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MillersvilleEri's avatar
MillersvilleEri
Icon for Nimbostratus rankNimbostratus
Jan 16, 2026

can't access on prem dns when using F5LTM as a gateway

The title is the tl/dr.  I have a server on an internal network that is set up to use our F5 as a gateway.  I have all of the forwarding vip's set up and routed through snat pools.  and if i set the ...
dns
gateway
LTM F5
MillersvilleEri's avatar
MillersvilleEri
Icon for Nimbostratus rankNimbostratus
Jan 19, 2026

Running tmsh list /sys management-route does not show our dns server in the results.  just the gateway for the management network.

and yes the bigip has an interface with a self ip and floating ip on the vlan with the dns servers.  
no, there is not a speciffic tmm route for the third vlan.  at least i do not think so.  here is an output of tmsh show /net route if that is helpful.

 

Injeyan_Kostas's avatar
Injeyan_Kostas
Icon for Nacreous rankNacreous
Jan 20, 2026

ok so having an interface in DNS vlan will never work as forwarding without SNAT because of asymetric routing
your solution as mentioned before is to either use SNAT or create a Performance L4 VS matchning only DNS destination and use your ext vlan next hop as pool
You will also need to define * as port in the pool and also deselect Address and Port Translation on VS.

So you will actually create a Policy Based Routing to forward DNS traffic through your Ext vlan