Firewall → Settings → Advanced → Disable reply-to on WAN rules → check → Save → Apply.

Symptom: a port-forward or WAN rule answers from any internet IP, but from a host that lives in the same subnet as the firewall’s WAN everything times out (SSH, HTTPS, even ping), even though the rule says from any.

With a single WAN this is safe: the firewall stops forcing replies through the gateway and goes back to its routing table.

The setup

1
2
3
4
5
6
7
8

                203.0.113.0/24  (same L2 segment)
   ┌────────────────────┬────────────────────┬────────────────────┐
   │                    │                    │                    │
 gateway             fw01 (OPNsense)      neighbor             internet
 203.0.113.1         WAN 203.0.113.40     203.0.113.50         (via gateway)
                        │ rdr :22 → 192.168.1.10
                        ▼
                     LAN server

• From the internet: ssh -p 22 203.0.113.40 reaches the LAN server. Fine.
• From neighbor (203.0.113.50): every port times out.

What reply-to does

OPNsense generates the rules on WAN-type interfaces (those with a gateway) with reply-to pointing at that gateway:

1

pfctl -sr | grep reply-to

1

pass in quick on vtnet0 reply-to (vtnet0 203.0.113.1) inet proto tcp from any to 192.168.1.10 port = ssh flags S/SA keep state

reply-to is a pf option. When a packet comes in and creates a state, pf records in that state that every reply must leave through vtnet0 toward 203.0.113.1. Those replies skip the routing table: pf picks the next hop on its own.

It exists for multi-WAN. If you have two providers and a client comes in on WAN2, the reply must leave through WAN2. If it leaves through the default route (WAN1), it carries a source IP that provider 1 does not recognize and gets lost. reply-to guarantees a symmetric return path without thinking about routes.

Why it breaks neighbors

For an internet client, “reply to the gateway” is exactly what the routing table would do anyway, so nothing looks wrong.

For the neighbor it is different. Its IP (203.0.113.50) is on a connected network of the firewall. Without reply-to, the firewall would ARP for its MAC and answer directly. With reply-to, the SYN-ACK leaves with the gateway’s MAC as destination:

1
2

# on the OPNsense box (csh shell: wrap in sh -c)
sh -c "tcpdump -lnei vtnet0 host 203.0.113.50 and tcp port 22"

1
2

<neighbor-mac> > <fw01-mac>          203.0.113.50.49612 > 203.0.113.40.22: Flags [S]    ← arrives directly
<fw01-mac>     > 00:00:5e:00:01:<vrid> 203.0.113.40.22 > 203.0.113.50.49612: Flags [S.]   ← leaves to the gateway

(00:00:5e:00:01:xx is the VRRP virtual MAC: the gateway was a redundant pair.)

From there it depends on the gateway. To it, the packet arrives on the same interface it would have to leave through, and if it runs a stateful filter it sees a SYN-ACK for a connection whose SYN it never saw. In the lab, the gateway simply did not send it back onto the segment. On the neighbor you only see retried SYNs and no [S.].

The fingerprint on the firewall is a half-open state:

1

pfctl -ss | grep 203.0.113.50

1

all tcp 192.168.1.10:22 (203.0.113.40:22) <- 203.0.113.50:57792   SYN_SENT:ESTABLISHED

The server already answered (ESTABLISHED) and the client is still waiting (SYN_SENT): the reply is lost on the way back, not on the way in. The filter is not blocking anything.

What the fix changes

With Disable reply-to on WAN rules checked, OPNsense regenerates the rules without reply-to:

1

pass in quick on vtnet0 inet proto tcp from any to 192.168.1.10 port = ssh flags S/SA keep state

The state no longer pins the next hop, so replies go through the normal routing table:

The last row is the cost. With multi-WAN, do not disable it globally. Instead, drop reply-to only on the affected port-forward’s rule: in the rule, Advanced → reply-to. Check which options your version offers.

