NAT on a Trident/Qumran(/or other?) equipped whitebox?

Paul Zugnoni paulzugnoni at
Thu Oct 11 05:04:25 UTC 2018

The key to answering the question of NAT support on a Broadcom switch
forwarding chip, is... another question: What /flavour of NAT/ you're
looking for. Generally Trident (1,2,3), Tomahawk(1,2) and I believe Jericho
all support varying degrees of swapping parts of an IP or Eth header for
other parts - i.e. TTL of 249 in, TTL of 248 out, MPLS tag 500 in, MPLS tag
513 out. And, to your benefit, SRC IP of in, SRC IP of
out. That can be handled at line rate (yes 10G); how many of those rules
depends on the chip.

So that's perfectly fine for static NAT. Problem with static NAT (i.e. 1:1)
isn't what I suspect most of us are looking for. PAT, or "nat overload" -
i.e. your internal 10.x or 192.168.x networks to the internet using one or
a few public IPv4's - requires stateful tracking, which is not what any of
those chips do. So you're dependent on what route engine and software is in
use to supply stateful NAT / PAT, and the requirement being higher there
generally means you'll need a firewall or router (which, btw, might
actually be using one of the aforementioned Broadcom switch chips for the
forwarding plane!). To achieve line rate for stateful NAT / PAT there's
more than the switch chip and software in the equation, and can be the
limiting factor to achieving "line rate" for a set of 10G ports.


On Wed, Oct 10, 2018 at 12:20 PM Wes Felter <wmf at> wrote:

> On 10/9/18 10:35 AM, Jason Lixfeld wrote:
> > Has anyone played around with this?  Curious if the BCM (or whatever
> other chip) can do this, and if not, if any of the box vendors have tried
> to find a way to get these things to do a bunch of NAT - say some flavour
> of NAT, line-rate @ 10G.  If so, anyone know of a NOS that has support for
> it?  OcNOS, Cumulus Linux, PicOS and Switch Light OS seem to have none, but
> not sure if there are others out there.
> For 10G I would use software NAT like a firewall or CGN virtual
> appliance. Switch ASICs generally don't support NAT well; Tofino and
> maybe Jericho II can probably do it but at high cost and as you
> discovered the market isn't trying very hard to provide "routing" or
> "firewalling" functionality on "switching" ASICs.
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