Posted on August 10, 2020 9:05 am
 |  Asked by Ismail Kalolwala
 |  133 views
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Hi All,

We are new to Arista VXLAN and EVPN Setup. What we have seen is, we have two data centers, and we have observed that in our DC1, we can show host-flap entries when we execute show bgp evpn host-flap. This is not seen in my DC2. Difference in between DC1 and DC2 is software version.

DC1 is on 4.21.10M where as DC2 is 4.20.10M

Also leaf models are Arista DCS-7160-48YC6-R

Anyone have come across this kind of issues, and can provide inputs, would be appreciated.

 

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Answered on August 10, 2020 9:43 am

Hi Ismail,

Thank you for contacting Arista.

If a host is flapping/moving continuously across multiple VM's, then you would have got similar log msgs as below:(You can check under "show logging" output).

32806 Aug 10 21:48:40 switch Bgp: 3076: %EVPN-3-BLACKLISTED_DUPLICATE_MAC: MAC address 00:16:3e:80:00:15 on VLAN 32 has been blacklisted for moving 5 or more times within the past 180 seconds.

EVPN host-flap blacklist will prevent the advertisement of the MacIP route if the switch detected multiple mac moves within a short period of time.In this case if mac-moves for a particular mac-address occurs  5 times within a period of 180 seconds you would observe above message which prevents the mac address(mac-ip) from getting advertised to other BGP EVPN peers.

Starting from EOS 4.21.3F, we can check such MAC addresses listing by running :
show bgp evpn host-flap

Since DC2 is running 4.20.10M this would not be shown.

To clear the list of all the MAC addresses which were blocked to advertised in EVPN :
clear bgp evpn host-flap

In order to enable/disable this feature:

You can use the below commands to change the default values (timeout/threshold) of this feature or disable it completely for the EVPN address family in BGP:
router-bgp <asn>
address-family evpn
"[ no | default ] host-flap detection window <timeout>"
"[ no | default ] host-flap detection threshold <threshold>"

Could you please answer the below:

1)Why is the host flapping?Is this expected in your EVPN Vxlan environment?

If this is expected in your network you can follow the above procedure.

However in case if this is not expected and is causing impact you can drop a mail to support@arista.com by collecting tech-support log which would open a case with Arista TAC and we can further troubleshoot this issue there.

Below is the procedure to collect tech-support log:

show tech-support | no

Thanks,

Bhavana.

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Posted by Alexis Dacquay
Answered on August 10, 2020 2:08 pm

Ismail,

An EVPN MAC mobility (flap count) is part of the EVPN standard, I would not recommend disabling it, because it would mean you are removing an EVPN loop-protection, except if the frequent flap is by purposeful design.

I suggest to identify the root cause of the MAC Flap, which might be that different switches in DC1 are learning the same MAC address. The switches advertise a route type-2 as soon as they learn it from a locally attached port.

If there is flap, it means that several switches learn that same MAC address locally, alternatively.

Maybe you have a loop between these switches, or unknowingly a duplicate MAC address?

 

To help you in this task I recommend you configuring event-monitor

https://www.arista.com/en/um-eos/eos-section-6-5-event-monitor

 

config

event monitor

event monitor sync

 

Then after some flaps the output from "show event-monitor mac" would show you the changes and were it was locally learnt from.

 

Regards,

Alexis

 

 

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Posted by Ismail Kalolwala
Answered on September 16, 2020 3:23 pm

Thanks for the responses to the query. We have applied a Event Handler which removes any blacklisting.

Once again appreciated.

Regards,

Ismail Kalolwala

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Posted by Ismail Kalolwala
Answered on September 16, 2020 3:23 pm

Thanks for the responses to the query. We have applied a Event Handler which removes any blacklisting.

Once again appreciated.

Regards,

Ismail Kalolwala

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