Issue Definition*:
6RD and IPv6 allocation policy
Jan Žorž (Go6 Institute Slo)
Mark Townsley (Cisco)
*Or, Why we had to wake up on Friday
to be here?
1
Aspects of IPv6 Transition Mechanisms
Tunnel
or
Translate
Stateless
or
Stateful
SP-Managed
or
not SP-Managed
6rd is a Stateless, SP-Managed, Tunneling Protocol
2
IPv6 Prefix from an IPv4 Address
 The following construction is what allows 6rd to be
SP-managed and Stateless
0
ISP 6rd
IPv6 Prefix
Subscriber
IPv4 address
2001:db8
198.51.100.1
/n
Subnet-ID
/m
Interface ID
64
Subscriber Delegated IPv6 Prefix
3
6rd – Encapsulation and Packet Flow
“…externally 6rd looks, feels and smells like native IPv6 ” – RIPE Labs
6rd
6rd
Dual Stack
IPv4
Dual Stack
Dual Stack
Dual Stack
6rd Border
Relays
CE
IPv4-only Access Network
 IPv6 in IPv4 (protocol 41) encapsulation
 Within a domain, IPv6 traffic follows IPv4 routing
 CEs reach BRs via IPv4 anycast
4
6rd – CE Provisioning
6rd
6rd
Dual Stack
IPv4
Dual Stack
Dual Stack
CE
Dual Stack
6rd Border
Relays
 Each 6rd CE within a 6rd Domain requires a single DHCP
option* carrying 4 values
6rdPrefix
6rdPrefixLen
IPv4MaskLen
6rdBRIPv4Address
 These 4 values are the same for all CEs within the domain
*May also be configured with TR-69 or otherwise
5
6rd – Deployments
6rd
6rd
Dual Stack
IPv4
Dual Stack
Dual Stack
CE
Dual Stack
6rd Border
Relays
 Defined in RFC 5969
 Commercially available products from a number of vendors
 First deployment in 2007, multiple deployments today
6
Q: What should /n and /m be?
0
ISP 6rd Prefix
IPv4 (0-32 bits)
2001:db8
198.51.100.1
/n
Subnet-ID
/m
Interface ID
64
7
Starting simple: /n = 28, /m = 60
ISP 6rd IPv6 Prefix
198.51.100.1
2001:db8
0
32 bits
/28
Subnet-ID
/60
Interface ID
64
 One 6rd domain
 6rd provisioning is identical for all CEs
 Convenient conversion between subscriber IPv6 and IPv4
address
 Allows 16 IPv6 subnets in the home
 ISP needs a /27 or shorter
8
But what if you cannot get a /27?
/n = 32, /m = 64
32 bits
ISP 6rd IPv6 Prefix
198.51.100.1
2001:db8
0
/32
Interface ID
/64
 Still a single domain, but /64 does not allow multiple
subnets for the subscriber
• No subnets, no routing
• Common features such as Guest + Home SSIDs become
very difficult
• Support for 802.15.4 for Sensors, Zigbee, etc.
• Ultimately leads to IPv6 NAT
9
Using less than 32 bits of IPv4
 If the IPv4 space is an aggregate, 6rd need not carry the
common bits
 For example, in a CGN world of 10/8, we just don’t carry around
the 10
24 bits
.51.100.1
2001:db8
0
/32
/56
/36
Interface ID
64
.51.100.1
2001:db80:0
0
Subnet-ID
Interface ID
/60 6
4
10
Multiple 6rd Domains
ISP 6rd IPv6 Prefix
IPv4 /12
32 bits
4 bits
IPv4 /16
32 bits
IPv4 /14
32 bits
4 bits
IPv4 /11
32 bits
3 bits
8 bits
Distinct IPv4 Aggregates
8 bits
Interface ID (64 bits)
8 bits
Interface ID (64 bits)
18 bits
8 bits
Interface ID (64 bits)
19 bits
8 bits
Interface ID (64 bits)
20 bits
16 bits
 More efficient in terms of IPv6 space usage
 However, CEs in different domains require different configuration
 Operations begin to get more complicated, traffic patterns not as
efficient, etc.
11
How do I get my /27?
"2^(48-(P+1))"
"2^(48-(P+1)) + Growth"
Growth ->
20%
10%
5%
0%
Years ->
3
3
3
0
22
33,554,432
19,418,074
25,209,941
28,985,580
33,554,432
23
16,777,216
9,709,037
12,604,971
14,492,790
16,777,216
24
8,388,608
4,854,519
6,302,485
7,246,395
8,388,608
25
4,194,304
2,427,259
3,151,243
3,623,197
4,194,304
26
2,097,152
1,213,630
1,575,621
1,811,599
2,097,152
27
1,048,576
606,815
787,811
905,799
1,048,576
28
524,288
303,407
393,905
452,900
524,288
29
262,144
151,704
196,953
226,450
262,144
30
131,072
75,852
98,476
113,225
131,072
31
65,536
37,926
49,238
56,612
65,536
Prefix Size
 /27 yields /60 for the home
 /29 yields /62 for the home
12
Possible solutions
1. Declare this is a non-problem
2. Special 6rd policy. e.g., /27 granted based on
ability and intention to deploy more rapidly with
6rd
3. Allow /29 to anyone
4. Others?
13