Hi,

although this is no longer fully related to dnsmasq, just a few sentences on 
top:

> >> There's a slightly more special case for us: We have one central firewall
> (which
> >> gets the full /56 net on the upstream interface routed to it) and most
> gateways
> >> are separate nodes
> >> (i.e. most VLANs are not connected to the central FW).
> >> So I believe in that case I just need an ip6tables rule (per /64 subnet) 
> >> on the
> >> central firewall to redirect all traffic to the gateway for the /64 subnet,
> right?
> >
> > It's important to don't have the /56 or /64 network assigned to an interface
> on the router (otherwise you would need proxyNDP)!
> 
> Noted. Indeed, that's reasonable, and achieved by design for those VLANs not
> connected to the central router ;-).
> 
> > If it's prefix delegation, don't assign the 64 or 54 subnet to any 
> > interface on
> the main router, just bring interfaces up and assign link-local-addresses to
> them! On the central firewall just do routing with link-local addresses
> (basically, this subnet goes to this adaptor and this mac address - as link 
> local
> addresses are basically MAC addresses). Of course the packet filtering uses 
> the
> global addresses, but the routing is done with link-local.
> >
> > The router box gets the packets from the provider all delegated to its own
> link-local address of the upstream interface (that's what most providers do,
> including DSL providers with PPP or servers in data centers like Hetzner). So 
> all
> incoming packets are sent to the same fe80:XXXX address based on the MAC
> known to upstream or negotiated via PPP and the router just forwards them
> based on the global address inside of the packets.
> 
> In our case, they waste a dedicated /64 global address network for the
> connection network between our firewall and their endpoint... That also works,
> but it's rather wasteful of course ;-).

That's not so bad, because you get a global IPv6 address on the upstream 
router, so it can appear on traceroutes (see below). So that's not too bad. If 
you won't have that, to correctly make the router inbetween appear in 
traceroutes, you would have to assign some other IPv6 from another /64 subnet. 
Now you have that one on the upstream interface, the router can respond with 
ICMPv6 messages as reply on traceroute or unroutable addresses. Otherwise the 
response from e.g., traceroute would get lost.

> > In the routing table of the main firewall you just add entries like global
> subnetA/64 goes to link-local address fe80:xxxx on interface XY, and so on. If
> you don't like the automatic assigned link-local-addresses based on the mac
> interface you can easily change them. In my office I have the router assigned
> fe80::1, you could assign fe80::2, fe80::3 to the secondary routers's network
> interfaces and then routing tables look easy:
> >
> > 2001:abcd:1234:1::/64 => fe80::2@en1
> > 2001:abcd:1234:2::/64 => fe80::3@en1
> > 2001:abcd:1234:3::/64 => fe80::4@en1.24 (a VLAN #24 on en1)
> > 2001:abcd:1234:3::/64 => fe80::4@en2 (other network interface)
> >
> > Fe80::2, 3, 4 are the separate boxes which route the traffic and have the
> dnsmasq. If you don't want to use fe80 link-local addresses, you can use ULAs,
> but for routing purposes the link-local ones with interface name are the 
> easiest.
> 
> Thanks, that example clarified it for me. Good thinking in using the 
> link-local
> addresses here, that's completely sufficient. It really helps to talk about 
> these
> things to clear up my mind from the IPv4 legacy of thinking.

This is generally known as "next-hop routing". A router just gives the correct 
link-local address, so the packet with a global address can get closer to its 
target. This makes routing tables easy to maintain.

The general recommendation is to always only use link-local addresses in 
routing tables (because otherwise the router would need to send NDP packets on 
its own, just to find the next-hop target!

Nevertheless, each router should have a global address, too (so it can be 
pinged). You can assign it to the interface with the corresponding prefix. On 
the upstream router / firewall it would be the one from the "wasted network" 
(see above); on the client-facing router one from the target /64 network 
(2001:xxxxxx::1). Between upstream router and client facing routers, only 
link-local addresses are used.

> > Another idea is to use one of the /64 subnets as the "inter-router"
> communication, but that's not needed for IPv6, because we have link-local-
> addresses for that purpose!

As noted before, nevertheless all nodes on the route *should* have a global 
address, too (but those should not be used in the routing table). The 
global/routeable address is needed to transfer ICMPv6 messages. The router 
can't otherwise be pinged by traceroute or tell the client that a route is not 
working via ICMP.

> > On the internal routers you only assign the full global 64 subnet to the 
> > client
> facing network adaptors. The connection to the router uses a link-local 
> address
> only (as described before). No additional firewalling is needed, you just 
> need to
> setup routing entries like above (the other way round).
> 
> Thanks, that cleared up my last question completely. Now I just have to 
> explain
> my colleagues and we can start implementing that in the next weeks (in slow
> steps, but it seems much more straightforward than I thought) :-).

Good luck,
Uwe


_______________________________________________
Dnsmasq-discuss mailing list
Dnsmasq-discuss@lists.thekelleys.org.uk
http://lists.thekelleys.org.uk/mailman/listinfo/dnsmasq-discuss

Reply via email to