docs: salvage network operations patterns

2026-05-15 13:23:13 +08:00 · 2026-05-11 07:51:08 -04:00
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+---
+name: homelab-network-setup
+description: Practical home and homelab network planning for gateways, switches, access points, IP ranges, DHCP reservations, DNS, cabling, and common beginner mistakes.
+origin: community
+---
+
+# Homelab Network Setup
+
+Use this skill to design a home or small-lab network that can grow without
+needing a full rebuild.
+
+## When to Use
+
+- Planning a new home network or redesigning an ISP-router-only setup.
+- Choosing gateway, switch, and access point roles.
+- Designing IP ranges, DHCP scopes, static reservations, and DNS.
+- Preparing for future VLANs, Pi-hole, NAS, lab servers, or VPN access.
+- Troubleshooting a new network that has double NAT, unstable Wi-Fi, or changing
+  server addresses.
+
+## How It Works
+
+Start by separating device roles:
+
+```text
+Internet
+  |
+Modem or ONT
+  |
+Gateway or router      NAT, firewall, DHCP, DNS, inter-VLAN routing
+  |
+Managed switch         wired clients, AP uplinks, optional VLAN trunks
+  |
+Access points          Wi-Fi only; ideally wired backhaul
+Servers and NAS        stable addresses, DNS names, monitoring
+Clients and IoT        DHCP pools, isolated later if VLANs are available
+```
+
+Pick a gateway that matches the operator, not just the feature checklist:
+
+| Option | Best fit | Notes |
+| --- | --- | --- |
+| ISP router | Basic internet only | Limited control and often poor VLAN support |
+| UniFi gateway | Managed home network | Good UI, ecosystem lock-in |
+| OPNsense or pfSense | Flexible homelab | Strong VLAN, firewall, VPN, and DNS control |
+| MikroTik | Advanced network users | Powerful, but easy to misconfigure |
+| Linux router | Tinkerers | Document rollback before using as primary gateway |
+
+## IP Plan
+
+Avoid the most common default, `192.168.1.0/24`, when you expect to use VPNs.
+It often conflicts with hotels, offices, and ISP routers.
+
+```text
+Example small homelab plan:
+
+192.168.10.0/24  trusted clients
+192.168.20.0/24  IoT and media devices
+192.168.30.0/24  servers and NAS
+192.168.40.0/24  guest Wi-Fi
+192.168.99.0/24  network management
+
+Gateway convention: .1
+Infrastructure reservations: .2 through .49
+Dynamic DHCP pool: .50 through .240
+Spare room: .241 through .254
+```
+
+Use `home.arpa` for local names. It is reserved for home networks and avoids the
+leakage/conflict problems of ad hoc names like `home.lan`.
+
+```text
+nas.home.arpa
+pihole.home.arpa
+gateway.home.arpa
+switch-01.home.arpa
+```
+
+## DHCP And DNS
+
+- Use DHCP reservations for anything you SSH into, bookmark, monitor, or expose
+  as a service.
+- Hand out the gateway as DNS until a local resolver is intentionally deployed.
+- If using Pi-hole or another DNS filter, give it a reservation first, then point
+  DHCP DNS options at that address.
+- Keep a small static/reserved range per subnet so replacements do not collide
+  with dynamic leases.
+
+## Cabling And Wi-Fi
+
+- Prefer wired AP backhaul over mesh when you can run Ethernet.
+- Use a PoE switch for APs and cameras if the budget allows it.
+- Label both ends of each cable and keep a simple port map.
+- Put the gateway, switch, DNS server, and NAS on UPS power if outages are common.
+
+## Examples
+
+### Beginner Upgrade
+
+Goal: Keep the ISP router but stabilize a small lab.
+
+1. Set DHCP reservations for NAS, Pi, and any SSH hosts.
+2. Move local names to `home.arpa`.
+3. Disable duplicate DHCP servers on secondary routers or APs.
+4. Wire the main AP instead of relying on wireless backhaul.
+
+### VLAN-Ready Plan
+
+Goal: Prepare for future segmentation without enabling it immediately.
+
+1. Choose non-overlapping /24 ranges for trusted, IoT, servers, guest, and
+   management.
+2. Reserve .1 for the gateway and .2-.49 for infrastructure on every subnet.
+3. Buy a gateway and switch that support VLANs and inter-VLAN firewall rules.
+4. Document which SSIDs and switch ports will eventually map to each network.
+
+## Anti-Patterns
+
+- Double NAT without a reason or documentation.
+- Using `192.168.1.0/24` when VPN access is planned.
+- Dynamic addresses for NAS, Pi-hole, Home Assistant, or other service hosts.
+- Consumer routers repurposed as APs while their DHCP servers are still enabled.
+- Flat networks with cameras, smart plugs, laptops, and servers all sharing the
+  same trust boundary.
