Correct syntax for dnat in inet table?

Correct syntax for dnat in inet table?

[Frank-Ulrich Sommer]

Hello,

I'm using "nftables v0.9.0 (Fearless Fosdick)" on a Debian Buster based Raspberry Pi OS.

I'm getting syntax errors when trying to redirect a port to another host via nftables.conf with the two lines starting with "iif eth0.100". The file does not contain a complete setup because I removed all rules not related to the problem.

The first line produces "nftables.conf:10:41-42: Error: syntax error, unexpected to, expecting newline or semicolon". According to the manpage I would have expected the correct syntax for an inet table to be "...dnat ip to..."

The second line without "to" produces "nftables.conf:11:56-56: Error: syntax error, unexpected newline".

What would be the correct syntax if I want e.g. to forward traffic to port 1234 to IPv4 123.123.123.123 in an inet table?

Here is the reduced nftables.conf causing these errors:

#!/usr/sbin/nft -f

flush ruleset

table inet myfilter {

  chain port_forwarding {
    type nat hook prerouting priority 0; policy accept;

    iif eth0.100 tcp dport 1234 dnat ip to 123.123.123.123
    iif eth0.100 tcp dport 2345 dnat ip 123.123.123.123
  }
}

Kind regards
Frank



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Re: Correct syntax for dnat in inet table?

[kfm]

On 05/08/2020 17:04, Frank-Ulrich Sommer wrote:
> 
> 
> Hello,
> 
> I'm using "nftables v0.9.0 (Fearless Fosdick)" on a Debian Buster based Raspberry Pi OS.
> 
> I'm getting syntax errors when trying to redirect a port to another host via nftables.conf with the two lines starting with "iif eth0.100". The file does not contain a complete setup because I removed all rules not related to the problem.
> 
> The first line produces "nftables.conf:10:41-42: Error: syntax error, unexpected to, expecting newline or semicolon". According to the manpage I would have expected the correct syntax for an inet table to be "...dnat ip to..."
> 
> The second line without "to" produces "nftables.conf:11:56-56: Error: syntax error, unexpected newline".

Both error messages are of poor quality.

> 
> What would be the correct syntax if I want e.g. to forward traffic to port 1234 to IPv4 123.123.123.123 in an inet table?
> 
> Here is the reduced nftables.conf causing these errors:
> 
> #!/usr/sbin/nft -f
> 
> flush ruleset
> 
> table inet myfilter {
> 
>    chain port_forwarding {
>      type nat hook prerouting priority 0; policy accept;
> 
>      iif eth0.100 tcp dport 1234 dnat ip to 123.123.123.123

"eth0.100" isn't a valid iface_index. Use iifname instead.

-- 
Kerin Millar

Re: Correct syntax for dnat in inet table?

[Florian Westphal]

Frank-Ulrich Sommer <orofuhin@gmail.com> wrote:
> I'm using "nftables v0.9.0 (Fearless Fosdick)" on a Debian Buster based Raspberry Pi OS.
> 
> I'm getting syntax errors when trying to redirect a port to another host via nftables.conf with the two lines starting with "iif eth0.100". The file does not contain a complete setup because I removed all rules not related to the problem.
> 
> The first line produces "nftables.conf:10:41-42: Error: syntax error, unexpected to, expecting newline or semicolon". According to the manpage I would have expected the correct syntax for an inet table to be "...dnat ip to..."
> 
> The second line without "to" produces "nftables.conf:11:56-56: Error: syntax error, unexpected newline".
> 
> What would be the correct syntax if I want e.g. to forward traffic to port 1234 to IPv4 123.123.123.123 in an inet table?
> 
> Here is the reduced nftables.conf causing these errors:
> 
> #!/usr/sbin/nft -f
> 
> flush ruleset
> 
> table inet myfilter {
> 
>   chain port_forwarding {
>     type nat hook prerouting priority 0; policy accept;
> 
>     iif eth0.100 tcp dport 1234 dnat ip to 123.123.123.123
>     iif eth0.100 tcp dport 2345 dnat ip 123.123.123.123
>   }
> }
nft list ruleset
table inet myfilter {
        chain port_forwarding {
                type nat hook prerouting priority filter; policy accept;
                iif "lo" tcp dport 1234 dnat ip to 123.123.123.123
        }
}
nft --version
nftables v0.9.5 (Capital Idea)

(I had to use different interface name because iif requires the name to exist
when parsing).