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

adamv0025 at adamv0025 at
Mon Oct 15 09:05:23 UTC 2018

Interesting, but isn’t stateful tracking once again just swapping, but in this case port 123 in port 32123 out? 

So none of the chips you named below support swapping parts of L4 header and that part is actually done with SW assistance please?  

So for example the following:

- wouldn’t be at line-rate please?


Thank you



::carrier-class solutions for the telecommunications industry::


From: NANOG [mailto:nanog-bounces at] On Behalf Of Paul Zugnoni
Sent: Thursday, October 11, 2018 6:04 AM
To: wmf at
Cc: nanog at
Subject: Re: NAT on a Trident/Qumran(/or other?) equipped whitebox?


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 <mailto: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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