WLC 1815i Error for connection

[Ahmed ElShanab]

I have an WLC 1815i and 21 AP 1815i 

All APs joined controller well but all Clients connected to SSIDs on this controller have more packet loss
please help me to solve this problem.

this configuration from management interface for controller:

(Cisco Controller) >show interface detailed management

Interface Name................................... management
MAC Address...................................... 0c:75:bd:d4:ed:60
IP Address....................................... 172.16.20.30
IP Netmask....................................... 255.255.255.0
IP Gateway....................................... 172.16.20.1
IP Address Type.................................. Static
External NAT IP State............................ Disabled
External NAT IP Address.......................... 0.0.0.0
Link Local IPv6 Address.......................... fe80::e75:bdff:fed4:ed60/64
STATE ........................................... NONE
Primary IPv6 Address............................. ::/128
STATE ........................................... NONE
Primary IPv6 Gateway............................. ::
Primary IPv6 Gateway Mac Address................. 00:00:00:00:00:00
STATE ........................................... NONE
VLAN............................................. untagged
Quarantine-vlan.................................. 0
Physical Port.................................... 1
DHCP Proxy Mode.................................. Global
Primary DHCP Server.............................. Unconfigured
Secondary DHCP Server............................ Unconfigured

--More-- or (q)uit
DHCP Option 82................................... Disabled
DHCP Option 82 bridge mode insertion............. Disabled
IPv4 ACL......................................... Unconfigured
IPv6 ACL......................................... Unconfigured
mDNS Profile Name................................ Unconfigured
AP Manager....................................... Yes
Guest Interface.................................. No
L2 Multicast..................................... Enabled

this configuration from the port connected to controller:

interface GigabitEthernet1/0/24
description Connected To Access Point
switchport trunk native vlan 20
switchport trunk allowed vlan 2-7,11,20
switchport mode trunk
end

Note: 

 GUI connected well and every thing is well if I take IP from controller and AP Subnet only

[Scott Fella]

How are the pings when you ping the gateways for 11.1 or 20.1? When a client is associated to the ssid, can they connect to resources on the network and the internet? How are the pings between wireless and wireless or wireless and a local wired server or wired device?

[Ahmed ElShanab]

The ping to 11.1 or 20.1 is very stable, I can ping from any vlan to another as well, only 

Controller and APs have packet loss. 

[balaji.bandi]

Can you also share ping results to .1 gateway? is this good?  is the same device connect to other AP and Controller works good?

Looks for me you get alternative ping success,  Do you have a topology map, (not sure as of now, there may be routing loops i see (but we need your topology map).

[Ahmed ElShanab · Accepted solution]

The problem is I found to interface vlan 20 with same ip on 2 different Switches.

when I removed one everything become okay.