Issues configuring nftables

Installing and Using OpenWrt Network and Wireless Configuration
1

Installed OpenWRT for the first time today on Redmi AX6S (whatever today's snapshot was). It has nftables instead of iptables that I'm used to. And I'm having some issues with nftables.

I have an OpenVPN connection at 10.8.0.100/24 and LAN at 192.168.101.1/24. I want to be able to route between those networks. Here's how my UCI firewall config looks.

root@OpenWrt:~# cat /etc/config/firewall

config defaults
        option input 'ACCEPT'
        option output 'ACCEPT'
        option synflood_protect '1'
        option forward 'REJECT'

config zone
        option name 'lan'
        list network 'lan'
        option input 'ACCEPT'
        option output 'ACCEPT'
        option forward 'ACCEPT'
        option log '1'
        option log_limit '1000'

config zone
        option name 'VPN'
        option input 'ACCEPT'
        option output 'ACCEPT'
        option forward 'ACCEPT'
        list network 'VPN'
        option log '1'
        option log_limit '1000'

config zone
        option name 'wan'
        list network 'wan'
        list network 'wan6'
        option input 'REJECT'
        option output 'ACCEPT'
        option forward 'REJECT'
        option mtu_fix '1'
        option masq '1'

config rule
        option name 'Allow-DHCP-Renew'
        option src 'wan'
        option proto 'udp'
        option dest_port '68'
        option target 'ACCEPT'
        option family 'ipv4'

config rule
        option name 'Allow-Ping'
        option src 'wan'
        option proto 'icmp'
        option icmp_type 'echo-request'
        option family 'ipv4'
        option target 'ACCEPT'

config rule
        option name 'Allow-IGMP'
        option src 'wan'
        option proto 'igmp'
        option family 'ipv4'
        option target 'ACCEPT'

config rule
        option name 'Allow-DHCPv6'
        option src 'wan'
        option proto 'udp'
        option src_ip 'fc00::/6'
        option dest_ip 'fc00::/6'
        option dest_port '546'
        option family 'ipv6'
        option target 'ACCEPT'

config rule
        option name 'Allow-MLD'
        option src 'wan'
        option proto 'icmp'
        option src_ip 'fe80::/10'
        list icmp_type '130/0'
        list icmp_type '131/0'
        list icmp_type '132/0'
        list icmp_type '143/0'
        option family 'ipv6'
        option target 'ACCEPT'

config rule
        option name 'Allow-ICMPv6-Input'
        option src 'wan'
        option proto 'icmp'
        list icmp_type 'echo-request'
        list icmp_type 'echo-reply'
        list icmp_type 'destination-unreachable'
        list icmp_type 'packet-too-big'
        list icmp_type 'time-exceeded'
        list icmp_type 'bad-header'
        list icmp_type 'unknown-header-type'
        list icmp_type 'router-solicitation'
        list icmp_type 'neighbour-solicitation'
        list icmp_type 'router-advertisement'
        list icmp_type 'neighbour-advertisement'
        option limit '1000/sec'
        option family 'ipv6'
        option target 'ACCEPT'

config rule
        option name 'Allow-ICMPv6-Forward'
        option src 'wan'
        option dest '*'
        option proto 'icmp'
        list icmp_type 'echo-request'
        list icmp_type 'echo-reply'
        list icmp_type 'destination-unreachable'
        list icmp_type 'packet-too-big'
        list icmp_type 'time-exceeded'
        list icmp_type 'bad-header'
        list icmp_type 'unknown-header-type'
        option limit '1000/sec'
        option family 'ipv6'
        option target 'ACCEPT'

config forwarding
        option src 'lan'
        option dest 'wan'

config forwarding
        option src 'VPN'
        option dest 'lan'

config forwarding
        option src 'lan'
        option dest 'VPN'

I thought that having the last two config forwarding blocks would be enough to allow forwarding between VPN and lan. However, this is not the case. Here is the output of nft list ruleset.

root@OpenWrt:~# nft list ruleset
table inet fw4 {
        chain input {
                type filter hook input priority filter; policy accept;
                iifname "lo" accept comment "!fw4: Accept traffic from loopback"
                ct state established,related accept comment "!fw4: Allow inbound established and related flows"
                tcp flags syn / fin,syn,rst,ack jump syn_flood comment "!fw4: Rate limit TCP syn packets"
                iifname "br-lan" jump input_lan comment "!fw4: Handle lan IPv4/IPv6 input traffic"
                iifname "wan" jump input_wan comment "!fw4: Handle wan IPv4/IPv6 input traffic"
        }

