When using an FQDN on a forwarding server which resolved as IPv4 and IPv6, FortiGate has the possibility to use the IPV6 address as the forwarding server, even though there is no IPv6 configuration on the FortiGate.
edit "testingFQDN.fortinet.local"
set addr-type fqdn
set fqdn "testingFQDN.fortinet.local"
set port 8080
next
Example of IPv6 resolution in WAD debug:
[I][p:3522] wad_lb_server_dns_resolve :502 DNS look up testingFQDN.fortinet.local (len: 18)
[I][p:3522] __wad_dns_send_query :863 0:0: sending DNS request for remote peer testingFQDN.fortinet.local id=0 IPv4
[I][p:3522] __wad_dns_send_query :863 0:0: sending DNS request for remote peer testingFQDN.fortinet.local id=0 IPv6
[I][p:3522] wad_dns_parse_name_resp :253 0: DNS response received for remote host testingFQDN.fortinet.local req-id=0 ipv4=0
[V][p:3522] wad_dns_parse_name_resp :399 testingFQDN.fortinet.local: resp_type=2 notify=1 cdata=0 27b3:df61:e9c5:b023:7c92:99ca:6ad2:4b38
[I][p:3522] wad_lb_server_dns_req_done :473 DNS req done. server = 0x7fb43deb5328, addr_type: 2. resolved testingFQDN.fortinet.local to 27b3:df61:e9c5:b023:7c92:99ca:6ad2:4b38
[I][p:3522] wad_fwd_svr_update_health_status :2237 server = testingFQDN.fortinet.local(0x7fb43deb5328) lnkmt-name = WEBP-0-testingFQDN.fortinet.local-1 state = 0
[W][p:3522] wad_dns_parse_resp :751 receive response with unknown id=0 ipv4=1
Example of IPv4 resolution in WAD debug:
[I][p:3522] wad_lb_server_dns_resolve :502 DNS look up testingFQDN.fortinet.local (len: 18)
[I][p:3522] __wad_dns_send_query :863 0:0: sending DNS request for remote peer testingFQDN.fortinet.local id=0 IPv4
[I][p:3522] __wad_dns_send_query :863 0:0: sending DNS request for remote peer testingFQDN.fortinet.local id=0 IPv6
[I][p:3522] wad_dns_parse_name_resp :253 0: DNS response received for remote host testingFQDN.fortinet.local req-id=0 ipv4=1
[V][p:3522] wad_dns_parse_name_resp :399 testingFQDN.fortinet.localk: resp_type=1 notify=1 cdata=0 10.0.0.10
[I][p:3522] wad_lb_server_dns_req_done :473 DNS req done. server = 0x7fb43deb5328, addr_type: 2. resolved testingFQDN.fortinet.local to 10.0.0.10
[I][p:3522] wad_fwd_svr_update_health_status :2237 server = testingFQDN.fortinet.local(0x7fb43deb5328) lnkmt-name = WEBP-0-testingFQDN.fortinet.local-0 state = 0
[W][p:3522] wad_dns_parse_resp :751 receive response with unknown id=0 ipv4=0
If the FortiGate only has configuration on IPV4, this will result in an issue when forwarding the traffic to the next proxy server: there will be a '(nil) fwd_srv_ip=' message in the WAD debug.
connect svr orig 10.50.0.10:36415->10.50.0.15:8080 out 10.50.0.10:36415->142.250.197.78:8080
[I][p:3519][s:16925889][r:16998674] wad_http_upd_ses_ctx_by_req :1069 wad http session 0x7f2ef7950f20 forward (nil) fwd_srv_ip=
As a workaround, do not use FQDN and use a static IP instead on the forwarding server.
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