802.1Q VLAN Trunk Configuration

[s76602061]

I think there are 2 ways 802.1Q VLAN Trunk Configuration as following.

My understanding is just configuration is different but function is same,

and [Pattern 1] is used for L3 port, and [Pattern 2] is used for L2 port.

Does my understanding is correct?

[Pattern 1]
interface GigabitEthernet1.1
encapsulation dot1Q 100
ip address xx.xx.xx.xx xx.xx.xx.xx

[Pattern 2]
interface GigabitEthernet1
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 100
switchport mode trunk
!
interface Vlan100
ip address xx.xx.xx.xx xx.xx.xx.xx

[Joseph W. Doherty]

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Posting

Are you talking switches or routers?

On a switch, pattern 2 can support L3, as the switch might be hosting SVIs.

On a router, a variation of pattern 1 would be used.  The encapsulation would be applied to the main interface, and then you can define subinterfaces with IPs (although the main interface can have an IP too).

[s76602061]

Hi, thank you so much for your comment. It is really appreciated.

[Masoud Pourshabanian]

You are most welcome,

Masoud

[Masoud Pourshabanian]

Hello,

I am just adding to Joseph answer.

Pattern 1 is configured on the router interfaces while pattern 2 is cofigured on switch interfaces. In both case, the main interface (interface GigabitEthernet1) is trunk.  interface GigabitEthernet1.1 in pattern 1 is called subinterface and interface Vlan100 in pattern2 is called SVI.

On higher level switches and routers, you can find both configurations depending on the types of interfaces.

subinterface is a division of one physical interface into multiple logical interfaces.

SVI is a virual L3 interface.

Masoud

[s76602061]

Thank you very much for your additional comment. It is really helpful for detail understanding.

[mehulnangru]

[Pattern 1] is used for L3 port -

Yes , this kind of configuration for a sub interface and this is done on routers only and yes router is a layer 3 device,

[Pattern 2] is used for L2 port. -

I slightly contradict with you here . First part of pattern 2 could be for a Trunk link between a switch<>Router or may be a switch<>switch .

HOWEVER 

part 2 of pattern 2 is a layer 3 interface on a switch (called as SVI - switches virtual interface).

Hope I have been able to explain in simple language .

[s76602061]

Thank you very much for your detailed comment, I have also agreed that your comment for [Pattern2].

[Ganesh Hariharan]

Hello,

[Pattern 1]
interface GigabitEthernet1.1
encapsulation dot1Q 100
ip address xx.xx.xx.xx xx.xx.xx.xx

GI :- Yes , It is router main interface which is L3 and used for sub interface configuration.

[Pattern 2]
interface GigabitEthernet1
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 100
switchport mode trunk
!
interface Vlan100
ip address xx.xx.xx.xx xx.xx.xx.xx

GI:- You are making Gig1 port as layer 2 port with trunking VLANS till router port.

Having interface Vlan 100 , you are creating L3 SVI to route traffic to other Layer 3 interface thus eliminating the need for a physical router.

Hope it Helps..

-GI

[s76602061]

thank you for your detailed answer, it same as my understanding. thank you.