docs: document IPv4 pool allocators and range limits

Signed-off-by: Denys Fedoryshchenko <denys.f@collabora.com>

1 files changed, 23 insertions, 3 deletions

diff --git a/accel-pppd/accel-ppp.conf.5 b/accel-pppd/accel-ppp.conf.5
index b6e8528c..eba8a39f 100644
--- a/accel-pppd/accel-ppp.conf.5
+++ b/accel-pppd/accel-ppp.conf.5
@@ -1449,16 +1449,36 @@ avoid breaking existing configuration files.
 .BI "tunnel=" range
 Specifies range of remote address of ppp interfaces if form:
 .br
-.B x.x.x.x/mask[,name=pool_name][,next=next_pool_name]
+.B x.x.x.x/mask
+.br
+.B x.x.x.x-y
 .br
-.B x.x.x.x-y[,name=pool_name][,next=next_pool_name]
+Both forms accept the modifiers [,name=pool_name], [,allocator=p2p|net30],
+and [,next=next_pool_name].
 .TP
-.BI "x.x.x.x/mask[,name=pool_name][,next=next_pool_name] or x.x.x.x-y[,name=pool_name][,next=next_pool_name]"
+.BI "x.x.x.x/mask or x.x.x.x-y"
 Also specifies range of remote address of ppp interfaces.
+The same name, allocator, and next modifiers as for tunnel= are accepted.
 .br
 You may also omit the "name=" key and use a shorthand pool name after the comma, e.g.
 .br
 .B 10.0.0.0/24,pool1
+.PP
+The allocator modifier selects how a range is divided. The default
+.B p2p
+allocator supplies one client address per allocation. The
+.B net30
+allocator divides the range into four-address blocks and supplies the
+address at offset 2 in each block; any incomplete trailing block is ignored.
+The local PPP address still comes from
+.BR gw-ip-address .
+For example:
+.br
+.B 192.0.2.0/24,name=pool1,allocator=net30
+.PP
+Each range is limited to 16777216 (2^24) allocation units: one address for
+p2p or one four-address block for net30. Larger ranges are skipped and an
+error is logged. Check existing ranges against this limit when upgrading.
 .TP
 .BI "attr=" attribute
 Specifies which Radius attribute contains pool name.