Adversaries may use fallback or alternate communication channels if the primary channel is compromised or inaccessible in order to maintain reliable command and control and to avoid data transfer thresholds.
JHUHUGIT tests if it can reach its C2 server by first attempting a direct connection, and if it fails, obtaining proxy settings and sending the connection through a proxy, and finally injecting code into a running browser if the proxy method fails.
Mis-Type first attempts to use a Base64-encoded network protocol over a raw TCP socket for C2, and if that method fails, falls back to a secondary HTTP-based protocol to communicate to an alternate C2 server.
WinMM is usually configured with primary and backup domains for C2 communications.
Network intrusion detection and prevention systems that use network signatures to identify traffic for specific adversary malware can be used to mitigate activity at the network level. Signatures are often for unique indicators within protocols and may be based on the specific protocol used by a particular adversary or tool, and will likely be different across various malware families and versions. Adversaries will likely change tool C2 signatures over time or construct protocols in such a way as to avoid detection by common defensive tools. 
Analyze network data for uncommon data flows (e.g., a client sending significantly more data than it receives from a server). Processes utilizing the network that do not normally have network communication or have never been seen before are suspicious. Analyze packet contents to detect communications that do not follow the expected protocol behavior for the port that is being used. 
- Mandiant. (n.d.). APT1 Exposing One of China’s Cyber Espionage Units. Retrieved July 18, 2016.
- Mandiant. (n.d.). Appendix C (Digital) - The Malware Arsenal. Retrieved July 18, 2016.
- Baumgartner, K. and Garnaeva, M.. (2014, November 3). BE2 custom plugins, router abuse, and target profiles. Retrieved March 24, 2016.
- Grunzweig, J.. (2017, April 20). Cardinal RAT Active for Over Two Years. Retrieved December 8, 2018.
- ESET. (2016, October). En Route with Sednit - Part 2: Observing the Comings and Goings. Retrieved November 21, 2016.
- Fidelis Cybersecurity. (2016, February 29). The Turbo Campaign, Featuring Derusbi for 64-bit Linux. Retrieved March 2, 2016.
- ClearSky. (2016, January 7). Operation DustySky. Retrieved January 8, 2016.
- US-CERT. (2019, April 10). MAR-10135536-8 – North Korean Trojan: HOPLIGHT. Retrieved April 19, 2019.
- ESET. (2016, October). En Route with Sednit - Part 1: Approaching the Target. Retrieved November 8, 2016.
- Levene, B, et al. (2017, May 03). Kazuar: Multiplatform Espionage Backdoor with API Access. Retrieved July 17, 2018.
- Symantec Security Response Attack Investigation Team. (2018, April 23). New Orangeworm attack group targets the healthcare sector in the U.S., Europe, and Asia. Retrieved May 8, 2018.
- Novetta Threat Research Group. (2016, February 24). Operation Blockbuster: Unraveling the Long Thread of the Sony Attack. Retrieved February 25, 2016.
- Novetta Threat Research Group. (2016, February 24). Operation Blockbuster: Remote Administration Tools & Content Staging Malware Report. Retrieved March 16, 2016.
- Zhou, R. (2012, May 15). Backdoor.Linfo. Retrieved February 23, 2018.
- Kaspersky Lab's Global Research & Analysis Team. (2013, February 27). The MiniDuke Mystery: PDF 0-day Government Spy Assembler 0x29A Micro Backdoor. Retrieved April 5, 2017.
- Gross, J. (2016, February 23). Operation Dust Storm. Retrieved September 19, 2017.
- FireEye Labs. (2015, April). APT30 AND THE MECHANICS OF A LONG-RUNNING CYBER ESPIONAGE OPERATION. Retrieved May 1, 2015.
- Falcone, R. and Lee, B. (2017, July 27). OilRig Uses ISMDoor Variant; Possibly Linked to Greenbug Threat Group. Retrieved January 8, 2018.
- Lee, B., Falcone, R. (2018, July 25). OilRig Targets Technology Service Provider and Government Agency with QUADAGENT. Retrieved August 9, 2018.
- Baumgartner, K., Golovkin, M.. (2015, May). The MsnMM Campaigns: The Earliest Naikon APT Campaigns. Retrieved April 10, 2019.
- Gardiner, J., Cova, M., Nagaraja, S. (2014, February). Command & Control Understanding, Denying and Detecting. Retrieved April 20, 2016.