Arista EOS: how to ping link local address under VRF

Here is the subinterface configuration:

interface Ethernet34.4007
   description =>v7:Sp4-ck478
   mtu 9214
   encapsulation dot1q vlan 4007
   vrf cust
   ipv6 address fe80::1/64 link-local

To ping the remote link-local address, we could use 

RtrA#ping vrf cust ipv6 fe80:: interface et34.4007
PING fe80::(fe80::) from fe80::1%et34.4007 et34.4007: 72 data bytes
80 bytes from fe80::1%et31.4007: icmp_seq=1 ttl=64 time=0.076 ms
80 bytes from fe80::1%et31.4007: icmp_seq=2 ttl=64 time=0.029 ms
80 bytes from fe80::1%et31.4007: icmp_seq=3 ttl=64 time=0.027 ms
80 bytes from fe80::1%et31.4007: icmp_seq=4 ttl=64 time=0.027 ms
80 bytes from fe80::1%et31.4007: icmp_seq=5 ttl=64 time=0.032 ms