The config can contain these tags and attributes. Some of them are mandatory, others optional.
The mandatory helper start and end tag defines the helper. This tag can only be used once in a helper configuration file. There is one mandatory and two optionsl attributes for helpers:
The mandatory module of the helper. This is one of the netfilter conntrack helper modules. The name starts with
nf_conntrack_ and has one or several module aliases that start with
nfct-helper-. The nf conntrack helpers are located in the
/lib/modules/$(uname -r)/kernel/net/netfilter/ directory.
The optional family of the helper. This can be one of these ipv types:
ipv6. If the family is not specified, then the helper is usable for IPv4 and IPv6.
The optional version of the helper.
Is an optional start and end tag and is used to give a helper a more readable name.
Is an optional start and end tag to have a description for a helper.
Is an empty-element tag and can be used several times to have more than one port entry. All attributes of a port entry are mandatory:
The port string can be a single port number or a port range portid-portid or also empty to match a protocol only.
The protocol value can either be tcp or udp.