It is been a while that I read some papers about EVC, flexible matching, … But I have not found a good paper explaining EVC and a way to understanding well except to cisco configuration guide.
This figure is exactly what I searched for. This example is simple but enough to understand well how it works.
My misunderstanding was about “ingress” and “symmetric” : I didn’t understand, but now with the figure that it is clear that :
- encapsulation dot1q 10 : match all frames where a dot1Q tag is present with value 10
- “rewrite ingress tag pop 1 symmetric” : We pop 1 tag on this frame
- Give this frame to the MPLS xconnect without any tag
When a frame comes from the xconnect :
- It arrives without any tag
- With “symmetric”, we push the 10 dot1q tag
- put in TX the frame through the GigabitEthernet 0/2
You can ask me : “Ok this is really complicated your configuration, why don’t you use xxxx” ?
Where xxx is :
int gi 0/2 switchport trunk encapsulation dot1q switchport trunk allow vlan 10 switchport mode trunk int vl 10 xconnect 192.168.1.1 33 encapsulation mpls
I will reply : “Have you declare your vlan 100 on your switch ? What does it involve for the scalability ?”
=> Yes, you understand well : you are limited by the number of vlans.
=> With EVC : the “encapsulation dot1q 10” is local to the port. So no limitation.
=> Yes it is really great !!!!!
I urge you to read these papers :
- https://supportforums.cisco.com/document/85231/understanding-ethernet-virtual-circuits-evc
- http://ccie-in-3-months.blogspot.fr/2009/06/evc-flexible-frame-matching.html
- http://ccie-in-3-months.blogspot.fr/2009/06/evc-flexible-vlan-tag-rewrite.html
- http://ccie-in-3-months.blogspot.fr/2009/09/evc-flexible-service-mapping.html