# Measuring the Centrality of DNS Infrastructure in the Wild
## 4 Methodology
### Client-Side DNS Infrastructure Measurement
#### 4.2.3 Advantage and Disadvantage  
Table 2 lists the comparison of resolver pool discovery methods, including our proposed approach. As described in Section 4.1, we have demonstrated the limitations of the _CNAME_ chain-based approach through empirical experiments. Our experiments reveal that merely 270 out of 2441 public DNSes utilize multiple resolvers to trace _CNAME_ redirections, resulting in a disappointing coverage of 11.06%. The experimental findings indicate that the _CNAME_ chain-based approach has limited performance on the modern internet. Although there are already some measurement platforms such as RIPE or PlanetLab [2; 24], their abilities and applications are still constrained. For instance, the limited scale of the platform can impact the effectiveness of measurements, and acquiring platform authorization can be challenging. Our resolver pool measurement approach can find the implicit resolver pool structure of the client-side DNS infrastructure by a single probing point. It turns the featured resolvers into distributed probes by carefully designing the domain resolution process. Owing to implementation shortcomings, these featured resolvers issue requests with the RD flag set, just as clients do. On the other hand, unlike the _CNAME_ chain method that relies on public DNS implementation features, our approach does not depend on public DNS implementation and can discover resolver pools for any public DNS.  
**Limitations.** Previous research shows that the location of measurement points on the internet can have an impact on measurement accuracy [33]. Therefore, our measurement results might also be subject to such bias due to single-point measurements. However, we argue that our single-point measurement scheme can largely meet the goal of revealing the forwarding relations between the client-side DNS infrastructure, as most FDNSes are Open resolvers that can be accessed from anywhere on the Internet [12]. Additionally,  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Methodology** & \multicolumn{2}{c}{**Distributed Measurement Platform**} & \multicolumn{1}{p{113.8 pt}}{**CNAME Chain**} & \multicolumn{1}{p{113.8 pt}}{**Our Method**} \\ \hline Mechanisms & Public DNS assigns various backend resolvers to users based on their geographical locations. & Public DNS initiates _CNAME_ record queries using different backend resolvers. & Open forwarders carry the RD flag when forwarding requests. & Open forwarders carry the RD flag when forwarding requests. \\ Condition & Researchers need authorization from the measurement platform. & Researchers need control authoritative name servers to construct _CNAME_ chains. Public DNS that meets specific conditions. & Researchers need to control authoritative servers to build NS chains. \\ Measurement Scope & Public DNS. & & Public DNS that meets specific conditions. & Public DNS. \\ \hline \hline \end{tabular}
\end{table}
Table 2: Comparison of resolver pool discovery methods.  
Figure 5: Resolver pool measurement method.  
we can mitigate the bias by choosing various measurement points and merging their measurement results.