+
+## See Also
+
+- Skill: `network-interface-health`
+- Skill: `network-config-validation`
--- a/skills/network-config-validation/SKILL.md
+++ b/skills/network-config-validation/SKILL.md
@@ -0,0 +1,210 @@
+---
+name: network-config-validation
+description: Pre-deployment checks for router and switch configuration, including dangerous commands, duplicate addresses, subnet overlaps, stale references, management-plane risk, and IOS-style security hygiene.
+origin: community
+---
+
+# Network Config Validation
+
+Use this skill to review network configuration before a change window or before
+an automation run touches production devices.
+
+## When to Use
+
+- Reviewing Cisco IOS or IOS-XE style snippets before deployment.
+- Auditing generated config from scripts or templates.
+- Looking for dangerous commands, duplicate IP addresses, or subnet overlaps.
+- Checking whether ACLs, route-maps, prefix-lists, or line policies are referenced
+  but not defined.
+- Building lightweight pre-flight scripts for network automation.
+
+## How It Works
+
+Treat config validation as layered evidence, not as a complete parser. Regex
+checks are useful for pre-flight warnings, but final approval still needs a
+network engineer to review intent, platform syntax, and rollback steps.
+
+Validate in this order:
+
+1. Destructive commands.
+2. Credential and management-plane exposure.
+3. Duplicate addresses and overlapping subnets.
+4. Stale references to ACLs, route-maps, prefix-lists, and interfaces.
+5. Operational hygiene such as NTP, timestamps, remote logging, and banners.
+
+## Dangerous Command Detection
+
+```python
+import re
+
+DANGEROUS_PATTERNS: list[tuple[re.Pattern[str], str]] = [
+    (re.compile(r"\breload\b", re.I), "reload causes downtime"),
+    (re.compile(r"\berase\s+(startup|nvram|flash)", re.I), "erases persistent storage"),
+    (re.compile(r"\bformat\b", re.I), "formats a device filesystem"),
+    (re.compile(r"\bno\s+router\s+(bgp|ospf|eigrp)\b", re.I), "removes a routing process"),
+    (re.compile(r"\bno\s+interface\s+\S+", re.I), "removes interface configuration"),
+    (re.compile(r"\baaa\s+new-model\b", re.I), "changes authentication behavior"),
+    (re.compile(r"\bcrypto\s+key\s+(zeroize|generate)\b", re.I), "changes device SSH keys"),
+]
+
+def find_dangerous_commands(lines: list[str]) -> list[dict[str, str | int]]:
+    findings = []
+    for line_number, line in enumerate(lines, start=1):
+        stripped = line.strip()
+        for pattern, reason in DANGEROUS_PATTERNS:
+            if pattern.search(stripped):
+                findings.append({
+                    "line": line_number,
+                    "command": stripped,
+                    "reason": reason,
+                })
+    return findings
+```
+
+## Duplicate IPs And Subnet Overlaps
+
+```python
+import ipaddress
+import re
+from collections import Counter
+
+IP_ADDRESS_RE = re.compile(
+    r"^\s*ip address\s+"
+    r"(?P<ip>\d{1,3}(?:\.\d{1,3}){3})\s+"
+    r"(?P<mask>\d{1,3}(?:\.\d{1,3}){3})\b",
+    re.I | re.M,
+)
+
+def extract_interfaces(config: str) -> list[dict[str, str]]:
+    results = []
+    current = None
+    for line in config.splitlines():
+        if line.startswith("interface "):
+            current = line.split(maxsplit=1)[1]
+            continue
+        match = IP_ADDRESS_RE.match(line)
+        if current and match:
+            ip = match.group("ip")
+            mask = match.group("mask")
+            network = ipaddress.ip_interface(f"{ip}/{mask}").network
+            results.append({"interface": current, "ip": ip, "network": str(network)})
+    return results
+
+def find_duplicate_ips(config: str) -> list[str]:
+    ips = [entry["ip"] for entry in extract_interfaces(config)]
+    counts = Counter(ips)
+    return sorted(ip for ip, count in counts.items() if count > 1)
+
+def find_subnet_overlaps(config: str) -> list[tuple[str, str]]:
+    networks = [ipaddress.ip_network(entry["network"]) for entry in extract_interfaces(config)]
+    overlaps = []
+    for index, left in enumerate(networks):
+        for right in networks[index + 1:]:
+            if left.overlaps(right):
+                overlaps.append((str(left), str(right)))
+    return overlaps
+```
+
+## Management-Plane Checks
+
+Parse VTY blocks by section so access-class checks do not spill across unrelated
+lines.
