Parsing Cisco Configs

Parsing Cisco ASA / FTD Configurations

Overview

Use this skill to parse Cisco ASA and ASA-style FTD running configurations into the shared vendor-neutral firewall intermediate schema. It focuses on line-oriented show running-config text with parent commands and indented subcommands, including interfaces/nameifs, ACLs/access-groups, network and service objects, object-groups, NAT, routes, VPN, failover, and system settings.

FMC- and FDM-managed policy is not parsed here. An FMC or FDM JSON export has no syntactic overlap with LINA CLI — its policy lives in Access Control Policy rules, security-zone objects, and intrusion/file policies rather than in access-list and access-group lines. Route those exports to parsing-firepower-configs. If an FMC-managed device's LINA running-config is supplied, parse it here and warn that it is the compiled result of an FMC policy, not the policy source.

Scope and routing

Use only for Cisco ASA or FTD syntax. Hand off FortiOS config/edit/next/end blocks to parsing-fortinet-configs, PAN-OS XML or set deviceconfig to parsing-palo-configs, and Junos hierarchy or set security to parsing-srx-configs. Hand off FMC or FDM JSON exports to parsing-firepower-configs. Verify production-bound results against current device documentation and output. Downstream consumers are the audit, conversion, and diff skills.

Runtime intake

Before starting the workflow, inspect the request, supplied artifacts, and available approved read-only evidence. If unresolved facts could materially change safety, scope, correctness, confidence, or the requested output, read references/runtime-intake.md.

For each unresolved material fact whose catalog condition is true, invoke Claude AskUserQuestion or Codex request_user_input before continuing or issuing an open-ended request. Ask at most three single-select catalog questions per round. After each response, ask another round whenever any unresolved material catalog condition remains true; continue only when none remain. Do not repeat answered questions or show the full catalog. Without a native tool, present each selected catalog question with its 2-3 labeled choices and a free-text Other path in concise plain text; do not substitute a generic checklist.

Never request secrets or unredacted customer data. Treat intake answers as task context, not approval for a live change; obtain separate explicit approval before configuration, commit, upgrade, reboot, delete, or failover actions.

Input Format

Cisco ASA configs are line-oriented with indented sub-commands:

interface GigabitEthernet0/0
 nameif outside
 security-level 0
 ip address 203.0.113.1 255.255.255.0
!
object network web-server
 host 10.0.1.10
 nat (inside,outside) static 203.0.113.10
!
access-list outside_in extended permit tcp any object web-server eq 443
access-group outside_in in interface outside

Key syntax rules:

• Top-level commands start at column 0
• Sub-commands are indented with one space
• ! separates logical sections
• Named interfaces use nameif (e.g., inside, outside, dmz)
• security-level (0-100) determines trust level

Building Command Blocks

Group indented lines under their parent top-level command — see references/parsing-patterns.md "Building Command Blocks" for the algorithm and worked example.

Extraction Pipeline

1. Interfaces

Source: interface <hardware-id> blocks Extract from sub-commands:

• nameif <name> — the logical name used everywhere else
• security-level <0-100> — trust level
• ip address <ip> <mask> — IP and subnet mask
• vlan <id> — VLAN assignment
• shutdown — interface is administratively down
• description <text>
• bridge-group <id> — transparent mode bridge group membership
• ip address dhcp — DHCP client mode (no static IP)
• ipv6 address <ipv6/prefix> [eui-64] — IPv6 address
• mtu <value> — MTU setting
• management-only — management-only interface flag
• channel-group <N> — LAG/EtherChannel membership (Port-channel parent)
• tunnel source interface <name> — VPN tunnel source
• tunnel destination <ip> — VPN tunnel destination
• tunnel protection ipsec profile <name> — IPsec profile binding

Interface types: detect Port-channel* as lag, Tunnel* as tunnel, Loopback* as loopback, Management* as management. Sub-interfaces contain . in name (e.g., GigabitEthernet0/0.100) — derive parent from name before the dot.

