I have a question about vlangroup.

안녕하세요 
최근에 vlangroup을 테스트 하다가 궁금한게 생겼습니다.
vlangroup을 설정하고 icmp를 통과시키고  tcpdump를 확인하면
두가지 유형으로 나옵니다.
사례 1

17:34:00.673678 6c:29:d2:a4:5b:82 > c6:f7:d5:79:71:46, ethertype 802.1Q (0x8100), length 85: vlan 11, p 0, ethertype IPv4, 10.65.154.22 > 165.244.178.4: ICMP echo request, id 19, seq 10242, length 40 in slot1/tmm0 lis=

17:34:00.673744 6e:29:d2:a4:5b:82 > c4:f7:d5:79:71:46, ethertype 802.1Q (0x8100), length 95: vlan 30, p 0, ethertype IPv4, 10.65.154.22 > 165.244.178.4: ICMP echo request, id 19, seq 10242, length 40 out slot1/tmm1 lis=_vlangroup

17:34:00.675591 c4:f7:d5:79:71:46 > 02:00:0c:07:ac:0a, ethertype 802.1Q (0x8100), length 85: vlan 30, p 0, ethertype IPv4, 165.244.178.4 > 10.65.154.22: ICMP echo reply, id 19, seq 10242, length 40 in slot1/tmm0 lis=

17:34:00.675611 c6:f7:d5:79:71:46 > 00:00:0c:07:ac:0a, ethertype 802.1Q (0x8100), length 95: vlan 11, p 0, ethertype IPv4, 165.244.178.4 > 10.65.154.22: ICMP echo reply, id 19, seq 10242, length 40 out slot1/tmm1 lis=_vlangroup

Case 2

If you look at the sequence number, there are 4 packets generated for each pass, sometimes only 2 vlangroups pass through at the end and sometimes all 4. What is the difference between the two?

thank you