DNS ipv6 syn/ack packets not leaving host, getting dropped?

firebladed

New Member
Mar 13, 2025
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Im having a strange problem with ipv6 dns queries and bind9 in a vm

First i currently have no Firewalls enabled or configured anywhere

for udp dns queries have no issues, but for tcp something odd is happening

if i send a tcp dns query from a device in same network it works

Code:
dig +tcp corp.firebladeautomationsystems.co.uk @2001:8b0:b197::1

if i send the same query from lightsail host in aws it just times out

packet captures on the pfsense gateway see packets going in from internet

packet captures in the vm see syn and syn/ack packets

packet captures in the host from the bridge (vmbr0) see both syn and syn/ack packets

e.g

Code:
00:15:42.530608 IP6 2a05:d01c:f10:9d00:7549:280:6deb:8f19.35173 > 2001:8b0:b197::1.53: Flags [S], seq 3058031343, win 64660, options [mss 1220,sackOK,TS val 3448874250 ecr 0,nop,wscale 7], length 0
00:15:42.530907 IP6 2001:8b0:b197::1.53 > 2a05:d01c:f10:9d00:7549:280:6deb:8f19.35173: Flags [S.], seq 1607815693, ack 3058031344, win 65232, options [mss 1220,sackOK,TS val 156823063 ecr 3448874250,nop,wscale 7], length 0
00:15:43.531723 IP6 2001:8b0:b197::1.53 > 2a05:d01c:f10:9d00:7549:280:6deb:8f19.35173: Flags [S.], seq 1607815693, ack 3058031344, win 65232, options [mss 1220,sackOK,TS val 156824064 ecr 3448874250,nop,wscale 7], length 0
00:15:43.539265 IP6 2a05:d01c:f10:9d00:7549:280:6deb:8f19.35173 > 2001:8b0:b197::1.53: Flags [S], seq 3058031343, win 64660, options [mss 1220,sackOK,TS val 3448875259 ecr 0,nop,wscale 7], length 0

however

packet captures in the host from the interface (enp7s0) only sees the syn packets

e.g
Code:
00:15:42.530608 IP6 (flowlabel 0xd6cb7, hlim 53, next-header TCP (6) payload length: 40) 2a05:d01c:f10:9d00:7549:280:6deb:8f19.35173 > 2001:8b0:b197::1.53: Flags [S], cksum 0xc9a4 (correct), seq 3058031343, win 64660, options [mss 1220,sackOK,TS val 3448874250 ecr 0,nop,wscale 7], length 0
00:15:43.539265 IP6 (flowlabel 0x5fe66, hlim 53, next-header TCP (6) payload length: 40) 2a05:d01c:f10:9d00:7549:280:6deb:8f19.35173 > 2001:8b0:b197::1.53: Flags [S], cksum 0xc5b3 (correct), seq 3058031343, win 64660, options [mss 1220,sackOK,TS val 3448875259 ecr 0,nop,wscale 7], length 0