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RPS-2300 router compatibility with 2921 Router (ISR-G2)

Raghavendra Rai

Hello all,

Apologies if this is not the correct place to ask this question.

I have ordered a Cisco 2921 Router with RPS-2300, and CAB-RPS2300 cable to connect RPS to 2921 Router.

According to the below document in CAB-RPS2300 is the correct partnumber to connect any RPS supported devices other than Catalyst 3750-E and 3560-E Series Switches.

"Users may order either the CAB-RPS2300-E=  compatible with Cisco Catalyst 3750-E and 3560-E Series Switches or the  CAB-RPS2300= compatible with all other network devices. Extra cables  must be ordered separately or as spares."

Now I have recieved a Cable with 22-pin connector at one end and 14 pin connector at other end.

But in Router and in the RPS we have 22 pin Connectors

Is it a mistake in shipment? is it mistake in ordering? or is it an error in the document?

Can you please help?



15 Replies 15

Richard Ayres

Hi Raghavendra,

Whilst I cannot see a reply to your question on the forum, I wondered if you've solved this mystery by another means?

I'm just about to order RPS2300 cables for ISR G2 series routers (i.e. 2911, 2921, 2951) and based on the ordering guide would naturally order the CAB-RPS2300=.  However, based on your experience, now wonder if this order should be for the CAB-RPS2300-E= part!



I guess you need to have the below RPS adaptor in 2921 router while using external RPS.

RPS-ADPTR-2921-51=Cisco 2921/2951 RPS Adapter for use with External RPS

Hi Johny,

Correct - the RPS-ADPTR-2921-51= is another requirement of this setup.  However, to solve the original puzzle posed by Raghavendra we need to know if this RPS Adapter has a 22-pin or 14-pin socket on the front.  Based on Raghavendra's description, it seems to be 22-pin.

Therefore, contrary to the sources quoted above and somewhat counter-intuitively (if you base your assumptions on Cisco's official part description - shown in italics below), the correct cable to link an RPS2300 to a 2900 Series router seems to be the CAB-RPS2300-E= [Spare RPS2300 Cable for 3750E/3560E and 2960 PoE Switches] and not the more likely sounding CAB-RPS2300= [Spare RPS2300 Cable for Devices other than E-Series Switches].

Are we all agreed?


I need to order the same solution and would appreciate some clarification on this as well!

I haven't looked myself, but if you read the the hardware installation guide for the devices discussed, you will find drawings and sometime even pinouts, that may help clarify the issue.

In this document on page 5 - 36 there is a diagram of the RPS adapter for 2921/51 routers and it has 22 pins so it would appear that the correct cable is indeed the CAB-RPS2300-E=.

On page 5-40 there is a table that indicates that you will need 2 PSUs in the RPS2300 or it will not power the 2921/51.  This seems odd to me since it seems that a single 750W PSU should be able to provide enough power to serve as a backup.  Can anyone confirm this?

So if I am understanding correctly, here is the part list needed to make it all happen:

  1. PWR-RPS2300
  2. C3K-PWR-750WAC (QTY 2)
  3. CAB-RPS2300-E=
  4. RPS-ADPTR-2921-51=

Hi bascheew,

Your kit list exactly matches what I would now specify for this setup (with the link cable included in the price of the RPS2300 bundle, along with the country-specific power cables).


We were investigating the same thing for a 2911 router.  This thread and another seems to have answered my concern.  I hate people actually had to buy the wrong cable to find out the hard way.  The thing that made me question it was the fact that the E cable was specifically designed for the 3560/3750-E switches but the documentation also clearly indicates this has been extended to include the latest 2960 switches as well as the 3560/3750-V2s.  The documentation that discusses the non-E cable specifically notes compatibility only up to the 2800 series routers.  The document itself is dated before the 2900 series routers.

So by logical deduction then, Cisco has apparently created the adapter to be compatible with the E cable.

Hello all,

Sorry for not seeing the thread for such a long time.

CAB-RPS2300-E= with 22 pin on both ends is the right part number needs to be ordered.

I was in soup by ordering CAB-RPS2300 where I realized that it was a wrong part in the field itself.

But Cisco TAC was really helpful they accepted their documentation error and within 2 days they sent me a CAB-RPS2300-E= cable for no additional cost.

I should admit the fact that it was World Class support from Cisco.

Answering to bascheew

Yes, Cisco documents indicates that you will need 2 750W PSUs in the RPS2300 or it will not power the 2921/51.

It looks odd, but i tried to power-on 2921 loaded with a 24 port switch (Service-module) with a single 750W PSU RPS

It works fine. I think Single 750W PSU is enough as long as you dont power PoE ports in the switch modules.



Motherboard Components Power consumption = 79.1 W

NM/SM slot 1 Power consumption = 27.6 W

Total System Power consumption is: 106.7 W



I have the same issue, and based on the documentation, i ordered the wrong cable

Now i will open a case to have it replaced.

I will order a RPS2300 for a 2921 now and understand that I need to order the CAB-RPS2300-E. But is the adapter then necessary (RPS-ADPTR-2921-51=)?

And will the configuration work with one 750w power or do I need two powers?



Hi Thomas,

Yes, you definitely require the adapter  (RPS-ADPTR-2921-51=).  You'll have to make your own mind up about the number of 750W power  supplies.  Some contributors to this thread feel that one is sufficient  in some circumstances, however the guidelines from Cisco are very clear -  two are required!  Below are sources for my reasoning.


"The redundant power supply (RPS) for the Cisco  2911, Cisco 2921, and Cisco 2951 router is an external Cisco RPS 2300.  To connect the RPS, the router must be fitted with an RPS adapter."

Figure 5-30     Cisco 2921 and 2951 Power Supply Components

The adapter is item number 4 above.

Table 5-3     RPS 2300 Backup Capabilities 

Power Mode
Quantity and Type of RPS 2300 FRU
Quantity 1 C3K-PWR-750WAC
Quantity 2 C3K-PWR-750WAC
Quantity 1 C3K-PWR-1150WAC
Quantity 2

2911 in RPS





2921, 2951 in RPS





2911 in POE Boost





2921, 2951 in POE Boost





Table 5-3 shows RPS 2300 backup capabilities when coupled with Cisco 2900 series ISRs.

I was told from a customer that Cisco TAC told them they needed a quantity of 2 "

CAB-RPS2300-E" with a Cisco 2921/2951 router to connect to the RPS2300.  Is this true?  I only see one 22 PIN connector from the installation guide.

Hi Brian,

As you say - each Cisco 2900 Series router can only accept one connection from the RPS2300 (via a CAB-RPS2300-E cable and RPS-ADPTR-2921-51= adapter).  Is somebody perhaps getting muddled up with the number of  power supplies required in the RPS2300?  As you'll see from elsewhere in this thread, Cisco's documentation states that two 750W PSUs are required to support a single router chassis...


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