Can't set don't frag socket option on ICMPV6 sockets

Hi,

I'm writing a test app to send ICMPv6 packets.
When I try to set the IPV6_DONTFRAG socket option, I get the error "operation not permitted" (EPERM).

I am able to set the IPV6_DONTFRAG socket option on UDP sockets running IPv6. I am also able to set the IP_DONTFRAG socket option on ICMPv4 sockets.

To summarize:

• UDP - IPV4, don't fragment option can be set

• UDP - IPV6, don't fragment option can be set

• ICMP - IPV4, don't fragment option can be set

• ICMP - IPV6, don't fragment option can't be set

Is there a reason/workaround to get this to work?

Another example, if the following command, I get that output

Code Block language
 ~ % ping6 -D www.google.com            
ping6: IPV6_DONTFRAG: Operation not permitted

If I run

Code Block language
sudo ping6 -D -s 1600 www.google.com

the pings start to be sent, but according to a packet capture, they are fragmented. It seems like the socket option is not set/not followed?

Thanks