the CDN connects into the network core of the ixp member and the ISP members transit connection is used for the Cashville IXP members will peer with s100 which is the peering router a shown in the diagram I explain more see if the riots originated by the CDN as well as those originated by es 100 yes 100 announces routes to be served to the CDN and this could depend on a s 100 agreement with each of its peering partners yes 100 might well charge for access to the CDN content because they have to pay for the backhaul and yes 100 may even limit access to the CDN content to certain peering partners as well so in addition to the previous advice paying attention to the a s path length is quite important CD ends may well pay attention to BGP attributes so make sure the shortest path to the CDN is via the IXP member rather than your own transit links and this is similar to the case when the ixp host the CDN directly and stay in close touch with the member whose give you access to the CDN or the CDN content cache especially for any change in policy is special for any bandwidth or latency issues if their bandwidth issues or latency issues it could well happen that the CDN would prefer to feed traffic to your network directly over your transit link rather than from the local instance of their CDN or their cache finally if you're connecting to a CDN in two different locations and this can happen with many operators where they see the CDN through the local internet exchange point or via the local exchange for member and they see the same CDN through the transit provider or even a regional IXP they might participate in how do they ensure that the end users access the local CDN are not the one hosted via the transit provider Sirians normally pay attention to bgp announcements but there's an open question about whether they will accept traffic engineering or not some do some do not CDNs normally pay attention to round-trip times they often pay attention to the end-user quality being able to measure how the end users accessing their data the solution is always to talk to the CDN and discuss the situation we want the best for their eyeballs their end users like the operator wants the best for the end users.
© Produced by Philip Smith and the Network Startup Resource Center, through the University of Oregon.
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