Router throughput question

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Sep 8th, 2008
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For a DR test, my company would like to restore approximately 5 servers from a Backup/Restore server.

The five servers will reside on one Ethernet interface (subnet) of a router and the Backup/Restore server will sit on another Ethernet interface on the same router.

I need to perform one-to-one NAT on the router as well.

Which router model could give us 1 Gbps in throughput with NAT functioning too?

I thinking about using a layer-3 switch too, but it looks like only the 6500 IOS software supports NAT. Why is that so?

Thanks for your help.


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Overall Rating: 3.5 (2 ratings)
Richard Burts Mon, 09/08/2008 - 07:21
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In general Cisco has looked at NAT and classified it as a "router" function.

Many of us have looked at layer 3 switches as if they were hardware based routers (which is especially easy to do since most of them run IOS rather than CatOS) and tended to assume that they provide the same functionality. And as far as routing IP is concerned they are pretty much the same. But there are other services, such as NAT, that continue to provide a differentiation between a "router" and a layer 3 switch.

To get interfaces that support Gig capacity I think that you might want to look at something like the 2821 router.



msrohman Mon, 09/08/2008 - 07:49
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Thanks Rick,

Would a 2821 router support 1 Gbps throughput between Ethernet interfaces on at router with 5 or so static NATs configured?

My Cisco rep. said I should look at a high-end ASA or a 7200 / 7600 series router.

Thanks again,


Giuseppe Larosa Mon, 09/08/2008 - 08:14
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Hello Mike,

under the hypothesis that packets will be big in the file transfer a cisco 7206VXR NPE-G2 could do the job including NAT support.

Or you could try to look at the new ASR 1000.

I suppose you need NAT becuase IP addresses are overlapping between main site and DR site.

NAT requires a lot of work in software: for example all adjustments in TCP flows for sequence numbers and so on, translation of embedded ip info at higher layer when supported.

So it is more complex then PBR for example that can be easily implemented in TCAM by using an action that point to the next hop.

So PBR can be done in lower level multilayer switches and NAT is not supported on the same devices.

Hope to help


Joseph W. Doherty Mon, 09/08/2008 - 16:20
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fyi: The router performance chart, provides expected performance for minimal packet sizes, as the packet size increase, often thoughput increases. What's a real wildcard is the impact of NAT.

Might you be able to avoid NAT using something like static routes on the one router, even host routes? In a real DR, would you NAT then, or run from the same IP addressed subnets that existed earlier?


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