Sat Aug 29 21:23:27 2020 user.crit syslog: get_param value: add
Sat Aug 29 21:29:23 2020 daemon.notice netifd: ppp_4 (2555): udhcpc: sending renew to 10.28.165.50
Sat Aug 29 21:29:23 2020 daemon.notice netifd: ppp_4 (2555): udhcpc: bind(UDP): Cannot assign requested address
Sat Aug 29 21:29:23 2020 daemon.notice netifd: ppp_4 (2555): udhcpc: sending renew to 0.0.0.0
Sat Aug 29 21:29:23 2020 daemon.notice netifd: ppp_4 (2555): udhcpc: lease of 10.28.165.49 obtained, lease time 7200
Sat Aug 29 21:29:23 2020 local1.info hotplug-gsmstate[20809]: envACT: ifupdate
Sat Aug 29 21:29:23 2020 local1.info hotplug-gsmstate[20809]: envDEV: wwan0
Sat Aug 29 21:29:29 2020 local1.notice fwblock[21203]: Started fwblock
Sat Aug 29 21:29:29 2020 local1.notice fwblock[21203]: Applying SSH blocks
Sat Aug 29 21:29:29 2020 local1.notice fwblock[21203]: Applying WebUI blocks
Sat Aug 29 21:29:30 2020 daemon.info dnsmasq[8407]: exiting on receipt of SIGTERM
Sat Aug 29 21:29:31 2020 user.notice dnsmasq: DNS rebinding protection is active, will discard upstream RFC1918 responses!
Sat Aug 29 21:29:31 2020 user.notice dnsmasq: Allowing 127.0.0.0/8 responses
Sat Aug 29 21:29:36 2020 daemon.info dnsmasq[21661]: started, version 2.79 cachesize 150
Sat Aug 29 21:29:36 2020 daemon.info dnsmasq[21661]: compile time options: IPv6 GNU-getopt no-DBus no-i18n no-IDN DHCP DHCPv6 no-Lua TFTP no-conntrack no-ipset no-auth no-DNSSEC loop-detect inotify
Sat Aug 29 21:29:36 2020 daemon.info dnsmasq-dhcp[21661]: DHCP, IP range 192.168.61.200 -- 192.168.61.249, lease time 1h
Sat Aug 29 21:29:36 2020 daemon.info dnsmasq-dhcp[21661]: DHCP, IP range 10.28.165.49 -- 10.28.165.50, lease time 8h
Sat Aug 29 21:29:36 2020 daemon.info dnsmasq[21661]: using local addresses only for domain lan
Sat Aug 29 21:29:36 2020 daemon.info dnsmasq[21661]: reading /tmp/resolv.conf.auto
Sat Aug 29 21:29:36 2020 daemon.info dnsmasq[21661]: using local addresses only for domain lan
Sat Aug 29 21:29:36 2020 daemon.info dnsmasq[21661]: using nameserver 139.7.30.125#53
Sat Aug 29 21:29:36 2020 daemon.info dnsmasq[21661]: using nameserver 139.7.30.126#53
Sat Aug 29 21:29:36 2020 daemon.info dnsmasq[21661]: read /etc/hosts - 1 addresses
Sat Aug 29 21:29:36 2020 daemon.info dnsmasq-dhcp[21661]: read /etc/ethers - 0 addresses
Sat Aug 29 21:29:37 2020 user.notice firewall: Reloading firewall due to ifupdate of ppp_4 (wwan0)
Sat Aug 29 21:29:37 2020 local1.notice fwblock[21692]: Started fwblock
Sat Aug 29 21:29:37 2020 local1.notice fwblock[21692]: Applying SSH blocks
Sat Aug 29 21:29:37 2020 local1.notice fwblock[21692]: Applying WebUI blocks
Sat Aug 29 21:29:38 2020 local1.info hotplug-gsmstate[21732]: envACT: ifupdate
Sat Aug 29 21:29:38 2020 local1.info hotplug-gsmstate[21732]: envDEV: wwan0
Sat Aug 29 21:29:40 2020 user.notice firewall: Reloading firewall due to ifupdate of ppp_4 (wwan0)
Sat Aug 29 21:29:40 2020 local1.notice fwblock[21833]: Started fwblock
Sat Aug 29 21:29:40 2020 local1.notice fwblock[21833]: Applying SSH blocks
Sat Aug 29 21:29:40 2020 local1.notice fwblock[21833]: Applying WebUI blocks
Sat Aug 29 21:39:09 2020 user.notice root: WebUI password auth succeeded for 'admin' from HTTP LAN 192.168.61.89
Sun Aug 30 16:00:00 2020 cron.info crond[1790]: USER root pid 23852 cmd /etc/init.d/rut_fota start
Sun Aug 30 16:32:48 2020 daemon.notice netifd: ppp_4 (2463): udhcpc: sending renew to 10.29.87.176
Sun Aug 30 16:32:48 2020 daemon.notice netifd: ppp_4 (2463): udhcpc: lease of 10.29.87.175 obtained, lease time 7200
Sun Aug 30 17:00:00 2020 cron.info crond[1790]: USER root pid 1877 cmd /etc/init.d/rut_fota start
Sun Aug 30 17:32:48 2020 daemon.notice netifd: ppp_4 (2463): udhcpc: sending renew to 10.29.87.176
Sun Aug 30 17:32:48 2020 daemon.notice netifd: ppp_4 (2463): udhcpc: lease of 10.29.87.175 obtained, lease time 7200
Sun Aug 30 18:00:00 2020 cron.info crond[1790]: USER root pid 11845 cmd /etc/init.d/rut_fota start
And there is no interruption with the internet access.
So I guess the reason for the 15-20 seconds interruption in bridge mode is due to the different renewal handling.