I have recently moved to Lausanne, Switzerland. Broadband Internet
access is not as cheap as in France. Free, a French ISP, is
providing an FTTH access with a bandwith of 1 Gbps1 for
about 38 € (including TV and phone service), Swisscom is providing
roughly the same service for about 200 €2. Swisscom
fiber access was available for my appartment and I chose the 40 Mbps
contract without phone service for about 80 €.
Like many ISP, Swisscom provides an Internet box with an
additional box for TV. I didn’t unpack the TV box as I have no use for
it. The Internet box comes with some nice features like the ability to
setup firewall rules, a guest wireless access and some file sharing
possibilities. No shell access!
I have bought a small PC to act as router and replace the Internet
box. I have loaded the upcoming Debian Jessie on it. You can find
the whole software configuration in a GitHub repository.
This blog post only covers the Swisscom-specific setup (and QoS). Have
a look at those two blog posts for related topics:
Staging a Netfilter ruleset in a network namespace
Intel Wireless 7260 as an access point
Ethernet
The Internet box is packed with a Siligence-branded 1000BX
SFP3. This SFP receives and transmits data on the same fiber
using a different wavelength for each direction.
Instead of using a network card with an SFP port, I bought a
Netgear GS110TP which comes with 8 gigabit copper ports and 2
fiber SFP ports. It is a cheap switch bundled with many interesting
features like VLAN and LLDP. It works fine if you don’t expect too
much from it.
IPv4
IPv4 connectivity is provided over VLAN 10. A DHCP client is
mandatory. Moreover, the DHCP vendor class identifier option (option
60) needs to be advertised. This can be done by adding the following
line to /etc/dhcp/dhclient.conf when using the ISC DHCP client:
The first two numbers are here to identify the service you are
requesting. I suppose this can be read as requesting the Swisscom
residential access service. You can put whatever you want after
that. Once you get a lease, you need to use a browser to identify
yourself to Swisscom on the first use.
IPv6
Swisscom provides IPv6 access through the 6rd protocol. This is a
tunneling mechanism to facilitate IPv6 deployment accross an IPv4
infrastructure. This kind of tunnel is natively supported by Linux
since kernel version 2.6.33.
To setup IPv6, you need the base IPv6 prefix and the 6rd gateway. Some
ISP are providing those values through DHCP (option 212) but this is
not the case for Swisscom. The gateway is 6rd.swisscom.com and the
prefix is 2a02:1200::/28. After appending the IPv4 address to the
prefix, you still get 4 bits for internal subnets.
Swisscom doesn’t provide a fixed IPv4 address. Therefore, it is not
possible to precompute the IPv6 prefix. When installed as a DHCP hook
(in /etc/dhcp/dhclient-exit-hooks.d/6rd), the following script
configures the tunnel:
The computation of the IPv6 prefix is offloaded to Ruby instead of
trying to use the shell for that. Even if the ipaddr module is
pretty “basic”, it suits the job.
Swisscom is using the same MTU for all clients. Because some of them
are using PPPoE, the MTU is 1472 instead of 1480. You can easily check
your MTU with this handy online MTU test tool.
It is not uncommon that PMTUD is broken on some parts of the
Internet. While not ideal, setting up TCP MSS will alievate any
problem you may run into with a MTU less than 1500:
QoS
UPDATED: Unfortunately, this section is incorrect, including its
premise. Have a look at Dave Taht comment for more details.
Once upon a time, QoS was a tacky subject. The Wonder Shaper was a
common way to get a somewhat working setup. Nowadays, thanks to the
work of the Bufferbloat project, there are two simple steps to get
something quite good:
Reduce the queue of your devices to something like 32
packets. This helps TCP to detect congestion and act accordingly
while still being able to saturate a gigabit link.
Change the root qdisc to fq_codel. A qdisc receives packets
to be sent from the kernel and decide how packets are handled to
the network card. Packets can be dropped, reordered or
rate-limited. fq_codel is a queuing discipline
combining fair queuing and controlled delay. Fair queuing
means that all flows get an equal chance to be served. Another way
to tell it is that a high-bandwidth flow won’t starve the
queue. Controlled delay means that the queue size will be
limited to ensure the latency stays low. This is achieved by
dropping packets more aggressively when the queue grows.
Maximum download speed is 1 Gbps, while maximum
upload speed is 200 Mbps. ↩
This is the standard Vivo XL package rated at
CHF 169.– plus the 1 Gbps option at CHF 80.–. ↩
There are two references on it: SGA 441SFP0-1Gb and
OST-1000BX-S34-10DI. It transmits to the 1310 nm wave length
and receives on the 1490 nm one. ↩