# Measuring the Centrality of DNS Infrastructure in the Wild
## 5 Resolver Centrality Analysis
### Resoler Pool  
**Finding 2: The top 5 public DNS providers serve approximately 40% of all FDNSes, with the resoler pool operated by Google Public DNS serving more than 22.22% of the total FDNSes. ** In order to assess the impact of centralization arising from the widespread adoption of resolver pooling techniques, we analyzed the resoler pools of major public DNS providers. Owing to the lack of ground truth data, it is challenging to evaluate the efficiency of the resoler pool discovery method. Therefore, we assess the effectiveness of our method by verifying with Google Public DNS official data [37]. Specifically, we found that 2274 indirect resolvers, distributed cross 119/24 prefixes, accounted for 75.8% of that published by Google. The measurement outcomes validate the efficacy of our methodology. Furthermore, it is salient to note that the scope of our approach is in fact broader than the recorded figure, given that we ascertained some IP ranges cited in the official data were entirely inactive. We correlate our Internet-wide measuring data with discovered resoler pool of public DNS to assess the usage of these pools by FDNSes. Table 4 lists the top five public DNS providers in regard to their pool size and the number of FDNS. Note that the count of FDNSes in Table 4 corresponds to the scale of the union of FDNSes discovered during our ten rounds of Internet-wide measurement. Cloudflare operates the largest resolver pool, comprising of 8593 resolvers distributed in 263/24 prefixes, with more than 32 resolvers per/24 on average. While the number of FDNS served by it is relatively small, just ranking \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Round**} & \multicolumn{2}{c}{**FDNS**} & \multicolumn{2}{c}{**dRDNS**} & \multicolumn{2}{c}{**iRDNS**} \\ \cline{2-7}  & **R2 \#** & **R1 \#** & **R2 \#** & **R1 \#** & **R2 \#** & **R1 \#** \\ \hline
1 & 2,422,618 & 5,582,383 & 51,223 & 58,028 & 55,109 & 64,136 \\
2 & 2,045,257 & 5,309,418 & 42,471 & 55,116 & 51,978 & 63,410 \\
3 & 2,327,287 & 5,217,285 & 48,324 & 54,712 & 54,698 & 63,988 \\
4 & 2,331,808 & 5,250,101 & 47,498 & 54,969 & 54,007 & 63,535 \\
5 & 2,370,049 & 5,266,898 & 49,224 & 55,805 & 54,640 & 63,692 \\
6 & 2,256,663 & 5,205,243 & 44,935 & 55,009 & 53,250 & 64,128 \\
7 & 2,288,812 & 5,129,975 & 47,156 & 54,139 & 54,017 & 63,185 \\
8 & 2,376,106 & 5,293,396 & 46,327 & 55,387 & 53,732 & 63,917 \\
9 & 2,350,699 & 5,117,815 & 44,914 & 52,881 & 53,150 & 63,071 \\
10 & 2,339,042 & 5,179,783 & 48,873 & 55,071 & 54,535 & 63,376 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Overview of measurement results. Figure 6: Cumulative distribution of iRDNSes and FDNSes. The x-axis is descendingly sorted by the number of served FDNSes. four in the top five public DNS providers. Although Google operates a smaller number of resolvers, they serve 4.27 M FDNSes, accounting for 22.22% of the total population of FDNS. Our results provide another evidence of the central position that Google holds in the global resolver market. Interestingly, despite employing different measurement methods, our findings closely align with previous studies [2], which observed that 22.36% of Internet users directed queries to Google Public DNS. This could indicate that the quantity of Internet end-users is generally proportional to the number of FDNSes, considering the multifarious usage scenarios of FDNSes. **Finding 3: Load distribution varies substantially across resolvers within a resolver pool, which reinforces the centrality of a limited subset of resolvers in that pool. ** Although the number of FDNSes largely corresponds with the quantity of Internet end-users, upon aggregating FDNSes that are served by Google's iRDNSes in each/24 prefix, we discovered that the number of FDNSes is not strictly proportional to the number of the iRDNS in a/24 prefix, as shown in Figure 7. This could signify an uneven allocation of loads across the diverse resolvers within the same pool.