Below are links to some resources I used to help myself study and pass the 210-250:

Exam Blueprint:
https://learningcontent.cisco.com/cln_storage/text/cln/marketing/exam-topics/210-250-secfnd.pdf

Official Cert Guide:
http://www.ciscopress.com/store/ccna-cyber-ops-secfnd-210-250-official-cert-guide-9781587147029?ranMID=24808

Free Trial Version – Understanding Cisco Cybersecurity Fundamentals (SECFND) v1.0:
(I did not buy this. I just used the Trial, which is access to only the 1st two lessons. It’s enough to cover the first exam topic – Network Concepts)
https://learningnetworkstore.cisco.com/ccna-cyber-ops/understanding-cisco-cybersecurity-fundamentals-secfnd-v1-0-elt-secfnd-v1-0-020708

• https://ics-cert.us-cert.gov/advisories/ICSA-14-269-01A
• http://omgcissp.com/content/cryptography-algorithm-cheatsheet
• https://unicode.org/charts/PDF/U0000.pdf
• http://packetlife.net/library/cheat-sheets/
• https://www.cisco.com/c/en/us/about/security-center/next-generation-cryptography.html#8
• https://community.cisco.com/t5/security-blogs/cryptography/ba-p/3100259
• https://www.faqforge.com/linux/distributions/debian/linux-how-to-view-log-files-on-the-shell/
• https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180416-tsa18-106a
• https://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html
• http://www.firewall.cx/networking-topics/protocols/870-ipsec-modes.html
• https://ensiwiki.ensimag.fr/images/b/b3/Cheat.pdf
• https://cjs6891.github.io/el7_blog/texts/cisco-ccna-cyber-ops-secfnd-9/#Basic%20File%20System%20Navigation%20and%20Management%20Commands