Here's an example of when it hits 10.10.25.14 (on dcr01s24) through bc01n01:
SYN through bc01n01:
bc01n01 $ tcpdump -i eno1 -vv -n -e host 10.10.25.14 and tcp port 9092
00:46:19.295852 00:1c:73:11:8a:83 > 00:23:ae:fe:83:c4, ethertype IPv4 (0x0800), length 74: (tos 0x0, ttl 63, id 61506, offset 0, flags [DF], proto TCP (6), length 60)
185.236.240.38.39384 > 10.10.25.14.9092: Flags [S], cksum 0xf440 (correct), seq 1319813603, win 64240, options [mss 1460,sackOK,TS val 3893286313 ecr 0,nop,wscale 7], length 0
SYN and SYN/ACK on dcr01s24
dcr01s24 $ tcpdump -i enp130s0f0 -vv -n -e host 10.10.25.14 and port 9092
00:46:15.039772 90:1b:0e:08:12:b8 > 90:1b:0e:31:bb:6a, ethertype IPv4 (0x0800), length 74: (tos 0x0, ttl 62, id 2005, offset 0, flags [DF], proto TCP (6), length 60)
185.236.240.38.39380 > 10.10.25.14.9092: Flags [S], cksum 0x1453 (correct), seq 2397532729, win 64240, options [mss 1460,sackOK,TS val 3893282056 ecr 0,nop,wscale 7], length 0
00:46:15.039917 90:1b:0e:31:bb:6a > 00:23:ae:fe:45:8c, ethertype IPv4 (0x0800), length 74: (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto TCP (6), length 60)
10.10.25.14.9092 > 185.236.240.38.39380: Flags [S.], cksum 0xcd59 (incorrect -> 0x365b), seq 1341792797, ack 2397532730, win 65236, options [mss 1400,sackOK,TS val 434785853 ecr 3893282056,nop,wscale 7], length 0
And SYN, SYN/ACK, ACK on boston (different flow):
00:50:36.884468 00:23:ae:fe:45:8c > 00:1c:73:11:8a:83, ethertype IPv4 (0x0800), length 74: (tos 0x0, ttl 64, id 19559, offset 0, flags [DF], proto TCP (6), length 60)
185.236.240.38.39386 > 10.10.25.14.9092: Flags [S], cksum 0xcd59 (incorrect -> 0x7951), seq 1150572718, win 64240, options [mss 1460,sackOK,TS val 3893543902 ecr 0,nop,wscale 7], length 0
00:50:36.884823 90:1b:0e:31:bb:6a > 00:23:ae:fe:45:8c, ethertype IPv4 (0x0800), length 74: (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto TCP (6), length 60)
10.10.25.14.9092 > 185.236.240.38.39386: Flags [S.], cksum 0x54a5 (correct), seq 2657360781, ack 1150572719, win 65236, options [mss 1400,sackOK,TS val 435047699 ecr 3893543902,nop,wscale 7], length 0
00:50:36.884867 00:23:ae:fe:45:8c > 00:1c:73:11:8a:83, ethertype IPv4 (0x0800), length 66: (tos 0x0, ttl 64, id 19560, offset 0, flags [DF], proto TCP (6), length 52)
185.236.240.38.39386 > 10.10.25.14.9092: Flags [.], cksum 0xcd51 (incorrect -> 0x8014), seq 1, ack 1, win 502, options [nop,nop,TS val 3893543902 ecr 435047699], length 0
So that looks fine so far - SYN from boston goes through intermediary host, SYN/ACK from other side, and boston sends an ACK. But the first sign of trouble is if we look further down at dcr01s24 logs:
00:46:15.039917 90:1b:0e:31:bb:6a > 00:23:ae:fe:45:8c, ethertype IPv4 (0x0800), length 74: (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto TCP (6), length 60)
10.10.25.14.9092 > 185.236.240.38.39380: Flags [S.], cksum 0xcd59 (incorrect -> 0x365b), seq 1341792797, ack 2397532730, win 65236, options [mss 1400,sackOK,TS val 434785853 ecr 3893282056,nop,wscale 7], length 0
00:46:16.095067 90:1b:0e:31:bb:6a > 00:23:ae:fe:45:8c, ethertype IPv4 (0x0800), length 74: (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto TCP (6), length 60)
10.10.25.14.9092 > 185.236.240.38.39380: Flags [S.], cksum 0xcd59 (incorrect -> 0x323c), seq 1341792797, ack 2397532730, win 65236, options [mss 1400,sackOK,TS val 434786908 ecr 3893282056,nop,wscale 7], length 0
that's a SYN/ACK retransmit! And then even further down:
00:46:17.013760 00:23:ae:fe:83:20 > 90:1b:0e:31:bb:6a, ethertype IPv4 (0x0800), length 74: (tos 0x0, ttl 62, id 58262, offset 0, flags [DF], proto TCP (6), length 60)
185.236.240.38.39382 > 10.10.25.14.9092: Flags [S], cksum 0x0ae5 (correct), seq 3264954427, win 64240, options [mss 1460,sackOK,TS val 3893284030 ecr 0,nop,wscale 7], length 0
another SYN received from boston for a different flow.
So it seems like dcr01s24 never gets the ACK from boston, and retransmits SYN/ACKs, while boston attempts another connection.
That's odd.