Eompls SD Tag

Unanswered Question
Apr 6th, 2010
User Badges:
  • Cisco Employee,

hi All,

   i have a setup as below


CE1 -----PE1 ---------PE--- ( Sniffer )-----PE----------PE2--------CE2


PE1  to CE1

==========

service instance 10 ethernet
  encapsulation dot1q 10
  xconnect 10.192.168.105 100 encapsulation mpls
!

PE2 to CE2

=========

interface TenGigabitEthernet5/0/0
no ip address
mls qos trust dscp
service instance 10 ethernet
  encapsulation dot1q 20
  xconnect 10.192.168.104 100 encapsulation mpls pw-class Test

!

No rewrites are done.


The VC type used is Type 4 ( i.e ETH VLAN )


Capturing packet at the Sniffer

========================

When i send traffic from CE1 to CE2 i see SD tag added on the packet as 10

When i send traffic from CE2 to CE1 i see SD tag added on the packet as 20.


Can u let me know how the SD Tag is determined in the above setup?


More Info

========

Packet captured looks like

    [ L2 Header ] [Two Label MPLS STACK ] [CW] [ Actual Ethernet Frame ]


Actual Ethernet frame lookes like below

============================

   [ L2 header ] [SD tag ] [ Vlan TAG from CE ] [ Data]


Thanks in advance

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Loading.
judebryant Tue, 04/06/2010 - 07:27
User Badges:

the statement "encapsulation dot1q vlan-id" defines the matching criteria to be used in order to map ingress dot1q frames on an interface to the appropriate service instance.
If the packet comes in without the vlan-id being matched to a service instance, the packet is dropped.
So in your configuration, the packets comming in are already tagged and processed across the VC.
Put your sniffer in front of the interface with the service instance configured and you will see this.
Regards
Jude Bryant
Pioneer Telephone
jjacobj Tue, 04/06/2010 - 09:49
User Badges:
  • Cisco Employee,

So the SD Tag Added would be is present in the "encapsulation Dot1q ".

This leaves me with one basic question


1 : What is the use of adding SD tag for VC type 4 ?

        In my setup The SD Tag gets poped when sent out towards CE

judebryant Tue, 04/06/2010 - 12:42
User Badges:

here are your options


vlanid 10 ===>  (mpls) <=== vlanid 20


so you would have to manipulate the vlan tags in order for acceptance at the other end

left to right...translate 10 to 20

right to left ..translate 20 to 10


Router A                          Router B


interface 1/0/1                    interface 1/0/1

vlanid 10 ===> (mpls) <=== vlanid 10


Router A

interface 1/0/1

service instance 10 ethernet

encapsulation dot1q 10

xconnect (router b) 110 encapsulation mpls


Router B

interface 1/0/1

service instance 10 ethernet

encapsulation dot1q 10

xconnect (routera) 110 encapsulation mpls



interface 1/0/2                    interface 1/0/1

vlanid 10 ===> (mpls) <=== vlanid 10


Router A

interface 1/0/2

service instance 10 ethernet

encapsulation dot1q 10

xconnect (router b) 110 encapsulation mpls


Router B (this will not work because you already have an encapsulation dot1q 10 defined on this interface)

interface 1/0/1

service instance 10 ethernet

encapsulation dot1q 10

xconnect (routera) 110 encapsulation mpls


so you will have to do this

interface 1/0/1

service instance 20

encapsulation default (any tagged traffic comming in, not looking at the vlan-id, however a vlan-id other than 10 will pass thru this)

rewrite ingress tag translate 1 to 1 dot1q 10 (changing the vlan-id to 10)

xconnect (routera) 120 encapsulation mpls


In summary, vlan tags are significant only to the port.  So you can use the same vlan id on another port.


Jude Bryant

Pioneer Telephone

Actions

This Discussion