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routing – Can’t ping between cabled interfaces on different VRFs on same switch (Cisco 3548)

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#routing #ping #cabled #interfaces #VRFs #switch #Cisco

As an experiment I’ve created a non-default VRF, directly cabled between an L3 port on the default VRF and an L3 port on the non-default VRF, and am trying to ping between them. Neither interface can resolve the other.

The setup is:

  • eth1/34 has IP 10.10.1.211/24 on VRF1
  • eth1/6 has IP 10.10.1.111/24 on default VRF
  • eth1/6 is connected to eth1/34 by a cat 5 cable

When I try to ping between them, each reports the other is unreachable. With a monitor session active on the connection, the problem appears to be unanswered ARP requests in each direction:

switch1# ping 10.10.1.111 source-interface ethernet 1/34
PING 10.10.1.111 (10.10.1.111): 56 data bytes
36 bytes from 10.10.1.211: Destination Host Unreachable
Request 0 timed out
36 bytes from 10.10.1.211: Destination Host Unreachable
Request 1 timed out
36 bytes from 10.10.1.211: Destination Host Unreachable
Request 2 timed out
36 bytes from 10.10.1.211: Destination Host Unreachable
Request 3 timed out
36 bytes from 10.10.1.211: Destination Host Unreachable
Request 4 timed out


switch1# ping 10.10.1.211 source-interface ethernet 1/6
PING 10.10.1.211 (10.10.1.211): 56 data bytes
36 bytes from 10.10.1.111: Destination Host Unreachable
Request 0 timed out
36 bytes from 10.10.1.111: Destination Host Unreachable
Request 1 timed out
36 bytes from 10.10.1.111: Destination Host Unreachable
Request 2 timed out
36 bytes from 10.10.1.111: Destination Host Unreachable
Request 3 timed out
36 bytes from 10.10.1.111: Destination Host Unreachable
Request 4 timed out

From the monitor session:

17:53:04.716375 ARP, Request who-has 10.10.1.111 (Broadcast) tell 10.10.1.211, length 46
17:53:06.721173 ARP, Request who-has 10.10.1.111 (Broadcast) tell 10.10.1.211, length 46
17:53:10.724456 ARP, Request who-has 10.10.1.111 (Broadcast) tell 10.10.1.211, length 46
17:53:18.727720 ARP, Request who-has 10.10.1.111 (Broadcast) tell 10.10.1.211, length 46
...
17:54:35.932830 ARP, Request who-has 10.10.1.211 (Broadcast) tell 10.10.1.111, length 46
17:54:37.934559 ARP, Request who-has 10.10.1.211 (Broadcast) tell 10.10.1.111, length 46
17:54:41.937869 ARP, Request who-has 10.10.1.211 (Broadcast) tell 10.10.1.111, length 46

I know that this is an unusual setup, but is there actually something I’m missing that would stop this setup from working? What I think are the relevant parts of the configuration are below.

switch1(config-)# show running-config int ethernet 1/34

!Command: show running-config interface Ethernet1/34
!Running configuration last done at: Thu Jan  4 17:33:19 2024
!Time: Thu Jan  4 17:33:22 2024

version 9.3(9) Bios:version 5.5.0 

interface Ethernet1/34
  description "TO 6"
  no switchport
  speed 1000
  vrf member VRF1
  ip address 10.10.1.211/24

switch1(config)# show running-config int ethernet 1/6

!Command: show running-config interface Ethernet1/6
!Running configuration last done at: Thu Jan  4 17:33:19 2024
!Time: Thu Jan  4 17:34:03 2024

version 9.3(9) Bios:version 5.5.0 

interface Ethernet1/6
  description "TO 34"
  no switchport
  speed 1000
  ip address 10.10.1.111/24

switch1(config)# show ip route
IP Route Table for VRF "default"
'*' denotes best ucast next-hop
'**' denotes best mcast next-hop
'[x/y]' denotes [preference/metric]
'%<string>' in via output denotes VRF <string>

10.10.1.0/24, ubest/mbest: 1/0, attached
    *via 10.10.1.111, Eth1/6, [0/0], 00:06:36, direct
10.10.1.111/32, ubest/mbest: 1/0, attached
    *via 10.10.1.111, Eth1/6, [0/0], 00:06:36, local

switch1(config)# show ip route vrf VRF1
IP Route Table for VRF "VRF1"
'*' denotes best ucast next-hop
'**' denotes best mcast next-hop
'[x/y]' denotes [preference/metric]
'%<string>' in via output denotes VRF <string>

10.10.1.0/24, ubest/mbest: 1/0, attached
    *via 10.10.1.211, Eth1/34, [0/0], 00:06:49, direct
10.10.1.211/32, ubest/mbest: 1/0, attached
    *via 10.10.1.211, Eth1/34, [0/0], 00:06:49, local