BVI, encapsulation failed

[Wassim Aouadi]

Hi guys,
I'm seeing an error trying to ping from CPE to PE, although interface is up and configured:

TNRTAGCS01057#ping 192.168.206.17
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.206.17, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
 

When I do a "debug ip packet", I see the following error:

Jul 22 15:52:59.919 CET: IP: s=192.168.206.18 (local), d=192.168.206.17 (BVI2), len 100, sending
*Jul 22 15:52:59.919 CET: IP: s=192.168.206.18 (local), d=192.168.206.17 (BVI2), len 100, encapsulation failed
*Jul 22 15:53:01.919 CET: IP: s=192.168.206.18 (local), d=192.168.206.17 (BVI2), len 100, sending
*Jul 22 15:53:01.919 CET: IP: s=192.168.206.18 (local), d=192.168.206.17 (BVI2), len 100, encapsulation failed

topology:
CPE SHDSL card (ATM/BVI configured) -------- PE DSLAM
192.168.206.18 ------------------------------------------- 192.168.206.17

CPE configuration:

controller SHDSL 0/1/0
 termination cpe
 dsl-group 0 pairs  0
  shdsl rate auto
 !
bridge irb
!
!
interface ATM0/0/0
 description --- ADSL interface ---
mtu 1500
 no ip address
 ip ospf network non-broadcast
 no atm ilmi-keepalive
 bridge-group 1
 pvc 0 0/35
 !

interface ATM0/1/0
 description --- SHDSL physical interface ---
 no ip address
 no atm ilmi-keepalive
 bridge-group 2
 pvc 0 0/35
!
interface BVI2
 description WAN SHDSL
 bandwidth 1000
 ip address 192.168.206.18 255.255.255.240
!
bridge 1 protocol ieee
bridge 1 route ip
bridge 2 protocol ieee
bridge 2 route ip
 !

Also a "debug arp" output:

*Jul 22 16:48:59.747 CET: IP ARP: sent req src 192.168.206.18 0000.0c68.a214,
                 dst 192.168.206.17 0000.0000.0000 BVI2
*Jul 22 16:49:01.747 CET: IP ARP: sent req src 192.168.206.18 0000.0c68.a214,
                 dst 192.168.206.17 0000.0000.0000 BVI2
*Jul 22 16:49:03.747 CET: IP ARP: sent req src 192.168.206.18 0000.0c68.a214,
                 dst 192.168.206.17 0000.0000.0000 BVI2
*Jul 22 16:49:08.963 CET: IP ARP: sent req src 192.168.206.18 0000.0c68.a214,
                 dst 192.168.206.17 0000.0000.0000 BVI2
*Jul 22 16:49:10.963 CET: IP ARP: sent req src 192.168.206.18 0000.0c68.a214,
                 dst 192.168.206.17 0000.0000.0000 BVI2
*Jul 22 16:49:12.963 CET: IP ARP: sent req src 192.168.206.18 0000.0c68.a214,
                 dst 192.168.206.17 0000.0000.0000 BVI2
*Jul 22 16:49:14.963 CET: IP ARP: sent req src 192.168.206.18 0000.0c68.a214,
                 dst 192.168.206.17 0000.0000.0000 BVI2
*Jul 22 16:49:16.963 CET: IP ARP: sent req src 192.168.206.18 0000.0c68.a214,
                 dst 192.168.206.17 0000.0000.0000 BVI2
 

Any idea?

[Richard Burts]

The issue seems pretty clear. The error message about encapsulation failed is usually an indication that you are trying to send data and do not have the layer 2 address for the destination. This explanation is confirmed by the debug arp output. You can see lots of requests being sent for 192.168.206.7 but no responses. So that is your problem - you are attempting to communicate with 192.168.206.17 and it is not responding to your arp request.

HTH

Rick

[Wassim Aouadi]

There's no special reason to using bridging. It's that I'm using it as part of a validated CPE configuration template. It worked in the past. However, this time, the link between the CPE and the PE seems up but ping fails.

The issue appears on our 2911 router. I tried with a 1921 test router. I noticed that the same config (with bridging) does work. However I can not keep this router because it belongs to the provider.

I do have the L2 address of the 192.168.206.17 host, obtained from another site's ARP table. But I could not add a static ARP entry with the following command:

TNRTAGCS01057(config)#arp 192.168.106.17 001b.0de6.f040 arpa bvi2
Bad ARP command - Interface may only be specified when bridging IP
TNRTAGCS01057(config)#

I appreciate your help

[Peter Paluch]

Wass,

Okay, I get the point. Nonetheless, can you try the configuration as suggested by me? I've tested it in the lab, it worked for me.

Best regards,
Peter

[Wassim Aouadi]

Yes I tried it. I got the same "encapsulation failed" error.

[Peter Paluch]

Wass,

Have you specifically used the bridge spanning-disabled command on the subinterface? For some reason, I seem to have had problems with the topology if the STP was not enabled on the interfaces. In other words, have you replicated my configuration exactly down to the letter?

If this does not help then would you perhaps mind posting a debug of debug atm packet command when you try pinging the remote device?

Best regards,
Peter

[Wassim Aouadi]

Yes, I replicated the configuration as you suggested, and checked it with a "sh run".

I'll post the output of "debug atm packet" as soon as I come back to the office.

[Wassim Aouadi]

update: the provider did something to the network. For the sake of curiosity and documentation, I'm waiting for a reply from them. With the configuration I outlined (with BVI), the issue disappeared.

Thank you Peter and Richard for your precious time.

[Peter Paluch]

Hello Wass,

Is there a specific reason why you want to use a Bridged Virtual Interface to configure an IP connection? Are you planning to do some kind of bridging between a local interface and the PVC circuit? This is not a typical configuration you are attempting to use.

In any case, for bridging, you will need to use a different style of configuration. This is an example, I will explain right away:

bridge irb
!
interface ATM0/1/0
 no shutdown
 no ip address
!
interface ATM0/1/0.1 point-to-point
 bridge-group 2
 bridge-group 2 spanning-disabled
 pvc 0/35
  protocol bridge broadcast
  encapsulation aal5snap
!
interface BVI2
 ip address 192.168.206.18 255.255.255.0
!
bridge 2 route ip
bridge 2 protocol ieee

First of all, you have to define the bridging specifically for a subinterface, not for all possible PVCs on the physical ATM interface - you are going to use only PVC 0/35, anyway.

You have to enable to use the PVC for a specific purpose, in this case, bridging. That is the reason for the protocol bridge broadcast, also allowing broadcast frames to be bridged across.

The encapsulation you will need to use is AAL5SNAP. This has to be matched by the DSLAM as well but I suppose that it is already set at this value.

Once again - are you sure you want to run bridging in this setup? Why?

Best regards,
Peter