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There is no supported one-command importer that converts an arbitrary iptables ruleset into UFW commands. A safe migration is an inventory-and-translation job: save the active IPv4 and IPv6 rules, classify host filtering separately from forwarding and NAT, recreate simple rules with UFW syntax, keep unsupported logic in UFW’s iptables-restore-compatible files, then test before enabling the firewall. Protect SSH before you activate UFW, because enabling it can flush existing chains and interrupt connections.
What conversion actually means
UFW (Uncomplicated Firewall) is a command-line frontend for common stateful host-firewall policies. It makes ordinary allow, deny, reject, rate-limit, logging, insertion, and deletion operations readable, but it is not a universal translator for every iptables table, match, target, or custom chain. The UFW manual describes the boundary directly: “ufw is not intended to provide complete firewall functionality via its command interface, but instead provides an easy way to add or remove simple rules.”
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Plan the migration as two layers:
- UFW commands for straightforward INPUT and OUTPUT policy on the Linux host.
- UFW rule files for NAT, gateway forwarding, custom chains, unusual matches, and table-specific behavior that the command interface cannot express.
iptables and nftables remain the better fit when the policy depends on granular conditions such as packet-size or time-of-day matching, deep custom chains, or multi-layer inspection. nftables entered the mainline Linux kernel in version 3.13, released in 2014; the commands shown here concern UFW’s iptables-compatible interface, so validate syntax against the firewall backend installed on your distribution.
Prepare the host before changing anything
1. Save IPv4, IPv6, and table-specific state
Keep immutable copies of the active rules so you can audit what must be recreated and recover if a migration fails. Run the following as root or with sudo:
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sudo iptables-save > ~/iptables.v4.rules
sudo ip6tables-save > ~/iptables.v6.rules
sudo iptables -S > ~/iptables.v4.filter.txt
sudo ip6tables -S > ~/iptables.v6.filter.txt
sudo iptables -t nat -S > ~/iptables.v4.nat.txt
sudo ip6tables -t nat -S > ~/iptables.v6.nat.txtThe *-save files preserve restore-compatible syntax; the -S listings are easier to read while you classify rules. If your system uses other tables, export those as well, for example with iptables -t mangle -S or iptables -t raw -S.
2. Identify how you reach the machine
Record the management interface, SSH port, source addresses used by administrators, and whether a console or out-of-band recovery path exists. If the server is managed over SSH, open a second session before making changes. A second session lets you correct a rule while the first connection remains available.
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3. Preview every planned UFW change
UFW can show the commands it would apply without changing the live firewall:
sudo ufw --dry-run allow 22/tcp
sudo ufw --dry-run allow proto tcp from 203.0.113.10 to any port 22Use a dry run for each non-trivial rule and inspect the resulting syntax before you enable UFW.
Inventory and classify the existing rules
Do not translate lines in their original order until you know which traffic path each line controls. Put every rule in one of these categories:
| iptables location or purpose | What it controls | Migration destination |
|---|---|---|
INPUT |
Connections terminating on this host | Usually a UFW host rule such as ufw allow, deny, or reject |
OUTPUT |
Connections initiated by this host | UFW outbound rules and an intentional outgoing default |
FORWARD |
Packets routed through the machine | ufw route allow|deny|reject, forwarding policy, and kernel forwarding settings |
nat |
Address translation, port forwarding, and masquerading | UFW rule files, normally before.rules or the corresponding IPv6 file |
raw, mangle, or other tables |
Packet marking, connection tracking exceptions, and specialized processing | Rule files or the existing iptables/nftables configuration |
| Custom chains and unusual matches | Reusable or highly specific decision logic | Rule files if compatible, otherwise retain direct firewall management |
Also record the default policies, interface names, address ranges, comments, counters, and any rule that depends on a prior custom chain. A superficially similar UFW rule can have a different result if its interface, direction, address family, or position changes.
