Posted on May 15, 2017 6:22 pm
 |  Asked by Mina Naguib
 |  1897 views
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We implement attached topology with configuration:

 

A-R#sh run

 

interface Ethernet1

   no switchport

   ip address 10.10.10.1/24

!

interface Ethernet1.10

!

interface Ethernet1.20

   encapsulation dot1q vlan 20

   ip address 20.20.20.1/24

!

interface Ethernet2

!

interface Ethernet3

!

interface Management1

!

ip routing

!

!

end

A-SW#sh run

 

vlan 10,20,30,50

!

interface Ethernet1

   switchport mode trunk

!

interface Ethernet2

   switchport access vlan 10

!

interface Ethernet3

   switchport access vlan 20

!

interface Management1

!

no ip routing

!

!

end

  • when deploy this config VPC2 can reach router interface eth1.20 but VPC1 can’t reach router interface eth1.
  • so we exactly doesn’t know what this command “l2-protocol encapsulation dot1q vlan” do and its behavior on network and what is the different than “encapsulate dot1q vlan”, all we know that “l2-protocol encapsulation dot1q vlan” applied on interfaces while “encapsulate dot1q vlan” applied on sub interfaces.
  • on previous topology VPC1 can only reach router interface eth1 when configure switch interface eth1 with native vlan 10 not 1, which doesn’t make sense, even if remove “l2-protocol encapsulation dot1q vlan” from router VPC1 can reach router interface.

We need more information about this command.

Your support is highly appreciated.

 

 

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Posted by Tamas Plugor
Answered on May 16, 2017 9:10 am

Hi Mina,

 

From my understanding you’d like to do a router-on-a-stick setup. The reason why VPC1 cannot reach the router is because you didn’t apply dot1q encapsulation for the other subinterface. The correct config would be:

 

interface Ethernet1

 

   no switchport

 

   !

 

interface Ethernet1.10

 

 encapsulation dot1q vlan 10

 

 ip address 10.10.10.1/24

 

!

 

interface Ethernet1.20

 

   encapsulation dot1q vlan 20

 

   ip address 20.20.20.1/24

 

!

 

or if you leave the 10.10.10.1 ip on the main interface(as before) then you should specify native vlan 10 on the trunk port (as you saw)

 

‘l2-protocol encapsulation dot1q vlan’ enables Layer 2 802.1Q traffic encapsulation on the configuration mode interface for a specified VLAN; e.g. you would do this to accept dot1q tagged LACPDUs (so this is not needed in your setup)

 

‘encapsulation dot1q vlan’ is used for routed ports vlan translation or subinterface vlan assignment

 

More info on this you can find in our online configuration guide on the following link:

https://www.arista.com/en/um-eos-4182f/eos-section-18-4-vlan-configuration-commands#ww1155412

Let us know if you have further questions

 

Thanks,

Tamas

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