2. Zones (Derived from Interfaces)

ASA doesn't have explicit zones. Derive them from nameif values:

• Each unique nameif becomes a zone
• security-level values are parser-internal inference metadata used to determine relative trust ordering between zones (higher = more trusted). This is NOT emitted as a security_level or trust_level field in the intermediate schema — use it only to guide ordering or warn when ACLs are absent.
• Associate the interface with its zone

3. Network Objects

Source: object network <name> blocks Types from sub-commands:

• host <ip> → type: "host", value: ip + "/32" (or "/128" for IPv6)
• subnet <ip> <mask> → type: "subnet", value: ip + "/cidr" (convert mask to CIDR)
• range <start> <end> → type: "range", value: "start-end"
• fqdn v4 <domain> or fqdn v6 <domain> → type: "fqdn"

Note: bare fqdn <domain> (without v4/v6 qualifier) is also valid.

• subnet <ipv6-prefix> → for IPv6 subnets the value is already in CIDR form, no mask conversion needed.

Also extract: description, inline nat statement (for object/auto NAT).

4. Network Object Groups

Source: object-group network <name> blocks Members from sub-commands:

• network-object host <ip> → inline host
• network-object <ip> <mask> → inline subnet
• network-object object <name> → reference to named object
• group-object <name> → nested group reference

5. Service Objects

Source: object service <name> blocks Parse: service <protocol> [source <op> <port>] [destination <op> <port>] Operators: eq, range, gt, lt, neq

6. Service Object Groups

Source: object-group service <name> [<protocol>] blocks Members:

• port-object eq <port> / port-object range <start> <end>
• service-object <protocol> [destination <op> <port>]
• service-object object <name>
• group-object <name>

7. Protocol Object Groups

Source: object-group protocol <name> blocks Members: protocol-object <protocol-name-or-number>

8. Access Lists (Security Policies)

Source: access-list <name> extended <action> <protocol> <src> <dst> [<svc>]

ACL Remarks: access-list <name> remark <text> — attach as comment to the NEXT ACL entry.

ACL Line Parsing — Token by Token:

Format: access-list <id> extended <permit|deny> <protocol> <source> <dest> [<service>] [log] [time-range <name>]

Protocol field:

• ip — any IP protocol
• tcp, udp, icmp, sctp — specific protocols
• object-group <name> — protocol group reference

Address parsing (for both source and destination):

• any / any4 / any6 → "any"
• host <ip> → specific host
• object <name> → named network object
• object-group <name> → network object group
• <network> <mask> → network/subnet-mask pair (convert standard subnet mask to CIDR)
• interface <nameif> → the IP of that interface

Source port parsing (after source address, for TCP/UDP — optional):

• eq <port> / range <start> <end> → source port match (less common)

Service/port parsing (after destination address, for TCP/UDP):

• eq <port> → single port (use name or number)
• range <start> <end> → port range
• gt <port> → greater than
• lt <port> → less than
• neq <port> → not equal (warn: limited cross-platform support)
• object-group <name> → service group reference

ICMP parsing (for ICMP protocol):

• Optional ICMP type after destination: icmp <src> <dst> <type> [<code>]

Flags:

• log [<level>] [interval <secs>] → enable logging
• time-range <name> → schedule reference
• inactive → disabled

9. Access Groups (Binding ACLs to Interfaces/Zones)

Source: access-group <acl-name> <in|out> interface <nameif> Also: access-group <acl-name> global (applies to all interfaces)

Critical: Deriving Zone-Based Policies from ACLs

ACLs alone don't have zone info. Combine with access-groups:

• access-group outside_in in interface outside → policies from this ACL have:
  • src_zones: ["outside"] (traffic enters on this interface, so it is the source zone)
  • dst_zones: must be inferred (often "any" unless the ACL destination addresses map to a zone)
• For in direction: traffic is entering the named interface, so that interface is the source zone
• For out direction: traffic is leaving the named interface
• For global: applies regardless of interface

Build security policies by iterating ACL entries and attaching zone information from access-groups.

