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Syslog message: /kernel: rt_expand_bridge could not find l3_rt for the irb (549)

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Article ID: KB32564 KB Last Updated: 02 May 2018Version: 1.0
Summary:

This article explains why the "rt_expand_bridge could not find l3_rt for the irb" message is generated when an igmp join is received, and suggests a way to suppress this message.

Symptoms:

When an igmp join is received, the following debug message is logged:

/kernel: rt_irb_get_vrf_rt route does not exist in vrf
/kernel: rt_expand_bridge could not find l3_rt for the irb (549)
Cause:

In Junos OS code, rt_irb_get_vrf_rt is a method to get a route inside the Virtual Routing and Forwarding (VRF) table. This method has some IF clauses that are used to determine the course of action if a certain condition is met, such as when a route is not found. In this case, the IF statement says that if a route does not yet exist in the inet table of VRF, no expansion should be performed.

When an igmp join message is received, the mcsnoop [snooping] daemon tries to add an L2 route followed by the kernel, which tries to expand the L2 + L3 list. However, no corresponding L3 route is present (the attribute L3_rt in the code is NULL). So the debug message is logged. This happens when igmp joins are received before the L3 (S, G) route is programmed.

Solution:

These log messages are not indicative of any functionality issue and are used only for debugging purposes. They can be suppressed by configuring the following:

‚Äčlab@switch# show system syslog                 
     user * {
        any emergency;
     }
     file messages {
         any notice;
         authorization info;
         match "! (rt_irb_get_vrf_rt | rt_expand_bridge)";
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