US-based Internet service provider Cogent Communications has contacted customers based in Russia saying that they will be immediately terminating their commercial relationship.

Cogent operates one of the world's largest Internet backbones, with more than 60,676 route miles of intercity fiber and more than 39,559 metro fiber miles. It provides services to over 216 major markets and interconnects with over 7,569 other networks.

"In light of the unwarranted and unprovoked invasion of Ukraine, Cogent is terminating all of your services effective at 5pm GMT on March 4, 2022," the company wrote to Russian customers.

"All Cogent-provided ports and IP address space will be reclaimed as of the termination date."

After some pushback from customers, that deadline has been extended slightly for some customers on a case-by-case basis to allow them time to find alternative providers.

"For any colocation customers, your equipment will be powered off and kept in the rack for you to collect," Cogent added.

"If not collected within thirty days, the equipment will be removed from the rack and stored. For any utility computing customers, you will not have access to your servers after the termination of service. The servers will be disconnected and kept in storage by Cogent for an indeterminate period."

Network monitoring company Kentik found that the top five Russian customers of Cogent based on transited IPv4 space include Russian state telecom Rostelecom, national fiber backbone operator Transtelecom, and mobile telcos Megafon and VEON.

Yandex, which this week warned it might default on debt, and DDoS-mitigation website StormWall are also customers.

The firms currently have alternative providers they could turn to, including Vodafone, Telecom Italia Sparkle, Lumen, and Arelion (formerly Telia).

"A backbone carrier disconnecting its customers in a country the size of Russia is without precedent in the history of the Internet," Doug Madory, director of Internet analysis at Kentik, said.