+
+```python
+import re
+
+def iter_blocks(config: str, starts_with: str) -> list[str]:
+    blocks = []
+    current: list[str] = []
+    for line in config.splitlines():
+        if line.startswith(starts_with):
+            if current:
+                blocks.append("\n".join(current))
+            current = [line]
+            continue
+        if current:
+            if line and not line.startswith(" "):
+                blocks.append("\n".join(current))
+                current = []
+            else:
+                current.append(line)
+    if current:
+        blocks.append("\n".join(current))
+    return blocks
+
+def check_vty_blocks(config: str) -> list[str]:
+    issues = []
+    for block in iter_blocks(config, "line vty"):
+        if re.search(r"transport\s+input\s+.*telnet", block, re.I):
+            issues.append("VTY allows Telnet; require SSH only.")
+        if not re.search(r"\baccess-class\s+\S+\s+in\b", block, re.I):
+            issues.append("VTY block has no inbound access-class source restriction.")
+        if not re.search(r"\bexec-timeout\s+\d+\s+\d+\b", block, re.I):
+            issues.append("VTY block has no explicit exec-timeout.")
+    return issues
+```
+
+## Security Hygiene Checks
+
+```python
+SECURITY_PATTERNS = [
+    (re.compile(r"\bsnmp-server community\s+(public|private)\b", re.I),
+     "default SNMP community configured"),
+    (re.compile(r"\bsnmp-server community\s+\S+", re.I),
+     "SNMPv2 community string configured; prefer SNMPv3 authPriv"),
+    (re.compile(r"\bip ssh version 1\b", re.I),
+     "SSH version 1 enabled"),
+    (re.compile(r"\benable password\b", re.I),
+     "enable password is present; use enable secret"),
+    (re.compile(r"\busername\s+\S+\s+password\b", re.I),
+     "local username uses password instead of secret"),
+]
+
+BEST_PRACTICE_PATTERNS = [
+    (re.compile(r"\bntp server\b", re.I), "NTP server"),
+    (re.compile(r"\bservice timestamps\b", re.I), "log timestamps"),
+    (re.compile(r"\blogging\s+\S+", re.I), "logging destination or buffer"),
+    (re.compile(r"\bsnmp-server group\s+\S+\s+v3\s+priv\b", re.I), "SNMPv3 authPriv group"),
+    (re.compile(r"\bbanner\s+(login|motd)\b", re.I), "login banner"),
+]
+
+def check_security(config: str) -> list[str]:
+    return [message for pattern, message in SECURITY_PATTERNS if pattern.search(config)]
+
+def check_missing_hygiene(config: str) -> list[str]:
+    return [
+        f"Missing {description}"
+        for pattern, description in BEST_PRACTICE_PATTERNS
+        if not pattern.search(config)
+    ]
+```
+
+## Examples
+
+### Change-Window Preflight
+
+1. Run dangerous-command checks on the exact snippet to be pasted.
+2. Run duplicate IP and subnet overlap checks against the full candidate config.
+3. Confirm every referenced ACL, route-map, and prefix-list exists.
+4. Confirm rollback commands and out-of-band access before any management-plane
+   change.
+
+### Automation Preflight
+
+Use validation as a blocking gate before Netmiko, NAPALM, Ansible, or vendor API
+automation pushes a generated config. Fail closed on dangerous commands and
+credentials. Warn on best-practice gaps that are outside the change scope.
+
+## Anti-Patterns
+
+- Treating regex validation as a device parser.
+- Applying generated config without a dry-run diff.
+- Recommending SNMPv2 community strings as a monitoring requirement.
+- Checking VTY blocks with regex that can accidentally span unrelated sections.
+- Testing firewall behavior by disabling ACLs instead of reading counters/logs.
+
+## See Also
+
+- Agent: `network-config-reviewer`
+- Agent: `network-troubleshooter`
+- Skill: `network-interface-health`
--- a/skills/network-interface-health/SKILL.md
+++ b/skills/network-interface-health/SKILL.md
@@ -0,0 +1,152 @@
+---
+name: network-interface-health
+description: Diagnose interface errors, drops, CRCs, duplex mismatches, flapping, speed negotiation issues, and counter trends on routers, switches, and Linux hosts.
+origin: community
+---
+
+# Network Interface Health
+
+Use this skill when a network symptom might be caused by a physical link, switch
+port, cable, transceiver, duplex setting, or congested interface.
+
+## When to Use
+
+- A host or VLAN has packet loss, latency spikes, or intermittent reachability.
+- A switch or router interface shows CRCs, runts, giants, drops, resets, or flaps.
+- You need to compare both ends of a link before replacing hardware.
+- A change window needs before/after interface counter evidence.
+- Monitoring reports rising `ifInErrors`, `ifOutErrors`, or `ifOutDiscards`.
+
+## How It Works
+
+Interface counters are evidence, but the trend matters more than the absolute
+number. Capture a baseline, wait a measurement interval, capture again, then
+compare increments.
