local.m4: Add a prose commentary on address allocation.

The IPv4 allocation is summarized in the DNS zone repository; the IPv6
allocation wasn't described anywhere at all.

diff --git a/local.m4 b/local.m4
index 45e498b..23e6f6d 100644 (file)
--- a/local.m4
+++ b/local.m4
@@ -33,6 +33,83 @@ m4_divert(-1)
 ###--------------------------------------------------------------------------
 ### Packet classification.
 
+## IPv4 addressing.
+##
+## There are two small blocks of publicly routable IPv4 addresses, and a
+## block of RFC1918 private-use addresses allocated from the Cambridge G-RIN.
+## The former are as follows.
+##
+## 62.49.204.144/28
+##             House border network (dmz).  We have all of these, but .145
+##             is reserved for the router.
+##
+## 212.13.18.64/28
+##             Jump colocated network (jump).  .65--68 are used by Jump
+##             network infrastructure; we get the rest.
+##
+## The latter is the block 172.29.196.0/22.  Currently the low half is
+## unallocated (and may be returned to the G-RIN); the remaining addresses
+## are allocated as follows.
+##
+## 172.29.198.0/24  Untrusted networks.
+##     .0/25           house wireless net
+##     .128/28         iodine (IP-over-DNS) network
+##
+## 172.29.199.0/24  Trusted networks.
+##     .0/25           house wired network
+##     .128/27         mobile VPN hosts
+##     .160/28         reserved, except .160/30 allocated for ITS
+##     .176/28         internal colocated network
+##     .192/27         house safe network
+##     .224/27         anycast services
+
+## IPv6 addressing.
+##
+## There are five blocks of publicly routable IPv6 addresses, though some of
+## them aren't very interesting.  The ranges are as follows.
+##
+## 2001:470:1f08:1b98::/64
+##             Hurricane Electric tunnel network: only :1 (HE) and :2
+##             (radius) are used.
+##
+## 2001:470:1f09:1b98::/64
+##             House border network (dmz).
+##
+## 2001:470:9740::/48
+##             Main house range.  See below for allocation policy.
+##
+## 2001:ba8:0:1d9::/64
+##             Jump border network (jump): :1 is the router (supplied by
+##             Jump); other addresses are ours.
+##
+## 2001:ba8:1d9::/48
+##             Main colocated range.  See below for allocation policy.
+##
+## Addresses in the /64 networks are simply allocated in ascending order.
+## The /48s are split into /64s by appending a 16-bit network number.  The
+## top nibble of the network number classifies the network, as follows.
+##
+## 8xxx                Untrusted
+## 6xxx                Virtual
+## 4xxx                Safe
+## 0xxx                Unsafe, trusted
+##
+## These have been chosen so that network properties can be deduced by
+## inspecting bits of the network number:
+##
+## Bit 15      If set, the network is untrusted; otherwise it is trusted.
+## Bit 14      If set, the network is safe; otherwise it is unsafe.
+##
+## Finally, the low-order nibbles identify the site.
+##
+## 0           No specific site: mobile VPN endpoints or anycast addresses.
+## 1           House.
+## 2           Jump colocation.
+##
+## Usually site-0 networks are allocated from the Jump range to improve
+## expected performance from/to external sites which don't engage in our
+## dynamic routing protocols.
+
 ## Define the available network classes.
 m4_divert(42)m4_dnl
 defnetclass untrusted untrusted trusted mcast