ping fails, but ping -I eth5 works in Android shell

I am trying to enable Ethernet on my Android-7.1.2. Now, it can acquire ip address from DHCP server. ifconfig shows that the Ethernet port can receive lots of packets, but just sends a few out, as below:

  eth5

Link encap:Ethernet  HWaddr 00:04:9f:04:4d:51



  inet addr:10.193.20.83  Bcast:10.193.20.255  Mask:255.255.255.0



  inet6 addr: fe80::204:9fff:fe04:4d51/64 Scope: Link



  UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1



  RX packets:10513 errors:0 dropped:0 overruns:0 frame:0



  TX packets:22 errors:0 dropped:0 overruns:0 carrier:0



  collisions:0 txqueuelen:1000



  RX bytes:926773 TX bytes:2204



  Memory:1aea000-1aeafff

And ping -I eth5 10.193.20.64 can work:

layerscape:/ # ping -I eth5 10.193.20.64



PING 10.193.20.64 (10.193.20.64) from 10.193.20.83 eth5: 56(84) bytes of data.



64 bytes from 10.193.20.64: icmp_seq=1 ttl=64 time=0.345 ms



64 bytes from 10.193.20.64: icmp_seq=2 ttl=64 time=0.354 ms

However, ping 10.193.20.64 fails with:

layerscape:/ # ping 10.193.20.64



connect: Network is unreachable

And here is my route:

layerscape:/ # route -n

Kernel IP routing table

Destination
  Gateway

Genmask

Flags Metric Ref
 Use Iface



10.193.20.0
  0.0.0.0

255.255.255.0
U
  0

0

  0 eth5

What am I losing?