arp translates ip address to mac addresses.
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the following shows which interface has access to the the default gateway:
$ arp Address HWtype HWaddress Flags Mask Iface 172.28.128.2 ether 08:00:27:88:f1:e5 C enp0s10 172.28.128.1 ether 0a:00:27:00:00:04 C enp0s10 gateway ether 52:54:00:12:35:02 C enp0s3 192.168.56.100 ether 08:00:27:8a:11:d7 C enp0s8 192.168.56.100 ether 08:00:27:8a:11:d7 C enp0s9
This command shows the default gateway’s ip address:
$ arp -n Address HWtype HWaddress Flags Mask Iface 172.28.128.2 ether 08:00:27:88:f1:e5 C enp0s10 172.28.128.1 ether 0a:00:27:00:00:04 C enp0s10 10.0.2.2 ether 52:54:00:12:35:02 C enp0s3 192.168.56.100 ether 08:00:27:8a:11:d7 C enp0s8 192.168.56.100 ether 08:00:27:8a:11:d7 C enp0s9
This matches up with the information provided in the routing tables:
$ route -n Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 0.0.0.0 10.0.2.2 0.0.0.0 UG 100 0 0 enp0s3 10.0.2.0 0.0.0.0 255.255.255.0 U 100 0 0 enp0s3 172.28.128.0 0.0.0.0 255.255.255.0 U 100 0 0 enp0s10 192.168.56.0 0.0.0.0 255.255.255.0 U 100 0 0 enp0s9 192.168.56.0 0.0.0.0 255.255.255.0 U 101 0 0 enp0s8 192.168.122.0 0.0.0.0 255.255.255.0 U 0 0 0 virbr0
$ netstat -nr Kernel IP routing table Destination Gateway Genmask Flags MSS Window irtt Iface 0.0.0.0 10.0.2.2 0.0.0.0 UG 0 0 0 enp0s3 10.0.2.0 0.0.0.0 255.255.255.0 U 0 0 0 enp0s3 172.28.128.0 0.0.0.0 255.255.255.0 U 0 0 0 enp0s10 192.168.56.0 0.0.0.0 255.255.255.0 U 0 0 0 enp0s9 192.168.56.0 0.0.0.0 255.255.255.0 U 0 0 0 enp0s8 192.168.122.0 0.0.0.0 255.255.255.0 U 0 0 0 virbr0
or:
[root@localhost ~]# ip route list default via 10.0.2.2 dev enp0s3 proto static metric 100 10.0.2.0/24 dev enp0s3 proto kernel scope link src 10.0.2.15 metric 100 172.28.128.0/24 dev enp0s10 proto kernel scope link src 172.28.128.4 metric 100 192.168.56.0/24 dev enp0s9 proto kernel scope link src 192.168.56.104 metric 100 192.168.56.0/24 dev enp0s8 proto kernel scope link src 192.168.56.103 metric 101 192.168.122.0/24 dev virbr0 proto kernel scope link src 192.168.122.1