10. NAT Rules

Object NAT (Auto NAT): Found inside object network blocks as nat (<real-iface>,<mapped-iface>) <type> <mapped-addr>

• nat (inside,outside) static 203.0.113.10 → static 1:1 NAT
• nat (inside,outside) dynamic interface → dynamic PAT to interface
• nat (inside,outside) dynamic pat-pool <name> → dynamic PAT to pool

Twice NAT (Manual NAT): Top-level: nat (<real-iface>,<mapped-iface>) [after-auto] [<line>] source <type> <real-src> <mapped-src> [destination <type> <real-dst> <mapped-dst>] [service <real-svc> <mapped-svc>]

Parse source static|dynamic and optional destination static components. The optional numeric token is a line number — the rule's position within its manual NAT section — NOT a section selector. Derive the section from rule form: Section 1 = manual/twice NAT without after-auto (evaluated before object/auto NAT); Section 2 = object/auto NAT (rules inside object network blocks); Section 3 = manual NAT with the after-auto keyword (evaluated after all auto NAT).

11. Time Ranges (Schedules)

Source: time-range <name> blocks Sub-commands:

• absolute start <time> <date> end <time> <date>
• periodic <days> <start-time> to <end-time>

12. Routing

• Static routes (IPv4): route <nameif> <dest> <mask> <gateway> [<metric>]
• Static routes (IPv6): ipv6 route <nameif> <dest/prefix> <gateway> [<metric>]
• BGP: router bgp <asn> block — extract:
  • router-id, address-family ipv4 unicast
  • Per-neighbor: remote-as, description, update-source, password, timers (keepalive/hold), next-hop-self, soft-reconfiguration, route-reflector-client, shutdown
  • network statements (convert mask to CIDR)
  • redistribute (connected/static)
  • Note: route-map and prefix-list references are not converted (warn)
• OSPF: router ospf <pid> block — extract:
  • router-id, auto-cost reference-bandwidth
  • network <ip> <wildcard> area <id> — match interfaces to areas via wildcard mask comparison
  • Area types: stub, nssa, with no-summary; area default-cost; area authentication
  • passive-interface default + no passive-interface <nameif> exceptions
  • redistribute (connected/static with metric/metric-type)
  • Interface-level: ip ospf cost, ip ospf priority, ip ospf hello-interval, ip ospf dead-interval, ip ospf network point-to-point, ip ospf authentication message-digest + key
  • Normalize area IDs to dotted-decimal (0 → 0.0.0.0)
• OSPFv3: router ospfv3 block with address-family ipv6 unicast — similar structure to OSPFv2

13. Infrastructure

• Hostname: hostname <name> and domain-name <domain> → system metadata
• Version: asa version <X.Y> or firepower version <X.Y> → metadata.source_version
• HA/Failover: failover presence + failover lan unit primary|secondary (capture unit role), failover interface ip, failover link
• Screen/Threat Detection: threat-detection basic-threat + threat-detection rate entries
• DNS: dns server-group DefaultDNS block → extract name-server entries
• NTP: ntp server <ip> [prefer]
• Management Access: ssh|http|telnet <source> <mask> <nameif> — track which management protocols are accessible per zone
• Admin Users: username <name> password ... privilege <level> — map privilege 15=super-admin, 1-14=operator, 0=read-only. username <name> attributes block with ssh authentication publickey <key> for SSH keys.
• VPN/IPsec:
  • crypto ikev2 policy <seq> blocks: encryption, integrity, DH group, lifetime
  • crypto ikev1 policy <seq> blocks: authentication, encryption, hash, DH group, lifetime
  • crypto ipsec ikev2 ipsec-proposal <name>: protocol esp encryption/integrity
  • crypto ipsec ikev1 transform-set <name> <enc> <integ>
  • crypto ipsec profile <name>: link proposals to PFS groups
  • tunnel-group <ip> ipsec-attributes: PSK, certificates, authentication method
  • VTI assembly: match Tunnel interfaces to IPsec profiles, resolve tunnel source/destination, collect routes through tunnel nameifs
  • Canonicalize algorithm names (ASA encryption names are mostly already canonical; e.g., sha → sha1, esp-3des → 3des)
  • Flag weak algorithms (DES/3DES, MD5, DH group ≤ 5)
• Syslog: logging host <nameif> <ip>
• DHCP Server: dhcpd address <start>-<end> <nameif> (pool range), dhcpd dns <ip1> [<ip2>], dhcpd domain <domain>, dhcpd lease <seconds>, dhcpd enable <nameif> (commit trigger — binds staged options to interface). Derive network CIDR from the interface IP.
• DHCP Relay: dhcprelay server <ip> <iface> + dhcprelay enable <nameif>

14. Application Mapping (L7 → Canonical)

ASA/FTD is a port-based platform — it does not have native L7 application awareness in ACLs. However, when converting FROM ASA to an app-aware platform (PAN-OS, FortiGate), or comparing configs, the parser should attempt to resolve well-known port/protocol combinations to canonical application names.

