Category Archives: IPv6

How to prefer IPv4 over IPv6 for some hosts

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If an IPv6 address is unreachable, but you can reach the IPv4 one, you can set the preference to IPv4 for that particular address by adding a line such as this in /etc/gai.conf:

That will set the preference for host to IPv4.

See gai.conf(5) for details.


Linux IPv6 Router: RADVD + DHCPv6

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Unlike IPv4, which uses DHCP for configuration, IPv6 uses the Neighbor Discovery Protocol to configure addresses and gateways. Unfortunately, originally the protocol had no means of providing addresses of DNS servers to clients, making it necessary to use  DHCPv6 for that purpose. Modern Linux and Mac OS X machines are able to use the IPv6 Router Advertisement Options for DNS Configuration (RFC 6106), but to my knowledge, Windows clients are not able at the moment. Here’s how to configure a Linux router using radvd and the ISC DHCP daemon. Continue reading Linux IPv6 Router: RADVD + DHCPv6

Dynamic IPv6 routing with Cisco IOS and Quagga on OpenWRT

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Here’s how to make dynamic IPv6 routing work between a Cisco IOS router and an OpenWRT Linux Quagga router. I couldn’t find a similar howto anywhere, so I decided to write my own.

I am using OpenWRT Kamikaze 7.09 (kernel 2.4) on an ASUS WL-500gP wireless router. Any IPv6 enabled Cisco router should do.

I assume you have already installed the IPV6 kernel modules and userland tools, and set up static addresses for your interfaces (if you haven’t check out the OpenWRT IPv6 Howto).

I am using SixXS for tunneling an IPv6 /48 prefix over IPv4. Continue reading Dynamic IPv6 routing with Cisco IOS and Quagga on OpenWRT