i need a better understanding of DHCP, native vlan, and nat.

[dolanduck.]

question one 1 about DHCP i have 3 routers, and do i put dchp on all of them. and how do i use the IP helper command.  

question 2 when making vlans on a switch like vlan 2 and vlan 45, and for example i go to g0/1 and i enable trunking and do the switch port trunk native vlan 45. what does this command do and do i need to use the switch port trunk allowed vlan 2 and 45.

question 3 with sub interfaces and encapsulation can i split it up on two interfaces.

i would like to video call people to help. here is my number 505-589-0215 here is my email waffi1234@gmail.com. i really need help under standing this please. and thank you 

[Julio E. Moisa]

Hi

About Question 1, dhcp helper is used to relay the DHCP packets to DHCP servers out the router, in few words for external/remote DHCP servers o routers.  One condition is that the router where are you configuring the dhcp helper must have an entry to that remote server into the routing table, the router must know how to reach that server and vice versa. 

About the Question 2: The native vlan is not required to be filtered over a trunk, but you must have the same native vlan on both ends and created. All the frames sent out of the trunk interface are tagged to identify the destination VLAN, if a frame has an unknown tag it will be sent to the native vlan and discarded. Remember the VLANs are locally significant. 

for example:

SWITCH1 & SWITCH 2

interface g0/1

switchport trunk encapsulation dot1q

switchport mode trunk

switchport trunk allow vlan 2  

switchport trunk native vlan 45

The native vlan must not be used for other role than native vlan, so you cannot use this vlan (in this case 45) for end users (access mode).

About question 3, is not totally clear, so please correct me if Im wrong. 

Yes you can have multiple sub interface from a physical interface, example:

ROUTER

interface g0/0

no shutdown

interface g0/0.2

encapsulation dot1q 2

ip add 192.168.2.1 255.255.255.0

no shutdown

interface g0/0.15

encapsulation dot1q 15

ip add 192.168.15.1 255.255.255.0

no shutdown 

Hope it is useful

:-)

[dolanduck.]

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.

[dolanduck. · Accepted solution]

On Sat, Nov 18, 2017 at 6:21 PM, eric alvarado wrote:

> 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.
>
> question 3 i will leave a recording so you can better understand. i hate
> writhing
>