• 21 July 2026

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Juniper QFX Multichassis Link Aggregation Example

In this post, I will show you a basic MC-LAG topology and configure it on Juniper devices. Here is the topology as below;

Here are the QFX configurations;

set system host-name QFX_1
set chassis aggregated-devices ethernet device-count 5
set interfaces ge-0/0/46 unit 0 family ethernet-switching
set interfaces xe-0/0/46 ether-options 802.3ad ae2
set interfaces ge-0/0/47 unit 0 family ethernet-switching
set interfaces xe-0/0/47 ether-options 802.3ad ae1
set interfaces et-0/0/52 ether-options 802.3ad ae0
set interfaces et-0/0/53 ether-options 802.3ad ae0
set interfaces ae0 aggregated-ether-options lacp active
set interfaces ae0 unit 0 family ethernet-switching interface-mode trunk
set interfaces ae0 unit 0 family ethernet-switching vlan members ICCP_4001
set interfaces ae0 unit 0 family ethernet-switching vlan members DATA
set interfaces ae1 description EX3400
set interfaces ae1 aggregated-ether-options lacp active
set interfaces ae1 aggregated-ether-options lacp system-id 00:00:00:00:00:01
set interfaces ae1 aggregated-ether-options lacp admin-key 1
set interfaces ae1 aggregated-ether-options mc-ae mc-ae-id 1
set interfaces ae1 aggregated-ether-options mc-ae redundancy-group 1
set interfaces ae1 aggregated-ether-options mc-ae chassis-id 0
set interfaces ae1 aggregated-ether-options mc-ae mode active-active
set interfaces ae1 aggregated-ether-options mc-ae status-control active
set interfaces ae1 aggregated-ether-options mc-ae init-delay-time 240
set interfaces ae1 unit 0 family ethernet-switching interface-mode trunk
set interfaces ae1 unit 0 family ethernet-switching vlan members DATA
set interfaces ae2 description EX2300
set interfaces ae2 aggregated-ether-options lacp active
set interfaces ae2 aggregated-ether-options lacp system-id 00:00:00:00:00:02
set interfaces ae2 aggregated-ether-options lacp admin-key 2
set interfaces ae2 aggregated-ether-options mc-ae mc-ae-id 2
set interfaces ae2 aggregated-ether-options mc-ae redundancy-group 1
set interfaces ae2 aggregated-ether-options mc-ae chassis-id 0
set interfaces ae2 aggregated-ether-options mc-ae mode active-active
set interfaces ae2 aggregated-ether-options mc-ae status-control active
set interfaces ae2 aggregated-ether-options mc-ae init-delay-time 240
set interfaces ae2 unit 0 family ethernet-switching interface-mode trunk
set interfaces ae2 unit 0 family ethernet-switching vlan members DATA
set interfaces irb unit 3 family inet address 10.200.254.13/24
set interfaces irb unit 4001 family inet address 172.16.0.1/30
set multi-chassis multi-chassis-protection 172.16.0.2 interface ae0
set protocols iccp local-ip-addr 172.16.0.1
set protocols iccp peer 172.16.0.2 session-establishment-hold-time 340
set protocols iccp peer 172.16.0.2 redundancy-group-id-list 1
set protocols iccp peer 172.16.0.2 liveness-detection minimum-receive-interval 1000
set protocols iccp peer 172.16.0.2 liveness-detection transmit-interval minimum-interval 1000
set protocols lldp interface all
set protocols lldp-med interface all
set protocols igmp-snooping vlan default
set protocols mstp configuration-name MST_TEST
set protocols mstp msti 1 vlan 1-4094
set switch-options service-id 10
set vlans DATA vlan-id 3
set vlans DATA l3-interface irb.3
set vlans ICCP_4001 vlan-id 4001
set vlans ICCP_4001 l3-interface irb.4001
set system host-name QFX_2
set chassis aggregated-devices ethernet device-count 5
set interfaces ge-0/0/46 unit 0 family ethernet-switching
set interfaces xe-0/0/46 ether-options 802.3ad ae2
set interfaces ge-0/0/47 unit 0 family ethernet-switching
set interfaces xe-0/0/47 ether-options 802.3ad ae1
set interfaces et-0/0/52 ether-options 802.3ad ae0
set interfaces et-0/0/53 ether-options 802.3ad ae0
set interfaces ae0 aggregated-ether-options lacp active
set interfaces ae0 unit 0 family ethernet-switching interface-mode trunk
set interfaces ae0 unit 0 family ethernet-switching vlan members ICCP_4001
set interfaces ae0 unit 0 family ethernet-switching vlan members DATA
set interfaces ae1 description EX3400
set interfaces ae1 aggregated-ether-options lacp active
set interfaces ae1 aggregated-ether-options lacp system-id 00:00:00:00:00:01
set interfaces ae1 aggregated-ether-options lacp admin-key 1
set interfaces ae1 aggregated-ether-options mc-ae mc-ae-id 1
set interfaces ae1 aggregated-ether-options mc-ae redundancy-group 1
set interfaces ae1 aggregated-ether-options mc-ae chassis-id 1
set interfaces ae1 aggregated-ether-options mc-ae mode active-active
set interfaces ae1 aggregated-ether-options mc-ae status-control standby
set interfaces ae1 aggregated-ether-options mc-ae init-delay-time 240
set interfaces ae1 unit 0 family ethernet-switching interface-mode trunk
set interfaces ae1 unit 0 family ethernet-switching vlan members DATA
set interfaces ae2 description EX2300
set interfaces ae2 aggregated-ether-options lacp active
set interfaces ae2 aggregated-ether-options lacp system-id 00:00:00:00:00:02
set interfaces ae2 aggregated-ether-options lacp admin-key 2
set interfaces ae2 aggregated-ether-options mc-ae mc-ae-id 2
set interfaces ae2 aggregated-ether-options mc-ae redundancy-group 1
set interfaces ae2 aggregated-ether-options mc-ae chassis-id 1
set interfaces ae2 aggregated-ether-options mc-ae mode active-active
set interfaces ae2 aggregated-ether-options mc-ae status-control standby
set interfaces ae2 aggregated-ether-options mc-ae init-delay-time 240
set interfaces ae2 unit 0 family ethernet-switching interface-mode trunk
set interfaces ae2 unit 0 family ethernet-switching vlan members DATA
set interfaces irb unit 3 family inet address 10.200.254.14/24
set interfaces irb unit 4001 family inet address 172.16.0.2/30
set multi-chassis multi-chassis-protection 172.16.0.1 interface ae0
set protocols iccp local-ip-addr 172.16.0.2
set protocols iccp peer 172.16.0.1 session-establishment-hold-time 340
set protocols iccp peer 172.16.0.1 redundancy-group-id-list 1
set protocols iccp peer 172.16.0.1 liveness-detection minimum-receive-interval 1000
set protocols iccp peer 172.16.0.1 liveness-detection transmit-interval minimum-interval 1000
set protocols lldp interface all
set protocols lldp-med interface all
set protocols igmp-snooping vlan default
set protocols mstp configuration-name MST_TEST
set protocols mstp msti 1 vlan 1-4094
set switch-options service-id 10
set vlans DATA vlan-id 3
set vlans DATA l3-interface irb.3
set vlans ICCP_4001 vlan-id 4001
set vlans ICCP_4001 l3-interface irb.4001