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Translate ordinary iptables rules to UFW syntax
The following mappings cover common host-firewall patterns. Replace example addresses, ports, and interfaces with values from your inventory.
| iptables pattern | UFW command | Important detail |
|---|---|---|
iptables -A INPUT -p tcp --dport 22 -j ACCEPT |
sudo ufw allow 22/tcp |
Allows TCP connections to local port 22 from any source permitted by the other policy rules. |
| Allow SSH only from one address | sudo ufw allow proto tcp from 203.0.113.10 to any port 22 |
Use the administrator’s real public or management address; include a separate IPv6 rule when required. |
| Reject or deny a service | sudo ufw deny 23/tcpsudo ufw reject 23/tcp |
deny silently drops; reject returns a rejection to the sender. |
| Rate-limit SSH attempts | sudo ufw limit ssh/tcp |
UFW applies its built-in connection-rate limit to the SSH service. |
| Allow HTTP only through one interface | sudo ufw allow in on eth0 to any port 80 proto tcp |
The interface qualifier prevents the rule from applying to other interfaces. |
| Allow HTTPS with logging and a comment | sudo ufw allow log 443/tcp comment 'HTTPS' |
The comment makes later review easier; logging volume should be considered on busy services. |
| Outbound rule | sudo ufw allow out 53/udp |
Use out when the original rule belongs to OUTPUT rather than INPUT. |
UFW also accepts protocol, source, destination, and interface qualifiers together. For example:
sudo ufw allow in on eth0 proto tcp from 198.51.100.0/24 to any port 443If the application profile exists on the host, inspect it first:
sudo ufw app listThen you can use a named profile, such as sudo ufw allow OpenSSH, instead of a numeric port. Profiles differ by distribution and installed packages, so do not assume a profile exists merely because the daemon is installed.
Preserve rule order, insertion, and deletion behavior
iptables evaluates chains in order. UFW maintains its own numbered rule list, so an equivalent rule placed earlier or later can change the outcome when rules overlap. Review the planned order with:
sudo ufw status numberedInsert a rule at a specific position when a broad rule would otherwise match first:
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sudo ufw insert 1 allow 443/tcpDelete by number after checking the current list, or delete by repeating the rule specification:
sudo ufw delete 2
sudo ufw delete allow 443/tcpDo not use a saved line number after another deletion; run status numbered again because the remaining numbers shift.
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iptables rules often rely on a chain’s default policy. Set UFW defaults explicitly instead of assuming they match the old firewall:
sudo ufw default deny incoming
sudo ufw default allow outgoing
sudo ufw default deny routedChoose each value for the machine’s role. A workstation, public web server, and router have different requirements. If the old rules intentionally blocked outbound traffic or allowed routed traffic, reproduce that behavior rather than applying a generic hardening recipe.
Convert FORWARD rules with ufw route
A rule for traffic traversing the host is not an ordinary host-service rule. Use the route form:
sudo ufw route allow in on eth1 out on eth0 from 192.168.1.0/24 to any
sudo ufw route deny in on eth1 out on eth0 to 10.0.0.0/8These commands control forwarded packets between interfaces. They do not open a service listening on the firewall host itself.
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Enable kernel forwarding
UFW’s route rules cannot work if Linux forwarding is disabled. In /etc/default/ufw, set the forwarding policy required by your design, for example:
DEFAULT_FORWARD_POLICY="ACCEPT"In /etc/ufw/sysctl.conf, enable the relevant address family:
net/ipv4/ip_forward=1
net/ipv6/conf/all/forwarding=1Use the IPv6 setting only when the machine routes IPv6. Apply the settings using your distribution’s normal sysctl procedure, then verify that the values are enabled before testing routed traffic.
Separate host and routed tests
Test a local service from a client that should reach the firewall’s own address, and test a forwarded flow from a client on the inside interface to a destination beyond the outside interface. A successful SSH connection to the gateway does not prove that forwarding or NAT works.
Keep NAT and masquerading in UFW rule files
UFW’s command interface does not provide a complete NAT configuration language. Ubuntu documents /etc/ufw/*.rules as files loaded with iptables-restore; before.rules and after.rules are intended for legacy iptables rules, network gateways, and bridge-related logic.
For example, a gateway that masquerades an internal IPv4 network might merge a stanza like this into the existing NAT section of /etc/ufw/before.rules:
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:POSTROUTING ACCEPT [0:0]
-A POSTROUTING -s 192.168.1.0/24 -o eth0 -j MASQUERADE
COMMITThis is an illustration, not a drop-in policy: substitute the actual inside subnet and egress interface, preserve any existing *nat section, and do not create duplicate table headers or COMMIT lines. Add corresponding IPv6 logic only when the original design uses IPv6 translation and the installed backend supports it.
Keep custom chains, unusual matches, packet marks, bridge rules, and table-specific entries in the appropriate before or after file when their syntax is compatible. Validate the files for the installed iptables backend before reloading UFW. If a rule cannot be represented reliably in iptables-restore, retain direct iptables/nftables management for that part instead of silently weakening the policy.
