The Cisco ISR G2 routers have been around for a while now. Roughly a year ago, Cisco released the Cisco 4451-X router which was the first ISR running IOS-XE. Cisco has now added new routers to the 4000 family, which means that the ISR G2 family will eventually go away. Don’t panic though! That will not happen for a while but if you are looking to buy new ISR routers, then take a look at the new 4000 family.


One great thing about the new ISR 4000 routers is that they support upgrading of the bandwidth capacity by buying a license. That means that you can keep the same router for a longer time and grow into it, rather than doing a complete replacement as your demand for bandwidth increases. The new models are ISR 4321, 4331, 4351 and 4431.


If you need a router that does 10 Mbit/s, then you can get the 4321 and you can keep using it until you reach 100 Mbit/s. The 4331 will get you from 100-300 Mbit/s which would cover a lot of customers that I currently have.

The next slide shows some of the new features of the ISR 4000:ISR4000-architecture

The ISR 4000 runs IOS-XE which means that IOSd is running on Linux kernel. There is also the possibility of running virtualized applications on this kernel which was not available on ISR G2 routers. You also have the possibility of adding UCS to make the offering more complete.

The migration path from ISR G2 to ISR 4000 is shown below. With the ISR 4000 they have tried to keep the units smaller in size so that the number of RU is less than with the ISR G2. This is welcomed if you have racks with little space in them.


The EHWIC of the ISR G2 has been replaced by Network Interface Modules (NIM). The NIM can also be used for service containers running applications on them. The Enhanced Service Module is compatible with the ISR G2, the NIM is not compatible with EHWIC.ISR4000-IO

The ISR 4000 uses multiple cores and as mentioned earlier the IOSd runs on a kernel. Other services such as WAAS can be hosted as well.


The next slide shows the packet flow of the ISR 4000.


The ISR 4000 now can run VMs. Apps like WAAS, Energywise and future apps can then be hosted on the ISR 4000.



With the ISR 4000, HDs can be added and these are hot swappable. Even SSD can be added which is always nice.


Most modules are not backwards compatible. It’s always a challenge to be backwards compatible and innovative at the same time.


The ISR 4000 has plenty of connectivity options to make it fit for many WAN scenarios. It has Ethernet, T1/E1, T3/E3, and 3G/4G on the roadmap.


Like the ISR G2, there is a switch module available and it has PoE if you have a need for that. It has an optional license to enable L3 features on the switch module.


Additional routed ports can be added and for the first time, ISR will support 10GE! You can switch between 4x 1GE or 1x 10GE from the software. All GE ports are dual phy which makes it easy to use both copper and fibre and to protect your investment.


Voice modules are available, I don’t know much about voice but every card will have its own DSP. No DSP on the motherboard!


UCS E-Series blade can be hosted. This makes the ISR 4000 attractive for branches where you can put a router and also host VMs to make it an all in one type of offering.


There is also a double wide blade that has room for more RAM and for more cores on the CPU.


The modules are also Vmware, Hyper-V and Citrix certified.


The ISR 4000 looks like a nice addition to the Cisco family. I personally like the pay as you grow feature and the addition of dual phy and 10GE ports. You can find more information about the ISR 4000 here.

Cisco Adds New Routers In the ISR 4000 Family
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8 thoughts on “Cisco Adds New Routers In the ISR 4000 Family

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  • October 25, 2014 at 2:46 pm

    Hi Daniel, It may be worth pointing out that some folks will see less throughput with the new 4000 series platforms than the older ISR2 boxes if they are running larger packet sizes and not too many services.

    In my use case with PAT, QOS,bgp/bfd and larger packet sizes I’m achieving ~700mbps through a 2951 where the equivalent system a 4351 would cap me at 200mbps (or 400mbps licensed) running the same services.

    I have no doubt that the performance is better with oodles of services and small packet sizes, but if that’s not what your doing, the ISR2 could provide better performance. I do like the addition of the extra sfp ports, but still no internal redundant power and the ESM is still a seperate entity with its own firmware and configuration to manage.

    • October 26, 2014 at 8:32 am

      Interesting. It’s always difficult to get performance numbers on devices except for the best case numbers.

      Agree on the redundant power.

  • October 26, 2014 at 8:55 am

    Hi Daniel. Great post, as always. Do you know when the whole family will be orderable? If I’m not wrong, at present time only the ISR4431 is orderable, apart from the ISR4451X.

    Thank you.

  • October 26, 2014 at 4:51 pm

    I typically see minimum performance published for the platforms, and for the 2951, it’s 75mbps. The 4351 is a big increase over this, but if you’re not running bunches of features at min packet sizes, you often see substantially increased throughput over these numbers. In my case, i see about 10x more performance in a typical CPE configuration (including maybe not so typical PAT).

    Cisco does have this table which shows almost 300mbps for the 2951 at 64 byte packets, but i have no idea what services are enabled:

    Anyway, i thought it would be worthwhile pointing possible downsides of the new policed platforms.

  • January 10, 2015 at 1:56 pm

    Ohh that’s quite interesting. I myself have visited their official website and found that they just have improved the number of cores in their new devices. So it’s oblivious that the New multicore CPU architecture with support for multi-gigabit performance.


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