3 ms·

>I mean, I have no use for giving every single host a /64, but I've got five or six VLAN's and without at least a /56 I've got no way of actually deploying IPv6

by ra1n85 8y ago

>I mean, I have no use for giving every single host a /64, but I've got five or six VLAN's and without at least a /56 I've got no way of actually deploying IPv6 on my network. Why can't you subnet the /64? CenturyLink isn't doing dot1q tagging to you, so you must have a router with tagged interfaces on your network. Edit: Imagine this is because you want to use SLAAC.

y0ghur7_xxx 8y ago
because if you want slaac to work without nat, the smalles ipv6 subnet you can have is a /64. so if your provider gives you just a single static /64, all you can allocate is a single subnet.
snuxoll 8y ago
> Edit: Imagine this is because you want to use SLAAC. Not just because of SLAAC, prefixes smaller than /64 are likely to mess with all sorts of assumptions built into networking gear. It may not be "correct" since there are valid reasons for subnets as small as a /127 (though they are used infrequently enough at least), but a lot of networking gear cheats with IPv6 routes to keep the amount of TCAM memory needed down. Why spend 128-bits per route and quadruple the memory required when you can double it and go 64-bits per route and dump the longer ones to slower DRAM (I mean, you only use /127's for point-to-point links that don't need link-rate switching anyway)? Regardless of anyone's philosophy of address assignment strategies, prefixes smaller than /64's in IPv6 are un-wise unless you want to degrade into worst-case routing paths on your network gear.
- ra1n85 8y ago
  Somewhat of a good point, but I don't think it applies here - some implementations, particularly inexpensive devices like SOC's, do exact search on common prefix lengths like /64 and /48. I can't imagine this would be a huge problem within a home network, though. Even then, DRAM, which is essentially software switching, is rarely used. Further, you said you had 6 VLANs - this is well within the route scale of the vast majority of network devices regardless of how they implement their lookup data structures. Good example: The SRX300, a desktop router/firewall implemented on a MIPS based Cavium Octeon (both control and data plane) can handle up to 256K IPv6 routes: https://www.juniper.net/assets/us/en/local/pdf/datasheets/1000550-en.pdf https://www.juniper.net/assets/us/en/local/pdf/datasheets/10... The Trident series SOC's can do 8K by default, and 64K with ALPM enabled: https://www.juniper.net/us/en/local/pdf/datasheets/1000480-en.pdf https://www.juniper.net/us/en/local/pdf/datasheets/1000480-e... >(I mean, you only use /127's for point-to-point links that don't need link-rate switching anyway)? /126's and /127's are often used for PTP's for peering/transit. Line rate is table stakes. Bear in mind that the gear used in these situations has plentiful lookup memory (SRAM, RLDRAM, HMC, or HBM).

by ra1n85 8y ago

y0ghur7_xxx 8y ago

because if you want slaac to work without nat, the smalles ipv6 subnet you can have is a /64. so if your provider gives you just a single static /64, all you can allocate is a single subnet.

snuxoll 8y ago

> Edit: Imagine this is because you want to use SLAAC. Not just because of SLAAC, prefixes smaller than /64 are likely to mess with all sorts of assumptions built into networking gear. It may not be "correct" since there are valid reasons for subnets as small as a /127 (though they are used infrequently enough at least), but a lot of networking gear cheats with IPv6 routes to keep the amount of TCAM memory needed down. Why spend 128-bits per route and quadruple the memory required when you can double it and go 64-bits per route and dump the longer ones to slower DRAM (I mean, you only use /127's for point-to-point links that don't need link-rate switching anyway)? Regardless of anyone's philosophy of address assignment strategies, prefixes smaller than /64's in IPv6 are un-wise unless you want to degrade into worst-case routing paths on your network gear.

ra1n85 8y ago
Somewhat of a good point, but I don't think it applies here - some implementations, particularly inexpensive devices like SOC's, do exact search on common prefix lengths like /64 and /48. I can't imagine this would be a huge problem within a home network, though. Even then, DRAM, which is essentially software switching, is rarely used. Further, you said you had 6 VLANs - this is well within the route scale of the vast majority of network devices regardless of how they implement their lookup data structures. Good example: The SRX300, a desktop router/firewall implemented on a MIPS based Cavium Octeon (both control and data plane) can handle up to 256K IPv6 routes: https://www.juniper.net/assets/us/en/local/pdf/datasheets/1000550-en.pdf https://www.juniper.net/assets/us/en/local/pdf/datasheets/10... The Trident series SOC's can do 8K by default, and 64K with ALPM enabled: https://www.juniper.net/us/en/local/pdf/datasheets/1000480-en.pdf https://www.juniper.net/us/en/local/pdf/datasheets/1000480-e... >(I mean, you only use /127's for point-to-point links that don't need link-rate switching anyway)? /126's and /127's are often used for PTP's for peering/transit. Line rate is table stakes. Bear in mind that the gear used in these situations has plentiful lookup memory (SRAM, RLDRAM, HMC, or HBM).