| name | network-data-security |
| description | Use this skill when you need network security architecture, firewall policy design, IDS/IPS configuration, DNS security, email security (DMARC/DKIM/SPF), SSL/TLS certificate lifecycle management, DDoS protection, data loss prevention (DLP), PII/PHI data protection controls, encryption implementation (at-rest and in-transit), database security hardening, data classification, or information security governance. Trigger for network design reviews, data security programs, or encryption strategy. |
| license | Apache-2.0 |
| metadata | {"author":"aviskaar","version":"1.0","tags":["network-security","firewall","ids-ips","ssl-tls","dns-security","email-security","dlp","pii","encryption","database-security","data-classification","information-security"]} |
Network & Data Security โ Network and Data Protection Specialist
Role
The Network & Data Security specialist owns the defense of data in motion and at rest: network architecture, perimeter and internal controls, data classification, encryption, DLP, and information security governance. Every byte of sensitive data must be protected from unauthorized access, interception, and exfiltration.
Phase 1 โ Network Security Architecture
Defense-in-Depth Network Model:
Internet
โ
[DDoS Scrubbing / CDN] โ Cloudflare / AWS Shield Advanced / Akamai
โ
[Edge Firewall / WAF] โ NGFW + Web Application Firewall
โ
[Internet DMZ]
โ Web servers, load balancers, public APIs, email gateway
โ
[Internal Firewall] โ Zone-to-zone inspection, IPS enabled
โ
[Application Zone] โ App servers, microservices, APIs
โ
[Data Zone] โ Databases, data warehouses, queues
โ
[Management Zone] โ SIEM, monitoring, PAM, secrets vault
โ
[OT/IoT Zone] โ Air-gapped or strict one-way data diode
Firewall Policy Standards:
Default policy: DENY ALL (permit only explicitly required traffic)
Rule authoring requirements:
- Source: specific IP/subnet or group (never "any" on permit rules for inbound)
- Destination: specific IP/subnet, host, or group
- Service/Port: specific port(s) (never "any" on permit rules for inbound)
- Direction: inbound vs outbound clearly documented
- Justification: business reason in rule comment field
- Owner: team owning the rule; contact for renewal
- Expiry: time-limited rules (contractor access, temp rules) with auto-expiry
Rule review cadence:
- All rules: annual review; confirm still required
- High-risk rules (internet-facing permit): semi-annual
- Unused rules (no traffic 90+ days): flagged for removal
- Orphan rules (no documented owner): removed after 30-day grace period
Prohibited rule patterns:
โ permit any any (any source to any destination)
โ permit any to internal subnet (any internet source inbound)
โ Management ports (22/3389) open from internet
โ Flat network (no zone segmentation between DMZ and internal)
Phase 2 โ IDS/IPS Configuration
Intrusion detection strategy:
Network IDS/IPS placement:
- Internet perimeter: detect/prevent external attacks
- DMZ: detect/prevent attacks on public-facing services
- East-West (internal): detect lateral movement (critical for Zero Trust)
- Cloud VPC: VLAN tap or cloud-native IDS (AWS Network Firewall, Azure IDPS)
Signature management:
- Automatic signature updates: daily minimum
- Custom signatures: develop for internal-specific threats (after threat hunting)
- Tuning: reduce false positives to <5% per rule; excessive FP rules โ review
- Testing: validate new signatures in IDS-only mode for 7 days before IPS (active block)
Detection categories to enable (minimum):
- Port scanning and network reconnaissance
- Exploit attempts (CVE-based signatures)
- Brute force attacks (auth failures)
- SQL injection / XSS over network
- C2 communication patterns
- Data exfiltration indicators (large outbound, DNS tunneling)
- Malware communication signatures
- Protocol anomalies (DNS, HTTP, SMB)
Phase 3 โ DNS Security
DNS security controls:
DNS Architecture:
- Internal DNS: separate from external DNS; does not respond to internet queries
- External DNS: DNSSEC-signed zones; DNSSEC validation enabled
- DNS-over-HTTPS (DoH) for client queries (prevent DNS eavesdropping)
- RPZ (Response Policy Zones): block known malicious domains at DNS resolver
- DNS monitoring: all queries logged to SIEM; anomaly detection enabled
DNS-based Attack Prevention:
- DNS rebinding: bind DNS resolver to local network; refuse external resolution for internal ranges
- DNS tunneling: monitor query length (>100 chars) + query frequency per source
- Fast-flux domains: reputation feeds integrated into RPZ
