Round Trip Time of Ping Rely through a Cisco 1841 and to its WAN increases

Unanswered Question
Oct 24th, 2009

Good day to all!

I am currently installing a Cisco 1841 router with a WIC 1T CSU DSU on a branch office with around 5 workstations on the LAN. WAN BW is 256kbps fractional T1 to a MPLS VPN going to our hubsite. I tried to test the connectivity to our hubsite using just 1 workstation and tried ping and web access. Ping replies RTT was averaging 12 to 16ms but when I started browsing the web RTT jumped from 16 ms to 1200ms and averaged between 900ms to 1200ms. Then all access to the web became slow and application access to the hubsite became slow it took 3 to 5 mins for the application to come up.

Anybody experienced this?

I have this problem too.
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ohassairi Sat, 10/24/2009 - 23:26

may be this windows update or one virus that is using your BW.

try to use ACL to limit allowed TCP/UDP ports or IPs..

Joseph W. Doherty Sun, 10/25/2009 - 05:41

It could be just the simple issue you only have 256 Kbps bandwidth. Have you ever used a dial-up 56 Kbps modem? With average modem compression it might transfer around 100 Kbps, so your 256 Kbps is only about 2.5x as fast. [edit] An easy check on bandwidth utilization, what's the interface load stats on the fractional T1 show while such is happening? What about interface drop stats?

Better QoS bandwidth management of the 256 Kbps link should mitigate any bandwidth heavy flow from so adversely impacting another light bandwidth flow (i.e. ping times shouldn't jump as much while there's concurrent web browing). At branch egress, this might be as simple as activation of FQ. For branch ingress, it can be simple or complex. If all traffic is from the hub, FQ shaping its egress traffic to the branch to match branch bandwidth capacity should work. However, if there's multisite commumication (e.g. branch to branch), then you need to rely on MPLS vendor supported QoS.

If the correct QoS implementation doesn't resolve the issues (i.e. there's just still insufficient bandwidth), you'll need to either increase the branch bandwidth and/or use techniques that reduce the demand on WAN bandwidth (e.g. web caching proxy, a WAAS/WAFS implementation).

cbeltranpnbrci Sat, 10/31/2009 - 10:53

joseph,

Hi!

I have configured the the following on the router interface:

interface Serial0/0/0

ip address 10.27.116.1 255.255.255.252

encapsulation ppp

no peer neighbor-route

service-module t1 timeslots 1-4

no cdp enable

But when I verify the serial interface status it give me an available bandwidth of just 192 kbps.

As far as I know the "service-module t1 timeslots 1-4" dictates a bandwidth of 256kbps on the interface itself.

Is there anyway I could check where is the other 64kbps?

Thanks.

Joseph W. Doherty Sat, 10/31/2009 - 14:35

"But when I verify the serial interface status it give me an available bandwidth of just 192 kbps. "

What command are you using and/or where do you "see" 192 Kbps available bandwidth? As least for CBWFQ, by default it set asides 25% of the bandwidth, although it can be used.

cbeltranpnbrci Mon, 11/02/2009 - 10:21

Joseph,

Here is where I see that 192kbps available bandwidth:

show int s0/0/0

Serial0/0/0 is up, line protocol is up

Hardware is GT96K with integrated T1 CSU/DSU

Description: $FW_OUTSIDE$

Internet address is 10.27.19.1/30

MTU 1500 bytes, BW 256 Kbit/sec, DLY 20000 usec,

reliability 255/255, txload 1/255, rxload 2/255

Encapsulation PPP, LCP Open

Open: IPCP, loopback not set

Keepalive set (10 sec)

Last input 00:00:00, output 00:00:00, output hang never

Last clearing of "show interface" counters 3d15h

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 2

Queueing strategy: weighted fair

Output queue: 0/1000/64/0 (size/max total/threshold/drops)

Conversations 0/16/256 (active/max active/max total)

Reserved Conversations 0/0 (allocated/max allocated)

Available Bandwidth 192 kilobits/sec

5 minute input rate 3000 bits/sec, 5 packets/sec

5 minute output rate 2000 bits/sec, 5 packets/sec

1132951 packets input, 767993116 bytes, 0 no buffer

Received 0 broadcasts, 0 runts, 0 giants, 0 throttles

1 input errors, 1 CRC, 0 frame, 0 overrun, 0 ignored, 1 abort

870124 packets output, 120638001 bytes, 0 underruns

0 output errors, 0 collisions, 4 interface resets

0 unknown protocol drops

0 output buffer failures, 0 output buffers swapped out

3 carrier transitions

DCD=up DSR=up DTR=up RTS=up CTS=up

Or on this command:

show queueing interface s0/0/0

Interface Serial0/0/0 queueing strategy: fair

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 2

Queueing strategy: weighted fair

Output queue: 0/1000/64/0 (size/max total/threshold/drops)

Conversations 0/16/256 (active/max active/max total)

Reserved Conversations 0/0 (allocated/max allocated)

Available Bandwidth 192 kilobits/sec

Thanks

Joseph W. Doherty Mon, 11/02/2009 - 10:51

Yea, I think that's just an artifact of WFQ. Notice your show interface has "BW 256 Kbit/sec". I.e., believe you have all 256 Kbps and can utilize it.

[edit]

BTW, since WFQ is active, wouldn't expect ping times to jump so much unless the other side (of the link) is using FIFO.

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