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[EX] Troubleshooting inter-vlan communication problem on EX Series Ethernet switches

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Article ID: KB11170 KB Last Updated: 17 Aug 2020Version: 4.0
Summary:

The default configuration on EX Series Ethernet switches creates a single Virtual LAN (VLAN), and all traffic on the switch is part of that broadcast domain. Creating separate network segments (VLANs) reduces the span of the broadcast domain and allows you to group related users and network resources without being limited by physical cabling or by the location of a network device in the building or on the LAN.

The switch bridges traffic within a VLAN. For traffic passing between two VLANs, the switch routes the traffic by using a Layer 3 routed virtual interface (RVI) on which you have configured the IP address of the subnet.

Now inter-VLAN communication does not work on EX-series switches. How does one troubleshoot the problem? This article answers the question.

 

Solution:

Follow the steps below to troubleshoot any inter-vlan communication problems on EX Series Ethernet switches:

  1. Verify that the VLANs have been created.

user@switch> show  vlans
Name         Tag    Interfaces
default
                    ge-0/0/1.0, ge-0/0/2.0,  ge-0/0/5.0,
                    ge-0/0/6.0, ge-0/0/7.0, ge-0/0/8.0, ge-0/0/9.0,
                    ge-0/0/10.0*, ge-0/0/11.0, ge-0/0/12.0, ge-0/0/13.0*,
                    ge-0/0/14.0, ge-0/0/15.0, ge-0/0/16.0, ge-0/0/17.0,
                    ge-0/0/18.0, ge-0/0/19.0, ge-0/0/21.0, ge-0/0/23.0*,
                    ge-0/0/25.0, ge-0/0/27.0, ge-0/0/28.0, ge-0/0/29.0,
                    ge-0/0/30.0, ge-0/0/31.0, ge-0/0/32.0, ge-0/0/33.0,     
                    ge-0/0/34.0, ge-0/0/35.0, ge-0/0/36.0, ge-0/0/37.0,
                    ge-0/0/38.0, ge-0/0/39.0, ge-0/0/40.0, ge-0/0/41.0,
                    ge-0/0/42.0, ge-0/0/43.0, ge-0/0/45.0, ge-0/0/47.0,
                    ge-0/1/0.0*, ge-0/1/1.0*, ge-0/1/2.0*, ge-0/1/3.0*

sales
            10      ge-0/0/0.0*, ge-0/0/3.0, ge-0/0/20.0, ge-0/0/22.0

support
            20      ge-0/0/4.0, ge-0/0/24.0, ge-0/0/26.0, ge-0/0/44.0, ge-0/0/46.0*
  1. Verify that the interfaces are associated with the proper VLANs and their state is up.

user@switch> show ethernet-switching interfaces

Interface   State    VLAN members           Blocking
ge-0/0/0.0  up       sales                  unblocked
ge-0/0/1.0  up       default                unblocked     
ge-0/0/2.0  up       default                unblocked
ge-0/0/3.0  up       sales                  unblocked
ge-0/0/4.0  up       support                unblocked 
  1. Verify that L2 switching works by issuing an Internet Control Message Protocol (ICMP) ping between two end devices connected to the same VLAN. If this fails, verify that the devices are properly connected to the interfaces on the EX Series switch and that those switch interfaces are assigned to the same VLAN. Also verify that the interface status is "up" and that the port is unblocked by using the following command:

user@switch> show ethernet-switching interfaces

Interface   State    VLAN members           Blocking
ge-0/0/0.0  up       sales                  unblocked
ge-0/0/1.0  up       default                unblocked     
ge-0/0/2.0  up       default                unblocked
ge-0/0/3.0  up       sales                  unblocked
ge-0/0/4.0  up       support                unblocked
  1. Initiate an ICMP ping from a device connected to the EX Series switch to its corresponding L3 interface on the switch. For example, ping from an end device on VLAN sales to the L3 interface defined for VLAN sales. For example, if the switch is configured with L3 interface 10.10.0.1/24 for VLAN sales with vlan-id 10 (subnet 10.10.0.0/24) and if a host with IP address 10.10.0.50/24 is connected to the switch on the same VLAN sales, you would ping from 10.10.0.50 to 10.10.0.1. To view the L3 interfaces on the switch, issue the following command:

user@switch>  show interfaces vlan terse
Interface               Admin Link Proto    Local                 Remote
vlan                    up    up
vlan.10                 down  up   inet     10.10.0.1/24
vlan.20                 down  up   inet     10.20.0.1/24

If this is unsuccessful, verify that the end device's default gateway points to the corresponding VLAN L3 interface and the subnet masks are correct. Also verify using the above command that the L3 interface status is "up".

  1. Initiate a ping from the end device in one VLAN to the L3-interface of another VLAN.

  2. Initiate a ping from the end device in one VLAN to the end device in another VLAN. If the ping test is successful in step 5 above but fails in step 6, verify that the default gateway on the end devices is configured correctly.

 

Modification History:

2020-08-17: Article checked for accuracy; article found valid and relevant; EOS product series references removed

 

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