- DGA (Domain Generation Algorithm): ML-based detection for beacon-like DNS patterns
- Typosquatting: monitor for domains similar to brand names
DNSSEC Implementation:
- Sign all authoritative zones with DNSSEC (RSA-2048 or ECDSA P-256)
- Key Signing Key (KSK): rotated annually; offline storage
- Zone Signing Key (ZSK): rotated monthly (automated)
- DS record: published in parent zone; chain of trust validated
- Monitoring: alert on DNSSEC validation failure in resolver logs
Phase 4 โ Email Security
Email security stack (all three layers required):
Layer 1 โ Sending Authentication (SPF / DKIM / DMARC):
SPF Record:
v=spf1 include:_spf.google.com include:_spf.salesforce.com ip4:[authorized-IPs] -all
(hard fail -all; reject any sender not in SPF record)
DKIM:
- 2048-bit RSA key (minimum); Ed25519 preferred
- Key rotation: annual; old key retained for 30 days post-rotation for validation
- All outbound mail signed; verify inbound DKIM on receipt
DMARC:
- Policy progression: p=none (monitoring) โ p=quarantine โ p=reject (enforce within 90 days)
- Target: p=reject on all domains (including subdomains: sp=reject)
- RUA/RUF reports: configured and monitored daily
- DMARC record: v=DMARC1; p=reject; rua=mailto:dmarc@[domain]; ruf=mailto:dmarc-forensic@[domain]; sp=reject; adkim=s; aspf=s
Layer 2 โ Anti-Spam and Anti-Phishing:
- Email security gateway: Proofpoint/Mimecast/Google/Microsoft Defender for O365
- Sandboxing: all attachments detonated in sandbox before delivery
- URL rewriting: all URLs rewritten and scanned at click-time
- Impersonation protection: executive name spoofing; lookalike domain detection
- Attachment types: block .exe, .bat, .cmd, .vbs, .js, .ps1, .msi by default
Layer 3 โ User-Level Controls:
- External email banner: all external emails labeled [EXTERNAL]
- Report phishing button: one-click reporting; auto-intake to SOC queue
- Quarantine: suspicious email held for review (not delivered; not deleted)
- Mail flow monitoring: alerts on mass email send, unusual recipients, large attachments outbound
Phase 5 โ SSL/TLS Certificate Lifecycle Management
Certificate inventory and lifecycle:
Certificate Inventory Requirements:
- All certificates cataloged: hostname, CA, expiry, owner, purpose
- Automated discovery: scan for unknown/rogue certificates quarterly
- Certificate types tracked: DV, OV, EV, wildcard, internal CA, code signing
- Responsible team: certificate owner notified of all lifecycle events
Expiry Management:
- Alert at: 90 days, 60 days, 30 days, 14 days, 7 days before expiry
- Auto-renewal: ACME protocol (Let's Encrypt) or CA API for automated renewal
- Manual renewal: triggered 60 days out for internal CA and non-ACME certs
- Emergency: certificate expiry in production = P2 incident; immediate escalation
Certificate Standards:
Minimum:
TLS: TLS 1.2 with strong ciphers (disable RC4, 3DES, MD5, SHA-1)
Key size: RSA 2048+ or ECDSA P-256+
SAN: Subject Alternative Names; no CN-only matching
HSTS: Strict-Transport-Security: max-age=31536000; includeSubDomains; preload
Preferred:
TLS: TLS 1.3 (forward secrecy built-in)
Key: ECDSA P-256 (smaller, faster, equally secure)
Certificate validity: 90 days (short-lived; auto-renewed)
CT: Certificate Transparency logging (required for public trust)
Prohibited:
โ Self-signed certificates in production (internal CA = acceptable)
โ Wildcard certificates for high-security applications (use individual certs)
โ SHA-1 signed certificates (deprecated; rejected by browsers)
โ Certificates with validity >1 year for public-facing (398-day limit)
โ Private key stored in version control or config file
Phase 6 โ Data Loss Prevention (DLP)
DLP implementation across all channels:
DLP Coverage Matrix:
Channel | Tool | Policy
------------------------|-------------------------|----------------------------------
Email outbound | Email gateway DLP | Block PII/PHI/PCI; quarantine suspicious
Web upload | Proxy / CASB DLP | Block upload of classified data
Cloud storage sync | CASB (Netskope/MCAS) | Block sensitive file sync to personal
Endpoint (USB/print) | Endpoint DLP agent | Block USB; watermark prints
Chat/collaboration | M365 Purview / DLP API | Alert on PII in Slack/Teams/email
Database export | DAM + DLP | Alert on bulk export; require approval
API responses | API gateway | Scan for PII in API responses; mask if found
DLP Policy for PII (GDPR / CCPA minimum):
Detect:
- SSN pattern: \b\d{3}-\d{2}-\d{4}\b
- Credit card: Luhn-validated 13-19 digit sequences
- Email addresses in bulk (>10 in document)
- Date of birth + name combination
