[c-nsp] Understanding ethertype

[Jason Lixfeld]

I'm running into an issue with a carrier NNI circuit that is manifesting itself as one-way traffic over an EoMPLS VC.  I believe this behaviour to be the result of the ethertype that the carrier requires us to set on this interface.

By and large, the IOS-(XE|XR) default seems to be 0x8100, but in this case, the carrier needs 802.1ad/0x88a8.  If I set this ethertype and put an IP address on the subinterface, I can ping across the 802.1ad circuit without issue, like so:

!
interface GigabitEthernet0/0/2
 dot1q tunneling ethertype 0x88A8
!
interface GigabitEthernet0/0/2.3000
 encapsulation dot1Q 3000
 ip address 1.1.1.1 255.255.255.252
!

router#show arp
Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet  1.1.1.1          -   c89c.1d1d.c902  ARPA   GigabitEthernet0/0/2.3000
Internet  1.1.1.2          0   001c.25be.63da  ARPA   GigabitEthernet0/0/2.3000
bpe01.151front711#ping 1.1.1.2

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 58/58/59 ms
router#

Now if I attach an EoMPLS tail to this subinterface, ie:

!
interface GigabitEthernet0/0/2
 dot1q tunneling ethertype 0x88A8
!
interface GigabitEthernet0/0/2.3000
 encapsulation dot1Q 3000
 xconnect 10.10.10.10 69 encapsulation mpls
!

With the far end of the vc being port based, like so:

!
interface GigabitEthernet0/16
 xconnect 11.11.11.11 69 encapsulation mpls
!

And I stick a wireshark enabled laptop on Gi0/16, I see traffic coming from behind the 802.1ad link, but they don't see anything coming back from me.

That leads me to believe that there is something with the ethertype possibly not being re-written to 0x88a8 when it's trying to exit the carrier NNI port.  I don't know enough about Ethertype behavior, so I can't be sure this is plausible.

While I wait for a TAC engineer to research and comment on my issue, I figured I'd ask hear to maybe learn something in the mean time.

Thanks in advance.