        chain forward {
                type filter hook forward priority filter; policy drop;
                ct state established,related accept comment "!fw4: Allow forwarded established and related flows"
                iifname "br-lan" jump forward_lan comment "!fw4: Handle lan IPv4/IPv6 forward traffic"
                iifname "wan" jump forward_wan comment "!fw4: Handle wan IPv4/IPv6 forward traffic"
                jump handle_reject
        }

        chain output {
                type filter hook output priority filter; policy accept;
                oifname "lo" accept comment "!fw4: Accept traffic towards loopback"
                ct state established,related accept comment "!fw4: Allow outbound established and related flows"
                oifname "br-lan" jump output_lan comment "!fw4: Handle lan IPv4/IPv6 output traffic"
                oifname "wan" jump output_wan comment "!fw4: Handle wan IPv4/IPv6 output traffic"
        }

        chain handle_reject {
                meta l4proto tcp reject with tcp reset comment "!fw4: Reject TCP traffic"
                reject comment "!fw4: Reject any other traffic"
        }

        chain syn_flood {
                limit rate 25/second burst 50 packets return comment "!fw4: Accept SYN packets below rate-limit"
                drop comment "!fw4: Drop excess packets"
        }

        chain input_lan {
                ct status dnat accept comment "!fw4: Accept port redirections"
                jump accept_from_lan
        }

        chain output_lan {
                jump accept_to_lan
        }

        chain forward_lan {
                jump accept_to_wan comment "!fw4: Accept lan to wan forwarding"
                jump accept_to_VPN comment "!fw4: Accept lan to VPN forwarding"
                ct status dnat accept comment "!fw4: Accept port forwards"
                jump accept_to_lan
        }

        chain accept_from_lan {
                iifname "br-lan" counter packets 19793 bytes 3591155 accept comment "!fw4: accept lan IPv4/IPv6 traffic"
        }

        chain accept_to_lan {
                oifname "br-lan" counter packets 0 bytes 0 accept comment "!fw4: accept lan IPv4/IPv6 traffic"
        }

        chain input_VPN {
                jump accept_from_VPN
        }

        chain output_VPN {
                jump accept_to_VPN
        }

        chain forward_VPN {
                jump accept_to_lan comment "!fw4: Accept VPN to lan forwarding"
                jump accept_to_VPN
        }

        chain accept_from_VPN {
        }

        chain accept_to_VPN {
        }

        chain input_wan {
                meta nfproto ipv4 udp dport 68 counter packets 12227 bytes 3741292 accept comment "!fw4: Allow-DHCP-Renew"
                icmp type echo-request counter packets 134 bytes 9380 accept comment "!fw4: Allow-Ping"
                meta nfproto ipv4 meta l4proto igmp counter packets 0 bytes 0 accept comment "!fw4: Allow-IGMP"
                ip6 saddr fc00::/6 ip6 daddr fc00::/6 udp dport 546 counter packets 0 bytes 0 accept comment "!fw4: Allow-DHCPv6"
                ip6 saddr fe80::/10 icmpv6 type . icmpv6 code { mld-listener-query . no-route, mld-listener-report . no-route, mld-listener-done . no-route, mld2-listener-report . no-route } counter packets 0 bytes 0 accept comment "!fw4: Allow-MLD"
                icmpv6 type { destination-unreachable, time-exceeded, echo-request, echo-reply, nd-router-solicit, nd-router-advert } limit rate 1000/second counter packets 0 bytes 0 accept comment "!fw4: Allow-ICMPv6-Input"
                icmpv6 type . icmpv6 code { packet-too-big . no-route, parameter-problem . no-route, nd-neighbor-solicit . no-route, nd-neighbor-advert . no-route, parameter-problem . admin-prohibited } limit rate 1000/second counter packets 0 bytes 0 accept comment "!fw4: Allow-ICMPv6-Input"
                ct status dnat accept comment "!fw4: Accept port redirections"
                jump reject_from_wan
        }

        chain output_wan {
                jump accept_to_wan
        }

        chain forward_wan {
                icmpv6 type { destination-unreachable, time-exceeded, echo-request, echo-reply } limit rate 1000/second counter packets 0 bytes 0 accept comment "!fw4: Allow-ICMPv6-Forward"
                icmpv6 type . icmpv6 code { packet-too-big . no-route, parameter-problem . no-route, parameter-problem . admin-prohibited } limit rate 1000/second counter packets 0 bytes 0 accept comment "!fw4: Allow-ICMPv6-Forward"
                ct status dnat accept comment "!fw4: Accept port forwards"
                jump reject_to_wan
        }

        chain accept_to_wan {
                oifname "wan" counter packets 35030 bytes 2991778 accept comment "!fw4: accept wan IPv4/IPv6 traffic"
        }

        chain reject_from_wan {
                iifname "wan" counter packets 25904 bytes 1777242 jump handle_reject comment "!fw4: reject wan IPv4/IPv6 traffic"
        }