+
+```text
+show interfaces <interface>
+show interfaces <interface> status
+show logging | include <interface>|changed state|line protocol
+```
+
+On Linux hosts:
+
+```text
+ip -s link show <interface>
+ethtool <interface>
+ethtool -S <interface>
+```
+
+## Counter Reference
+
+| Counter | Meaning | Common cause |
+| --- | --- | --- |
+| CRC | Received frame checksum failed | Bad cable, dirty fiber, bad optic, duplex mismatch |
+| input errors | Aggregate receive-side errors | Check sub-counters before concluding |
+| runts | Frames below minimum Ethernet size | Duplex mismatch, collision domain, faulty NIC |
+| giants | Frames larger than expected MTU | MTU mismatch or jumbo-frame boundary |
+| input drops | Device could not accept inbound packets | Burst, oversubscription, CPU path, queue pressure |
+| output drops | Egress queue discarded packets | Congestion, QoS policy, undersized uplink |
+| resets | Interface hardware reset | Flapping, keepalive, driver, optic, power |
+| collisions | Ethernet collision counter | Half duplex or negotiation mismatch |
+
+## Diagnosis Flow
+
+### CRCs Or Input Errors
+
+1. Confirm counters are incrementing, not just historical.
+2. Check both ends of the link. Receive-side errors usually point to the signal
+   arriving on that side, not necessarily the port reporting the error.
+3. Replace patch cable or clean/replace fiber and optics.
+4. Confirm speed/duplex settings match on both sides.
+5. Check logs for flap events around the same timestamp.
+
+### Drops
+
+1. Separate input drops from output drops.
+2. Compare interface rate against capacity.
+3. Check QoS policy, queue counters, and whether the link is an oversubscribed
+   uplink.
+4. Treat queue tuning as secondary. First prove whether the link is congested.
+
+### Duplex And Speed
+
+Prefer auto-negotiation on modern Ethernet links when both sides support it. If
+one side must be fixed, configure both sides explicitly and document why. Never
+mix fixed speed/duplex on one side with auto on the other.
+
+```text
+show interfaces <interface> | include duplex|speed
+```
+
+## Safe Parser Example
+
+Slice each interface block from one header to the next. Do not use an arbitrary
+character window; large interface blocks can cause counters to be missed or
+assigned to the wrong port.
+
+```python
+import re
+from typing import Any
+
+HEADER_RE = re.compile(
+    r"^(?P<name>\S+) is (?P<status>(?:administratively )?down|up), "
+    r"line protocol is (?P<protocol>up|down)",
+    re.I | re.M,
+)
+ERROR_RE = re.compile(r"(?P<input>\d+) input errors, (?P<crc>\d+) CRC", re.I)
+DROP_RE = re.compile(r"(?P<output>\d+) output errors", re.I)
+DUPLEX_RE = re.compile(r"(?P<duplex>Full|Half|Auto)-duplex,\s+(?P<speed>[^,]+)", re.I)
+
+def parse_show_interfaces(raw: str) -> list[dict[str, Any]]:
+    headers = list(HEADER_RE.finditer(raw))
+    interfaces = []
+    for index, header in enumerate(headers):
+        end = headers[index + 1].start() if index + 1 < len(headers) else len(raw)
+        block = raw[header.start():end]
+        errors = ERROR_RE.search(block)
+        drops = DROP_RE.search(block)
+        duplex = DUPLEX_RE.search(block)
+        interfaces.append({
+            "name": header.group("name"),
+            "status": header.group("status"),
+            "protocol": header.group("protocol"),
+            "duplex": duplex.group("duplex") if duplex else "unknown",
+            "speed": duplex.group("speed").strip() if duplex else "unknown",
+            "input_errors": int(errors.group("input")) if errors else 0,
+            "crc_errors": int(errors.group("crc")) if errors else 0,
+            "output_errors": int(drops.group("output")) if drops else 0,
+        })
+    return interfaces
+```
+
+## Examples
+
+### CRCs On One Switch Port
+
+1. Capture counters on the local port.
+2. Capture counters on the connected remote port.
+3. Replace the cable or optic before changing routing or firewall rules.
+4. Clear counters only after recording the baseline.
+5. Recheck after a fixed interval.
+
+### Internet Slow But LAN Is Fine
+
+1. Check WAN interface drops/errors.
+2. Check LAN uplink utilization and output drops.
+3. Check gateway CPU if the WAN link is clean but throughput is still low.
+4. Compare wired and wireless tests before blaming upstream service.
+
+## Anti-Patterns
+
+- Clearing counters before saving a baseline.
+- Looking at only one side of a link.
+- Assuming all historical CRCs are active problems without a time window.
+- Mixing auto-negotiation on one side with fixed speed/duplex on the other.
+- Treating output drops as a cable problem before checking congestion.
+
+## See Also
+
+- Agent: `network-troubleshooter`
+- Skill: `network-config-validation`
+- Skill: `homelab-network-setup`