Resolution from port-based services: For each service object or inline port match, check if the protocol+port maps to a known application:

ASA named port keywords: Map ASA port names to numbers before resolving — full table in references/parsing-patterns.md "Port Name Resolution". Caution: ASA literals predate IANA assignments (radius=1645, radius-acct=1646, kerberos=750) — do not "correct" them from prior knowledge; use the reference table.

On policy output: When a service match resolves to a known application, populate the policy's apps array with { vendor_name: "tcp/443", canonical: "https", confidence: 1.0, category: "web" }. The services array still keeps the port-based match. This enables downstream converters to use the app-aware rule on platforms that support it.

Unresolvable services: Complex port ranges, non-standard ports, or protocol groups that don't map to a single known application → keep as port-based services only, no apps entry.

15. Application Groups

ASA does not have application groups. However, when converting FROM an app-aware platform, object-group service entries that resolve entirely to known applications should be flagged as potential application_groups in the IR for downstream use.

16. Anonymous Objects

When inline addresses/services appear in ACLs or object groups without a named reference (e.g., host 10.0.1.10 directly in an ACL line), create anonymous objects with auto-generated names (e.g., anon-1-host, anon-2-net). This ensures every IR reference points to a named object.

17. Residual Config Capture

Capture unrecognized top-level commands verbatim. Categorize into: VPN/IPsec, AAA, QoS, PKI/Certificates, IPv6, Other. Store in residual_raw for manual review.

18. Transparent Mode

Detect: firewall transparent in config When in transparent mode:

• Interfaces are in bridge-groups instead of having IPs
• bridge-group <id> on interfaces
• BVI interfaces (interface BVI<id>) carry the management IP
• Zones derived from nameifs still work the same way

19. Implicit Rules

The ASA implicit deny is scoped per bound ACL, not global: each ACL applied via access-group ends with an implicit deny for that interface/direction only. Applying an ACL on one interface does NOT disable security-level defaults for other interface pairs.

After building all policies from ACLs + access-groups, append:

• Implicit: Default Deny — one per access-group binding — action: "deny", src_zones: [<bound nameif>] for in direction (dst_zones for out; all any for global), remaining fields any, _implicit: true
• When every traffic-passing interface has a bound ACL (or a global access-group exists), the per-binding denies may be collapsed into a single final any→any deny, _implicit: true
• For interfaces with NO ACL bound: do not fabricate a deny — security-level defaults still apply (higher-to-lower permitted, lower-to-higher denied). Add a metadata.warnings entry ("no ACL bound on — security-level high-to-low permit applies") and, if downstream consumers need explicit rules, model the default permit as an _implicit: true allow policy from that zone to lower-security zones

Implicit-rule name values (e.g. "default-deny", "Implicit: Default Deny") are free-form labels; consumers must match implicit rules on _implicit: true, never on the name.

Output Format

Present results in the intermediate schema format documented in references/intermediate-schema.md.

Note: schema sections not yet populated by this pipeline (e.g., security_profile_objects, routing_contexts) are emitted empty ([]/{}); any unhandled source constructs are captured in residual_raw rather than dropped.

Full intermediate-schema emission is optional for single live-device work. The complete JSON schema exists primarily for cross-vendor conversion and multi-config diffing. When interpreting or auditing a single live device pulled via SSH/API for an ops/audit task, it is fine to reason directly from the running config and skip full schema emission — extract the sections relevant to the question. Emit the full schema when the parse will feed firewall-config-conversion, firewall-config-diff, or another config for comparison.

