3 virtual machines are in my network, all running Ubuntu Desktop. I've configured one of them as a router and the other two can ping each other flawlessly in LAN. But after adding a NAT adapter(ens37), when I ping google.com, it still asks my Ubuntu router(ens33) for it. Something wrong with default gateway? How to make it work?

Pinging google from the guest after adding NAT:

PING google.com (216.239.38.120) 56(84) bytes of data.
From _gateway (10.0.0.1) icmp_seq=1 Destination Net Unreachable
From _gateway (10.0.0.1) icmp_seq=2 Destination Net Unreachable

--- google.com ping statistics ---
2 packets transmitted, 0 received, +2 errors, 100% packet loss, time 1002ms

The guest's gateway:

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         10.0.0.1        0.0.0.0         UG    20100  0        0 ens33
0.0.0.0         192.168.26.2    0.0.0.0         UG    20101  0        0 ens37
10.0.0.0        0.0.0.0         255.0.0.0       U     100    0        0 ens33
169.254.0.0     0.0.0.0         255.255.0.0     U     1000   0        0 ens33
192.168.26.0    0.0.0.0         255.255.255.0   U     101    0        0 ens37

Thanks.