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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 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