为什么我不能从 PC-B ping S1，但可以 ping PC-A？

S1#show running-config 
Building configuration...

Current configuration : 1638 bytes
!
version 16.3.2
no service timestamps log datetime msec
no service timestamps debug datetime msec
service password-encryption

hostname S1

enable secret 5 $1$mERr$9cTjUIEqNGurQiFU.ZeCi1

no ip cef

ipv6 unicast-routing

no ipv6 cef

no ip domain-lookup

spanning-tree mode pvst

interface GigabitEthernet1/0/1

interface GigabitEthernet1/0/2

interface GigabitEthernet1/0/3

interface GigabitEthernet1/0/4

interface GigabitEthernet1/0/5

interface GigabitEthernet1/0/6

interface GigabitEthernet1/0/7

interface GigabitEthernet1/0/8

interface GigabitEthernet1/0/9

interface GigabitEthernet1/0/10

interface GigabitEthernet1/0/11

interface GigabitEthernet1/0/12

interface GigabitEthernet1/0/13

interface GigabitEthernet1/0/14

interface GigabitEthernet1/0/15

interface GigabitEthernet1/0/16

interface GigabitEthernet1/0/17

interface GigabitEthernet1/0/18

interface GigabitEthernet1/0/19

interface GigabitEthernet1/0/20

interface GigabitEthernet1/0/21

interface GigabitEthernet1/0/22

interface GigabitEthernet1/0/23

interface GigabitEthernet1/0/24

interface GigabitEthernet1/1/1

interface GigabitEthernet1/1/2

interface GigabitEthernet1/1/3

interface GigabitEthernet1/1/4

interface Vlan1

 no ip address
 
ipv6 address FE80::1 link-local
 
ipv6 address 2001:DB8:ACAD:1::B/64

ip classless

ip flow-export version 9

banner motd ^CUNAUTHORIZED ACCESS PROHIBITED!^C

line con 0
 password 7 0822455D0A16
 login

line aux 0

line vty 0 4
password 7 0822455D0A16
 login

line vty 5 15
 password 7 0822455D0A16
 login

end