after upgrade xUbuntu-16.04 to xUbuntu-18.04 (Experia-Box v10 gives) no internet

Can you ping the router's internal IP?
Can you ping 8.8.8.8?
Can you ping bbc.co.uk and get a resolution to an IP?
Do systems on the same connection get web access OK?

Andrew,

i can ping as well the internal as the external IP from modem (router)

PC on cable can NOT ping to any other IP ( so 8.8.8.8 and bbc.co.uk fails )
LapTop on the same cable CAN ping everything on the internet

PC gets DHCP address ending on xxx.xxx.2.8
laptop gets DHCP address ending on xxx.xxx.2.5

Connection this morning running 16.04 was OK, so
i assume 18.04 does 'something' with the NetXtreme BCM57760 Gigabit network card that is not accepted by the Experia-Box
( a ZTE H369A fibre modem from Dutch provider KPN )

Do you have a gateway IP set for the interface?

Andrew,

nothing was SET by me...
i let NetWorkManager do the Wired-Connection-Setting.

I am not at the location of the PC,
tomorrow i will look at the settings....

I also will try to set some DNS-servers manually in the Wired-Connection settings....

Results will be posted here;
thanks for your reactions here!

# -- NetworkSettings of the wired connection to Experia-Box modem-router

Network-Manager-icon in upper right corner gives this info about the wired connection to the Experia-Box modemrouter.

settings wired connection Laptop : works OK to internet
SAME settings connection PC : internet refused by modem

eth0 ( my-mac-address )
MTU automatic
wake on LAN : all empty
link-negotiate : discard
802.1x-security : all empty
DCB : empty
proxy : methode none
IPv4-settings : automatic & required ( no DNS-servers given )
IPv6-settings : automatic & extentions-OFF & stable-privacy

RESULT:
laptop can connect all websites,
PC can ping only inside-IP and external-IP of modem and no other IP addresses

# -- lshw -C net gives on both machines...

on PC (not able to connect)

description: Ethernet interface
Prod : NetXtreme BCM57760 Gigabite Ethernet PCIe
Logical Name: eth0
size: 1Gbit/s
capabilities: pm msi pciexpress bus_master cap_list ethernet physical tp mii 10bt 10bt-fd 100bt 100bt-fd 1000bt 1000bt-fd autonegotiate
configuration: autonegotiate=ON broadcast=yes driver=tg3 driver-version=3.137 duplex=full firmware=sb v2.07 ip=192.168.2.8 latency=0 link=yes multicast=yes port=MII speed=1Gbit/sec
resources: irq:26 memory:febf0000-febfffff

on laptop (able to connect)
description: Ethernet interface
product: 88E8001 Gigabit Ethernet Controller
vendor: Marvell Technology Group Ltd.
logical name: eth0
size: 1Gbit/s
capacity: 1Gbit/s
capabilities: pm vpd bus_master cap_list rom ethernet physical tp 10bt 10bt-fd 100bt 100bt-fd 1000bt 1000bt-fd autonegotiation
configuration: autonegotiation=on broadcast=yes driver=skge driverversion=1.14 duplex=full ip=192.168.2.5 latency=64 link=yes maxlatency=31 mingnt=23 multicast=yes port=twisted pair speed=1Gbit/s
resources: irq:20 memory:fa9f8000-fa9fbfff ioport:d800(size=256) memory:fa9c0000-fa9dffff

?!?!?

see text above added on febr.28
+ PC relocated
+ PING (ip4 numbers works)
+ PING names doe not work

# -- 2020 march : only ROOT-partition fresh installed

On a new location the root partition was reinstalled using an Xubuntu-usb-stick 18.04.3 LTS i586 Desktop.
The HOME-partition was NOT mounted during this process.
All went conform expectations.
Created the same groups and users (still all on the ROOT-partition), using the 'old' GID and UID.
/etc/fstab modified so that the 'old' HOME partition also is going to be mounted on /home/.
Everything under /home/ on the ROOT-partition was removed.
After reboot upgraded Xubuntu.
PC located on its old location (cat5-wired on the ExperiaBox modem).

Everything seems to work fine now.

Result:
PC-owner can work on the PC.
But no further investigation on the problem can be done here.
So: case closed.

Let's keep enjoying linux !

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