MySQL: Don't require a lease to have expired if we reallocate it to the previous...

The current default allocate_find query causes per-client IP allocation
instability that starts when allocate_clear rate limiting comes into
effect.

With initial pool conditions the default alloc_find query selects from
the pool of all *expired* leases. It selects the least recently used IP
address (i.e. the one with the oldest expiry_time) unless a matching
username and/or callingstationid exists in the table in which case these
are prioritised in order to issue the client with their previous lease.
Normally picking the least recently used address helps to avoid issuing
the address to a different client, maximising the chance of stickiness,
which is desirable.

However, if a user makes successive authentication attempts whilst
allocate_clear rate limiting is active they are always allocated a
different IP address because their existing address is unavailable (has
not yet expired and has not been explicitly expired by allocate_clear),
with the effect that there are now multiple rows in the table containing
the same pool_key, username and callingstationid.

The normal ordering then has the undesirable effect of ensuring that
successive future IP address selections for the client will flip-flop
between addresses because username + callingstationid are first
prioritied then the *oldest expiry_time* is chosen (rather than the most
recent expiry relating to the most recent lease). This behaviour
persists once allocate_clear rate limiting is no longer in effect.

We can avoid getting having multiple rows with the same client details
by amending the allocate_find query to include an existing row matching
nasipaddress and pool_key in the available set of IP addreses regardless
of whether the lease has expired or not (i.e. re-allocation of a current
lease to the same client).

diff --git a/raddb/mods-config/sql/ippool/mysql/queries.conf b/raddb/mods-config/sql/ippool/mysql/queries.conf
index 9b00975a6c5c2140dea4aff850bb63c22f24c3f0..80a775eeeed643f325fc75fddcb2f310a7931da0 100644 (file)
--- a/raddb/mods-config/sql/ippool/mysql/queries.conf
+++ b/raddb/mods-config/sql/ippool/mysql/queries.conf
@@ -89,7 +89,10 @@ allocate_clear = "\
 allocate_find = "\
        SELECT framedipaddress FROM ${ippool_table} \
        WHERE pool_name = '%{control:Pool-Name}' \
-       AND (expiry_time < NOW() OR expiry_time IS NULL or expiry_time = 0) \
+       AND ( \
+               expiry_time < NOW() OR expiry_time IS NULL OR expiry_time = 0 \
+               OR ( nasipaddress = '%{NAS-IP-Address}' AND pool_key = '${pool_key}' ) \
+       ) \
        ORDER BY \
                (username <> '%{User-Name}'), \
                (callingstationid <> '%{Calling-Station-Id}'), \