        chain reject_to_wan {
                oifname "wan" counter packets 0 bytes 0 jump handle_reject comment "!fw4: reject wan IPv4/IPv6 traffic"
        }

        chain dstnat {
                type nat hook prerouting priority dstnat; policy accept;
                iifname "br-lan" jump dstnat_lan comment "!fw4: Handle lan IPv4/IPv6 dstnat traffic"
                iifname "wan" jump dstnat_wan comment "!fw4: Handle wan IPv4/IPv6 dstnat traffic"
        }

        chain srcnat {
                type nat hook postrouting priority srcnat; policy accept;
                oifname "br-lan" jump srcnat_lan comment "!fw4: Handle lan IPv4/IPv6 srcnat traffic"
                oifname "wan" jump srcnat_wan comment "!fw4: Handle wan IPv4/IPv6 srcnat traffic"
        }

        chain srcnat_wan {
                meta nfproto ipv4 masquerade comment "!fw4: Masquerade IPv4 wan traffic"
        }

        chain raw_prerouting {
                type filter hook prerouting priority raw; policy accept;
                iifname "br-lan" jump helper_lan comment "!fw4: lan IPv4/IPv6 CT helper assignment"
        }

        chain raw_output {
                type filter hook output priority raw; policy accept;
        }

        chain helper_lan {
        }

        chain helper_VPN {
        }

        chain mangle_prerouting {
                type filter hook prerouting priority mangle; policy accept;
        }

        chain mangle_postrouting {
                type filter hook postrouting priority mangle; policy accept;
        }

        chain mangle_input {
                type filter hook input priority mangle; policy accept;
        }

        chain mangle_output {
                type filter hook output priority mangle; policy accept;
        }

        chain mangle_forward {
                type filter hook forward priority mangle; policy accept;
                iifname "wan" tcp flags syn tcp option maxseg size set rt mtu comment "!fw4: Zone wan IPv4/IPv6 ingress MTU fixing"
                oifname "wan" tcp flags syn tcp option maxseg size set rt mtu comment "!fw4: Zone wan IPv4/IPv6 egress MTU fixing"
        }

        chain dstnat_lan {
             
        }

        chain srcnat_lan {
               
        }

        chain dstnat_wan {
        }
}

In the chain forward i can see jumps to two rulesets: forward_lan and forward_wan (where is forward_VPN?). First ruleset references accept_to_VPN, whch, for some reason, is empty. And I can't figure out why.

When I ping 10.8.0.1 from a device on LAN, I get ICMP response Destination port unreachable from the router, which, looking at handle_reject ruleset checks out. Changing forward default policy to accept fixes everything, so I imagine the issue is in the firewall.

PS. Another question. Is there a way to log/trace firewall decisions for easier troubleshooting? Preferrably with filters and ability to log stuff after/before specific rule.

2

Try changing this to:

list device 'tun+'
3

Hi Or tun0

4

For reference, VPN is an interface created from tun0

config interface 'VPN'
        option proto 'dhcp'
        option device 'tun0'

config device
        option name 'tun0'
        option macaddr 'e4:2c:e1:30:6e:6c'
        option ipv6 '0'

Chose tun0 in devices (list device 'tun0' instead of list network 'VPN'). Rules appeared and things started working. So, the question is, is uci config generator bugged?

5

No i has always use tun0

Then you will configurate your firewall zone for make a transfert

6

What are the interfaces then, exactly? Why does choosing interface not work, but choosing device works? Is this just a bug, or am I fundamentally misunderstanding something. I thought of them just as aliases of sorts, for configuration purposes.

PS. Don't know if that's relevant, but I can't see IP address for VPN interface. It is there in output of ip a s tun0

7

That shouldn't be the case and both configurations should work equally well. If you run fw4 reload on the cli, you should see it printing warnings if it is unable to resolve the VPN interface to a device.

8

It prints nothing (just one disabled rule I have). Could it be because it's an L3 tunnel that is fully managed by OpenVPN? Because, as I mentioned in previous comment, it doesn't show an IP address in Interfaces tab in LuCI. The "hardware" device didn't even have a MAC address assigned to it by default. I added one manually and it (in hindsight expectedly) changed absolutely nothing.
image

In the end it works, I just don't really understand what uci interfaces are supposed to be and how do they work. My current understanding is that default hardware interfaces are dumb and are managed by whatever is configued by /etc/config/network (is it just uci?). OpenVPN's tun0 is not a dumb interface and is fully controlled by OpenVPN. Meaning that uci can't do anything with it and setting up an interface assigned to tun0 device does nothing.

EDIT. Ok, I think that is the case. Remembered that there is an "Unmanaged" option when you create an interface. Switched VPN from "DHCP client" to that and now it works as expected.

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10

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