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Complex Real World Network Issue

Dear Friends,

This time I am stuck with one complex issue. So please tell me if you can help me with this.

Here is my issue and network setup:

Traffic Flow -> Broadband Customers -> Subscriber Module -> Access Point -> Backhaul Device (remote side) -> Backhaul Device (Our ISP end) -> Cisco Switch (3560)

On 3560 Switch -> Port 1,2 and Port 3 for example are in same vlan --> VLAN 5

Port 1 is connected to Backhaul device (ISP end)

Port 2 is connected to My laptop running windows os

Port 3 is connected to Laptop running Debain Linux

Now all Access Points and Backhaul devices are running on 172.25.x.x network

My Windows Laptop has IP 172.25.0.253

Laptop running Linux has got IP 172.25.0.230

From Backhaul to Backhaul we are using 5.8 Ghz band and from AP to SM we are using 2.4 Ghz band

.................................................................................

Issue -

When I ping any backhaul or access point, sitting right on my Windows laptop, I get one reply and then RTO starts coming. After that if I clear windows arp manually using arp -d command on command prompt. And tries to ping same destination again, I starts getting replies and some times again I faces same issue of one reply and other RTO. Also sometimes replies keeps coming back and than after 10-15 mins or so, again RTO..So I have to again clear windows arp manually.

At the same time if I ping any Backhaul or AP from Linux laptop, I dont get any RTO or drop. Which is very strange.

Now the things I have tried till now are following:

1. Connected diff windows laptop on port 2 but no luck

2. Connected Windows laptop on port 3 , where Linux pc was connected....still no luck

3. Changed port for Windows laptop like port 10 which is again in same vlan.....no luck

4. Ok finally I changed the 3560 switch and put a 3550 with same vlan configuration.....no luck

5. connected linux laptop on port 2..hmmm...it still pings everthing without even a single drop

Few days back...everything was working fine....but I dont know when this all started off. I only came to know when I saw our NMS running on Windows machine is showing our lots of Backhaul and APs as down. So I tried to ping those devices from Linux pc and It ping those without any drop

Just for you sake...We have so many APs and Backhaul Devices...and issue is with all of them almost while pinging.

Also problem can not be with MTU as I tried with varius machines. Its also not arp issue related on Windows...

So please suggest something ....

Thanks & Best Regards,

Deepak Arora

C:\Documents and Settings\Administrator>ping 172.25.10.43

Pinging 172.25.10.43 with 32 bytes of data:

Reply from 172.25.10.43: bytes=32 time=2ms TTL=30

Request timed out.

Request timed out.

Request timed out.

Ping statistics for 172.25.10.43:

Packets: Sent = 4, Received = 1, Lost = 3 (75% loss),

Approximate round trip times in milli-seconds:

Minimum = 2ms, Maximum = 2ms, Average = 2ms

C:\Documents and Settings\Administrator>arp -d

C:\Documents and Settings\Administrator>tracert 172.25.10.43

Tracing route to 172.25.10.43 over a maximum of 30 hops

1 1 ms 1 ms 1 ms 172.25.10.43

Trace complete.

C:\Documents and Settings\Administrator>ping 172.25.10.43

Pinging 172.25.10.43 with 32 bytes of data:

Reply from 172.25.10.43: bytes=32 time<1ms TTL=30

Reply from 172.25.10.43: bytes=32 time=1ms TTL=30

Reply from 172.25.10.43: bytes=32 time<1ms TTL=30

Reply from 172.25.10.43: bytes=32 time=1ms TTL=30

Ping statistics for 172.25.10.43:

Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),

Approximate round trip times in milli-seconds:

After 5 mins…

C:\Documents and Settings\Administrator>ping 172.25.10.43

Pinging 172.25.10.43 with 32 bytes of data:

Reply from 172.25.10.43: bytes=32 time=1ms TTL=30

Request timed out.

Request timed out.

Request timed out.

Ping statistics for 172.25.10.43:

Packets: Sent = 4, Received = 1, Lost = 3 (75% loss),

1 REPLY
Hall of Fame Super Silver

Re: Complex Real World Network Issue

Hello Deepack,

all the problems you have described make me think of an ARP related issue in the following terms:

a misbeahving device is sending gratuitous ARP (unsolicited broadcast frames) proposing its MAC address as the MAC of every IP in the subnet.

Not all OSes accept gratuitous ARPs so this could explain the difference between the two laptops.

To check this you should verify the entries in the ARP table on the windows PC on a second shell during ping test to see if there is any change.

When the offending device is off everything works well.

This is just a guess.

Hope to help

Giuseppe

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