When monitoring the traffic on the interface with the command monitor traffic interface <interface_name> on Juniper devices running with EVO, will list the ICMP packet as well along with the ARP request when arp is not resolved.
For Ex:
<-- There is no ARP entry on the router for the prefix 10.1.1.2
root@test> show arp no-resolve MAC Address Address Interface Flags 00:00:5b:0b:1f:1c 10.1.2.2 et-0/0/4.0 none Total entries: 1 root@test>
<-- Executing monitor traffic interface on the corresponding intf
root@test> monitor traffic interface et-0/0/3.0 no-resolve NOTE: MAC Addresses 00:00:00:00:00:00 are used when L2 header information in not available. For such packets, L2 headers are added by PFE when transmit and removed before being punted to RE Local vib interface has IP 128.0.0.4. reading from file -, link-type EN10MB (Ethernet), snapshot length 8192 12:11:56.335295 ARP, Request who-has 10.1.1.2 tell 10.1.1.1, length 106 12:11:56.357204 IP 10.1.1.1 > 10.1.1.2: ICMP echo request, id 20000, seq 27, length 64 12:11:57.336907 ARP, Request who-has 10.1.1.2 tell 10.1.1.1, length 106 12:11:57.381049 IP 10.1.1.1 > 10.1.1.2: ICMP echo request, id 20000, seq 28, length 64 12:11:58.337481 ARP, Request who-has 10.1.1.2 tell 10.1.1.1, length 106 12:11:58.405048 IP 10.1.1.1 > 10.1.1.2: ICMP echo request, id 20000, seq 29, length 64 12:11:59.338210 ARP, Request who-has 10.1.1.2 tell 10.1.1.1, length 106 12:11:59.429064 IP 10.1.1.1 > 10.1.1.2: ICMP echo request, id 20000, seq 30, length 64 12:12:00.453048 IP 10.1.1.1 > 10.1.1.2: ICMP echo request, id 20000, seq 31, length 64 12:12:00.455228 ARP, Request who-has 10.1.1.2 tell 10.1.1.1, length 106 12:12:01.456273 ARP, Request who-has 10.1.1.2 tell 10.1.1.1, length 106 12:12:01.477053 IP 10.1.1.1 > 10.1.1.2: ICMP echo request, id 20000, seq 32, length 64
On Juniper devices running with the EVO software its expected behavior.
Before sending the packet out on the interface PFE will verify whether arp is resolved or not.