I got a new FTTC connection few days ago, along with 8 additional IPv4 addresses, say 89.89.233.104/29 (don't test them, they're fake). The ISP modem has 89.89.233.110 (which is the default gateway), so available for use are from .105 to .109.
I attach my linux computer to the modem LAN, configure with
ifconfig eth0 89.89.233.108 netmask 255.255.255.248
route add default gw 89.89.233.110
From outside I can ping 110 and 108, but from my desktop if I ping outside I get the following:
# ping 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
From 89.89.233.110 icmp_seq=1 Destination Host Prohibited
From 89.89.233.110 icmp_seq=2 Destination Host Prohibited
From 89.89.233.110 icmp_seq=3 Destination Host Prohibited
How is this possible? Why from outside I can be pinged (and so my host is replying to the outside world), but from inside I cannot access internet? I disabled every firewall or whatever enhanced feature I could find on the ISP modem. I tried pinging and tracerouting even ISP's DNS, thinking I could have some DNS restrictions but nothing changed.
I made every possible test, using Linux, Windows 7, pfSense (FreeBSD), they all give the same result. I called the ISP and they're coming to make some test themselves, buf if any suggestion can come from the community I'll be happy to test.
Oh, on a side note, we also have a single Point-to-Point IP on the modem, and internet works perfectly from there (that is: getting DHCP from the modem itself). The modem is connected in Bridged + Routed mode, so apparently it's routing but not correctly bridging.
It was as supposed a modem problem. After 3h the ISP technician replaced it nd magically everything started to work 😀