1841 vs 1921

[ciscobigcat]

There is a Q/A page at cisco.com (http://www.cisco.com/en/US/prod/collateral/modules/ps5949/qa_c67-612908.html) and in there it talks about the 1921 not having a "backplane switch"....

Q. Why does the Cisco 1921 Integrated Services Router support only a single EHWIC switch module?

A. Unlike the Cisco 1941 and Cisco 2900 and 3900 Series ISRs, the Cisco  1921 platform does not have a backplane switch. The internal Gigabit  Ethernet link of the EHWIC switch is connected directly to one of the  internal CPU Gigabit Ethernet ports over a serializer/deserializer (SerDes). Thus the Cisco 1921 supports only one EHWIC switch module.

3 questions about this:

1. Does this make the 1921 NOT a good option to replace the 1841?
2. Does this mean the 1921 wont allow you to install 2 EHWICs (e.g. one 4-port EHWIC and one 4-port EHWIC-P)? Meaning that it forces you to install only one single card and then the second slot will not serve for anything??
3. Does this mean that when ordering a card for the 1921, you are stuck with buying a card that takes BOTH slots (can't remember the exact name of those cards but an example will be an 8-port EHWIC)?

The 1921s were looking like a good option at first but after digging a bit deeper, all these things make anybody think twice about them. I'm currently looking at these details because I need 9 routers for 9 different branches. In some of those offices I will be buying a 4-port EHWIC and T1 cards. Therefore, if I read the Q/A correctly, that will mean that once I put anything on the first slot, the second slot is lost...

Can anyone confirm?

Thank you gentlemen

[Leo Laohoo · Accepted solution]

In some of those offices I will be buying a 4-port EHWIC and T1 cards.

I think the Q&A was worded incorrectly.

You can get a standard width EHWIC (up to two) or a single double-width card.

[ciscobigcat]

Hi Leo, thank you for the response. I have been reading that Q/A over and over and it looks like later on the page they explain that the limitation is for the EHWICs....

"For scaling cascaded switch modules, you are no  longer limited to only two switch modules. The number of EHWIC slots on  the platform limits the number of EHWIC switch modules that can be  cascaded. Cascading is not supported on the Cisco 1921 because this  platform supports only one EHWIC switch."

From this explanation is where I am getting that the limitation is imposed upon the card being installed in the 1921 routers. The further explain this:

**********************************************************************

Q. Are there any restrictions or considerations I should be aware of?

A. Yes, Following is a summary of a few limitations when using the EHWIC switch:

•  When the EHWIC switch is used on a platform without the MGF (Cisco  1921), only a single module is supported because the externally  connected HWIC stacking feature is not supported on the EHWIC switch.

**********************************************************************

From this I gather that because of the absence of this MGF (I still not know 100% about this but currently looking into it) it is why you can't put 2 of the EHWICs on the 1921 routers but it looks like the paragrapgh implies that if you want to use another non-EHWIC card in the second slot, you will be able to make it work (like a T1 card).

Again, has anyone experience any of this? It is confusing for a customer and even calling cisco pre-sales they still do not know the answer and they start looking at the same documents I can find online. It is very frustrating.

[Leo Laohoo]

Hmmmmm ... I think you may be on to something.  Look at Q&A:  Cisco Integrated Services Router Generation 2, and look at Table 1.  Notice 1921 is not in the list.

My guess is this:  If you want to use two EHWIC cards, you'll need to consider the 1941 instead of the 1921. 

[ciscobigcat]

Hi Leo, I hope you mean I just found something interesting and not that I am into some substance

This Q/A you have just provided I think was the last piece of evidence I needed to make the final decision. It looks like the 1921 was not even part of the original ISR G2 generation of routers, which also explains why the limitations. This is the same reason why I was digging about them..

The 1941 I had looked at them before but they did not meet our requirements in terms of rack-size. They are strange-ugly looking router that for some reason are not the 1U size they should be. Instead they measure like 1U.5, enough to not fit in a 1U slot. Most of our servers rooms only accept 1U (long story, but long story short, the moment we jump to 2U of space, the price we must pay in our shared server rooms skys-rocket)

What do you think are other alternatives in 1U size routers?

[Leo Laohoo]

What do you think are other alternatives in 1U size routers?

You are stuck then.  1921 is the smallest one.  2900 and 3900 are bigger.

[ciscobigcat]

How does the 2901 sound to you? Too overkill? At least it is a 1U guy and yes, bigger but at least rack-mountable to only take 1U space

[Leo Laohoo]

I didn't even notice the 2901.  I could potentially work.  Just make sure your EHWIC are in the list of supported Interfaces and Modules.