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ELRP ingress port = egress port


Userlevel 3
Hi everybody!

I configured standalone ELRP-client on my SummitStack (two x480). So, after a couple of days I saw strange log messages...

ELRP.Report: Slot-1: [CLI:Default:2] LOOP DETECTED : 35590 transmited, 23 received, ingress slot:port (1:7) egress slot:port (1:7)[/code]ELRP.Report: Slot-1: [CLI:Default:2] LOOP DETECTED : 35550 transmited, 5 received, ingress slot:port (1:4) egress slot:port (1:4)[/code]It happens periodically, but only on stack. I have nine standalone x480 switches and ELRP works correctly on it. I've never seen this situation on it at any rate.

Can anybody suggest me something?

7 replies

Userlevel 4
there must be loop .
could you trace it down by following below steps
1.see what devices are conencted to 1:4 and 1:7
2.If it is a switch ---run elrp on that switch to indentify the loop.
Most possible cause are phones connecting to edge swicth are looped back within the ports in phone.
Have seen this problem for the past 10 years.
if you find thats the issue.
then the remedy on edge switch is to enable bpdu-restrict /edge safegurad features.
Userlevel 3
Ok. Thanks for this hint!
We see this with some older Cisco phones when switches get rebooted. After some research we found the Cisco phones are designed with a closed circuit that can loop back edp packets before the phone is powered up. We are currently forced to go through the switches after reboots and enable the ports that are disabled due to these "phantom loops".

Has anyone seen ports reported as elrp disabled but actually be active?

Userlevel 7
David Coglianese wrote:

We see this with some older Cisco phones when switches get rebooted. After some research we found the Cisco phones are designed with a closed circuit that can loop back edp packets before the phone is powered up. We are currently forced to go through the switches after reboots and enable the ports that are disabled due to these "phantom loops".

Has anyone seen ports reported as elrp disabled but actually be active?

The phone will still be powered by the switch but could have its data connection disabled by ELRP. Are you sure that's not what you're seeing?
David Coglianese wrote:

We see this with some older Cisco phones when switches get rebooted. After some research we found the Cisco phones are designed with a closed circuit that can loop back edp packets before the phone is powered up. We are currently forced to go through the switches after reboots and enable the ports that are disabled due to these "phantom loops".

Has anyone seen ports reported as elrp disabled but actually be active?

Last time I saw this we disabled the port and re-enabled it to get it to clear out of the elrp. I have also seen the ports because stuck in the disabled state. After hours today I plan to try disabling the port and re-enabling it.

I guess I was trying to find out if this is a known reported bug.

Thanks,
Userlevel 7
David Coglianese wrote:

We see this with some older Cisco phones when switches get rebooted. After some research we found the Cisco phones are designed with a closed circuit that can loop back edp packets before the phone is powered up. We are currently forced to go through the switches after reboots and enable the ports that are disabled due to these "phantom loops".

Has anyone seen ports reported as elrp disabled but actually be active?

If there is a known issue, it's one that I don't recall seeing. Just because I don't recall it doesn't mean there isn't an issue though.
Instead of disabling/re-enabling, you can try the [code]restart port[/code] command since that's a little quicker (note it won't reset inline-power, just the link).
David Coglianese wrote:

We see this with some older Cisco phones when switches get rebooted. After some research we found the Cisco phones are designed with a closed circuit that can loop back edp packets before the phone is powered up. We are currently forced to go through the switches after reboots and enable the ports that are disabled due to these "phantom loops".

Has anyone seen ports reported as elrp disabled but actually be active?

Wow,

This bring back bad memories.

In the interest of providing complete resolution.

We discovered that these older Cisco phones have a physical loop that opens when they receive power. The behavior we saw appeared to be the result of the data link coming up before power could get there to open the loop. As a result the elrp frames made it back to the switch and disabled the port.

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