This is a quick and short article on how to perform vlan-swapping on a Juniper QFX5100. I was used to tunneling vlans in a QFX5100 by using the push-operation available through a vlan-map. With this in mind I was struggling to get vlan translation on the QFX5100 working. I was trying to accomplish vlan-swapping through the same type of configuration.

Turns out swapping vlan-id’s is a lot easier. In the following lab setup, I will make the QFX translate vlans between two of the MX104’s interfaces:

VLAN swapping

On the MX104, I will configure a routing-instance ‘QFX-VLAN-501’ which will be tied to interface xe-1/2/0.501. This interface will be configured with vlan vlan-id 501. I will also configure a routing-instance called ‘QFX-VLAN-500’. Interface xe-1/3/0.500, with vlan-id 500, will be placed inside this routing instance. This is configured in the following way:

VLAN swapping

Now for the QFX part. On both of the QFX interfaces, the ‘extended-vlan-bridge’ encapsulation will need to be enabled. Besides the encapsulation, a logical interface with the desired vlan-id is also required. This can be configured like this;

VLAN swapping

At the bottom of the picture, I listed the vlan configuration that was applied to the QFX. Notice that vlan-id 501 was configured for interface xe-0/0/46 unit 501 in the interface configuration stanza. However, in the vlan configuration stanza, the interface itself was placed in vlan 500.

With this configuration, the QFX switch will (automagically) start swapping vlan-id’s in and out of interface xe-0/0/46.

Let’s examine both of the QFX interfaces with a simple show command;

play@Aether> show interfaces xe-0/0/46.501
  Logical interface xe-0/0/46.501 (Index 566) (SNMP ifIndex 525)
    Flags: SNMP-Traps 0x20004000 VLAN-Tag [ 0x8100.501 ] In(swap .500) Out(swap .501)  Encapsulation: Extended-VLAN-Bridge
    Input packets : 0
    Output packets: 0
    Protocol eth-switch, MTU: 1518

play@Aether> show interfaces xe-0/0/47.500
  Logical interface xe-0/0/47.500 (Index 569) (SNMP ifIndex 523)
    Flags: SNMP-Traps 0x20004000 VLAN-Tag [ 0x8100.500 ]  Encapsulation: Extended-VLAN-Bridge
    Input packets : 0
    Output packets: 0
    Protocol eth-switch, MTU: 1518                  

Interface xe-0/0/47 is not showing anything out of the ordinary. This is because nothing extra is happening on that interface. Interface xe-0/0/46 is showing the vlan-operation. Incoming frames have their vlan-id swapped to 500 and outgoing frames have their vlan-id swapped to 501.

Let’s verify this by sending some packets from the MX104 ‘QFX-VLAN-501’ instance to the ‘QFX-VLAN-500’ instance like this:

play@MX104-TEST-HB> ping routing-instance QFX-VLAN-501 source count 5
PING ( 56 data bytes
64 bytes from icmp_seq=0 ttl=64 time=0.687 ms
64 bytes from icmp_seq=1 ttl=64 time=0.601 ms
64 bytes from icmp_seq=2 ttl=64 time=0.648 ms
64 bytes from icmp_seq=3 ttl=64 time=0.625 ms
64 bytes from icmp_seq=4 ttl=64 time=0.619 ms

--- ping statistics ---
5 packets transmitted, 5 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.601/0.636/0.687/0.030 ms


So there is connectivity between the two interfaces. What just happened was the following:

VLAN swapping

Packets are send from the xe-1/2/0.501 interface of the MX104. These packets, tagged with vlan-id 501, are received on the QFX xe-0/0/46.501 interface. Upon the receipt of these packets, the QFX will rewrite the vlan-tag to 500 and perform all relevant lookups in the MAC table of vlan 500. After this lookup, the QFX will forward this packet out interface xe-0/0/47.500. The packet will arrive on the xe-1/3/0.500 interface with the correct vlan-id.

When consulting the MAC table, be sure to insert the vlan-id that the vlan was configured with. So in our case, vlan-id 500 will contain the mac-address of both the MX104’s interfaces. Vlan-id 501 will not contain any entries;

play@Aether> show ethernet-switching table vlan-id 500

MAC flags (S - static MAC, D - dynamic MAC, L - locally learned, P - Persistent static
           SE - statistics enabled, NM - non configured MAC, R - remote PE MAC)

Ethernet switching table : 2 entries, 2 learned
Routing instance : default-switch
    Vlan                MAC                 MAC         Age    Logical
    name                address             flags              interface
    VLAN-500-501        64:64:9b:dd:60:b7   D             -   xe-0/0/46.501
    VLAN-500-501        64:64:9b:dd:61:60   D             -   xe-0/0/47.500

play@Aether> show ethernet-switching table vlan-id 501


I was able to perform this on a QFX5100 running 13.2X51-D30.4. On this software level, it is possible to swap vlan-id’s between two interfaces that are configured with the ‘extended-vlan-bridge’ encapsulation. Hopefully, somewhere in future releases, Juniper will make it so that two interfaces with different encapsulations will also allow for vlan-swapping.