Linux BNG

Jérôme Nicolle jerome at
Sun Jul 15 03:09:11 UTC 2018

Hi Baldur,

Le 14/07/2018 à 14:13, Baldur Norddahl a écrit :
> I am investigating Linux as a BNG

As we say in France, it's like your trying to buttfuck flies (a local
saying standing for "reinventing the wheel for no practical reason").

Linux' kernel networking stack is not made for this kind of job. 6WIND
or may be right on the spot, but it's still a lot of dark magic
for something that has been done over and over for the past 20 years by
most vendors.

And it just works.

DHCP (implying straight L2 from the CPE to the BNG) may be an option
bust most codebases are still young. PPP, on the other hand, is
field-tested for extremely large scale deployments with most vendors.

If I were in you shooes, and I don't say I'd want to (my BNGs are scaled
to less than a few thousand of subscribers, with 1-4 concurrent session
each), I'd stick to plain old bitstream (PPP) model, with a decent
subscriber framework on my BNGs (I mostly use Juniper MXs, but I also
like Nokia's and Cisco's for some features).

But let's say we would want to go forward and ditch legacy / proprietary
code to surf on the NFV bullshit-wave. What would you actually need ?

Linux does soft-recirculation at every encapsulation level by memory
copy. You can't scale anything with that. You need to streamline
decapsulation with 6wind's turborouter or frameworks. It'll cost
you a few thousand of man-hours to implement your first prototype.

Let's say you got a woking framework to treat subsequent headers on the
fly (because decapsulation is not really needed, what you want is just
to forward the payload, right ?)… Well, you'd need to address
provisionning protocols on the same layers. Who would want to rebase a
DHCP server with alien packet forms incoming ? I gess no one.

Well, I could dissert on the topic for hours, because I've already spent
months to address such design issues in scalable ISP networks, and the
conclusion is :

- PPPoE is simple and proven. Its rigid structure alleviates most of the
dual-stack issues. It is well supported and largelly deployed.
- DHCP requires hacks (in the form of undocummented options from several
vendors) to seemingly work on IPv4, but the multicast boundaries for NDP
are a PITA to handle, so no one implemented that properly yet. So it is
to avoid for now.
- Subscriber frameworks, be it uniper's, Cisco's or Nokia's, are at the
core of the largest residentioal ISPs out there. It Just Works. Trust them.

That being said, I love the idea of NFV-ing all the things, let it be
BNGs first because those bricks in the wall are the most fragile we have
to maintain.

But I cleraly won't stand for an alternative to traditionnal offerings
just yet : it's too critical, and it's a PITA to build from scratch and

Best regards,

Jérôme Nicolle
+33 6 19 31 27 14

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