# Measuring the Centrality of DNS Infrastructure in the Wild
## 6 Name Server Centrality Analysis
### Service Provider  
To answer the first question, we extracted 210,446,494 domain names and 2,786,562 name servers from 1138 gTLDs. Then, we applied _ZDNS_[3] to collect the IP addresses of name servers. The detail is shown in Table 5.  
**Finding 1: More than 48.5% (102,245,486) of domain names depend on the top 10 NS providers. ** The leading providers maintain an absolute advantage in the DNS market. As shown in Figure 11, the top 10 NS providers offer service for more than 48.5% of all domain names, with GoDaddy alone serving 24.1% of domain names. Table 6 displays the information of the top 10 NS providers. We defined the _invalid rate_ for calculating the rate of invalid name servers for specific NS providers:  
\[invalid\ rate=\frac{|C_{1}|}{|C|} \tag{1}\]  
where \(C\) is the set of name servers for NS provider, and \(C_{1}\), a subset of \(C\), is the invalid name servers. \begin{table}
\begin{tabular}{l r} \hline \hline  & **Data Type** & **\#** \\ \hline domain name & 210,446,494 \\ name server & 2,786,562 \\ name server zone & 1,123,511 \\ name server IP & 754,404 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The domain name information. Surprisingly, as shown in Table 6, none of the top 10 providers are free from invalid name servers, which means that some name servers cannot provide services. There are possibly two reasons: (1) some name servers whose IP addresses we cannot find are dynamic; (2) NS providers fail to clear the invalid name servers in time. When a name server outages, providers should update the zone file, otherwise may cause other security risks [39]. **Finding 2: 21.6% of name server providers rely on just 10 IP providers. ** Filtering out the invalid IPs from 754,404 IPs of name servers, including 771 private addresses and 29 anycast addresses, we collect the owner information of IPs using MaxMind IPGeoLite2 [35] and finally discover 24,235 IP providers. Table 7 shows the top 10 IP providers. On the one hand, the top 10 IP providers account for 20% of all name server IP addresses we collected. On the other hand, the top 10 IP providers support 21.6% of name server providers. \begin{table}
\begin{tabular}{l r r r r l} \hline \hline
**Name Server Provider** & **NS \#** & **IP \#** & **Domain Name\#** & **Invalid Rate** & **ASO** \\ \hline GoDaddy & 180 & 97 & 50,807,891 & 0.44 & Host Europe GmbH ; GO-DADDY \\ Cloudflare & 1500 & 2821 & 9,420,340 & 0.32 & CLOUDFLARENET \\ DNS\_COM & 94 & 74 & 6,826,290 & 0.39 & S\({}_{1}^{a}\) \\ Google & 95 & 36 & 6,716,254 & 0.58 & Google \\ Namecheap & 307 & 132 & 6,713,315 & 0.26 & S\({}_{2}^{b}\) \\ HiChina & 70 & 113 & 5,700,130 & 0.40 & Hangzhou Alibaba Advertising Co.,Ltd \\ Wix & 139 & 12 & 5,463,090 & 0.03 & Google \\ IONOS & 607 & 568 & 4,067,655 & 0.08 & IONOS SE; Fasthosts Internet Limited \\ NameBright & 20 & 46 & 4,057,960 & 0.10 & Google; AMAZON-AES \\  & & & & & CLOUDFLARENET; \\ Network Solutions & 108 & 24 & 2,472,561 & 0.07 & NETWORK-SOLUTIONS-HOSTING \\ \hline \hline \end{tabular} \(S_{1}^{a}:\) NAMECHEAP-NET; ULTRADNS; Online S.a.s.; OVH SAS; AMAZON-02; RELIABELSTE; AS40676; Selfow S.N.C. Di Marco Brame & \(C.S_{2}^{b}:\) ZEN-ECN; China Mobile Communications Group Co., Ltd.; CHINAN UNKOM Chinan169 Backbone; WeiYi Network Technology Co., Ltd; Xiamen; CHINANET SHAANXI province Cloud Base network; AS Number for CHINANET Jiangsu province backbone; China Unicom Beijing Province Network; CHINANET Guangdong province network.  
\end{table} 
Table 6: Top 10 name server providers. Figure 11: Distribution of NS provider service coverage. **Finding 3: Name server providers are not independent but interdependent. ** The _ASO_ column of Table 6 shows the IP provider of each NS provider. As we can see, NS provider Wix relies entirely on Google, and NameBright uses both Google and Amazon. It means that whatever you choose, Wix or NameBright, Google may provide ultimate services for you, which may in turn degrade the redundant configuration of authoritative servers.