Router:Linux - Debian: Difference between revisions

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You'll need to use an ADSL or FTTC modem in bridge mode for this to work - see the page for your modem to see how to set that up.

This guide provides an example configuration for Debian Jessie.

This guide provides an example configuration for Debian Jessie, but it should largely work for future versions. This has been tested with Jessie, Stretch and Buster.

= Prerequsites =

* a Linux PC with Debian ~~Jessie~~ already installed and two network interfaces - one for the connection to the modem, and one for the connection to your LAN

* a Linux PC with Debian already installed and two network interfaces - one for the connection to the modem, and one for the connection to your LAN

* a ADSL or FTTC modem, or a fibre ONT (for FTTP) (as appropriate for your connection)

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* '''eth0''' is plugged directly into your modem or ONT

* '''eth1''' will be used for your LAN

Note that under Buster, you can expect naming conventions for the interfaces to be different, you'll therefore have to pay close attention to updating the interface names as you follow the guide.

= Enabling IP forwarding =

To tell our Linux router to actually forward traffic, you must first enable IP forwarding in '''/etc/sysctl.conf'''.

Look for this section in '''/etc/sysctl.conf''':

# Uncomment the next line to enable packet forwarding for IPv4

#net.ipv4.ip_forward=1

# Uncomment the next line to enable packet forwarding for IPv6

# Enabling this option disables Stateless Address Autoconfiguration

# based on Router Advertisements for this host

#net.ipv6.conf.all.forwarding=1

Uncomment the two lines starting with "net":

# Uncomment the next line to enable packet forwarding for IPv4

net.ipv4.ip_forward=1

# Uncomment the next line to enable packet forwarding for IPv6

# Enabling this option disables Stateless Address Autoconfiguration

# based on Router Advertisements for this host

net.ipv6.conf.all.forwarding=1

Now run:

sysctl -p

This will reload '''/etc/sysctl.conf''' - applying our changes.

= Setting up pppd =

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apt-get update

apt-get install ~~pppd~~ pppoe iproute2

apt-get install ppp pppoe iproute2

pppd uses several different configuration files:

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* '''noauth''' - don't require A&A to send authentication details

* '''persist''' - automatically reconnect if the connection drops

* '''maxfail 0''' - sets ~~the~~ the number of consecutive failed connection attempts before pppd gives up. Setting this to 0 means that pppd will retry forever

* '''maxfail 0''' - sets the number of consecutive failed connection attempts before pppd gives up. Setting this to 0 means that pppd will retry forever

* '''mtu 1492''' - sets the max MTU for packets inside the PPP connection - 1492 is a "safe" value for PPPoE on most hardware. Some modems will be able to use "baby jumbo frames" (RFC 4638). See the "Using a full 1500 MTU" section for more details.

* '''noaccomp''' - disables address/control compression

* '''default-asyncmap''' - disables the ~~negotation~~ of an asyncmap - forces all control characters to be escaped

* '''default-asyncmap''' - disables the negotiation of an asyncmap - forces all control characters to be escaped

* '''+ipv6''' - enable IPv6 support

* '''ipv6cp-use-ipaddr''' - use your IPv4 address as the local identifier for IPv6CP

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example@a.1 * YourLinePasswordGoesHere

Replace "YourLinePasswordGoesHere" with the password for your A&A connection, and "example@a.1" with your PPP login details, both available from the [https://control.aa.net.uk Control Pages]. The login and password are per-line unique values, so you have to find the "Broadband Circuit Details" page for each line. The password is in an obscured box which becomes visible on mouse-hover.

Replace "YourLinePasswordGoesHere" with the password for your A&A connection.

== Making IPv6 work with pppd ==

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iface aaisp inet ppp

provider aaisp

pre-up /sbin/ip link set eth0 up

auto eth1

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iptables -t nat -F

iptables -t mangle -F

iptables -t filter -X

iptables -t nat -X

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iptables -A INPUT -p icmp -m comment --comment "Accept all ICMP" -j ACCEPT

iptables -A INPUT -i eth1 -m comment --comment "Accept all from the LAN" -j ACCEPT

iptables -A INPUT -i pppoe-aaisp -m state RELATED,ESTABLISHED -m comment --comment "Allow return traffic" -j ACCEPT

iptables -A INPUT -i pppoe-aaisp -m state --state RELATED,ESTABLISHED -m comment --comment "Allow return traffic" -j ACCEPT

iptables -A INPUT -m comment --comment "Reject all remaining traffic" -j REJECT

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iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -o pppoe-aaisp -m comment --comment "Clamp MSS for traffic going via PPP" -j TCPMSS --clamp-mss-to-pmtu

iptables -A FORWARD -i eth1 -o pppoe-aaisp -m comment --comment "Allow traffic from LAN -> internet" -j ACCEPT

iptables -A FORWARD -i pppoe-aaisp -o eth1 -m state RELATED,ESTABLISHED -m comment --comment "Allow return traffic from internet -> LAN" -j ACCEPT

iptables -A FORWARD -i pppoe-aaisp -o eth1 -m state --state RELATED,ESTABLISHED -m comment --comment "Allow return traffic from internet -> LAN" -j ACCEPT

iptables -A FORWARD -m comment --comment "Reject all remaining traffic" -j REJECT

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# This file describes the network interfaces available on your system

# and how to activate them. For more information, see interfaces(5).

# The loopback network interface

auto lo

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iface aaisp inet ppp

provider aaisp

pre-up /sbin/ip link set eth0 up

auto eth1

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iptables -A INPUT -p icmp -m comment --comment "Accept all ICMP" -j ACCEPT

iptables -A INPUT -i eth1 -m comment --comment "Accept all from the LAN" -j ACCEPT

iptables -A INPUT -i pppoe-aaisp -m state RELATED,ESTABLISHED -m comment --comment "Allow return traffic" -j ACCEPT

iptables -A INPUT -i pppoe-aaisp -m state --state RELATED,ESTABLISHED -m comment --comment "Allow return traffic" -j ACCEPT

iptables -A INPUT -m comment --comment "Reject all remaining traffic" -j REJECT

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iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -o pppoe-aaisp -m comment --comment "Clamp MSS for traffic going via PPP" -j TCPMSS --clamp-mss-to-pmtu

iptables -A FORWARD -i eth1 -o pppoe-aaisp -m comment --comment "Allow traffic from LAN -> internet" -j ACCEPT

iptables -A FORWARD -i pppoe-aaisp -o eth1 -m state RELATED,ESTABLISHED -m comment --comment "Allow return traffic from internet -> LAN" -j ACCEPT

iptables -A FORWARD -i pppoe-aaisp -o eth1 -m state --state RELATED,ESTABLISHED -m comment --comment "Allow return traffic from internet -> LAN" -j ACCEPT

iptables -A FORWARD -m comment --comment "Reject all remaining traffic" -j REJECT

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== Using a full 1500 MTU ==

[[Category:3rd Party Routers|Debian]]