Map domain is configured as

• IPv6 src: 2001:db8:ffff::1
• IPv6 prefix: 2001:db8::/48
• IPv4 prefix: 20.0.0.0/16
• EA bits length: 16
• PSID length: 8
• PSID offset: 6

An IPv4 packet is send to 20.0.6.5 with UDP dst port 1232.
The computed IPv6 destination is 3401:db8::1400:605:34 witch is not from configured IPv6 preffix.

VAT configuration

sw_interface_add_del_address sw_if_index 1 2001:0::1/64
sw_interface_add_del_address sw_if_index 2 10.0.0.1/24
sw_interface_set_flags sw_if_index 1 admin-up
sw_interface_set_flags sw_if_index 2 admin-up

::/0 via 2001:0::2 sw_if_index 1
ip_neighbor_add_del sw_if_index 1 dst 2001:0::2 mac 08:00:27:46:2b:4c

map_add_domain ip4-pfx 20.0.0.0/16 ip6-pfx 2001:db8::/48 ip6-src 2001:db8:ffff::1 ea-bits-len 16 psid-offset 6 psid-len 8

Sending packet out of eth3
###[ Ethernet ]###
dst = 08:00:27:66:b8:57
src = 08:00:27:1a:17:8e
type = 0x800
###[ IP ]###
version = 4L
ihl = 5L
tos = 0x0
len = 28
id = 1
flags =
frag = 0L
ttl = 64
proto = udp
chksum = 0xfcca
src = 100.0.0.1
dst = 20.0.6.5
\options \
###[ UDP ]###
sport = 20000
dport = 1232
len = 8
chksum = 0x2ee8

Received packet on eth2
###[ Ethernet ]###
dst = 08:00:27:46:2b:4c
src = 08:00:27:f3:be:f0
type = 0x86dd
###[ IPv6 ]###
version = 6L
tc = 0L
fl = 0L
plen = 28
nh = IP
hlim = 63
src = 2001:db8:ffff::1
dst = 3401:db8::1400:605:34
###[ IP ]###
version = 4L
ihl = 5L
tos = 0x0
len = 28
id = 1
flags =
frag = 0L
ttl = 63
proto = udp
chksum = 0xfdca
src = 100.0.0.1
dst = 20.0.6.5
\options \
###[ UDP ]###
sport = 20000
dport = 1232
len = 8
chksum = 0x2ee8
###[ Padding ]###
load = '\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'

show trace
00:00:28:692049: dpdk-input
GigabitEthernet0/a/0 rx queue 0
buffer 0x10eb9: current data 0, length 60, free-list 0, totlen-nifb 0, trace 0x0
PKT MBUF: port 1, nb_segs 1, pkt_len 60
buf_len 2176, data_len 60, ol_flags 0x0, data_off 128, phys_addr 0x7d02ac80
packet_type 0x0
IP4: 08:00:27:1a:17:8e -> 08:00:27:66:b8:57
UDP: 100.0.0.1 -> 20.0.6.5
tos 0x00, ttl 64, length 28, checksum 0xfcca
fragment id 0x0001
UDP: 20000 -> 1232
length 8, checksum 0x2ee8
00:00:28:692096: ethernet-input
IP4: 08:00:27:1a:17:8e -> 08:00:27:66:b8:57
00:00:28:692100: ip4-input
UDP: 100.0.0.1 -> 20.0.6.5
tos 0x00, ttl 64, length 28, checksum 0xfcca
fragment id 0x0001
UDP: 20000 -> 1232
length 8, checksum 0x2ee8
00:00:28:692102: ip4-lookup
fib 0 adj-idx 5 : map flow hash: 0x00000000
UDP: 100.0.0.1 -> 20.0.6.5
tos 0x00, ttl 64, length 28, checksum 0xfcca
fragment id 0x0001
UDP: 20000 -> 1232
length 8, checksum 0x2ee8
00:00:28:692103: ip4-map
MAP domain index: 0 L4 port: 1232
00:00:28:692104: ip6-lookup
fib 0 adj-idx 16 : GigabitEthernet0/9/0
IP6: 08:00:27:f3:be:f0 -> 08:00:27:46:2b:4c flow hash: 0x00000000
IP_IN_IP: 2001:db8:ffff::1 -> 3401:db8::1400:605:34
tos 0x00, flow label 0x0, hop limit 64, payload length 28
00:00:28:692108: ip6-rewrite
tx_sw_if_index 1 adj-idx 16 : GigabitEthernet0/9/0
IP6: 08:00:27:f3:be:f0 -> 08:00:27:46:2b:4c flow hash: 0x00000000
IP6: 08:00:27:f3:be:f0 -> 08:00:27:46:2b:4c
IP_IN_IP: 2001:db8:ffff::1 -> 3401:db8::1400:605:34
tos 0x00, flow label 0x0, hop limit 63, payload length 28
00:00:28:692109: GigabitEthernet0/9/0-output
GigabitEthernet0/9/0
IP6: 08:00:27:f3:be:f0 -> 08:00:27:46:2b:4c
IP_IN_IP: 2001:db8:ffff::1 -> 3401:db8::1400:605:34
tos 0x00, flow label 0x0, hop limit 63, payload length 28
00:00:28:692109: GigabitEthernet0/9/0-tx
GigabitEthernet0/9/0 tx queue 0
buffer 0x10eb9: current data -40, length 100, free-list 0, totlen-nifb 0, trace 0x0
IP6: 08:00:27:f3:be:f0 -> 08:00:27:46:2b:4c
IP_IN_IP: 2001:db8:ffff::1 -> 3401:db8::1400:605:34
tos 0x00, flow label 0x0, hop limit 63, payload length 28

vppctl show version
load_one_plugin:63: Loaded plugin: /usr/lib/vpp_api_test_plugins/snat_test_plugin.so
load_one_plugin:63: Loaded plugin: /usr/lib/vpp_api_test_plugins/ioam_pot_test_plugin.so
vpp v16.09-rc0~233-gad2c9c0~b404 built by jenkins on ubnt-trusty-3ab at Thu Jul 14 14:53:37 UTC 2016