Hi @trieunq22 ,
You need to use the global unicast address as the default gateway, as follow:
PC1: 2001:DB8:1:1::1
PC2: 2001:DB8:1:3::1
PC3: 2001:DB8:1:5::1
You also need to add an IPv6 address on R2 se0/0/1 (2001:db8:1:4::1/64). It shows in the table you provided, but is not configured, which causes se0/0/1 not to be ipv6 enabled.
Regards,
Regards,
Harold Ritter, CCIE #4168 (EI, SP)