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[Junos] Duplicate IP Address log message alarm when using mc-lag and “mcae-mac-synchronize” feature on QFX

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Article ID: KB27725 KB Last Updated: 05 Mar 2017Version: 2.0
Summary:

When users configure the mcae-mac-synchronize feature on QFX, a "duplicate IP address" error message is seen. This article explains the reason for these messages.

Symptoms:

When users configure the mcae-mac-synchronize feature on QFX the following log messages are seen:

root# run show log messages | match dup
May 28 13:46:30 /kernel: KERN_ARP_DUPLICATE_ADDR: duplicate IP address 101.227.7.1! sent from address: f8:c0:01:3d:af:a8 (error count = 1)
Cause:

Solution:

The Layer 2 Address Learning Daemon was introduced in Junos OS 13.2; from this release onwards these log messages will not be seen.

For information on configuring multichassis link aggregation on the QFX fabric, see the technical document Configuring Multichassis Link Aggregation.

Once the link aggregation group is configured on the QFX, run the show log message command:

root# run show log messages | match dup
May 28 13:46:30 /kernel: KERN_ARP_DUPLICATE_ADDR: duplicate IP address 101.227.7.1! sent from address: f8:c0:01:3d:af:a8 (error count = 1)

These messages are harmless, they are seen because the same IP address would be configured on both the QFX boxes for MAC synchronization. The ARP entry also keeps changing because both the QFX could reply to the ARP request.


For example, consider the following topology:

MC-LAG is running between both the QFX3600s through ae1.

Both LAG links are configured as trunk vlan members all.

The mcae-mac-synchronize feature is enabled for vlan 201.

ICCP is enabled for vlan.100 on both the QFX-3600’s.

From the QFX3500 it is possible to ping the vlan.201 g/w 101.227.7.1 without an issue, but on the QFX3500s users will see a log message for the duplicate IP as shown below:

root# run show log messages | match dup
May 28 13:46:30 /kernel: KERN_ARP_DUPLICATE_ADDR: duplicate IP address 101.227.7.1! sent from address: f8:c0:01:3d:af:a8 (error count = 1)

ARP entry would be changing on the QFX3500. This is expected behavior because both the QFX3600s could reply to the ARP request.

root# run ping 101.227.7.1
PING 101.227.7.1 (101.227.7.1): 56 data bytes
64 bytes from 101.227.7.1: icmp_seq=0 ttl=64 time=7.998 ms
64 bytes from 101.227.7.1: icmp_seq=1 ttl=64 time=1.968 ms
64 bytes from 101.227.7.1: icmp_seq=2 ttl=64 time=2.250 ms
^C
--- 101.227.7.1 ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max/stddev = 1.968/4.072/7.998/2.778 ms

[edit interfaces vlan unit 201]
root# run show arp
MAC Address Address Name Interface Flags
f8:c0:01:3d:af:a8 101.227.7.1 101.227.7.1 vlan.201 none

root# run clear arp
101.227.7.1 deleted

[edit interfaces vlan unit 201]
root# run ping 101.227.7.1
PING 101.227.7.1 (101.227.7.1): 56 data bytes
64 bytes from 101.227.7.1: icmp_seq=0 ttl=64 time=6.658 ms
64 bytes from 101.227.7.1: icmp_seq=1 ttl=64 time=2.338 ms
^C
--- 101.227.7.1 ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max/stddev = 2.338/4.498/6.658/2.160 ms

[edit interfaces vlan unit 201]
root# run show arp
MAC Address Address Name Interface Flags
f8:c0:01:3d:b4:bc 101.227.7.1 101.227.7.1 vlan.201 none

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