nat: improve nat44-ed outside address distribution

Use client address hash to pick the first outside address
instead of just address high octet, becasue it may denegerate
into stable 10/172/192, depending on nat address count.

Fix outside address distribution test to acually test the
distribution, not the algo, so previous distribution will
fail with 65 nat addresses and 100 clients:

FAIL: Outside address distribution based on source address
Traceback (most recent call last):
  File ".../test/test_nat44_ed.py", line 2048, in test_outside_address_distribution
    msg="Bad outside address distribution")
AssertionError: 156.25 not less than 0.33 : Bad outside address distribution

Type: improvement
Change-Id: I604b1294422f20d211db5614c47559557a78a193
Signed-off-by: Vladislav Grishenko <themiron@yandex-team.ru>

1 files changed, 3 insertions, 1 deletions

diff --git a/src/plugins/nat/nat44-ed/nat44_ed_in2out.c b/src/plugins/nat/nat44-ed/nat44_ed_in2out.c
index deec0099933..4ba51bcaea6 100644
--- a/src/plugins/nat/nat44-ed/nat44_ed_in2out.c
+++ b/src/plugins/nat/nat44-ed/nat44_ed_in2out.c
@@ -155,7 +155,9 @@ nat_ed_alloc_addr_and_port (snat_main_t *sm, u32 rx_fib_index,
 {
   if (vec_len (sm->addresses) > 0)
     {
-      u32 s_addr_offset = s_addr.as_u32 % vec_len (sm->addresses);
+      u32 s_addr_offset = (s_addr.as_u32 + (s_addr.as_u32 >> 8) +
+			   (s_addr.as_u32 >> 16) + (s_addr.as_u32 >> 24)) %
+			  vec_len (sm->addresses);
       snat_address_t *a, *ja = 0, *ra = 0, *ba = 0;
       int i;