3 ms·

You're right, DOCSIS has nothing to do with it. The "classic" rationale to choose multicast over broadcast was to try and limit the amount of time to process N

by ay 12y ago

You're right, DOCSIS has nothing to do with it. The "classic" rationale to choose multicast over broadcast was to try and limit the amount of time to process NDP traffic vs. the time the hosts have to process the ARP broadcast traffic in IPv4. 15 years ago that took a nontrivial amount of host resources, and with the way NDP constructs the solicited node multicast, even if you just flood every packet on the link, you still can filter the packets that are not for you at the NIC HW level. And since there are 16 million unique solicited node multicast addresses, in principle the scaling is pretty impressive. Multicast is a definitely a good choice in the long term, though the "here and now" interaction with some protocols is a bit tricky - e.g. 802.11 WiFi (http://tools.ietf.org/html/draft-vyncke-6man-mcast-not-efficient-01 http://tools.ietf.org/html/draft-vyncke-6man-mcast-not-effic... and http://tools.ietf.org/html/draft-yourtchenko-colitti-nd-reduce-multicast-00 http://tools.ietf.org/html/draft-yourtchenko-colitti-nd-redu...) - though it's not the only offender and frequently not the biggest one (service advertisements may consume a comparable and bigger amount of bandwidth on the volatile network). On NBMA: you can have such a network today in a public WiFi scenario where you do not hosts directly talking to each other but want them to access the internet. In the wired case the moniker is "Private VLANs". With IPv6 you can clear the on-link bit, and make NBMA work quite elegantly. But, depending on the exact details, http://tools.ietf.org/html/rfc4903 http://tools.ietf.org/html/rfc4903 does list quite a few interesting challenges - quite an informative read. BTW, if you are interested more in the "why" rather than just "how" of IPv6, take a look at this: http://www.internetsociety.org/deploy360/resources/ebook-ipv6-for-ipv4-experts-available-in-english-and-russian/ http://www.internetsociety.org/deploy360/resources/ebook-ipv... It's a gem: free, very good quality material, and written as if you are co-designing with the author by solving various problems you see on IPv4 networks, and the protocol evolves into what is the IPv6 today.

smutticus 12y ago
Thanks again for the excellent response, and for the history lesson on why multicast was chosen over broadcast for NDP. I've done tons of work in private vlans over the years. I was part of a months long effort to find and document bugs in private vlans at a vendor, where my primary focus was to find and document bugs only in private vlans. Residential ISPs love private vlans because it prevents different customers from seeing each other's broadcast traffic. DHCP Snooping to prevent things like ARP spoofing, in combination with private vlans to limit broadcast traffic will mostly lock things down pretty well. It's funny you should provide a link to a resource from the Deploy360 Programme. I just finished doing a stint with the Deploy360 Programme as a writer working on, among other things, IPv6 resources. My real name is Andrew McConachie.
- ay 12y ago
  Very nice to meet you! Totally agreed on the residential ISPs loving PVLANs. And thanks for your work with deploy360 and helping to get better information to people !

by ay 12y ago

smutticus 12y ago

Thanks again for the excellent response, and for the history lesson on why multicast was chosen over broadcast for NDP. I've done tons of work in private vlans over the years. I was part of a months long effort to find and document bugs in private vlans at a vendor, where my primary focus was to find and document bugs only in private vlans. Residential ISPs love private vlans because it prevents different customers from seeing each other's broadcast traffic. DHCP Snooping to prevent things like ARP spoofing, in combination with private vlans to limit broadcast traffic will mostly lock things down pretty well. It's funny you should provide a link to a resource from the Deploy360 Programme. I just finished doing a stint with the Deploy360 Programme as a writer working on, among other things, IPv6 resources. My real name is Andrew McConachie.

ay 12y ago
Very nice to meet you! Totally agreed on the residential ISPs loving PVLANs. And thanks for your work with deploy360 and helping to get better information to people !