At 7:29 PM +0000 1/31/03, Chuck Church wrote:
>I got into this discussion kind of late, but here's my take:
>
>Functionally, you can configure either to do what you want. But a 1 armed
>router has a couple major limitations that a layer 3 switch doesn't. A
>layer 3 switch has ASICs (application specific integrated chip/circuit) that
>can perform MAC re-writes, RIB/FIB lookups, rate-limiting, QOS, and ACL at
>wire speed without bothering the CPU of the device.
As you point out, a little indirectly with the footnote about the VIP
in the table below, so do the 7500 and up. Even the 7000 can have
separate routing and switching processors.
Above the 7500, there's extensive use of ASICs and distributed
forwarding processors.
MAC rewrites are normal functions in commercial L2 chips, so that is an
issue.
The question really comes in the more sophisticated QoS and routing
functions, which, after all, tend to be more needed in the WAN.
> A 1 armed router needs
>to use the CPU for some of these functions, and will quickly become a
>bottleneck after a certain level of traffic is passing through.
Agreed, if it is a single CPU router. ASICs even appear on some
lower-end devices for things like encryption.
>Also, a 1
>armed router is limited by it's 1 arm :) That link will be limited to 100
>mb/sec (unless you move up to a 72xx or higher router, where gig is
>possible).
True.
> So for instance if you're copying a large file between VLANs,
>it'd be pretty easy to use up all the bandwidth of that 100 mbit full duplex
>link, even if the CPU wasn't working hard on the 1 armed router.
Looking at the broader picture, it isn't necessarily
route-versus-switch. A heavily used server can have multiple NICs in
multiple VLANs, with full speed on each (including GE). A L2 switch
can handle intra-VLAN switching.
> Moving to
>a layer 3 switch typically bumps that layer 3 device to layer 2 backplane a
>multi-gigabit speed connection. So if your traffic between vlans will ever
>exceed 100 mbit, you can either shell out huge bucks for a 72xx, or get a
>real QOS-friendly 3550 that is both faster and cheaper. Of course if you
>need WAN modules in the device that's another story. I was sent this chart
>a while ago listing speeds of various routers and switches:
>
>> Router Performance Specs
>>
>> Router Switching Performance - Performance based on 64 Byte packets
Obviously, there's a tremendous difference based on which switching
path is used. It can be very feature-, release-, and
platform-dependent if enabling a given feature drops you out of CEF,
fast switching, etc.
It's been my experience this is more likely to happen in an L3
switch or low-end router. This isn't necessarily bad design. Many
of these features are more critical in WANs than LANs, and switches
are, reasonably enough, optimized for LANs.
> >
>> Platform Process Fast Fast
>> Switching Switching Switching
>> (PPS) (Mb/S)
I suspect >>> is bps
> > -------------------------------------------------------
>> 1400 600 4,000 2,048,000
>> 1600 600 4,000 2,048,000
>> 1700 1,500 8,400 4,300,800
>> 2500 800 4,400 2,252,800
>> 261X 1,500 15,000 7,680,000
>> 262X 1,500 25,000 12,800,000
>> 265X 2,000 37,000 18,944,000
>> 3620 2,000 40,000 20,480,000
>> 3640 4,000 80,000 40,960,000
>> 3660 12,000 120,000 61,440,000
>> MC3810 2,000 10,000 5,120,000
>> 4000 1,800 14,000 7,168,000
>> 4500 5,000 40,000 20,480,000
>> 4700 7,000 50,000 25,600,000
>> 7120 13,000 175,000 89,600,000
> > 7140 20,000 300,000 153,600,000
>> 7200-NPE100 7,000 100,000 51,200,000
>> 7200-NPE150 10,000 150,000 76,800,000
>> 7200-NPE175 9,000 175,000 89,600,000
>> 7200-NPE200 13,000 200,000 102,400,000
>> 7200-NPE225 13,000 225,000 115,200,000
>> 7200-NPE300 20,000 300,000 153,600,000
>> 7200-NPE400 20,000 400,000 204,800,000
>> 7200-NSE-1 20,000 300,000 153,600,000
>> uBR-NPE150 10,000 100,000 51,200,000
>> uBR-NPE200 13,000 150,000 76,800,000
>> 7000-RP 2,500 30,000 15,360,000
>> 7500-RSP2 5,000 220,000 112,640,000
>> 7500-RSP4 8,000 345,000 176,640,000
>> 7500-RSP8 22,000 470,000 240,640,000
>> Cat 2948G-L3 N/A 10,000,000 5,120,000,000
>> Cat 4908G-L3 N/A 12,000,000 6,144,000,000
>> Cat 4232-L3 N/A 6,000,000 3,072,000,000
>> Cat -RSM 14,000 175,000 89,600,000
>> Catalyst-RSFC 170,000 87,040,000
>> Catalyst-RSFC/NFFCII 2,000,000 1,024,000,000
>> Catalyst-MSFC (IP,IPX) 15,000,000 7,680,000,000
>> Catalyst-MSFC (Other) 170,000 87,040,000
>> Catalyst-MSFC2 (IP,IPX) 15,000,000 7,680,000,000
>> Catalyst-MSFC2 (Other) 680,000 348,160,000
>> Catalyst-MSFC (X-bar) 30,000,000 15,360,000,000
>>
>> NOTE: VIP2 Distributed Switching significantly increases
> > the performance on RSP platforms.
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=62288&t=62273
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