Routers in Data Centers

Richard A Steenbergen ras at
Sat Sep 25 01:28:37 UTC 2010

On Fri, Sep 24, 2010 at 03:52:22PM +0530, Venkatesh Sriram wrote:
> Hi,
> Can somebody educate me on (or pass some pointers) what differentiates
> a router operating and optimized for data centers versus, say a router
> work in the metro ethernet space? What is it thats required for
> routers operating in data centers? High throughput, what else?

A "datacenter router" is a box which falls into a particular market 
segment, characterized by extremely low cost, low latency, and high 
density ethernet-centric boxes, at the expense of "advanced" features 
typically found in more traditional routers. For example, these boxes 
tend to lack any support for non-ethernet interfaces, MPLS, advanced 
VLAN tag manipulation, advanced packet filters, and many have limited 
FIB sizes. These days it also tends to mean you'll be getting a box with 
only (or mostly) SFP+ interfaces, which are cheaper and easier to do 
high density 10GE with, but at the expense of "long reach" optic 

A "metro ethernet" box also implies a particular market segment, 
typically a smaller box (1-2U) that has certain advanced features which 
are typically not found in other "small" boxes. Specifically, you're 
likely to see advanced VLAN tag manipulation and stacking capabilities, 
MPLS support for doing pseudowire/vpn PE termination, etc, that you 
might normally only expect to see on a large carrier-class router.

Also, an interesting side-effect of the quest for high density 10GE at 
low prices is that modern datacenter routers are largely built on third 
party "commodity" silicon rather than the traditional in-house ASIC 
designs. Many of the major router vendors (Cisco, Juniper, Foundry, 
Force10, etc) are currently producing "datacenter routers" which are 
actually just their software (or worse, someone else's software with a 
little search and replace action on a few strings) wrapped around third 
party ASICs (EZchip, Marvell, Broadcom, Fulcrum, etc). These boxes can 
definitely offer some excellent price/performance numbers, but one 
unfortunate side effect is that many (actually, most) of these chips 
have not been fully baked by the years of experience the more 
traditional router vendors have developed. Many of them have some very 
VERY serious design flaws, causing everything from preventing them from 
fully implementing some of the features you would normally except from a 
quality rouer (multi-label stack MPLS, routed vlan interface counters, 
proper control-plane DoS filter/policing capabilities, etc), or worse 
(in some cases, much, much worse). YYMV, but the 30 second summary is 
that many vendors consider "datacenter" users and/or use cases to be 
unsophisticated, and they're hoping you won't notice or care about some 
of these serious design flaws, just the price per port. Depending on 
your application, that may or may not be true. :)

Richard A Steenbergen <ras at>
GPG Key ID: 0xF8B12CBC (7535 7F59 8204 ED1F CC1C 53AF 4C41 5ECA F8B1 2CBC)

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