OpenWRT notes

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Atheros AR81-Based Products

Hardware Comparison

Vendor Product CPU Flash RAM USB OpenWRT info Comment
Linksys WRT160NL MIPS24Kc AR9132r2 400 MHz 8 MB 32 MB 1 Wiki, Forum
TP-Link WR-841N(D) v5 ? 4 MB 32 MB 0 USB on board but unpopulated, missing DC/DC converter
TP-Link WR-941N(D) v3 MIPS24Kc AR9132r2 400 MHz 4 MB 32 MB 0 USB on board but unpopulated, missing DC/DC converter

TP-Link devices

Updating firmware with mtd

mtd -r write openwrt.bin firmware

IPTables Configuration

This section is specific to OpenWRT in that the kamikaze standard chains are explained. There must be some document in one of the OpenWRT wikis, but I couldn't easily find it.

In addition, I need EBTables in the picture as well, so a few comments on where you'd add layer 2 rules will be included.

Call Graph

The OpenWRT standard rule set defines a few more or less default actions that you probably will want to keep: do not accept incoming connectins from the WAN interface (except for DHCP/bootp replies), NAT all outgoing traffic, and allow pretty much anything on the LAN interface. If you want to add your own rules to drop or allow additional things, there's a chain specifically for that. To understand which of these chains to add your rules to, look at this call graph. It is helpful to look at one of the EBTables tutorials, for example ebtables/iptables interaction. It contains a good overview of how packets traverse the various points.

mangle Table

OpenWRT does not add any chains to the mangle table.

filter Table

  • INPUT → input_rule
  • INPUT → input → zone_lan → input_lan
  • INPUT → input → zone_wan → input_wan
  • FORWARD → forwarding_rule
  • FORWARD → forward → zone_lan_forward → forwarding_lan
  • FORWARD → forward → zone_wan_forward → forwarding_wan
  • OUTPUT → output_rule

nat Table

  • PREROUTING → zone_wan_prerouting → prerouting_wan
  • PREROUTING → zone_lan_prerouting → prerouting_lan
  • PREROUTING → postrouting_rule
  • POSTROUTING → prerouting_rule
  • POSTROUTING → zone_wan_nat

Link List

Building and installing

Configuration

Hardware and software alternatives