[strongSwan] AWS EC2 IKEv2 tunnel up but no throughput

[Lewis Shobbrook]

Hi Guys,
I have an IKEv2 tunnel that is established and up, but I am unable to
route any packets across it.
All ACL's are configured to allow UDP 500,4500 & protocols 50, 51 &
icmp to/from the non aws end.
Local iptables are permissive with default policys ACCEPT
Security groups also allow anything outbound and the above ports &
protos inbound.
Here are a few particulars typically requested ahead of time.
ip_forward is enabled rp_filter disabled as follows...
net.ipv4.ip_forward = 1
net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.default.send_redirects = 0
net.ipv4.tcp_max_syn_backlog = 1280
net.ipv4.icmp_echo_ignore_broadcasts = 1
net.ipv4.conf.all.accept_source_route = 0
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.all.secure_redirects = 0
net.ipv4.conf.all.log_martians = 1
net.ipv4.conf.default.accept_source_route = 0
net.ipv4.conf.default.accept_redirects = 0
net.ipv4.conf.default.secure_redirects = 0
net.ipv4.icmp_echo_ignore_broadcasts = 1
net.ipv4.icmp_ignore_bogus_error_responses = 1
net.ipv4.tcp_syncookies = 1
net.ipv4.conf.all.rp_filter = 0
net.ipv4.conf.default.rp_filter = 0
net.ipv4.tcp_mtu_probing = 1

tcpdump just shows one way requests
Looking at the 220 rt table I can see that the auto added route
appears to be correct, and the xfrm policy nothing obvious to me, with
no xfrm vi's used.
Obfuscated ip's naturally...
ip r li ta 220
198.168.248.0/29 via 48.138.201.65 dev eth0 proto static src 48.138.201.70
ip xfrm policy
src 48.138.201.64/26 dst 198.168.248.0/29
    dir out priority 371839 ptype main
    tmpl src 48.138.201.70 dst 68.169.15.170
        proto esp spi 0x2c1e849e reqid 1 mode tunnel
src 198.168.248.0/29 dst 48.138.201.64/26
    dir fwd priority 371839 ptype main
    tmpl src 68.148.15.170 dst 48.138.201.70
        proto esp reqid 1 mode tunnel
src 198.168.248.0/29 dst 48.138.201.64/26
    dir in priority 371839 ptype main
    tmpl src 68.148.15.170 dst 48.138.201.70
        proto esp reqid 1 mode tunnel
src 0.0.0.0/0 dst 0.0.0.0/0
    socket in priority 0 ptype main
src 0.0.0.0/0 dst 0.0.0.0/0
    socket out priority 0 ptype main
src 0.0.0.0/0 dst 0.0.0.0/0
    socket in priority 0 ptype main
src 0.0.0.0/0 dst 0.0.0.0/0
    socket out priority 0 ptype main
src ::/0 dst ::/0
    socket in priority 0 ptype main
src ::/0 dst ::/0
    socket out priority 0 ptype main
src ::/0 dst ::/0
    socket in priority 0 ptype main
src ::/0 dst ::/0
    socket out priority 0 ptype main
src 198.168.248.0/29 dst 48.138.201.64/26
    dir fwd priority 371840 ptype main
    tmpl src 68.148.15.170 dst 48.138.201.70
        proto esp reqid 2 mode tunnel
src 198.168.248.0/29 dst 48.138.201.64/26
    dir in priority 371840 ptype main
    tmpl src 68.148.15.170 dst 48.138.201.70
        proto esp reqid 2 mode tunnel
src 48.138.201.64/26 dst 198.168.248.0/29
    dir out priority 371840 ptype main
    tmpl src 48.138.201.70 dst 68.169.15.170
        proto esp reqid 2 mode tunnel

ipsec statusall
Status of IKE charon daemon (strongSwan 5.7.2, Linux
4.14.232-177.418.amzn2.x86_64, x86_64):
  uptime: 54 minutes, since Jul 05 06:10:30 2021
  malloc: sbrk 2846720, mmap 0, used 1023696, free 1823024
  worker threads: 11 of 16 idle, 5/0/0/0 working, job queue: 0/0/0/0,
scheduled: 1
  loaded plugins: charon pkcs11 tpm aesni aes des rc2 sha2 sha1 md4
md5 mgf1 random nonce x509 revocation constraints acert pubkey pkcs1
pkcs7 pkcs8 pkcs12 pgp dnskey sshkey pem openssl gcrypt fips-prf gmp
curve25519 chapoly xcbc cmac hmac ctr ccm gcm curl attr kernel-netlink
resolve socket-default farp stroke vici updown eap-identity eap-sim
eap-aka eap-aka-3gpp eap-aka-3gpp2 eap-md5 eap-gtc eap-mschapv2
eap-dynamic eap-radius eap-tls eap-ttls eap-peap xauth-generic
xauth-eap xauth-pam xauth-noauth dhcp led duplicheck unity counters
Listening IP addresses:
  48.138.201.70
Connections:
tunnel1:  %any...68.148.15.170  IKEv2
tunnel1:   local:  uses pre-shared key authentication
tunnel1:   remote: uses pre-shared key authentication
tunnel1:   child:  48.138.201.64/26 === 198.168.248.0/29 TUNNEL
Security Associations (1 up, 0 connecting):
tunnel1[2]: ESTABLISHED 24 minutes ago,
48.138.201.70[48.138.201.70]...65.169.15.170[65.169.15.170]
tunnel1[2]: IKEv2 SPIs: d3e732eb14d78aec_i* b06860d1ceee2f9a_r,
rekeying disabled
tunnel1[2]: IKE proposal: AES_GCM_16_256/PRF_HMAC_SHA2_384/ECP_384
tunnel1{2}:  INSTALLED, TUNNEL, reqid 2, ESP in UDP SPIs: cb651f89_i 479cff91_o
tunnel1{2}:  AES_GCM_16_256, 0 bytes_i, 0 bytes_o, rekeying disabled
tunnel1{2}:   48.138.201.64/26 === 198.168.248.0/30

VPC flow logs show no proto 50, only 4500 & 500.
I've also tried to clamp mss not that I expect it would have changed 0
throughput
iptables -t mangle -A FORWARD -m policy --pol ipsec --dir in -p tcp -m
tcp --tcp-flags SYN,RST SYN -m tcpmss --mss 1361:1536 -j TCPMSS
--set-mss 1360

I've spent hours searching but have not found anything to help.
Hoping someone here may have a suggestion ot two?
Cheers,

Lew