If you want to provide PING / ICMP high priority so you wont get any high delay in ping reply Use the following Code.
/ip firewall mangle add chain=prerouting protocol=icmp action=mark-connection new-connection-mark=icmp-con passthrough=yes comment="" disabled=no add chain=prerouting protocol=icmp connection-mark=icmp-con action=mark-packet new-packet-mark=icmp-pkt passthrough=no comment="" disabled=no /queue tree add burst-limit=0 burst-threshold=0 burst-time=0s disabled=no limit-at=1024k max-limit=2048k name=Hi-Prio-to-icmp-aacable packet-mark=icmp-pkt parent=global-in priority=1 queue=default
Admins Line 
Good work , It’s a very useful post , It’s working good with me , Thank you and waiting for more
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Thanks, i am working on some new scenarios which will be help full for your networks.
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