[j-nsp] /kernel: %KERN-6: MTU for ff02::0005 reduced to 1500

[Stacy W. Smith]

On May 8, 2012, at 11:58 AM, Alex D. wrote:
> Hi list,
> 
> i manually set IPv6 mtu to 1500 on M- an MX-Series routers running JunOS 10.4R8.5
> After configuration, following message appears in syslog:
> /kernel: %KERN-6: MTU for ff02::0005 reduced to 1500
> 
> Is it a problem or why does the router inform about the change ?
> Whith manually set IPv4 MTU, there are no such messages in the logfile.
> 
> Regards,
> Alex

I believe this is expected behavior. When you have interfaces with different MTUs configured, you will see one of these messages for each PMTU timeout period for locally-generated IPv6 multicast traffic (in this case ff02::0005 or OSPFv3 hellos) as the new PMTU is discovered for the traffic. 

--Stacy