Router - ArchWiki

# Router

This article is a tutorial for turning a computer into an internet gateway/router. To strengthen its security it should not run any services available to the outside world. Towards the LAN, run only gateway specific services especially do not run httpd, ftpd, samba, nfsd, etc. as those belong on a server in the LAN since they introduce security risks.

This article does not attempt to show how to set up a shared connection between 2 PCs using cross-over cables. For a simple internet sharing solution, see Internet sharing.

## Hardware Requirements

- At least 1 GB of hard drive space. The base install will take up around 500MB of space and if you want to use a caching web proxy, you will need to reserve space for the cache as well.
- At least two physical network interfaces: a gateway connects two networks with each other (actually router can be made using single physical interface that underlay two VLAN interfaces and connected to VLAN-aware switch, so-called router-on-a-stick configuration, but it is not covered in this article). You will need to be able to connect those networks to the same physical computer. One interface must connect to the external network, while the other connects to the internal network.
- A hub, switch or UTP cable: You need a way to connect the other computers to the gateway

## Conventions

Conventions in this guide will be to use non-realistic interface names, to avoid confusion about which interface is which.

- intern0: the network card connected to the LAN. On an actual computer it will probably have the name enp2s0, enp1s1, etc.
- extern0: the network card connected to the external network (or WAN). It will probably have the name enp2s0, enp1s1, etc.

## Network interface configuration

### Persistent naming and Interface renaming

Systemd automatically chooses unique interface names for all your interfaces. These are persistent and will not change when you reboot. If you would like to rename interface to user friendlier names read Network configuration#Device names.

### IP configuration

Now you will need to configure the network interfaces. The best way to do so is using netctl profiles. You will need to create two profiles.

Note: If you will be connecting to the Internet only via PPPoE (you have one WAN port) you do not need to setup or enable the extern0-profile. See below for more information on configuring PPPoE.

- `/etc/netctl/extern0-profile`

    Description='Public Interface.'
    Interface=extern0
    Connection=ethernet
    IP='dhcp'

- `/etc/netctl/intern0-profile`

    Description='Private Interface'
    Interface=intern0
    Connection=ethernet
    IP='static'
    Address=('10.0.0.1/24')

Note: The example configuration above assumes a full subnet. If you are building the gateway for a small amount of people, you will want to change the CIDR suffix to accommodate a smaller range. For example /27 will give you 10.0.0.1 to 10.0.0.30. You can find many CIDR calculators online.

Next up is to set up the interfaces with netctl.

    # netctl enable extern0-profile
    # netctl enable intern0-profile

## ADSL connection/PPPoE

Using rp-pppoe, we can connect an ADSL modem to the `extern0` interface of the firewall and have Arch manage the connection. Make sure you put the modem in bridged mode though (either half-bridge or RFC1483), otherwise the modem will act as a router too. Install the rp-pppoe package.

It should be noted that if you use only PPPoE to connect to the internet (ie. you do not have other WAN port, except for the one that connects to your modem) you do not need to set up the `extern0-profile` as the external pseudo-interface will be ppp0.

### PPPoE configuration

You can use netctl to setup the pppoe connection. To get started

    # cp /etc/netctl/examples/pppoe /etc/netctl/

and start editing. For the interface configuration choose the interface that connects to the modem. If you only connect to the internet through PPPoE this will probably be `extern0`. Fill in the rest of the fields with your ISP information. See the pppoe section in netctl.profile man page for more information on the fields.

## DNS and DHCP

We will use dnsmasq, a DNS and DHCP daemon for the LAN. It was specifically designed for small sites. Install it with the dnsmasq package.

Dnsmasq needs to be configured to be a DHCP server with a configuration similar to the following:

    /etc/dnsmasq.conf

    interface=intern0 # make dnsmasq listen for requests only on intern0 (our LAN)
    expand-hosts      # add a domain to simple hostnames in /etc/hosts
    domain=foo.bar    # allow fully qualified domain names for DHCP hosts (needed when
                      # "expand-hosts" is used)
    dhcp-range=10.0.0.2,10.0.0.255,255.255.255.0,1h # defines a DHCP-range for the LAN:
                      # from 10.0.0.2 to .255 with a subnet mask of 255.255.255.0 and a
                      # DHCP lease of 1 hour (change to your own preferences)

Somewhere below, you will notice you can also add "static" DHCP leases, i.e. assign an IP-address to the MAC-address of a computer on the LAN. This way, whenever the computer requests a new lease, it will get the same IP. That is very useful for network servers with a DNS record. You can also deny certain MAC's from obtaining an IP.

