Maximum allowed NAT/PAT Translations on Sup720

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Jan 19th, 2010

Trying to figure out maximum allowed NAT/PAT Translations allowed on a WS-SUP720-BASE.  At any one time we can expect about 30k active users browsing the internet.    Trying to find out if it supports 300k+ translations.

I have this problem too.
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Giuseppe Larosa Wed, 01/20/2010 - 06:33

Hello Charles,

NAT is declared hardware assisted on sup720 datasheet

so I wouldn't expect the system to be able to handle more NAT entries then the size of its TCAM tables used for multilayer switching operations.

for sup 720 3B

256,000 route entries

128,000 netflow entries

see table 1 of above document

I'm not sure that  NAT rate limiting feature described in the link provided by Ganeshh applies to a C6500 where NAT is not performed only in SW.

a check should be done with feature navigator

search by feature NAT rate limiting NAT translation  among supported platforms I see C7600 with RSP720/MSFC4 or SW based routers like C7200 or ISR.

but it is supported NAT- Perfomance enhacement - Translation table opmitization

and Hardware-Assisted NAT as declared in datasheet

Hope to help


rsimoni Tue, 10/11/2011 - 00:48

Hi All,

unfortunately this info cannot be disclosed on the forum. If you are entitled to do so and you have signed a NDA you can get in touch with your Account team (if you have it) and ask for some performance specs as we do have some.

General rules are:

- the Sup720 is not conceived to NAT all the traffic handled by it. It can do it of course but since the feature is hardware assisted, as Giuseppe correctly pointed out, which means that it cannot be entirely performed in hardware but requires the assistance of software (read CPU) there are scalability considerations to be aware of.

In other words if you require that all the traffic (or vast majority of it) going through your system has to be NAT'ted it is better that you use another device for that (a software based router is better equipped for that). NAT on Sup720 can be used as a temporary measure or for limited traffic volume.

- Performance depends on some variables such as packet size, transport protocol (TCP vs UDP), and type of NAT (static vs dynamic; NAT vs PAT).

NAt is more performing than PAT with UDP being slighlty more performing than TCP.

Cannot add more unfortunately 


rsimoni Mon, 10/17/2011 - 01:19

it means that the forwarding cannot be entirely handled in hardware circuitry (PFC etc) but requires the assistance of the CPU in software.



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