In this section, we provide the base for our idea to resolve Handle-PIDs through DNS proxy resolvers. Therefore, we outline several techniques, which are applied to accelerate domain name resolution. In addition, we examine the efficiency of these techniques to improve the resolution time of Handle-PID. We will see that their efficiency in the DNS system is essentially based on the high density of DNS proxy resolvers.
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6.2.1 Caching
Caching is primarily applied to hold data in faster, and usually also smaller, storage. However, in the particular case of DNS, it is applied to shorten the traversal path. This is achieved by tem-porarily store resolution responses from previous requests at the traversed nodes. A later resolution request for the same domain name can then be answered directly from a particular node, without the need to traverse until the responsible nameserver.
Thus, for example, caching at a DNS proxy resolver can enable the resolution request to be di-rectly responded by the proxy resolver itself. The resolution time then would be composed of the communication overhead between the requestor and the proxy resolver (Figure 6.2: step 1 and
8 ) including an internal processing time.
Since caching is a well established technique for several use cases, also in the Handle System it finds its usage.
6.2.2 Load Balancing
In order to ensure high availability and robustness, an individual DNS zone usually consists of multiple nameservers, on which the incoming resolution requests are distributed on. The applica-tion of this technique usually results in the reducapplica-tion of the internal processing times of the name-servers, which is based on the reduced load. Note that we already discussed the load-dependent processing times in Chapter 4.
Also this technique is applied in the Handle System, since an individualLocal Handle Service (LHS) is often composed of a primary Handle server and multiple mirror Handle servers.
6.2.3 Anycasting
The technique ofanycastis often used to redirect the requests to the nearest possible DNS server.
Anycast is especially suitable for zones, which consists of multiple geographically distributed nameservers. TheTop Level Domains (TLDs) zones are a typical example for that.
The ”de.”-TLD zone for example, consists of many nameservers, which are globally distributed.
A request submitted by an application, which is hosted in Europe will be directed to the European cluster of nameservers responsible for the ”de.” zone. Whereas a request originating from the USA will be answered by the nameservers located in the USA.
In anycast, multiple nodes are reachable by exactly the same IP-address. As an example, the public Google DNS resolver is reachable by the IP-address 8.8.8.8. However, since the public Google DNS proxy resolver is globally distributed among the world-wide Google data centers, a request of an individual client will be directed to one of the nearest Google DNS resolvers.
The request routing decision in anycast is made at the network switch level, which choose the particular path, which corresponds to the shortest hop count (number of to be traversed switches) among a set of possible other paths. However, the efficiency of anycasting is also highly dependent on the global distribution of the nodes, which are addressed by a single IP-address.
In the Handle System, there is currently no significant use of anycasting. It is currently only applied within a testbed of the GPR. However, it is less efficient, because of the already indicated low number of GPR servers.
6.2.4 Content Distribution Networks
Incontent distribution networks (CDNs), however, a request routing solely relying on anycasting is usually not efficient enough. This is due to the fact, that static routing decisions based on the hop count, do not cover the dynamic load behavior in CDNs. Therefore, in CDNs, special DNS servers ( [111]) have proven to provide a reliable request routing for redirecting an individual requestor to the current most efficient content server. These special DNS servers are usually equipped with probing information, collected from previous requests. Based on these probing information, these special DNS servers enable to apply various complex routing decision algorithms, which take far more parameters than only the sole hop count into account.
The Handle System is currently not deployed within a CDN. However, a CDN can also not be considered as a reasonable platform to improve the resolution time of Handle-PID. The request routing based on DNS would again cause a considerable overhead into the overall Handle-PID resolution time. In addition, the usage of a CDN is often associated with high costs.
6.2.5 Proxy Resolver Latency Reduction
Proxy resolver latency reduction means to reduce the network latency between a requesting appli-cation and the proxy resolver.
In DNS, there are myriads of publicly available proxy resolvers offered by specific service providers, which also apply anycasting for their cluster of proxy resolvers. Moreover, institutes belonging to a larger organization usually also have their own domain name zone including a DNS proxy resolver, which can be used by all the participants within the internal network infrastructure.
A similar situation can be found for the private Internet connections, where individual users are connected with the Internet via the network provided by a specificInternet Service Provider(ISP).
Also within such a network, there are multiple DNS proxy resolvers provided by the ISP.
This means that an individual application can usually choose a DNS proxy resolver in its close vicinity (in terms of network latency).
As already mentioned, the number of proxy resolvers within the Handle System is currently only five. Therefore, in contrast to the DNS system, an individual application can often not choose a Handle proxy resolver with a low network latency.
The result is that from the perspective of an individual application, in particular the technique of caching at the Handle proxy resolvers has a usually a much lower efficiency than with the DNS proxy resolvers, which is also true for the technique of anycasting.
Therefore, to globally reduce the communication overhead between an application and the GPR, it is first of all necessary to increase the number of globally distributed proxy resolvers. This could be done by a manual setup, which is theoretically possible but associated with high costs and administration efforts.
The next option would be to make use of an already publicly available and globally widespread resolution infrastructure: the DNS proxy resolvers. The great benefit of this option is that one can make use of the myriad of globally available public DNS proxy resolvers without additional costs and administrative overheads. The result would be an increased efficiency of the technique of caching at the proxy resolver for Handle-PID resolution. The downside, however, is that it requires a translation process between the Handle and DNS protocol.
Finally, in this chapter, we emphasize on:
• The realization of Handle-PID resolution through DNS proxy resolver.
Therefore, the following section discusses the possibilities to enable this approach.