1- On Cisco routers, after you configured an IPv6 address on an interface, will the router start sending router advertisement messages or no ipv6 nd suppress-ra command needed?
2- For prefix delegation, can CPE router start router advertisement after take a prefix from delegating server? What about if I restart CPE router? Does it continue advertise same prefix to its clients with RA?
It is some confusing...
1) as the default is no ipv6 unicast-routing then the router won't send any RA and won't reply to any RS.
Once you have enabled ipv6 routing then it send RAs and reply to RS unless you configure ipv6 nd suppress-ra on the interface
I don't know for question 2 as I've never used nor labbed the prefix delegation feature yet.
"no ipv6 nd suppress-ra" command is needed only for when I use ipv6 nd suppress-ra. Is it true?
I wonder that if I configure RA message with MTU and some others paremeters, and than if I restart Cisco and enable routing again, RA message includes same parameters as before resart? Or are there default parameters at system statrup?
if you want to suppress RA then you need to do ipv6 nd suppress-ra on the interface because by default if ipv6 unicast-routing is turned on it will send RAs and reply to RS.
If you don't save the config then indeed you will get the default params from RAs.