Verify

1
2
3

# on the OPNsense box
sh -c "pfctl -sr | grep -c reply-to; grep -n disablereplyto /conf/config.xml"
# expected: 0  and  <disablereplyto>yes</disablereplyto>

1
2

# from the neighbor
nc -z -w5 203.0.113.40 22 && echo open

Traps

• “Disable force gateway” is not this. It sits on the same page with a similar name, but it only affects traffic originated by the firewall itself (DNS, NTP, updates). It does not touch replies to inbound traffic.
• A static route on the gateway does not help. The gateway already has the subnet as connected; the problem is that it will not send the packet back onto the same segment, not that it does not know the way.
• csh shell. Over SSH, OPNsense drops you into csh, and things like 2>/dev/null fail with Ambiguous output redirect. Use sh -c "..." or ssh root@fw01 sh <<'EOF'.
• Test every port, not one. If only one port fails it is a different problem (rule, NAT, service). If they all fail, ping included, and only from the same subnet, suspect reply-to.

See also

• OPNsense docs, firewall settings: https://docs.opnsense.org/manual/firewall_settings.html
• pf.conf(5), route-to / reply-to options: https://man.freebsd.org/cgi/man.cgi?query=pf.conf

1
2
3
4
5
6
7
8
9

pfctl -sT                                    # loaded tables
pfctl -t <table> -T show                     # contents
pfctl -t <table> -T add 192.168.1.10         # add an IP or network (10.20.0.0/16 works too)
pfctl -t <table> -T delete 192.168.1.10
pfctl -t <table> -T test 192.168.1.10        # is it inside? (match / no match)
pfctl -t <table> -T flush                    # empty the table
pfctl -t <table> -T replace -f /path/list    # replace the whole contents from a file

pfctl -t sshguard -T flush                   # pfSense: clear the failed-login lockout

What a table is

A PF table is a set of addresses and networks that rules reference as <name>. It changes live, without reloading the ruleset, and holds thousands of entries with fast lookups; that is why PF uses tables for block lists, bogons, and anything that changes more often than the rules.

In pf.conf:

1
2

table <blocklist> persist file "/etc/pf/blocklist.txt"
block in quick from <blocklist>

persist keeps the table even when no rule uses it at the moment; file loads it from a file (one IP or network per line).

Commands

All in the form pfctl -t <table> -T <command>:

And without -t:

1
2
3
4

pfctl -sT                    # names of all tables
pfctl -vvsT                  # global info per table: entries, evaluations, references
pfctl -T load -f /etc/pf.conf   # reload only the table definitions from pf.conf
pfctl -sr | grep '<name>'    # which rules use a table

Tables on pfSense

• Aliases are tables. A Host, Network, or URL Table alias called Admins exists in PF as <Admins>; pfctl -t Admins -T show shows what pfSense resolved, including the FQDNs it already turned into IPs.
• sshguard: where IPs blocked for failed SSH or webGUI logins land. If you locked yourself out, pfctl -t sshguard -T flush (documented by Netgate under Locked out of the WebGUI).
• virusprot: hosts blocked for exceeding a rule’s Max. src. conn. rate or Max. states limits. pfctl -t virusprot -T show and -T delete <ip> to release one.
• snort2c: Snort/Suricata blocks in legacy mode. -T flush to unblock everything.
• bogons / bogonsv6: the lists that update themselves when you enable Block bogon networks on an interface.
• pfBlockerNG: every list is a pfB_* alias. To know whether an IP is blocked by one: pfctl -t pfB_Top_v4 -T test 203.0.113.7.

On OPNsense the mechanics are the same (pfctl -sT to see the names); the login lockout table is called sshlockout.

What gets lost on reload

Any -T add, -T delete, or -T flush lives until the next filter reload: saving almost anything in the GUI, Filter Reload under Status → Filter Reload, or the alias update cron. At that point pfSense regenerates every table from its alias and your manual changes are gone. To make something permanent, edit the alias; for quick tests and unblocking, pfctl is perfect.

Beyond tables

What gets used most alongside the above:

1
2
3
4
5
6
7

pfctl -sr                    # loaded rules (with -vv, counters and rule numbers)
pfctl -ss                    # state table
pfctl -si                    # global statistics
pfctl -k 192.168.1.10        # kill a host's states
pfctl -F states              # kill all states (cuts every connection)
pfctl -d / pfctl -e          # disable / enable PF (no PF means no NAT: only to get out of a lockout)
pfctl -nf /etc/pf.conf       # syntax check without loading

Full reference: the OpenBSD Handbook’s pfctl cheat sheet and man pfctl on FreeBSD.