Why I can't ping between two siblings macvlans in bridge mode?

Question

In a Ubuntu 20.04 machine connected to my home LAN, I created macvlans under my ethernet device:

$ sudo ip link add macvlan1 link enp37s0 type macvlan mode bridge
$ sudo dhclient macvlan1
$ sudo ip link add macvlan2 link enp37s0 type macvlan mode bridge
$ sudo dhclient macvlan2

By chance, they got the following addresses from DHCP:

• macvlan1: 192.168.0.40
• macvlan2: 192.168.0.41

I could ping my router from each of them:

$ ping 192.168.0.1 -I macvlan1
PING 192.168.0.1 (192.168.0.1) from 192.168.0.40 macvlan1: 56(84) bytes of data.
64 bytes from 192.168.0.1: icmp_seq=1 ttl=64 time=0.713 ms
64 bytes from 192.168.0.1: icmp_seq=2 ttl=64 time=1.25 ms
64 bytes from 192.168.0.1: icmp_seq=3 ttl=64 time=1.20 ms
^C
--- 192.168.0.1 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2034ms
rtt min/avg/max/mdev = 0.713/1.052/1.245/0.240 ms

$ ping 192.168.0.1 -I macvlan2
PING 192.168.0.1 (192.168.0.1) from 192.168.0.41 macvlan2: 56(84) bytes of data.
64 bytes from 192.168.0.1: icmp_seq=1 ttl=64 time=1.15 ms
64 bytes from 192.168.0.1: icmp_seq=2 ttl=64 time=1.13 ms
64 bytes from 192.168.0.1: icmp_seq=3 ttl=64 time=1.07 ms
64 bytes from 192.168.0.1: icmp_seq=4 ttl=64 time=0.548 ms
64 bytes from 192.168.0.1: icmp_seq=5 ttl=64 time=0.619 ms
^C
--- 192.168.0.1 ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 4030ms
rtt min/avg/max/mdev = 0.548/0.903/1.148/0.263 ms

Since they are were created in bridge mode, virtual devices should be connected to each other. But I can't ping one from the other:

$ ping 192.168.0.40 -I macvlan2
PING 192.168.0.40 (192.168.0.40) from 192.168.0.41 macvlan2: 56(84) bytes of data.
^C
--- 192.168.0.40 ping statistics ---
5 packets transmitted, 0 received, 100% packet loss, time 4128ms

$ ping 192.168.0.41 -I macvlan1
PING 192.168.0.41 (192.168.0.41) from 192.168.0.40 macvlan1: 56(84) bytes of data.
^C
--- 192.168.0.41 ping statistics ---
3 packets transmitted, 0 received, 100% packet loss, time 2039ms

Why I can't ping one from another? How to fix this?

Answer 1

The Linux kernel detects incoming packets with a local source address, considers them a routing mistake (packets that a particular computer sends out should never come back), and drops them to prevent network flooding.

Try to put each macvlan into a different network namespace (after all, macvlans were designed to be used from network namespaces). Then it should work.