100M WAN link

[joao]

What is the most adequated router for a 100Mb WAN link?

[tdrais]

You will need to provide much more information to get a answer on that one.

Router thoughtput are almost always messured in packets/second rather than bits/second. So to a point it will depend on the size of your packets.

The biggest issue is what the interface is you want to run 100m over. Is it a ethernet or something like a oc3.

If all you need is ethernet and you are not running large routing tables and do not need to do things like NAT a small layer 3 switch may be your best bet. If you get a router that can do 100m throughput you will also be paying for the ablility to run all the interface cards that you do not need.

If you are going to run something other than a ethernet then you need to select your router based on that.

If you want a general guess you can most likely use a smaller 7200 or maybe a 3845 if it can support the interfaces you need.

[joao]

It is a STM-1 link, terminated in a ADM, with a FastEthernet Port. The Router will an FE to the ADM and will provide another FE to LAN. It will have NAT and BGP.

Is this enough?

Where can i find more information about this subject?

thx!

[ilya.varlashkin]

Cisco 2851 seems to be the lowest end that may fit your requirements. It can do 112Mbps with ideal packet size and minimum config.

All depends on which features you're going to put on the top of it (QoS, NAT, firewall, NetFlow etc.), the more features the more higher from that router you'll need to go. And this is with assumption that you actually won't utilize 100Mbps all the time (else you would be going for higher bandwidth if your link is always 100% utilised).

[joao]

2851 is capable of processing 220kpps.

If i use 64-byte packets i will be able to process 112M.

But if I use just for Ethernet processing (for example 2 FE) with 1500-byte packtes i will process 2,6Gbps (=1500*8*220000).

Is this so?

[ilya.varlashkin]

No, it is not. If narrowest in-box path is capable of only 112Mbps, then this is all you gonna have. So you can put there 220K 64Byte packets, or significantly less 1500Byte packets.

[joao]

why then tdreis said it should be mesaured in pps?

[ilya.varlashkin]

Because if you want to achieve wirespeed you need to be sure that you have enough pps. On the other hand, let say you have 64Byte packets and 100Mbps link. If you want to fill the 100Mbit pipe every second, then you have to send roughly 195 thousand packets per second. Suppose now you decide to use 1500Byte packets, it doesn't mean that you still can squeeze 195K packets into that 100Mbit link - they simply won't fit. Same with the router internals.

[joao]

let's see if got it...

you calculated:

pps = (Bandwidth required) / (packet size*8)

So, for a 1500-byte packet

pps = 100Mbps/(1500*8) = 8333 pps.

So I need a router that suport 8kbps. right?

[ilya.varlashkin]

That would be correct if you intend to send only 1500 byte packets all the time and never anything else. Since this is very unlikely, then choosing a router you need to look at both - bps should be high enough to handle your intended traffic volume and PPS should be high enough to handle that volume at smallest packet size.

[paolagallegos]

but this pps is only for egress traffic, what about local traffic...

[jackyoung]

Could you please advise the information of the PPS with egress traffic only ?

What I think the PPS is the whole router processing power. Moreover, not all traffic will be the largest packet size (1500 byte). Most of them may be 64 byte only. So you have to based on the traffic pattern to calcuilate the worst situation then define the router platform requirement.

Hope this helps.