DNS Query - reply from unexpected source

Hi Guys,

I'm new to F5, and something annoy me i can't find why it happen.

My topology:

Network (Public IP - Pretend its 100.100.100.0/24) --> Switch Stack --> LAG --> Viprion LTM --> Cisco CRS --> WWW

I have Viprion 4800 and for now i just wanna allow traffic to go outside, here are my questions :

1. I've added virtual-server with 0.0.0.0/0.0.0.0 as Forwarding (IP) to allow the LAN to have connectivity.

but unless i open virtual server back inside (100.100.100.0/255.255.255.0) i have no connectivity. Isn't it statefull ?

2. After i open the rule I talked about in (1). i have this message when i try simple resolving from server behind the F5.

[ip@qa-env ~]$ host google.com 8.8.4.4

;; reply from unexpected source: 8.8.4.425965, expected 8.8.4.453

tcpdump show this

22:45:39.033309 IP 100.100.100.40.39945 > 8.8.4.4.53: 8917+ A? google.com. (27)

22:45:39.033315 IP 100.100.100.40.39945 > 8.8.4.4.53: 8917+ A? google.com. (27)

22:45:39.123868 IP 8.8.4.4.53 > 100.100.100.40.39945: 8917 1/0/0 A 173.194.41.69 (43)

22:45:39.123884 IP 8.8.4.4.25965 > 100.100.100.40.39945: UDP, length 43

So the packets goes all good until the return packet back to the F5 and then he alter the port!

What am i missing ?

*remember, i have public ip on the server. i just changed it to 100.100.100.40 for the example.

my Virtuals

ltm virtual MNG_ALLOW_ALL_OUT {

description "Management Rule - Allow All Traffic Outside"

destination 0.0.0.0:any

ip-forward

mask any

profiles {

fastL4 { }

}

translate-address disabled

translate-port disabled

vlans {

DNS_LAN

LDAP_LAN

RADIUS_LAN

}

vlans-enabled

}

ltm virtual MNG_QA_ENV_IN {

description "Management Rule - Allow Radius traffic in"

destination 100.100.100.0:any

ip-forward

mask 255.255.255.0

profiles {

fastL4 { }

}

translate-address disabled

translate-port disabled

vlans {

CRS1.WAN

CRS2.WAN

}

vlans-enabled

}