Invisible public IP of ubuntu 16.04 lts

I have configured two network interfaces in my server based on Ubuntu 16.04 LTS. Below is configuration from /etc/network/interfaces:

Code:

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto enp1s0 enp2s0
iface enp1s0 inet static
        address 192.168.100.206
        network 192.168.100.0
        netmask 255.255.255.0
        broadcast 192.168.100.255
        #gateway 192.168.100.2
        #dns-nameservers 192.168.100.2

iface enp2s0 inet static
        address X.X.X.181
        network X.X.X.176
        netmask 255.255.255.248
        gateway X.X.X.177
        dns-nameservers Y.Y.Y.Y Z.Z.Z.Z

Below is routing table:

Code:

sadmin@scolo006:~$ route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         X.X.X.177  0.0.0.0         UG    0      0        0 enp2s0
X.X.X.176  0.0.0.0         255.255.255.248 U     0      0        0 enp2s0
192.168.100.0   0.0.0.0         255.255.255.0   U     0      0        0 enp1s0

Code:

sadmin@scolo006:~$ ip route
default via X.X.X.177 dev enp2s0 onlink
X.X.X.176/29 dev enp2s0  proto kernel  scope link  src X.X.X.181
192.168.100.0/24 dev enp1s0  proto kernel  scope link  src 192.168.100.206

I can ping public interface (ping command executed from this server, it's his public interface):

Code:

sadmin@scolo006:~$ ping X.X.X.181
PING X.X.X.181 (X.X.X.181) 56(84) bytes of data.
64 bytes from X.X.X.181: icmp_seq=1 ttl=64 time=0.027 ms
^C
--- X.X.X.181 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.027/0.027/0.027/0.000 ms

But I can't ping gateway, google.com, 8.8.8.8, one word - anything:

Code:

sadmin@scolo006:~$ ping google.com
ping: unknown host google.com
sadmin@scolo006:~$ ping X.X.X.177
PING X.X.X.177 (X.X.X.177) 56(84) bytes of data.
From X.X.X.181 icmp_seq=1 Destination Host Unreachable
From X.X.X.181 icmp_seq=2 Destination Host Unreachable
From X.X.X.181 icmp_seq=3 Destination Host Unreachable
^C
--- X.X.X.177 ping statistics ---
4 packets transmitted, 0 received, +3 errors, 100% packet loss, time 3016ms
pipe 3
sadmin@scolo006:~$ ping 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
From X.X.X.181 icmp_seq=1 Destination Host Unreachable
From X.X.X.181 icmp_seq=2 Destination Host Unreachable
From X.X.X.181 icmp_seq=3 Destination Host Unreachable
^C
--- 8.8.8.8 ping statistics ---
4 packets transmitted, 0 received, +3 errors, 100% packet loss, time 3013ms
pipe 3

I have one more Linux server based on Ubuntu 14.04. There "ip route" gives a little another output - there isn't "onlink":

Code:

default via X.X.X.177 dev em4

Other things like routing table looks identical. No idea what is wrong...