Routes Help solve a problem

Hello,
I need your help.
I can’t ping from my PBX - Debian 9 and connect to SBC’s servers through our Mikrotik but from the router I can ping and I have a response from the SBC’s servers.
On IP → Firewall → Connections I can see SBC’s src. address to PBX dst. address but the inverse connectivity from PBX to SBC’s address is missing.
Bridge 1 has IP 192.168.17.3 and has ping to all in 192.168.17/29 and to SBC’s servers 172.26.20.1 and 172.27.30.2.
but PBX is with IP 192.168.17.2 and has a ping only to IP 192.168.17/29 but not to the SBC’s servers 172.26.20.1 and 172.27.30.2.
In attachment is my the scheme.
And my settings are very few because the network is a closed type with direct optical connectivity to the provider.

# 2022-12-13 18:44:42 by RouterOS 7.11
# software id = R13V-Z57Q
#
# model = RB951G-2HnD
# serial number = ....
/interface bridge
add arp=proxy-arp ingress-filtering=no name=Bridge1 pvid=21 \
    transmit-hold-count=10 vlan-filtering=yes
/interface ethernet
set [ find default-name=ether1 ] arp=proxy-arp
set [ find default-name=ether2 ] arp=proxy-arp
set [ find default-name=ether3 ] arp=proxy-arp auto-negotiation=no \
    full-duplex=no loop-protect=on speed=100Mbps
set [ find default-name=ether4 ] arp=proxy-arp
set [ find default-name=ether5 ] arp=proxy-arp
/interface wireless
set [ find default-name=wlan1 ] antenna-gain=0 arp=proxy-arp band=2ghz-b/g/n \
    channel-width=20/40mhz-Ce country=brazil disabled=no frequency-mode=\
    manual-txpower hide-ssid=yes mode=ap-bridge name=PPH-2.4Ghz ssid=AUIPit \
    station-roaming=enabled wps-mode=disabled
/interface lte apn
set [ find default=yes ] ip-type=ipv4 use-network-apn=no
/interface wireless security-profiles
set [ find default=yes ] authentication-types=wpa2-psk eap-methods="" mode=\
    dynamic-keys supplicant-identity=MikroTik
/interface bridge port
add bridge=Bridge1 fast-leave=yes ingress-filtering=no interface=ether2 pvid=\
    21 trusted=yes
add bridge=Bridge1 fast-leave=yes ingress-filtering=no interface=ether5 pvid=\
    21 trusted=yes
add bridge=Bridge1 interface=ether1 pvid=21 trusted=yes
add bridge=Bridge1 fast-leave=yes interface=ether3 pvid=21 trusted=yes
add bridge=Bridge1 fast-leave=yes interface=ether4 pvid=21 trusted=yes
/interface bridge settings
set use-ip-firewall-for-pppoe=yes use-ip-firewall-for-vlan=yes
/ip firewall connection tracking
set enabled=yes
/ip neighbor discovery-settings
set discover-interface-list=!dynamic
/ip settings
set max-neighbor-entries=8192
/ipv6 settings
set disable-ipv6=yes max-neighbor-entries=8192
/interface bridge vlan
add bridge=Bridge1 disabled=yes tagged=ether1,ether2,ether3 untagged=ether4,ether5 \
    vlan-ids=21
/interface ovpn-server server
set auth=sha1,md5
/ip address
add address=192.168.17.3/29 interface=Bridge1 network=192.168.17.0
/ip cloud
set ddns-enabled=yes ddns-update-interval=10m
/ip cloud advanced
set use-local-address=yes
/ip firewall filter
add action=accept chain=input comment=\
    "Accept established and related packets" connection-state=\
    established,related disabled=yes
add action=accept chain=input comment=\
    "Accept all connections from local network" disabled=yes
add action=accept chain=forward comment=\
    "Accept all connections from local network" disabled=yes
add action=accept chain=forward comment=\
    "Accept established and related packets" connection-state=\
    established,related disabled=yes
/ip firewall service-port
set ftp disabled=yes
set tftp disabled=yes
set h323 disabled=yes
set pptp disabled=yes
set dccp disabled=yes
set sctp disabled=yes
/ip route
add disabled=no distance=1 dst-address=0.0.0.0/0 gateway=192.168.17.1 \
    pref-src="" routing-table=main scope=30 suppress-hw-offload=no \
    target-scope=10
/ip service
set telnet disabled=yes
set ftp disabled=yes
set www disabled=yes
set ssh disabled=yes
set api disabled=yes
set winbox address=0.0.0.0/0
set api-ssl disabled=yes
/routing bfd configuration
add disabled=no
/system note
set show-at-login=no

How can solve this problem?
MTtoSBC.png

So basically Mikrotik is used as bridge/switch between PBX and provider’s router. Or is it? Is PBX properly configured with route towards SBCs (either default route or specific routes, using provider router’s address as gateway?

If you connect PBX directly to provider’s router, is the connectivity with SBCs OK then?

Your config is hard to read due to many disabled config items … and if you decide to enable that bridge/vlan config line, it’s bound to give you problems on ether1 (under bridge/port it is untagged (it has pvid set) while under bridge/vlan it’s in the tagged port list).