Changes between Version 1 and Version 2 of RefIDChanges

Timestamp:

09/06/15 08:54:39 (7 years ago)

Author:

stenn@…

Comment:

--

RefIDChanges

@@ -3 +3 @@
 There are several problems with around `refid`s in the current RFC.
 
-* The decision to use an IPv4 address was convenient and is no longer useful
-  * S2+ `refid`s are being used as IPs for tracing
+* The decision to use an IPv4 address was convenient and is no longer useful:
+  * S2+ `refid`s are being used as IPs for tracing.
   * S2+ IPv6 `refid`s are colliding with valid IPv4 addresses
+* The concept of a "time loop" is not well-defined.  From the document, it's clear that the timing loop being detected is one involving (only) 2 machines.
+* The specification was written when computers generally only had 1 IP address.
 
 It doesn't help that the stock `ntpq -p` output shows the `refid` as an IPv4 address and does not display the association ID.  That will be changing soon:
 * http://bugs.ntp.org/2778
 * http://bugs.ntp.org/278
+
+The proposal is comprised of two parts.  One is a change to the `refid` value for IPv6 addresses, and the other goes to a recommended way of selecting a `refid` that will identify the current host.
+
+To select an IP to be used as the basis for a host's `refid`:
+
+* load any list of "do-not-use IPs"
+* Scan the list of "up" IPs, ignoring any in the "do-not-use" list
+
+Call the IPs we have found "list A".
+
+If a mechanism exists to identify when there is a change to an interface, repeat the above steps, saving the results in "list B".
+
+For each IP in "list A", see if that IP is in "list B".  If it is not, remove the IP from "list A".
+
+For each IP in "list B", see if that IP is in "list A".  If it is not, add the IP to the end of "list A".
+
+Assign the first entry in "list A" to `candidate_IP`.
+
+For each of the remaining IPs in "list A", see if the new IP is "more routable" than the `candidate_IP`.  If it is, remember it as the new `candidate_IP`.
+
+The following list shows how "routable" an IP is.
+
+For IPv4 addresses, the following list goes from least to most routable:
+* an address in 127.0.0.0/8
+* an address in RFC1918 space
+* any other address
+
+For IPv6 addresses, the following list goes from least to most routable:
+* a localhost address
+* an interface-local address
+* …
+* Unicast addresses
+
+If the `candidate_IP` is an IPv4 address, use that value for the `refid`.
+
+If the `candidate_IP` is an IPv6 address:
+* Generate an `md5` hash of the address
+* set the `refid` to (0xF0000000. 0xF0000000, or 0xFF000000)
+* get the high-order 32 bits of the hash.
+* AND these 32 bits with (0x0FFFFFFF, 0x07FFFFFF, or 0x00FFFFFF)
+* OR this result with the `refid`.
+