4 ms·

> ...when you get to the network edge. I'm not a networking guy. Where is the difference? One table entry for the /48 should be enough? Where is the difference

by nisa 11y ago

> ...when you get to the network edge. I'm not a networking guy. Where is the difference? One table entry for the /48 should be enough? Where is the difference to a /64 that still allows enough IP addresses to blow something up? I can't image that a lot of people map their ULA network 1:1 to a /48 or is this the reason? As far as I undetstand it it shouldn't matter because the prefix translation is happening on the server itself on not on the router. So a single router should suffice? Wasn't at least the IPv6 header explicitly designed to be more router friendly?

devicenull 11y ago
At the edge, the last router before your server has to have a mapping that a single particular IPv6 address maps to a specific MAC address. You can't really condense this down to a single entry, because any given switchport might have multiple MAC addresses active (think of the case where you have a dumb switch attached to your router, and 20 servers attached to that dumb switch. You're looking at 20 different mac addresses, so no way to condense that down to a few entries). Even a /64 is more then enough to blow up a router at this point. The /48 just makes it a lot more likely that that will happen. The simplest solution here is to route the entire /48 at a specific IPv6 address. This brings you back down to a couple table entries, but requires that your customer configure things properly.
- X-Istence 11y ago
  That's when you do DHCP-PD and the router (last hop before your server) sets up a route for that entire /48 to the link-local address of your server. Or you set up a static route (as a provider this would be recommended) or let the edge do a BGP announcement of it's address space.
  - simoncion 11y ago
    Why do either of these solve the problem mentioned, and why would you allocate a /48 to a single server?
    - simoncion 11y ago
      Wait, when you said "...the router (last hop before your server) sets up a route for that entire /48 to the link-local address of your server." Was "your server" the ISP's server, or the customer's server? If the former, why are you saying "server", rather than "router"?
      - X-Istence 11y ago
        It's the customers server. If they need a /48 of address space, you just want to route all of it to them.

by nisa 11y ago

devicenull 11y ago

At the edge, the last router before your server has to have a mapping that a single particular IPv6 address maps to a specific MAC address. You can't really condense this down to a single entry, because any given switchport might have multiple MAC addresses active (think of the case where you have a dumb switch attached to your router, and 20 servers attached to that dumb switch. You're looking at 20 different mac addresses, so no way to condense that down to a few entries). Even a /64 is more then enough to blow up a router at this point. The /48 just makes it a lot more likely that that will happen. The simplest solution here is to route the entire /48 at a specific IPv6 address. This brings you back down to a couple table entries, but requires that your customer configure things properly.

X-Istence 11y ago
That's when you do DHCP-PD and the router (last hop before your server) sets up a route for that entire /48 to the link-local address of your server. Or you set up a static route (as a provider this would be recommended) or let the edge do a BGP announcement of it's address space.
- simoncion 11y ago
  Why do either of these solve the problem mentioned, and why would you allocate a /48 to a single server?
  - simoncion 11y ago
    Wait, when you said "...the router (last hop before your server) sets up a route for that entire /48 to the link-local address of your server." Was "your server" the ISP's server, or the customer's server? If the former, why are you saying "server", rather than "router"?
    - X-Istence 11y ago
      It's the customers server. If they need a /48 of address space, you just want to route all of it to them.