Note: This article is deprecated - The content is no longer applicable to releases subsequent to Junos OS version 15.2 Users are unable to ping between two directly connected IRB interfaces, which are configured between two MX routers as part of a Multi-Chassis Link Aggregation Group (MC-LAG) Active/Active setup. This article describes the issue and suggests a workaround.
User is unable to ping between two directly connected IRB interfaces, which are configured between two MX routers as part of a multi-chassis link aggregation group (MC-LAG) Active/Active setup. IRB interfaces are called under the Bridge Domains. In MC-LAG A/A setup, IRB interface needs to be configured for Virtual Router Redundancy Protocol (VRRP) and called under Bridge Domains. This configuration will be done in both MX-1 and MX-2. But the ping from MX-1 IRB interface to MX-2 IRB interface, which is part of the same VLAN, will not be able to ping each other. OSPF will be stuck in ExStart on each MX.
In an MC-LAG A/A setup, both the InterChassis Link (ICL) interface and MC-AE interface are called under the same Bridge Domain. The ARP replies are dropped on the ICL link by default, hence the ping will not work between two IRB interfaces from MX-1 to MX-2.
This problem is an expected behavior in the MC-LAQ A/A setup. The only way to make the IRB to IRB ping between the MX-1 and MX-2 is to configure a Static ARP at both the IRB interfaces:
+---------+ +----------+ | | ae0 (ICL) | | | MX-1 |--------------| MX-2 | | |--------------| | +---------+ +----------+ | ae1 | ae1 | | | | | | | +-------------+ | +-----| EX-Switch |----+ +-------------+
Configuration required in MX-1:
set interfaces irb unit 21 family inet address 192.168.10.2/24 arp 192.168.10.3 l2-interface ae0.21 set interfaces irb unit 21 family inet address 192.168.10.2/24 arp 192.168.10.3 mac 80:00:00:10:a0:30
Configuration required in MX-2:
set interfaces irb unit 21 family inet address 192.168.10.3/24 arp 192.168.10.2 l2-interface ae0.21 set interfaces irb unit 21 family inet address 192.168.10.3/24 arp 192.168.10.2 mac 80:00:00:10:b0:41
Where ae0.21 is the ICL interface connecting the two MX and mac is the IRB interface mac address of the peer, found with:
show interface extensive irb
Physical interface: irb, Enabled, Physical link is Up Interface index: 132, SNMP ifIndex: 504 Type: Ethernet, Link-level type: Ethernet, MTU: 1514 Device flags : Present Running Interface flags: SNMP-Traps Link type : Full-Duplex Link flags : None Current address: 80:00:00:10:b0:41, Hardware address: 80:00:00:10:b0:41 Last flapped : Never Input packets : 0 Output packets: 0
Refer to Multichassis Link Aggregation Features, Terms, and Best Practices for additional details.
2021-07-14: This is no longer applicable after 15.2 version. 2019-06-03: Content reviewed for accuracy. Example 'show interface extensive irb' output added.