4.5 - no reachability.. not really EIGRP issue

R6 - encapsulation failure


I'm at section 4.5 and when I try just to bring up the neighbors I notice the adjacency doesn't form. After some troubleshooting I discover that I don't have any PING across the segment regardless. I know "why" in the sense that my debug on R6 clearly shows the failure. But I don't know "why" I'm failing.

R2 - S2 - S1 - S4 - R6

R2 is fine and the trunking across all the switches looks fine. On R6, I'm getting an encapsulation failure on eth0/0.26 when I attempt to ping Can anyone see anything in the below config that might tell me why? Yes, I figured out the the initial config had flipped IPs. Crazy proctors...

Rack1R6(config-router)#do sho run int eth0/0
Building configuration...

Current configuration : 57 bytes
interface Ethernet0/0
 no ip address

Rack1R6(config-router)#do sho run int eth0/0.6
Building configuration...

Current configuration : 90 bytes
interface Ethernet0/0.6
 encapsulation dot1Q 6
 ip address

Rack1R6(config-router)#do sho run int eth0/0.26
Building configuration...

Current configuration : 93 bytes
interface Ethernet0/0.26
 encapsulation dot1Q 26
 ip address



Mar  1 01:34:18.715: IP: s= (local), d= (Ethernet0/0.26), len 100, sending
*Mar  1 01:34:18.719: IP: s= (local), d= (Ethernet0/0.26), len 100, encapsulation failed
*Mar  1 01:34:18.755: IP: s= (local), d= (Ethernet0/0.26), len 60, sending
*Mar  1 01:34:18.755: IP: s= (local), d= (Ethernet0/0.26), len 60, encapsulation failed.


Any help would be appreciated. Thanks.


  • I'm trying to throw in my 2 cents by first saying "I'm no expert".

    Router side looks ok except the native vlan not adjusted (as required in the task).   What about the config on SW2's Fa1/6 ?  Needs trunking and native vlan on 6 with dot1q encap there.

  • AC439,

          Thanks for the response. I'm trying to understand your comment on the native VLAN. 1.3 calls for a native VLAN for the trunk between SW1 and SW3. I don't see anything in the 4.x sections hinting at a native VLAN. Am I missing something? Also, the encapsulation is failing on R6 so my focus was there. I'll look more this afternoon. Let me know your thoughts.

  • In task 1.5, it requires the native vlan to be set on the switch's interface.  Assuming you have successfully completed this task (1.5), the config on the router side should have a matching native vlan configured as well.

    In your config, the router side is using native vlan 1.  The switch side (again, assuming you config it correctly), is set to native vlan 6.  Actually, I expect native vlan mismatch message instead of encap failure.  Try putting the correct native vlan on the router side and see what happen.  I'd be interested to know if this clear the problem.

    R6 and R2 are connecting to the same switch (SW2).  The traffic between them do not need to go through the trunk link in task 1.3.

  • THAT'S IT!

    I did not have native VLAN 6 on S2 Fa1/6. Once I corrected that, the EIGRP peering came up before I could even get back to the router to troubleshoot. Life is good.



          Thank you for your assistance. It's the simple things that will make a difference in the lab and I have to do better than that. My focus right now is rock solid on IGP/EGP before moving into services/QOS/MCast/ETC. I guess I stared at the document too long.


  • Glad I can help, Charles! 

    I also started on the big labs not too long ago and currently on lab 3.  I found my mind easily goes blank with big labs while I thought I have a good handle of the individual technologies.  When they put everything together into a big lab, things are getting nasty and I can miss simple things !  I even doubted myself after a "long drag finish" on lab 1.  But things seem to have improved for me.  Sometimes, I feel I need two brains to do CCIE.  Those who bear multiple CCIE titles must have a head as big as an alien !


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