Showing results for 
Search instead for 
Did you mean: 

Cisco ISR 2900 throughput

Hi, Cisco guys,


In a network, which needs two routers facing ISP connections we have deployed ISR 4331, but with default license, and now we have routers with 1 Gbps interfaces, but with 100 Mbps throughput, and we can reach speed no more than 100 Mbps. We have old routers - ISR 2921 and 2901, and I am wondering can we use them to reach real speed up to 1 Gbps (I mean to receive, process, and transmit 1 Gbps). The old ISR-s are with 10/100/1000 interfaces. We want to be sure for the capabilities of this routers before put them on real traffic.


Can you share some info regarding how to check the real capabilities for the above mentioned devices? I have tried to find info in the net but I am a little bit confused. I found different statistics:


Cisco ISR G2 RFC 2544-Based Performance -> 

Cisco 2901 - 3114 Mbps (1500-byte packets)

Cisco 2921 - 3502 Mbps (1500-byte packets)


WAN Circuit Speed ->

Cisco 2901 - 50 Mbps

Cisco 2921 - 25 Mbps


I am not sure which info is for my case.


Any help will be valuable.


Thanks in advance.







Hall of Fame Master

Hello Preslav,

I am afraid you cannot use C2901 or C2921 to support full GE speeds bidirectional on two interfaces (WAN side and LAN side).


The Cisco official whitepaper about performance is in attachment.


Being SW based routers the more features you use the less performance you can get.

So  the performance with only routing enabled are higher then when you use NAT.

IF you add IPSec encryption the performance are even lower.

If you use ACL or other security features like Zone Based Firewall again there is a performance penalty.


You should consider to buy performance licenses and boost licenses on your current modern ISR routers.


The performance results with IP packets of size 1500 are misleading as the SW based routers  have limits in pps packet per seconds they can process see the tables in the attached document.

The real traffic is a mix of packets with different sizes.

At least NAT is needed for internet access in addition to routing.



this document is of year 2012 but C2900 routers are already present inside it.


Hope to help





Hi, Giuseppe,

I have read the same document (Cisco official whitepaper) before a day, and it was the source of my confusion, but already understood that the old routers(2900) are not constructed for such volume of real traffic...
May be I will pursue to buy performance licenses and boost licenses for the new devices.

Thanks for the explanation and have a nice day.

Hall of Fame Expert

"Can you share some info regarding how to check the real capabilities for the above mentioned devices?"

As detailed in the whitepaper Giuseppe provided, ISR performance varies greatly. The two most important considerations are how the router is configured and what the traffic "looks like"; especially packet size.

The only real way to know for sure how an older ISR (or a 4K ISR with boost license) will perform is to actually subject it to your traffic and your configuration.

BTW, the first performance statistic you cite is for maximum (standard) size Ethernet packets (with minimal config) and the second performance statistic is Cisco's recommendation (which is very conservative - it pretty much insures the router can always meet that level of performance regardless of router configuration or traffic mix).

Also BTW, here's a reference for 4K ISR performance (see table 4):

Also keep in mind if you had a duplex gig link, you potentially might need 2 gig of performance; i.e. you need to account for the aggregate of traffic that could pass through the router.


Hello, Joseph,

Thanks for the answer. The info provided from you and Giuseppe was valuable for me. In my opinion the answer is licenses for the 4K routers...