Router-on-a-Stick VLAN not passing traffic

[joshua.parrish@esc9.net]

I'm having an issue getting traffic across a trunk link to a router-on-a-stick. I have a Cisco Catalyst 4500 switching VLAN traffic to a Cisco ASR 1000 router. Catalyst links to ASR between int Gi2/11 (Cata) and Gi0/0/3 (ASR). Another device attaches to the Catalyst on port Gi2/15 (and tags the VLAN).

All relevant interfaces show status up up. I can ping from the attached device (10.30.0.3) to the Catalyst VLAN 30 interface (10.30.0.2), but cannot get any response from the ASR interface. I can ping the 10.30.0.1 internally on the ASR, but cannot reach other IPs. Everything to my eye seems correct. Am I missing something??

Catalyst switch has the following relevant configuration:

vlan 30

interface GigabitEthernet2/11

   description uplink to ASR

   switchport trunk allowed vlan 30

   switchport mode trunk

interface GigabitEthernet2/15

   description uplink to ASR

   switchport trunk allowed vlan 30

   switchport mode trunk

interface Vlan30

   description test int vlan30

   ip address 10.30.0.2 255.255.255.0

ASR has the following relevant config:

interface GigabitEthernet0/0/3

   description uplink to Catalyst

   no ip address

   negotiation auto

interface GigabitEthernet0/0/3.30

   encapsulation dot1q 30

   ip address 10.30.0.1 255.255.255.0

[Reza Sharifi]

Do you have a default route on the 4500 pointing to the ip address of the ASR?

ip route 0.0.0.0 0.0.0.0 10.30.0.1

[joshua.parrish@esc9.net]

I actually have a default route on the catalyst to another interface on the
ASR. But, that shouldnt matter, should it? Since these two interfaces are
in the same subnet, they should be reachable at the link layer.

I ultimately hope to use this VLAN with a VRF interface on the ASR to
create an isolated internal-use subnet. But I can’t start with VRF until I
can get this VLAN link issue resolved.

[Reza Sharifi]

For test purpose, can you make a change at a time and test?

remove the ip address from the svi on the 4500 or just delete it and see if you can reach the ASR from the laptop.

If that does not help and if this is not in production, can try removing the default route that is pointing to the other interface temporarily and test.

HTH 

[Julio E. Moisa]

Hi

Are you able to make ping from the Catalyst?

ping 10.30.0.1 source vlan 30

do you see up up the interfaces?

[joshua.parrish@esc9.net]

I do see up up on the ASR interface and subinterface, and Catalyst switch interface and VLAN interface. I cannot ping from either side, which is the source off my confusion. I’ve double checked syntax and have tried specifying a source IP (or VLAN). Not sure why they would not be reachable? I can pinging from the attached device on Catalyst int 2/15 to the Catalyst VLAN 30 interface and back. 

[Richard Burts]

Could you post the output from these commands

show interface trunk on the switch

show ip interface brief on both switch and ASR

show cdp neighbor on both switch and ASR

show arp on the ASR

HTH

Rick

[joshua.parrish@esc9.net]

Catalyst switch:

show int trunk

Port        Mode  Encapsulation     Status Native vlan

Gi2/11     on      802.1q    trunking 1

Gi2/15     on      802.1q    trunking 1

Port           Vlans allowed on trunk

Gi2/11       30

Gi2/15       30,40

Port           Vlans allowed and active in management domain

Gi2/11       30

Gi2/15       30,40

Port           Vlans in spanning tree forwarding state and not pruned

Gi2/11       30

Gi2/15       30,40

show ip int br

Interface                      IP-Address OK? Method     Status    Protocol

GigabitEthernet2/11     unassigned YES    unset up                                up

GigabitEthernet2/15     unassigned YES    unset up                                up

Vlan30                          10.30.0.2 YES manual     up      up

show cdp neighbor

No info on relevant interfaces

ASR Router:

show ip int br

Interface                      IP-Address OK? Method     Status    Protocol

GigabitEthernet0/0/3    unassigned YES    manual up                               up

Gi0/0/3.30                    10.30.0.1 YES manual      up    up

show cdp neighbors

No info on relevant interfaces

show arp Gi0/0/3.30

Protocol      Address             Age (min) Hardware Addr    Type Interface

Internet       10.30.0.1                         - b0aa.779a.0c05 ARPA GigabitEthernet0/0/3.30

[Richard Burts · Accepted solution]

Thanks for the information. The output of show interface trunk does confirm that the switch is carrying vlan 30 on the trunk. The output of show ip interface brief does confirm correct addressing and that interfaces are up. The interesting and more important outputs are the fact that there is no arp information indicates that the devices are not communicating at layer 2, and that show cdp neighbor does not indicate that the devices are seeing each other on this connection. Both these things seem to indicate some problem in the connection. I would suggest that you check the connections carefully (trace cables, disconnect a cable and see if both devices react to that. etc)

HTH

Rick

[joshua.parrish@esc9.net]

You were right. I just swapped out the SFP modules on both the catalyst and ASR. After replacement, both sides of the link are now reachable using ICMP. I do have the Catalyst's VLAN352 interface MAC in the ARP table of the ASR now. It appears that it was some physical layer issue, even though both interfaces showed up up.

Thanks everyone for your time and insight.

[Richard Burts]

I am glad to know that you have been able to solve this problem and that my suggestion pointed you in the right direction. It is an interesting aspect of this discussion that the interfaces showed as being up even though they were not passing traffic. When we are facing a problem we tend to start by looking for configuration issues. A lesson that some readers of the forum may take away from this discussion is that we also need to be open to the possibility that the problem might be a physical one.

HTH

Rick