Newbie: Why Upgrade Memory?

Unanswered Question
Aug 26th, 2007

I'm looking to get some Cisco Routers for our outer offices. I've settled in on the 1811 unit.

What exactly is the Flash memory and why would I need or want to upgrade that?

What is the RAM used for in the router and why would I need or want to upgrade that?

This stems from the horrendous cost of the Flash and RAM upgrades for the 1811. I'm just wondering whether or not I would need to worry about it. Even if I don't get the upgrades now, how will I know in the future if I need them?

I do plan to get the Advanced IP Services IOS for the additional features.

We are currently using SonicWALL units in our offices but are having trouble with them and VoIP. I would like to get one Cisco and get it configured and deployed to see if that resolves our issues.

The 1811 with the built-in modem seems to be the closest match to the SonicWALL TZ 170 SP with Enhanced OS.

I have this problem too.
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Edison Ortiz Sun, 08/26/2007 - 14:06

The Flash memory stores your IOS (it's the file system) and the DRAM enables you to load/run the IOS and all its services.

When you download an IOS, it will have the memory and flash requirements. These requirements may change over the years when you upgrade your current IOS.

Tony.henry Sun, 08/26/2007 - 14:21

Timothy,

Simply, Flash memory is where the routers software and config is loaded from, and RAM is where it is loaded too. Naturally there is more to it than that, but thats a good start I think.

I find that it's good to upgrade these things up front in preparation for services that you aren't running yet. Especially if they are really remote.

Hope that helps

Tony

Joseph W. Doherty Sun, 08/26/2007 - 16:55

Some additional tips:

Upgrading RAM usually means opening the box, so best done during planned maintenance.

Upgrading the flash is often just obtaining an external module that's larger. A much easier upgrade.

For both RAM and flash, Tony's point about remote access is important. Not too difficult, if necessary, talking someone through changing the flash module, but again, RAM upgrade is a bit more involved for the uninitiated.

Besides leaving some room for newer firmware versions, it's very nice to be able to have two images on the flash card. This allows you to boot into a newer version, yet revert to the old if there's some problem. Also on rare occasion you might have a problem downloading a new image. Annoying to have the system boot without any software but the boot loader.

Lastly, the newer routers often support a web interface that runs out of flash. You also might have need to save other files on the flash, such as PDLM modules or even versions of the box's config. Most of this latter stuff isn't real large, but if you size flash only slightly large than your image, you might have insufficient space for the additional stuff.

Richard Burts Sun, 08/26/2007 - 17:11

Timothy

Here is one more effort to answer your questions. Flash is used primarily to store the IOS image file (which is the operating system for the router). Flash can also have other files but the image is the main purpose. You will need to verify the requirements of the IOS version (and feature set) for flash. You also should consider the possibility that over the life of the router that you would want to run newer versions of the IOS. And so you should consider the possibility that newer versions of IOS will increase the requirements for flash. It will be much easier to order enough flash at the beginning than it will be to have to order and install additional flash later on.

RAM is the main operating memory of the router. It is used to hold the running version of the IOS code. It is also used to hold the routing table, the CEF tables, the ARP table, to supply memory for packet switching, to hold working tables for any routing protocol that you might be running (the OSPF Link State Data Base, the EIGRP topology table, etc). As with flash each version of IOS has a minimum requirement for RAM which you need to consider in what you order. And like flash you should consider that over the lifetime of the router that the requirements for RAM may increase.

HTH

Rick

TimothyGaray Mon, 08/27/2007 - 03:38

Thanks to all for your explanations. I think that's always been an issue for me for Cisco vs. any other brand: complexity. I totaly don't understand all the options for a Cisco. All the other brands are basically black boxes that you plugin and go with only firmware (OS) upgrades.

For remote access, all of the offices are within driving distance (some obviously farther than others). Not a big deal getting there. None of the offices are so critical that they can't be down for an hour while I upgrade RAM if need be.

The Flash memory is a good point. I know I've upgraded and downgraded the SonicWALL OSes many times in response to problems. That one is probably worth the up-front upgrade.

As for RAM, I'll wait and see. This is an experiment at the moment. The biggest office only has 5 users (6 if you count the roaming sales person). If you double that for VoIP phones, I'm not worried about a huge ARP table or any of the tables for that matter. Of course, my opinion and reality has often proved to be completely different...

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