Now start and enable `dnsmasq.service`.

## Connection sharing

Time to tie the two network interfaces to each other.

This can be done with Shorewall. See Shorewall for detailed configuration.

## IPv6 tips

This article or section is a candidate for merging with IPv6.

Notes: Merge into the main article, the topic is not specific to router configuration. The wording should be probably changed along the way. (Discuss in Talk:Router#)

Useful reading: IPv6 and the wikipedia:IPv6.

### Unique Local Addresses

You can use your router in IPv6 mode even if you do not have an IPv6 address from your ISP. Unless you disable IPv6 all interfaces should have been assigned a unique `fe80::/10` address.

For internal networking the block `fc00::/7` has been reserved. These addresses are guaranteed to be unique and non-routable from the open internet. Addresses that belong to the `fc00::/7` block are called Unique Local Addresses. To get started generate a ULA /64 block to use in your network. For this example we will use `fd00:aaaa:bbbb:cccc::/64`. Firstly we must assign a static IPv6 on the internal interface. Modify the `intern0-profile` we created above to include the following line

     IPCustom=('-6 addr add fd00:aaaa:bbbb:cccc::1/64 dev intern0')

This will add the ULA to the internal interface. As far as the router goes, this is all you need to configure.

### Global Unicast Addresses

If your ISP or WAN network can access the IPv6 Internet you can additionally assign global link addresses to your router and propagate them through SLAAC to your internal network. The global unicast prefix is usually either static or provided through prefix delegation.

#### Static IPv6 prefix

If your ISP has provided you with a static prefix then edit `/etc/netctl/extern0-profile` and simply add the IPv6 and the IPv6 prefix (usually /64) you have been provided

    IPCustom=('-6 addr add 2002:1:2:3:4:5:6:7/64 dev extern0')

You can use this in addition to the ULA address described above.

#### Acquiring IPv6 prefix via DHCPv6-PD

If your ISP handles IPv6 via prefix delegation then you can follow the instructions in the main IPv6 article on how to properly configure your router. Following the conventions of this article the WAN interface is `extern0` (or `ppp0` if you are connecting through PPPoE) and the LAN interface is `intern0`.

### Router Advertisement and Stateless Autoconfiguration (SLAAC)

To properly hand out IPv6s to the network clients we will need to use an advertising daemon. Follow the details of the main IPv6 article on how to setup `radvd`. Following the convention of this guide the LAN facing interfaces is `intern0`. You can either advertise all prefixes or choose which prefixes will be assigned to the local network.

## Optional additions

### UPnP

The above configuration of shorewall does not include UPnP support. Use of UPnP is discouraged as it may make the gateway vulnerable to attacks from within the LAN. However, some applications require this to function correctly.

To enable UPnP on your router, you need to install an UPnP Internet gateway daemon (IGD). To get it, install the miniupnpd package.

Read the Shorewall guide on UPnP for more information

### Remote administration

OpenSSH can be used to administer your router remotely. This is useful for running it "headless" (no monitor or input devices).

### Caching web proxy

See Squid or Polipo for the setup of a web proxy to speed up browsing and/or adding an extra layer of security.

### Time server

To use the router as a time server, see Network Time Protocol daemon.

Then, configure shorewall or iptables to allow NTP traffic in and out.

### Content filtering

Install and configure DansGuardian or Privoxy if you need a content filtering solution.

### Traffic shaping

Traffic shaping is very useful, especially when you are not the only one on the LAN. The idea is to assign a priority to different types of traffic. Interactive traffic (ssh, online gaming) probably needs the highest priority, while P2P traffic can do with the lowest. Then there is everything in between.

#### Traffic shaping with shorewall

See Shorewall#Traffic shaping

## See also

- Simple stateful firewall
- Internet sharing

Categories:

- Network sharing
- Security

Hidden category:

- Pages or sections flagged with Template:Merge