Disclaimer
The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.
Liability Disclaimer
In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.
Posting
Usually, modern equipment bandwidth performance ratings are given for minimum size Ethernet packets, but larger packets often allow for much higher bandwidth rates. Unfortunately, it's not clear exactly what 1 or 2 Gbps of performance means on a 4451. If the 4451's Gbps, is for minimum size Ethernet packets, then its possible bandwidth performance could be higher with the "normal" mix of packet sizes.
On ASRs, I've been told their bandwidth ratings are enforced "caps" across their backplane. If that's correct, they wouldn't allow more their defined maximum amount of bandwidth, regardless of packet sizes.
For something like a 10g interface on a 4451, the 10g interface might be still be useful, even if the router's "limit" is 1 or 2 Gbps, because with maximum size packets (especially if jumbos are supported and being used) the 4451 might be capable of sustaining 10g rate and/or when the router cannot sustain 10g, short 10g bursts might work fine. The later would reduce transmission latency, by a factor of 10, even for single packets.
If you wanted to support a 10g link, I would lean toward an ASR 1K over a 4451. Further, even the entry model 1Ks are a bit under spec for 10g.
Unless you have need for router features not found on L3 switches, L3 switches, that support 10g, would be less expensive.
