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Long and unabbreviatable IPv6 addresses with random overloaded bits, vs. tunnelbroker



On Sun, 18 Nov 2012, Bryan Fields wrote:

> On 11/18/12 5:53 PM, Constantine A. Murenin wrote:
>> edis.at gives you an IPv4 address of, for example, 158.255.21x.xxx,
>> and the IPv6 /112 that you get is 2a03:f80:ed15:158:255:21x:xxx:0/112
>> (really a /48), with 2a03:0f80:ed15::1 as the gateway.

By "KVM", I assume he's talking about cloud or VPS, i.e. a KVM based 
virtual machine.  With cloud in particular, I've been trying to decide how 
to dole out IPv6 space.  Because we're doing bridged networking for the 
VMs, we've been giving out IPv4 /32s to each VM and all VMs are in the 
same VLAN.

It seems insane to try to setup a proper IPv6 subnet and unique gateway 
for each VM, so I've been thinking something similar to what the host 
being complained about here has done is the only way to go.  Not down to 
the detail of making the IPv6 ip based on the IPv4 IP, but giving out 
"very small" v6 blocks, (i.e. maybe /120 or /124), out of a /48 with the 
prefix::1/48 IP as everyone's gateway.  Sure, IPv6 is big enough that we 
could give out /64s from that /48 and not run out of numbers, but I'm 
concerned about what happens when an abusive customer turns up 2^64 
addresses and overloads the neighbor discovery cache on our gear.  What's 
anyone really going to do with more than a few IP addresses on a VPS 
anyway?  Just as we do with additional v4 IPs, if someone really has a 
need for additional v6 subnets, those could be provided, likely for a fee.


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