The importance of RAM in Routers and Modems?

brunols

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May 10, 2013
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Hello!
I always used this forum to solve my questions, but theres some things that I can not find a pn answer. As this forum is huge with very experienced members, I decided to SignUp to ask and to help too!
So...

In my country everyone uses ADSL2 (VDSL2 in my case) connections.
I always setup a modem to Bridged, and use a dedicaded Router to use PPPoE with this bridged Modem.

Does the specs of the modem matter? The RAM, the CPU? For example, let's say I use a D-Link 500B to a 15MB ADSL2 Connection.

I Know the Router's CPU and RAM do matter, but, in what does it really matter? I have one Netgear WRND3700 that my friend bought for me when he went to canada.

I use many devices in my house, and a lot of Torrent.

Does the modem capabilities really matter when it is in Bridge mode?

Thanks in advance!
 
All the modem does is keep track of the mac address of your end device , router in this case, and convert data from ethernet to dsl. All it will use memory for is to keep the mac table (all of 1 device in consumer setups) and some small buffers to hold packets while it does the conversion. There likely is a artificial number of packets you can burst into the device before it drops them which is well below memory the actual memory limitation. CPU use should be non existent.

The only reason a router needs lots of cpu and to a point memory is that is must do NAT on every packet. This means it must change the ip and then recalculate the header check sums for every single packet. The memory use is based on the number of NAT sessions which of course bit torrent has a lot of.

NAT and VPN encryption are the 2 things that can kill a router. If you could not do those I suspect even very cheap routers could run many hundreds of meg/sec of data.



 

brunols

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I heared that Routers with big RAM memory are apropriate to Torrenting, since torrent creates a lot of threads, and if you push it too hard the connection can be lost... Is it right?

So it does not matter if the modem is just a simple modem if it is bridged to a powerfull router?

Could a simple modem bridged to a powerfull router and switch be OK for a lot of clients connected?

What about managed switchs? Does them have RAM memory, and does it matter?

If sure these questions will help a lot of users trying to find this on Google.
 
A bridge and a switch are sorta the same things except the bridge is going between dsl and ethernet and a switch is ethernet to ethernet. Switches only need memory to store mac addresses. Most store many thousands and few consumer grade switches will be connected to other switches so it limits the mac count to the port count in most cases.
 

brunols

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Are you sure? When we left the Modem in Bridged mode and use the Router, the router will process everything and give the DHCP and NAT and so on...

I heared one saying that he needed to replace his Router because it could not handle the higher speeds of his Connection and the ammount of devices connected was the same before he upgraded his Internet to such hi speeds. The hi speed and many devices attached just used to break his connection.

What about the bittorrent Threads breaking connections and routers hith a lot of RAM being recomended for torrent lovers... it shows that RAM is really important.

About the Bridge and the Switch being the same thing, I don't think it is right, as the Switch is just to add more Ports and the Router bridged to the Modem means the Router will connect "dial" the PPPoE...

 
You are correct a router needs to be sized based on traffic. It is only NAT that causes the issue DHCP is so minor it does not matter.

But you are just confusing things. This is why the network certifications make such a huge point of talking about LAYERS. A router is layer 3. A bridge and a switch are layer 2. A bridge by definition converts from one form of layer 2 connection to another. So when you put your modem in bridge mode all its doing is translating the data from ATM on the DSL side to ethernet packets on the lan side. It has no concept of IP addresses. It is very simplistic in function and does not need a lot of memory or processor to complete. All the other function related to NAT and such are layer 3 or higher functions are handled by a router. Now lets say you needed to convert from 1g fiber to 100m copper ethernet. This device is also a bridge but it is also a 2 port switch. People just do not call 24 port switches 24 port bridges but by definition that is what they are. In the case of a switch you only need to store mac addresses no ip...again its a layer 2 device.
When you look at the modem when used in a home environment it only has 2 addresses, the mac address of the router (or a pc if you directly plug it in) and the mac address of the router at the far end. (this is somewhat a lie since DSL uses ATM which does not really use mac but another identifier but it is still only 1 entry).

 

brunols

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Man you are the master!!

Thanks for your reply!

After reading a lot about networks and helping friends, and setting up my dad's office, I think Network Enginering may be a very, very cool thing to do.

Sadly where I live everyone uses Cappy Routers and always have connection problems lol.

You have some tip to tellme where to lean even more, please give a shout..

About the bittorrent consuming the routers RAM memory? Do you know something?
If the latest asus have 256mb of ram, a l3 switch may have much more?

 

Beachnative

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Your initial question posed was what is the importance of RAM in Routers and in Modems. All use buffers, in a nut shell the more RAM the better, the less they will rely on the buffer. Bufferbloat can occur if you have a robust internet connection and a low end router that has small buffers and not enough RAM. As data tried to reach it's destination and the router cannot handle the data stream packets are lost. What happens when packets are lost? They get retransmitted over till the destination is reached, then the traffic jam gets worse as large continuous streams of data are sent and received.
Here is a good website that helps understand bufferbloat:
http://www.bufferbloat.net/projects/bloat/wiki/Introduction
 
A layer 3 switch is a "router" that has all the features that would slow it down disabled. Pretty much they remove NAT, VPN, traffic shaping, and even simple things like GRE tunnels. These are normally called wirespeed because they can pass traffic on all ports at the full rated speed with all ports running at max at the same time. They need very little memory because they do not hold packets for long. Theory is they will never have more than 1 packet in and out on each interface. Also since they have removed all the complex stuff they use special asic chips to do all this work so the CPU is mostly used to manage the switch and handle exceptions.

Not a real useful box for your home user who's primary thing to use is NAT. If you had a real IP per machine then you could use layer 3 switches.
 

brunols

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All I can think about now is that a PC running pfSense can be a very very good thing, working with a good L2 umanaged switch. Am I right?

Let's say I need a good, fast and reliable LAN with 20 PCs... maybe a simple ADSL Modem in bridge mode, with a pfSense PC connecting in PPPoE, linked to a switch and a Wireless router somewhere in the end, would make a real good Network?
 
pfsense has many more features than your standard consumer router. Its going to depends what you are using. The intrusion detection and firewall options can put a tremendous load on a machine. This also supports VPN which is also a huge resource hog. Unless you need the features I would stay with a simple router. The code has been striped down and is optimized since it does not support extra stuff. You could I guess look at a router that could load dd-wrt if you really wanted more control.

In almost all cases you will run out of bandwidth well before you exceed a routers memory or processor ability.