Got it

Unable to create loop

Created: Dec 26, 2018 09:47:19Latest reply: Dec 27, 2018 01:31:35 825 6 0 0 0
  Rewarded HiCoins: 0 (problem resolved)

I have setup a switch and a hub and connected connection between them, but i cannot find bdu packets on any interfaces and neither the cpu usage going up.

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chenhui
Admin Created Dec 27, 2018 01:31:35

@Skynet_india hello!


I've just tested and found it worked when I created a loop using hub. Please refer to my method.


Topology as per below:


topology


Ping 10.1.11.2 (which can't exist in the topology) and capture the packets on the interface G0/0/2. In no more than 1 second, hundreds of thousands ARP request packets are captured, shown as below:


captured packets


By the way, when the loop occurs, the CPU usage is 4%; the value is 1% with no loop.

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mesbah
mesbah Created Dec 26, 2018 09:53:43

This post was last edited by mesbah at 2018-12-26 09:58. Please check if STP enabled :-

<HUAWEI> system-view


[HUAWEI] stp enable

# Edit STP, RSTP, MSTP, or VBST on GE1/0/1.
<HUAWEI> system-view
[HUAWEI] interface gigabitethernet 1/0/1
[HUAWEI-GigabitEthernet1/0/1] undo stp disable
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chenhui
chenhui Admin Created Dec 26, 2018 10:08:33

@Skynet_india hello sir, if you mean you created a physic loop by connecting two ports to a hub, and the CPU usage is normal, please notice that MSTP is enabled by default on switch, this will make one of the interface under discarding state, if you wanna a real loop, you can try diable stp on the switch and send a broadcast packet into switch, by then, check the CPU usage, you should get a high CPU usage.
by the way, please DO NOT try this in real network.
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Skynet_india
Skynet_india Created Dec 26, 2018 10:22:02

Posted by cWX611640 at 2018-12-26 10:08 @Skynet_india hello sir, if you mean you created a physic loop by connecting two ports to a hub, and ...
Friend,

I have disabled the stp globally, but stil no traffic is passing on physically connected interfaces.
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Skynet_india
Skynet_india Created Dec 26, 2018 10:24:00

Posted by mesbah at 2018-12-26 09:53 Please check if STP enabled :-<HUAWEI> system-view[HUAWEI] stp enable# Edit STP, RSTP, MSTP, or VBST ...
i have disabled stp globally, and checked the status " display stp brief " no interface is showing.
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Skynet_india
Skynet_india Created Dec 26, 2018 11:16:24

Posted by cWX611640 at 2018-12-26 10:08 @Skynet_india hello sir, if you mean you created a physic loop by connecting two ports to a hub, and ...
I have disabled the stp on a switch and created a loop using hub, but still no changes in cpu usage.

I am testing in ensp simulator.

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  • convention:

chenhui
chenhui Admin Created Dec 27, 2018 01:31:35

@Skynet_india hello!


I've just tested and found it worked when I created a loop using hub. Please refer to my method.


Topology as per below:


topology


Ping 10.1.11.2 (which can't exist in the topology) and capture the packets on the interface G0/0/2. In no more than 1 second, hundreds of thousands ARP request packets are captured, shown as below:


captured packets


By the way, when the loop occurs, the CPU usage is 4%; the value is 1% with no loop.

View more
  • x
  • convention:

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