Junos OS

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JUNOS Duplicate IP Addressing Issue

  • 1.  JUNOS Duplicate IP Addressing Issue

    Posted 07-04-2017 00:16

    Hello,

     

    Experieincing an unusual issue, I have a Juniper M120 router peering with a local exchange.

     

    I keep receiving logs of duplicate IP addressing for the ip configured on my end originating from the mac addresses below

     

    Jul  4 07:20:54 2017  XX-XX-RT01 /kernel: KERN_ARP_DUPLICATE_ADDR: duplicate IP address X.X.X.19! sent from address: a4:a1:c2:43:81:3a (error count = 245)
    Jul  4 07:29:43 2017  XX-XX-RT01 /kernel: KERN_ARP_DUPLICATE_ADDR: duplicate IP address X.X.X.19! sent from address: 00:02:3b:08:79:b4 (error count = 246)

     

    But when i check my arp table the mac addresses resolve to other ip addresses

     

    XX-XX-RT01> show arp no-resolve | match a4:a1:c2
    a4:a1:c2:43:81:3a X.X.X.41 xe-0/0/0.0 none

     

    XX-XX-RT01> show arp no-resolve | match 00:02:3b
    00:02:3b:08:79:b4 X.X.X.35 xe-0/0/0.0 none

     

     

     

     



  • 2.  RE: JUNOS Duplicate IP Addressing Issue

    Posted 07-04-2017 04:36

    Hello,

    00:02:3b:08:79:b4 & a4:a1:c2:43:81:3a belong to Ericsson.

    From experience, there are 2 possible causes:

    1/ someone configured X.X.X.19, perhaps as secondary IP, on their kit, and this kit keeps sending gratituous ARP - possble but not very likely

    2/ more likely cause - someone who owns that E/// kit , has X.X.X.19/32 static route configured and it seems this kit has "proxy-arp" ON by default. Therefore, anyone who needs to resolve X.X.X.19 IP gets two ARP responses: one from Your router, and second from that E/// kit. Due to MAC address timeouts & short-lived flooding, You are getting their ARP responses as well and that triggers syslog messages.

    Unfortunately, there is nothing You can do on Your M120 to resolve this. You'd need to contact exchange operator to get this resolved.

    HTH

    Thx
    Alex