EVC .. VPLS .. VS Type 4

[Sherif Atef Ahmed Ismail]

Dears

I have few questions regarding EVC and its assiciation with VPLS and would like your assistance please regarding them

1- Is there any difference between below options

Option 1a

************

interface GigabitEthernet3/0/0

service instance 100 ethernet

  encapsulation dot1q 100

  bridge-domain 100

Option 1b

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interface GigabitEthernet3/0/0

service instance 100 ethernet

  encapsulation dot1q 100

  rewrite ingress tag pop 1 symmetric     

  bridge-domain 100

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2- Is there a need need to define evc globally

i.e is there any advantage for one of below options over the other

Option 2a

************

ethernet evc evc-test

interface GigabitEthernet3/0/0

service instance 2001 ethernet evc-test

  encapsulation dot1q 2001

  rewrite ingress tag pop 1 symmetric

  bridge-domain 2001

interface vlan 2001

xconnect vfi vfi-test

l2 vfi vfi-test manual evc-test

vpn id 2001

neighbor 1.1.1.1 encapsulation mpls

Option 2b

************

interface GigabitEthernet3/0/0

service instance 2001 ethernet

  encapsulation dot1q 2001

  rewrite ingress tag pop 1 symmetric

  bridge-domain 2001

interface vlan 2001

xconnect vfi vfi-test

l2 vfi vfi-test manual

vpn id 2001

neighbor 1.1.1.1 encapsulation mpls

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3- What does "bridge-domain vlan" configured under "l2 vfi" do ?

R6(config-if-srv)#l2 vfi vfi-test manual evc-test

R6(config-vfi)#?

VFI configuration commands:

  bridge-domain  Bridge Domain

  cfm            Ethernet CFM EFP subcommands

  default        Set a command to its defaults

  exit          Exit from vfi configuration mode

  forward        Specify forwarding of types of traffic

  neighbor      VFI neighbor configuration

  no            Negate a command or set its defaults

  shutdown      Shutdown VFI

  status        Pseudowire status capabilities

  vpn            VPN configuration

R6(config-vfi)#bridge-domain ?

  <1-4094>  Bridge Domain vlan ID value

R6(config-vfi)#bridge-domain 2001 vlan ?

R6(config-vfi)#bridge-domain 2001 vlan

R6(config-vfi)#

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4- What is the use of VC type 4 cause as I understand the service delimiter tag or dummy tag that is added if packets are receievd from AC untagged are only local significant ; i.e. both ends may you different tags !

Am I missing something

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5- In XR what is the difference between "transport-mode vlan" & "transport-mode vlan passthrough" ?

I believe with passthrough no dummy tag will be added in case packets received from AC untagged so in this case packets will be sent to PW without any tag. As I know If packets received from AC untagged and VC Type is 4, a dummy tag is added before packet being send to PW/MPLS

Am I correct ?

l2vpn

pw-class PW-CLASS-TEST

  encapsulation mpls

  transport-mode vlan

l2vpn

pw-class PW-CLASS-TEST

  encapsulation mpls

  transport-mode vlan passthrough

Many Thanks

Regards

Sherif Ismail

[Sandip Rathod]

Hi Sherif

1)

rewrite ingress tag pop 1 symmetric command remove 1st upper tag from the packet it receives. In your case VLAN tag 100 is received on this interface it will be put into service instance 100. Since the incoming tag no longer has any inherent meaning beyond this specific interface we need a way to discard that tag before forwarding the frame on. The rewrite ingress command does just that.

Read this in detail for more clarification

https://supportforums.cisco.com/docs/DOC-21299

2) I need to look at 2nd question, will come back to you on later

3) As per my understanding, If you have packet coming from different VLAN, then you need to use this command.

4) VC Type 4 is used for Ethernet VLAN mode, you configure xconnect on a dot1q subinterface, look this for more detail

http://tools.ietf.org/html/draft-ietf-pwe3-ethernet-encap-10#page-8

5) You are correct, if you do not want dummy tag then use passthrough command

Hope this helps

Regards,

Sandip

[Sherif Atef Ahmed Ismail]

Hi Sandeep
Many thanks for your reply & assistance

l- so this means without popping tag packet would have 2 tags with same value Correct ?
If my understanding is correct then this type of configuration (without popping tag) would be needed in case of Q-in-Q

Hope my understanding is correct:)

2- I believe in case if no
specific global commands
configured for EVC as lmi
or Uni count then both
options would be the same .. that would be my guess
:)

3-But why traffic from other VLAN would match as "xconnect vfi" is configured only under my concerned vlan

4- my last quetion please how when I dummy tag is added (in case packets received are untagged and vc type is 4 and passthrough is not configured) how would remote router translate this dummy vlan to the correct vlan

Many thanks in advance
Sherif Ismail

[Sandip Rathod]

Hi Sherif,

1. Refer section 802.1Q Tunneling (QinQ) in  below document, I hope this will clarify your doubt, if still not, let me know

http://www.cisco.com/en/US/docs/switches/metro/me3600x_3800x/software/release/12.2_52_ey/configuration/guide/swevc.pdf

2. I thik so, but not 100% sure, I need to deep dive into this

4.

Without EVC on IOS (pure dot1q on subinterface) :

Consider:  CE1 ---- PE1 ------[ ~  MPLS CORE ~ ]------PE2 ---- CE2

The incoming VLAN tag from CE1 is removed, dummy VLAN tag of 0 is

added while it traverses the MPLS core.

However ,when the remote PE2 is reached, the dummy tag is removed,

the tag being imposed is based on the dot1q VLAN  configured on CE2.

So, even if CE1 and CE2 are in different VLAN's the tag rewrite process happens

automatically and traffic flows transparently across disparate VLAN's.

With EVC on IOS:

"rewrite ingress tag symmetric"  needs to be  configured on EVC for end-end

connectivity exists across disparate VLAN.

Regards,

Sandip

[Sherif Atef Ahmed Ismail]

Hi Sandip

Many thanks for your detailed reply

1- The document is great and really helped

For QinQ method 2 (P.11-19), method 2 should be similar to figure 11-10 (P.11-28) however I believe there is a small mistake

For the direction EVC --> switchport

Packet received with C-VLAN 20 (encapsulation should be 20 and not 10) then bridge over brigde-domain 10 and at egress of switchport VLAN equals to that of bridge-domain (S-VLAN) is pushed

For the direction switchport --> EVC

C-VLAN Packets received on switchport trunk will have their outer vlan popped (vlan 20) and then bridged to bridge-domain 10. Packets will reach EFP port with only 1 VLAN (C-VLAN 20) and cause there is no rewrite tag operation

If my analysis is correct, then as mentioned encapsulation should be 20

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2- If I understood correctly, behavior seems to look as below

For non EVC IOS VC type 4, incoming VLAN tag is removed and dummy tag 0 is added. On remote side this dummy tag is removed and VLAN configured on interface is added

For EVC & IOS XR VC type 4, dummy tag is added on top of incoming tag so packet is sent with both tags. With pass-through no dummy tag is added

Thanks

Regards

Sherif Ismail

[Sandip Rathod]

Hi Sherif,

Sorry for delay, got stuck in some urgent works

Your understanding is correct (not sure about IOS XR VC type 4)

Regards,

Sandip

[Sherif Atef Ahmed Ismail]

Many thanks Sandip for your assistance .. Much appreciated