In my MX Juniper router device, there have the IP's address:

admin@juniperMX> show arp no-resolve | match                      
0c:c4:7a:e2:da:3d   ae16.48                  none 

but I can not ping the, and after I deleted the arp:

clear arp hostname

then I ping the address from my router there get success. and now the MAC still is the same as the 0c:c4:7a:e2:da:3d.

So, what's the issue of my router arp progress? how to check the issue?

the command (show system statistics arp) get below information:

admin@juniper> show system statistics arp                                     
     55547805 datagrams received                                            
     15585252 ARP requests received                                         
     5672166 ARP replies received                                           
     1359509150 resolution request  received                                
     0 unrestricted proxy requests                                          
     0 restricted proxy requests                                            
     0 received proxy requests                                              
     0 unrestricted proxy requests not proxied                              
     0 restricted proxy requests not proxied                                
     0 datagrams with bogus interface                                       
     0 datagrams with incorrect length                                      
     0 datagrams for non-IP protocol                                        
     0 datagrams with unsupported op code                                   
     0 datagrams with bad protocol address length                           
     0 datagrams with bad hardware address length                           
     0 datagrams with multicast source address                              
     1532015 datagrams with multicast target address                        
     378 datagrams with my own hardware address                             
     370965 datagrams for an address not on the interface                   
     794 datagrams with a broadcast source address                          
     1 datagrams with source address duplicate to mine                      
     32382640 datagrams which were not for me                               
     719 packets discarded waiting for resolution                           
     21 packets sent after waiting for resolution                           
     2508270833 ARP requests sent                                           
     15585252 ARP replies sent                                              
     0 requests for memory denied                                           
     0 requests dropped on entry                                            
     0 requests dropped during retry                                        
     0 requests dropped due to interface deletion                           
     0 requests on unnumbered interfaces                                    
     0 new requests on unnumbered interfaces                                
     0 replies for from unnumbered interfaces                               
     0 requests on unnumbered interface with non-subnetted donor            
     0 replies from unnumbered interface with non-subnetted donor           
     0 arp packets rejected as family is configured with deny arp           
     0 arp response packets are rejected on mace icl interface              
     3594 arp replies are rejected as source and destination is same        
     0 arp probe for proxy address reachable from the incoming interface    
     0 arp request discarded for vrrp source address                        
     0 self arp request packet received on irb interface                    
     0 proxy arp request discarded as source ip is a proxy target           
     0 arp packets are dropped as nexthop allocation failed                 
     0 arp packets received from peer vrrp rotuer and discarded             
     0 arp packets are rejected as target ip arp resolve is in progress     
     0 grat arp packets are ignored as mac address is not changed           
     0 arp packets are dropped from peer vrrp                               
     0 arp packets are dropped as driver call failed                        
     0 arp packets are dropped as source is not validated 
  • If you are getting an ARP entry for that IP, it looks like ARP is working correctly. Not sure what the problem is exactly.
    – TheCaptain
    Jun 10 '19 at 11:01
  • Please provide a network description and configuration details, without that it's mostly guessing.
    – Teun Vink
    Jun 10 '19 at 11:45
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide and accept your own answer.
    – Ron Maupin
    Dec 15 '19 at 3:34

Based on the few details you gave there are several possibilities:

  1. The MX doesn't try to ping the destination due to some configuration - we don't know its configuration.
  2. The MX does ping the destination but that doesn't reply unless an ARP request has been made previously - we don't know anything about the destination.
  3. Something in between the MX and the destination filters either echo request or reply - we don't know a thing about your network.

You either need to give us a lot more information about your scenario - see https://networkengineering.stackexchange.com/help/how-to-ask for more details - or use packet capturing to find out what's going on.

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