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- Add management access first. For example, use a restricted SSH rule such as
sudo ufw allow proto tcp from 203.0.113.10 to any port 22, or the correct management subnet. Add IPv6 access separately if administrators connect over IPv6. - Review the complete list. Run
sudo ufw status numberedand check incoming, outgoing, and routed defaults. - Preview risky changes. Run
sudo ufw --dry-runwith each planned command, especially rules involving interfaces or routes. - Enable from a console or a live second session. UFW can flush chains when enabled and may drop existing connections. Keep the second SSH session or console open until new connections have been tested.
- Activate and verify. Run
sudo ufw enable, then inspectsudo ufw status verboseandsudo ufw status numbered. - Reload after file edits. When you change
before.rulesorafter.rules, reload UFW and check for syntax errors before declaring the migration complete.
If activation cuts off access, use the console or an existing session to run sudo ufw disable, restore the saved IPv4 and IPv6 rules with the appropriate iptables-restore commands, and correct the migration before trying again. Treat the saved files as recovery material, not as a substitute for testing.
Test both address families and every traffic path
A migration is complete only when the traffic that should work works and the traffic that should fail fails. Test from known clients rather than from the firewall host alone.
- Connect to each intentionally exposed TCP or UDP service from an allowed source.
- Attempt the same service from a source that should be blocked.
- Check SSH from the normal administration address and, if applicable, over IPv6.
- Test outbound services when OUTPUT policy is restricted.
- Test each forwarded path, including return traffic, between the correct interfaces.
- For a gateway, verify that the translated source address and external reachability match the old behavior.
- Inspect
sudo ufw status verboseandsudo ufw status numberedafter each correction so you know which rule changed.
When IPv6 is enabled, an IPv4-only migration is incomplete: IPv6 clients can otherwise follow a different policy. Export, translate, and test the IPv6 rules independently.
Know when not to convert a rule
Keep the original iptables or nftables design when any of these are central to the security policy:
- Several custom chains whose order and jumps are part of the logic.
- Matches for packet size, time of day, marks, connection state combinations, or other conditions without a direct UFW equivalent.
- Rules in
raw,mangle, or specialized tables. - Complex DNAT, SNAT, port-forwarding, bridge, or multi-interface gateway behavior.
- Inspection that spans multiple layers or depends on backend-specific nftables features.
UFW can coexist with file-based rules, but a split configuration needs clear ownership. Document which policy is managed by UFW commands, which lines live in before.rules or after.rules, and which service owns any remaining direct rules. Otherwise a later reload or package update can overwrite an assumption that was never recorded.
iptables, nftables, and UFW: choosing the right layer
| Decision axis | UFW | Direct iptables or nftables |
|---|---|---|
| Common host allow/deny rules | Readable commands, numbered review, simple insertion and deletion | More verbose and operationally manual |
| Custom chains and granular matches | Limited command interface; use rule files where compatible | Full control over chains, matches, tables, and targets |
| Forwarded traffic | Supported through ufw route plus forwarding policy and sysctl settings |
Direct control of FORWARD and related chains |
| NAT and gateway work | Normally requires before.rules/after.rules and careful restore syntax |
Native, explicit NAT configuration |
| Migration risk | Lower for ordinary host rules; unsupported behavior can be lost if translated blindly | Preserves the existing model but has a steeper operational burden |
| Best fit | Servers and workstations with straightforward stateful host policy | Routers, bridges, high-granularity policies, and systems requiring specialized inspection |
The practical choice is often mixed: express the host’s ordinary service policy in UFW, keep gateway and specialized rules in the rule files, and leave the entire configuration in direct iptables or nftables when the unsupported portion is the security-critical part.
Quick Recap
Migration checklist
- Saved active IPv4 and IPv6 rules, including NAT and non-filter tables.
- Recorded SSH access, interfaces, management sources, defaults, and recovery access.
- Separated INPUT, OUTPUT, FORWARD, NAT, raw, mangle, and custom-chain logic.
- Translated only rules that have a clear UFW equivalent.
- Added SSH access before enabling and previewed changes with
--dry-run. - Used
ufw routeand enabled kernel forwarding for routed traffic. - Placed NAT and unsupported rules in validated
before.rulesorafter.rulesfiles. - Checked numbered order, comments, logging, and both IPv4 and IPv6 behavior.
- Tested allowed, denied, outbound, forwarded, and translated traffic from known clients.
- Kept the original saves and a console-based rollback path until the new policy had operated successfully.
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