We want to buy a new router and I'm searching for the best option.
For Cisco routers I have found the 2900s series interesting but I was astounished to see that the WAN performance is only up to 75 Mbps
"They deliver virtualized applications and highly secure collaboration through the widest array of WAN connectivity at high performance that offers concurrent services at up to 75 Mbp"
Does that mean that if we are connected to a symmetrical 100 Mbit Internet connection the router would only support up to 75 Mbit? Is it for every seperate connection or all connections. How is the (theoretical) performance if you have only one connection (e.g. an FTP upload)?
If I need more would I have to upgrade to the 3900s series?
Greetings and thanks
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The reason for ISR "low" performance, they (and their predecessors) were really designed for being feature rich while working with "low speed" serial WAN links. Traditionally, 75 Mbps would be a rather fast WAN link.
Today WANs, running at LAN like speeds, often are LAN like media hand-offs, i.e. Ethernet. Cisco does have a line of MetroEthernet L3 switches, feature poor compared to ISRs, but they offer LAN forwarding performance.
In any case, the "fastest" 2900, the 2951, is Cisco recommended for up to 75 Mbps WAN bandwidth. As you note, this allows for "concurrent services". ISR performance depends very much on average packet sizes and how the router has been configured. At the other extreme, the 2951 is documented as being able to push 5 Gbps, with no services and with maximum size packets. Cisco recommendations are conservative, which means a 2900 series might be perfectly fine on your 100 Mbps link, or might not too. Much would depend on you configuration and what your traffic is like.
Cisco recommends the 3925 for up to 100 Mbps of WAN bandwidth.
I've attached a Cisco whitepaper, which provides much more information about ISR performance.