Could a 2811 saturate a 100Mbps Internet link?

Discussion in 'Cisco' started by Douglas Carmichael, Nov 18, 2004.

  1. I know that the 2800 series has two FastEthernet ports as-standard,
    but can, say, a 2811 connected to a 100Mbps Internet link fully
    saturate that link even with services like NAT/VPN/voice/QoS enabled?

    (Looking at the descriptions of the 2800 series on Cisco's site and
    the Miercom test report, it talks about being able to saturate a 2xT1
    link, but I don't know how well it would be able to saturate a full
    FastEthernet link.)

    --Douglas
     
    Douglas Carmichael, Nov 18, 2004
    #1
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  2. In article <>,
    Douglas Carmichael <> wrote:
    :I know that the 2800 series has two FastEthernet ports as-standard,
    :but can, say, a 2811 connected to a 100Mbps Internet link fully
    :saturate that link even with services like NAT/VPN/voice/QoS enabled?

    If you read between the lines a bit on the Miercom report, it cannot.
    Look on the bottom left of page 3, "2811 Router's Max Firewall
    Throughput". They had firewall and NAT running on a bidirection UDP
    flow, and saw 130 Mbps total. That's an average of
    65 Mbps in each direction, and that assumes maximum size packets.
    Voice isn't going to use maximum sized packets.

    *If* we suppose that 65 Mbps is the result of routing/processing
    instead of being a limit of the memory buffer speeds (100 Mbps
    memory buffer speeds has been out on devices for 4+ years),
    then we can back-calculate. 1460 bytes happens to be the maximum
    payload size for TCP, so that implies maximum size packets.
    If I recall correctly, once one includes the preamble, CRC,
    and intrafield gap (IFG), that's the equivilent of 1540 octets
    worth of bit-times per packet [close enough anyhow].
    65 M bits/second / (1540 octets/packet * 8 bits/octets) = 5276 packets/second .
    If we then move to minimum length packets,

    5276 packets/s * ((64 + 20) octets/packet * 8 bits/octet = ~ 3.5 megabits/s

    3.5 Mbps is a little over twice T1 speed, and thus agrees well with
    the marketing of the 2811 as being suitable for controlling dual T1's.

    (Note: the 5276 and 3.5 M figures are in each direction.)
    --
    IEA408I: GETMAIN cannot provide buffer for WATLIB.
     
    Walter Roberson, Nov 18, 2004
    #2
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