Russian TSPU Begins Intercepting UDP DNS Queries to Cloudflare and Google Public Resolvers

Starting on the evening of August 26, Russia's TSPU DPI system began actively intercepting plaintext DNS queries sent over UDP to public resolvers operated by Cloudflare and Google. Queries to 1.1.1.1 and 8.8.8.8 now return NXDOMAIN responses for blocked domains instead of the real IP addresses. The interception works exclusively on UDP; TCP-based DNS queries continue to receive legitimate answers from the original resolvers. Technical analysis shows the system performs targeted DNAT, rewriting the destination IP to the NSDI server at 195.208.5.1 only when a DNS query is detected inside the packet. Experiments with varying TTL values confirm that the redirection occurs after the traffic passes the TSPU node, and rapid successive queries can sometimes bypass the filter and return genuine records. The change affects netflow statistics visible to network operators, as traffic previously destined for foreign resolvers is now redirected domestically.

HabrAugust 27, 2026Translated from Russian

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Starting approximately on the evening of August 26, Russia's TSPU system began intercepting open DNS queries directed at major public resolvers operated by Cloudflare and Google (1.1.1.1 and 8.8.8.8). Previously, only encrypted DoH endpoints from these providers were blocked.

Users immediately observed that DNS resolution for blocked domains now returns an NXDOMAIN response. The following example illustrates the behavior when querying YouTube and Rutracker:

dig youtube.com @8.8.8.8 returns NXDOMAIN
dig rutracker.org @1.1.1.1 returns NXDOMAIN

Tcpdump captures confirm that the NXDOMAIN reply is generated almost instantly, indicating local interception rather than a response from the actual resolver. The mechanism functions only over UDP; queries sent with the +tcp flag receive genuine A records from the original servers.

Further testing revealed that the interception relies on TTL-based routing manipulation. When a DNS query is first sent with TTL 2 (stopping just after the TSPU node) and then repeated with TTL 64, the second query often bypasses the filter and receives the real IP addresses. Sending random non-DNS packets with low TTL does not trigger the same effect.

In one notable case, a DNS query with TTL 2 elicited an ICMP TTL Exceeded message whose source IP was not 8.8.8.8 but 195.208.5.1, the address of the Russian NSDI server. This confirms that the TSPU performs destination NAT specifically on packets containing DNS queries, replacing the original resolver IP with the domestic NSDI address.

When multiple identical queries are sent in rapid succession within the same flow, the system occasionally fails and returns both NXDOMAIN and legitimate answers in quick succession. Network operators downstream of the TSPU will therefore observe a measurable drop in netflow records destined for foreign public DNS servers.

Cloudflare Google Roskomnadzor TSPU NSDI

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