Multilink PPP vs ping times.

Discussion in 'Cisco' started by Mike Dorn, Mar 27, 2007.

  1. Mike Dorn

    Mike Dorn Guest

    OK, I'm new to multilink, so perhaps I'm missing something obvious...

    Two routers with 3 point-to-point T1s between them. One is a 7206VXR, the other
    is a 2821. I've bundled them together with PPP Multilink, intending to create a
    single fat pipe between the sites. (To replace the single T1 we'd been using,
    which will join the bundle once it's behaving properly.) I'm getting the
    increased overall bandwidth ok, but ping times have gone down the toilet. On a
    single T1, average ping time is 6ms; on the bundle it's about 34ms. If I do
    multiple pings for an extended time period, it repeatedly speeds up and slows
    down over about 1-second intervals. CPU times are reasonable: 2% on the 7206
    and 3% on the 2821.

    On 7206 12.2(4)BW1:
    interface Multilink1
    ip address 172.17.1.57 255.255.255.252
    no ip route-cache cef
    delay 2000
    no cdp enable
    ppp multilink
    ppp multilink fragment-delay 20
    ppp multilink interleave
    multilink-group 1
    interface Serial6/1:0
    no ip address
    encapsulation ppp
    no fair-queue
    ppp multilink
    multilink-group 1
    (same for s6/2:0, s6/3:0)

    On 2821 12.4(3g):
    interface Multilink1
    ip address 172.17.1.58 255.255.255.252
    delay 2000
    ppp multilink
    ppp multilink fragment delay 20
    ppp multilink interleave
    ppp multilink group 1
    interface Serial0/0/1:0
    no ip address
    encapsulation ppp
    no fair-queue
    ppp multilink
    ppp multilink group 1
    (same for s0/1/0:0, s0/1/1:0)

    Any ideas?
     
    Mike Dorn, Mar 27, 2007
    #1
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  2. Mike Dorn wrote:

    > OK, I'm new to multilink, so perhaps I'm missing something obvious...
    >
    > Two routers with 3 point-to-point T1s between them. One is a 7206VXR, the
    > other
    > is a 2821. I've bundled them together with PPP Multilink, intending to
    > create a
    > single fat pipe between the sites. (To replace the single T1 we'd been
    > using,
    > which will join the bundle once it's behaving properly.) I'm getting the
    > increased overall bandwidth ok, but ping times have gone down the toilet.
    > On a
    > single T1, average ping time is 6ms; on the bundle it's about 34ms. If I
    > do multiple pings for an extended time period, it repeatedly speeds up and
    > slows
    > down over about 1-second intervals. CPU times are reasonable: 2% on the
    > 7206 and 3% on the 2821.
    >
    >
    > Any ideas?


    Typically this would be because of competing traffic on the link. Remember
    that while your total bandwidth is (almost) tripled, individual packet
    fragments are still sent at T1 rates. You will need to configure quality of
    service if you have traffic which is overly delay sensitive (such as VoIP).

    Good luck and good hunting!
    --
    Vincent C Jones, Consultant Expert advice and a helping hand
    Networking Unlimited, Inc. for those who want to manage and
    Tenafly, NJ Phone: 201 568-7810 control their networking destiny
    http://www.networkingunlimited.com
     
    Vincent C Jones, Mar 29, 2007
    #2
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