There is a change in how Routing Engine (RE) generated packets have their type of service (ToS) values set when enhanced subscriber management is enabled. For more details, refer to Configuring Junos OS Enhanced Subscriber Management.

This article explains in detail what the change is and why it was made.

 

Enhanced subscriber management includes the bbe-smgd daemon. When it generates packets such as ICMP Echo Requests to a client, the packets go out with ToS set to 0xc0 or Internetwork Control, populating Queue 3 by default. When it is not enabled or when the router runs legacy releases (prior to Junos OS 15.1), ToS is set to 0x0.

When looking at the ToS values for RE-generated packets to a subscriber, the packets in the older code (releases prior to Junos OS 15.1) go out with 0x0, as seen with monitor traffic:

12:08:33.832067 bpf_flags 0x80, Out
        -----original packet-----
        84:18:88:f5:1f:c3 > 1c:76:81:19:00:00, ethertype 802.1Q (0x8100), length 102: vlan 12, p 0, ethertype IPv4, (tos 0x0, ttl  64, id 8741, offset 0, flags [none], proto: ICMP (1), length: 84) 151.202.27.1 > 151.202.27.48: ICMP echo request, id 54293, seq 0, length 64

However, with enhanced subscriber management, the packets use 0xc0 for Internetwork Control:

10:47:53.964790 Out
        Juniper PCAP Flags [no-L2]
        -----original packet-----
        PFE proto 2 (ipv4): (tos 0xc0, ttl 255, id 0, offset 0, flags [none], proto: ICMP (1), length: 84) 130.81.224.2 > 171.20.185.145: ICMP echo request, id 58273, seq 0, length 64

 

This is an intentional change with enhanced subscriber management. The packets are control frames so default ToS was not desirable.