There are some points to be carefull.

1- We use same service-id on both QFX switches
2- We use MC-AE mode active-active on both QFX switches.
3- QFX1’s status control is active, QFX2’s status control is standby.
4- We use same system-id and mc-ae-id on both QFX switches per ae interface.
5- Chassis-id’s are different.
6- We should be sure the VLAN used for ICCP is member of the link between two QFX switches.
7- We should be sure the VLAN used for ICCP is NOT member of the links we created mcae like EX2300 and EX3400 connections.

Now, we want to define l3 interfaces on QFX’es. To do that we configure VRRP. Let’s add it below.

root@QFX_1# show | display set | match 99 
set interfaces ae0 unit 0 family ethernet-switching vlan members 99
set interfaces ae1 unit 0 family ethernet-switching vlan members 99
set interfaces irb unit 99 family inet address 10.200.99.2/24 vrrp-group 99 virtual-address 10.200.99.1
set interfaces irb unit 99 family inet address 10.200.99.2/24 vrrp-group 99 priority 200
set interfaces irb unit 99 family inet address 10.200.99.2/24 vrrp-group 99 accept-data
set vlans DATA_99 vlan-id 99
set vlans DATA_99 l3-interface irb.99

root@QFX_2# show | display set | match 99 
set interfaces ae0 unit 0 family ethernet-switching vlan members 99
set interfaces ae1 unit 0 family ethernet-switching vlan members 99
set interfaces irb unit 99 family inet address 10.200.99.3/24 vrrp-group 99 virtual-address 10.200.99.1
set interfaces irb unit 99 family inet address 10.200.99.3/24 vrrp-group 99 priority 150
set interfaces irb unit 99 family inet address 10.200.99.3/24 vrrp-group 99 accept-data
set vlans DATA_99 vlan-id 99
set vlans DATA_99 l3-interface irb.99

root@QFX_2# run show vrrp 
Interface     State       Group   VR state VR Mode   Timer    Type   Address
irb.99        up             99   backup   Active      D  3.373 lcl    10.200.99.3    
                                                                vip    10.200.99.1    
                                                                mas    10.200.99.2

When we don’t use VRRP but have IP addresses both switches, we could reach both switches through these IP addresses but sometimes could not reach. Why, I don’t know, but when we use VRRP, there is no unreachability.

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