Cloud-based onion routing confronts censors with a collateral-damage dilemma: blocking a cloud provider's IP prefixes requires blocking all co-hosted services (Amazon EC2 hosted over 1 million instances sharing common IP prefixes in 2010), while allowing the traffic means circumvention succeeds. Rotating IP addresses—by retiring and spinning up new VM instances or via DHCP/gratuitous ARPs—reduces the window a blocked address remains in service, forcing censors into a perpetual cat-and-mouse game across all major cloud providers simultaneously.

In controlled benchmarks using TorPerf, the best COR circuit achieved a median file download time 7.6× faster than Tor across 50 KB, 1 MB, and 5 MB files (100 repetitions each). COR was also several times faster than Tor for downloading full web pages across the top 10 Alexa domains, even when COR relays were serving 50 simultaneous connections.

§4.1, §4.2, Figure 3 evaluation

COR does not solve the bootstrapping problem: a user's first connections to the COR bootstrapping network are vulnerable to the same IP-enumeration and blocking attacks as public Tor directory connections. To mitigate directory-partitioning attacks, directory retrieval is always performed through an existing COR circuit, and directories return only a random subset of available nodes rather than the full list—but this subset-delivery design is itself exploitable by a malicious directory that can fingerprint users via uniquely-assigned relay subsets.

§2.3, §3.1, §5 defense

COR circuit construction enforces four properties to prevent single-entity de-anonymization in a limited-provider setting: (1) entry and exit ASPs must differ; (2) entry and exit CHPs must differ; (3) the same ASP's relays must not surround another ASP's relay without an intervening hop of a distinct ASP; and (4) at least two relays per traversed datacenter so an adversary with only perimeter visibility cannot trivially correlate ingress/egress.

§2.4 defense

Running a COR network matching Tor's 2011 aggregate bandwidth (estimated at 150 MB/s end-user demand, ~376 TB/month) would cost approximately $61,200/month on Amazon EC2 at July 2011 pricing. A single EC2 node at 17¢/hour plus bandwidth charges can relay approximately 110 Mbps and support up to 100 concurrent users at ~1 Mbps each; m1.large and c1.medium instances handled 100+ concurrent connections while t1.micro struggled beyond 10.

§2.5, §4.3, Figure 3(right) evaluation

Brussee measures a systematic pattern of Chinese government websites actively blocking access from outside China (the "reverse Great Firewall"), publishing a CSV dataset of affected domains (available at zenodo.org/records/18172145). The paper frames this outbound geo-blocking as a cybersecurity-motivated practice — Chinese authorities classify foreign access to domestic government infrastructure as an attack surface — distinct from the inbound information control goal of the GFW.

2026-brussee-reverse-great-firewall §3, §5 ip-blockingasn-blackholing

Brussee develops a conceptual framework distinguishing two logics of government geo-blocking: (1) information control (blocking inbound foreign content from domestic users) and (2) data sovereignty / attack-surface reduction (blocking outbound access by foreign actors to domestic systems). Chinese government site blocking of external IPs is motivated primarily by the second logic, creating an asymmetric internet topology where CN citizens cannot reach the outside world, and outside actors cannot probe CN government infrastructure.

2026-brussee-reverse-great-firewall §2, §4 ip-blockingasn-blackholing

The April 2026 enforcement wave against Chinese VPN resellers operates primarily through administrative "reporting + line-cutting" (通报+拔线) mechanisms enforced via Ministry of Industry and Information Technology bulletins, not packet-level DPI changes. Operators report that newly acquired upstream resources are reported and cut with recovery periods described as "uncontrollable," and that upstream providers typically do not refund resellers after enforcement actions.

2026-ermao-april-airport-outage §一句话结论 / §这轮波动到底发生了什么 ip-blockingasn-blackholing

The dominant enforcement mechanism in April 2026 was administrative 'reporting + line-cutting' (通报 + 拔线) backed by MIIT bulletins, not protocol-level DPI changes. Operators reported that newly acquired upstream resources were reported to authorities quickly after acquisition, recovery timelines were uncontrollable, and some upstream providers refused refunds after enforcement actions, producing sustained capacity contraction across the shared VPN-reseller ecosystem.

2026-ermao-april-airport-outage §这轮波动到底发生了什么 ip-blockingasn-blackholing

The April 2026 enforcement cycle created a resource-scarcity feedback loop: upstream providers cut lines with no obligation to refund resellers, newly acquired replacement resources can themselves be reported and cut within days, and stable-resource availability windows are described as "越来越短" (increasingly short) while costs rise concurrently. The overall effect is systemic capacity contraction forecast to continue through at least May 2026.

2026-ermao-april-airport-outage §这轮波动到底发生了什么 / §四月后的趋势判断 ip-blockingasn-blackholingthrottling

Shared domestic-entry transit architectures (国内入口 + 海外转发) suffered disproportionate impact because all nodes sharing a single domestic entry point went down simultaneously when that entry was reported and cut. Operators described configurations degrading from 'three-line redundancy to single entry,' eliminating failover capacity under enforcement pressure.

2026-ermao-april-airport-outage §为什么中转机场这次受冲击更明显 ip-blockingasn-blackholing