- Driver's license numbers (per state patterns)
- Passport numbers
- Medical record numbers / PHI indicators
- Financial account numbers
Action on Detection:
- Internal transfer: audit log + alert SOC if unexpected
- External email: quarantine + notify sender + require manager approval
- Web upload: block + user education popup
- USB: block + alert + log
- Large bulk export: alert + require justification
Phase 7 โ Data Classification & Information Security
Data Classification Framework:
Level 1 โ Public:
Definition: Information approved for public distribution
Examples: Marketing materials, public documentation, press releases
Controls: None special; no access control required
Handling: May be shared freely
Level 2 โ Internal:
Definition: Business information not meant for public but not sensitive
Examples: Employee directories, internal policies, org charts
Controls: Authenticated access; do not share externally without approval
Handling: Standard access controls; no encryption required in transit on internal network
Level 3 โ Confidential:
Definition: Sensitive business information; exposure causes competitive harm
Examples: Customer lists, financial forecasts, M&A info, source code, vendor contracts
Controls: Role-based access; encryption at rest and in transit; DLP enabled
Handling: Need-to-know; NDA before sharing with third parties; no personal devices
Level 4 โ Restricted:
Definition: Highly sensitive; regulatory data or information whose exposure causes significant harm
Examples: PII, PHI, PCI data, trade secrets, executive compensation, legal privilege
Controls: Strict RBAC; encryption mandatory; MFA for access; DLP with block; audit all access
Handling: Minimum necessary; never on personal devices; third-party sharing requires legal review
Level 5 โ Secret:
Definition: Information whose exposure causes catastrophic harm (reserved for defense/regulated)
Examples: Encryption keys, HSM credentials, nation-state classified (ITAR/CMMC Level 3)
Controls: Physical controls; dedicated systems; dual-person access; FIPS 140-2 Level 3 HSM
Handling: Paper-based or air-gapped systems only; no email; strict chain-of-custody
Data handling requirements by classification:
Classification | Encryption at Rest | Encryption in Transit | DLP | Audit Logging | Retention
Public | Optional | Optional | No | Optional | Per policy
Internal | Optional | TLS 1.2+ | No | Optional | Per policy
Confidential | AES-256 | TLS 1.2+ | Yes | Yes | 3โ7 years
Restricted | AES-256 + KMS | TLS 1.3 | Yes | Yes (all) | 7 years min
Secret | FIPS 140-3 HSM | mTLS + TLS 1.3 | Yes | Yes (all) | Permanent
Phase 8 โ DDoS Protection
DDoS defense layers:
Layer 1 โ Upstream scrubbing (cloud-based):
- Provider: Cloudflare Magic Transit / AWS Shield Advanced / Akamai Prolexic
- Capacity: โฅ1 Tbps mitigation capacity
- Detection: <5 second automated detection; <60 second mitigation
- Anycast routing: traffic routed to nearest scrubbing center
Layer 2 โ CDN / Edge:
- Static assets served from CDN (reduce origin load)
- Rate limiting at CDN edge: per-IP, per-user, per-endpoint
- Bot management: distinguish legitimate users from bots; challenge suspicious
Layer 3 โ Application layer (L7) protection:
- WAF with DDoS rules: HTTP flood, slow POST, Slowloris detection
- Rate limiting: per-API endpoint (not just global)
- CAPTCHA: escalating challenges under load
- IP reputation: auto-block known DDoS infrastructure
DDoS Response Runbook:
1. Detection: CDN/WAF alert fires โ SOC notified within 5 minutes
2. Assessment: confirm DDoS vs. traffic spike (legitimate viral event?)
3. Mitigation: activate enhanced filtering at CDN; notify upstream scrubbing provider
4. Communication: internal status page updated; customer communication if >5min impact
5. Recovery: confirm clean traffic before scaling down mitigation
6. Post-incident: traffic analysis; update rate limits; WAF rule improvements
Non-Negotiable Network & Data Security Rules
- Default deny โ all firewall rules start from deny; only explicitly permitted traffic flows
- No cleartext sensitive data โ PII, PHI, PCI data never transmitted or stored unencrypted
- DMARC p=reject enforced โ no email domain sends unauthenticated mail
- Certificate expiry = incident โ expired TLS cert in production triggers immediate P2 response
- DLP is always on โ no gaps in DLP coverage for any channel handling classified data
- Network segmentation is mandatory โ flat networks are a security failure; zones enforced
- Firewall rules reviewed annually โ unused rules removed; undocumented rules removed
