I'd tried posting at dev.openwrt.org but got this super user-friendly response:

I hope someone with trusted account could post this in the openwrt's bug track.

System: CHAOS CALMER (15.05.1, r48532)
Router: Asus RT-N56U

What happens:
It seems that '--dport' option is not recognized for sctp by iptables. Command execution fails.

Expected result:
Command runs successfully and we can create rules with iptables to match by sctp and destination port.

Steps to reproduce:
First install these:
kmod-sctp
libsctp
sctp
sctp-tools

Try to run this:

iptables -A INPUT -p sctp --dport 1234 -j ACCEPT

Shows error:

iptables v1.4.21: unknown option "--dport"
Try `iptables -h' or 'iptables --help' for more information.

Try to run this:

iptables -A INPUT -p sctp -j ACCEPT

Works!

Try to reproduce the issue with a slightly newer source code base, like the LEDE 17.01. If the problem persist, report it to https://bugs.lede-project.org/, unless it has already been reported.

(Last edited by Antek on 9 Feb 2018, 16:11)

I quickly installed lede 17.01.1 r3316-7eb58cf109 in VirtualBox (according to the guide on wiki.openwrt.org/doc/howto/virtualbox). Commands behave the same way - this bug is present.

Any tips how to create issue on bugs.lede-project.org? I don't see any instruction or "create issue" button...

You can also use https://bugs.openwrt.org/ that is the new address for the same tracker https://bugs.lede-project.org/

click the "Login!" button in the upper right corner...

(anonymous bug reports are not accepted, you need to register first)

Reported:
bugs.openwrt.org/index.php?do=details&task_id=1339