Re: need help understanding native vlan and what it does also with dhcp and encapsolation on router

dolanduck. · ‎11-18-2017

need help understanding native vlan and what it does also when to use it.i also need help with dhcp and encapsulation on router

so i drew a circle what i need help on. so lets say that i do int g0/1. then i do switch-port mode trunk. then switch-port trunk native vlan45 but for only my trunk not for access. but for my access i did vlan36 for it. i did f0/1 then switch-port mode access then i did switch-port access vlan 36 now by doing that does it provide extra security. the trunking do i use native trunking for switch to switch.

and for the next question on the picture i put of the topology. on router3 i want that to be my dhcp server.

so on my router i have go/1 and that's connected to vlan36 and the serial i got both routers connected to vlan 15 and 30. but what i want to know is do i sub interface 15 and 30 for the serial and g0/1 i do sub interface 30. what i want to know is do i slit it up. if we can video call that would be nice here is my email waffi1234@gmail.com and voice recording on what i was trying to say.

Antonio Macia · ‎11-19-2017

Hello,

Regarding the DHCP on the Serial interface, you don't create subinterfaces there. You just create the DHCP pools for VLANs 15,30 in R3 and then configure R1 and R2 as DHCP relays, forwarding the DHCP requests from the clients in those VLANs to R3.

To configure the DHCP relay just enter the command ip helper address <R1 Serial IP Address>

As for the native VLAN, if you want to avoid VLAN hop attacks it's ok to change the default native VLAN to a different one. Just remember to allow the VLAN 36 in the trunk between the switch and R3.

Regards.

dolanduck. · ‎11-19-2017

so where do i create my sub interfaces for my other vlans and where do put
my dhcp

Antonio Macia · ‎11-19-2017

Actually you don't need subinterfaces for VLAN 15 and 30 since these are the only VLANs under R1 and R2. You can configure the IP directly on the physical interface.

The DHCP configuration is done in R3. Alternatively, you can have 3 DHCP servers, each one running on each router. Up to you.

dolanduck. · ‎11-19-2017

so if i have native vlan lets say 99 for native vlan so i can trunk. on
each network connected to the router do i need sub interfaces. or its the
same. trying to under stand because the cisco net cad does not explane
this very well. i read over the chapters so many times.

dolanduck. · ‎11-19-2017

so if i have native vlan lets say 99 for native vlan so i can trunk. on
each network connected to the router do i need sub interfaces. or its the
same. trying to under stand because the cisco net cad does not explane
this very well. i read over the chapters so many times.

Antonio Macia · ‎11-20-2017

If you trunk on the router and specify that the native VLAN is now 99 instead of 1, you should not need to create a subinterface for VLAN 99, only for those VLANs different than the native. I suggest you to test it, it is the best way to learn and understand networking.