Parser Quality Gates

Before returning a parse, run these common quality gates and include the results in the response:

1. Format and scope detection — report detected vendor, platform family, config format, version clues, virtual context names (VDOM/vsys/logical-system/routing-instance), and whether input appears complete or partial.
2. Schema conformance — emit the vendor-neutral JSON sections defined in references/intermediate-schema.md; use empty arrays/objects for absent sections rather than omitting expected top-level keys.
3. Object counts — summarize counts for zones, interfaces, address objects/groups, service/application objects/groups, policies, NAT rules, routes, VPNs, HA, admin users, and residual blocks.
4. Reference resolution — list unresolved object, service/application, zone/interface, profile, route, VPN, and NAT references with source rule/context where possible.
5. Ordering preservation — preserve security policy order, NAT order, route order when relevant, and inherited/pre/post/global ordering metadata with _rule_index or a vendor-specific context field.
6. State preservation — preserve disabled/inactive objects and rules, comments/descriptions, tags, schedules/time-ranges, negation flags, logging settings, and profile attachments.
7. Residual capture — put unsupported or ambiguous source lines/blocks into residual_raw with enough context for manual review. Do not silently drop unknown syntax.
8. Warnings and assumptions — populate metadata.warnings with parser limitations, partial-input assumptions, ambiguous conversions, and version-specific caveats.
9. Conversion readiness — if the user asks for migration/conversion, explicitly separate parsed facts from proposed target-platform design choices and call out non-isomorphic features.

A high-quality parse is not just valid JSON: it must make uncertainty visible. Prefer a complete parse with warnings and residuals over a clean-looking parse that hides unsupported constructs.

Analysis Checks

After extraction, run these checks and report findings:

1. Unused objects — network/service objects not referenced in any ACL
2. Shadowed ACL entries — rules that can never match due to earlier entries
3. Overly permissive — permit ip any any or broad rules
4. Missing logging — permit ACL entries without log keyword
5. Inactive entries — ACL entries with inactive flag
6. Duplicate objects — same value, different names
7. Empty groups — object-groups with no members
8. Unbound ACLs — access-lists without matching access-group (never applied)
9. Subnet mask validation — flag any non-standard subnet masks

Reference Files

• references/config-format.md — Cisco ASA config syntax reference
• references/intermediate-schema.md — Output schema specification
• references/parsing-patterns.md — Edge cases, port name mapping, security-level logic
• references/example-sample-parse.md — Worked end-to-end example (input config → parsed JSON)
• references/fixture-minimal-input.md — Minimal parser fixture input
• references/fixture-expected-output.json — Expected high-level intermediate-schema output for the minimal fixture

Secret Handling

Never emit secrets raw. Tunnel-group pre-shared keys, username ... password hashes, BGP neighbor passwords, and SNMP community strings must be masked as "****" (or represented as a presence flag) with a metadata.warnings entry noting the secret was redacted — matching the shared-schema convention ("psk": "****").

Common Pitfalls

1. Do not treat IOS wildcard masks as ASA subnet masks; ASA object subnets use standard dotted masks.
2. Do not infer policy direction from ACL names alone; bind ACLs to interfaces with access-group.
3. Object NAT and manual/twice NAT order matters. Preserve NAT section/order metadata and flag ambiguous translations.
4. Security levels are not zones by themselves, but they help infer trust roles when no explicit design notes exist.
5. FTD/FMC-managed output may omit policy context available in FMC; preserve gaps as warnings instead of fabricating rules.

Verification Checklist

• Input vendor/platform and config format were detected correctly
• All major object counts are reported: zones, interfaces, addresses, services/applications, policies, NAT, routes, VPN, HA, and system settings
• Output conforms to references/intermediate-schema.md
• Disabled/inactive rules and objects are preserved with explicit state
• Unresolved references, unsupported blocks, and parser assumptions are listed in metadata.warnings and/or residual_raw
• Rule order and NAT order are preserved with _rule_index or equivalent ordering metadata
• Cross-vendor conversion caveats are called out before suggesting target-platform config
• No raw secrets in output — PSKs masked as "****", routing-protocol passwords/keys reduced to presence flags with warnings