ubuntu arp problem with who-has x.x.x.x tell y.y.y.y

i have a single server which two VM(ubuntu) configured as ubuntu-edge(with frr module for routing - wan side) and ubuntu-fw(for lan side), between these machines there is a virtual internal interface. all the traffic form lan toward fw, and from ubuntu-fw with default route forward to ubuntu-edge. when someone try to reach from behind wan side of the ubuntu-edge to lan side(for example icmp or ssh) cant connect, the tcpdump output is here:

ubuntu@ubuntu-fw:~$ sudo tcpdump -n -i lan host 18.x.x.201
    tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
    listening on lan, link-type EN10MB (Ethernet), snapshot length 262144 bytes
    13:22:43.742256 IP 172.25.4.96 > 18.x.x.201: ICMP echo request, id 60418, seq 4404, length 40
    13:22:43.743299 ARP, Request who-has 172.25.4.96 tell 18.x.x.201, length 46
    13:22:48.861752 ARP, Request who-has 18.x.x.201 tell 18.x.x.1, length 28
    13:22:48.863665 ARP, Reply 18.x.x.201 is-at 74:86:0b:19:fe:c1, length 46
    13:25:42.226903 IP 172.25.4.96 > 18.x.x.201: ICMP echo request, id 60418, seq 4458, length 40
    13:25:42.231842 ARP, Request who-has 172.25.4.96 tell 18.x.x.201, length 46
    13:25:47.236840 IP 172.25.4.96 > 18.x.x.201: ICMP echo request, id 60418, seq 4459, length 40
    13:25:47.237899 ARP, Request who-has 172.25.4.96 tell 18.x.x.201, length 46
    13:25:47.549749 ARP, Request who-has 18.x.x.201 tell 18.x.x.1, length 28

and here is the local route table: ubuntu@ubuntu-fw:~$ ip route show default via 172.24.8.9 dev internal proto static 18.x.x.0/24 dev lan proto kernel scope link src 18.x.x.1 172.24.8.8/30 dev internal proto kernel scope link src 172.24.8.10 the ubuntu-edge, has the route of 172.25.4.96 via bgp dynamic route. what is the problem not forward packet ? by the way packet forwarding is enabled on the both machines. Thanks