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NAT helpers

As default the image does not contain many NAT helpers. To install extra helpers like SIP ALG use:

opkg update
opkg install kmod-nf-nathelper-extra

Modules listed inside inside /etc/modules.d/nf-nathelper-extra are automatically loaded.

The kmod-nf-nathelper-extra provides the following helpers: opkg files kmod-nf-nathelper-extra | grep -e '\.ko$' | cut -d'/' -f 5 | cut -d'.' -f1

nf_conntrack_pptp
nf_conntrack_broadcast
nf_conntrack_amanda
nf_nat_h323
nf_conntrack_tftp
nf_conntrack_sip
nf_nat_pptp
nf_conntrack_snmp
nf_nat_amanda
nf_nat_tftp
nf_conntrack_irc
nf_nat_sip
nf_nat_snmp_basic
nf_conntrack_h323
nf_nat_irc

SIP helper (SIP ALG)

To enable only SIP helper with default configuration and load it at boot, use:

echo nf_nat_sip > /etc/modules.d/nf-nat-sip
reboot

The nf_nat_sip module will automatically load the nf_conntrack_sip module.

Check if SIP helper is loaded:

lsmod | grep ^nf_nat_sip

List SIP helper module parameters, please note that parameters are under the nf_conntrack_sip module:

ls /sys/module/nf_conntrack_sip/parameters

From kernel source, these are the parameters of nf_conntrack_sip module:

  • ports: port numbers of SIP servers
  • sip_timeout: timeout for the master SIP session
  • sip_direct_signalling: expect incoming calls from registrar only (default 1)
  • sip_direct_media: expect Media streams between signalling endpoints only (default 1)
  • sip_external_media: expect Media streams between external endpoints (default 0)

Enable SIP helper with non-default parameters:

echo nf_conntrack_sip sip_external_media=1 sip_direct_media=1 > /etc/modules.d/nf-nat-sip
echo nf_nat_sip >> /etc/modules.d/nf-nat-sip
reboot