[PATCH] OSPF: Fix inverted path comparison for external

[Mantas Mikulėnas]

From: Mantas Mikulėnas <grawity at gmail.com>

For an ordinary E1 or E2 route exported by another Bird2 router in the
same area, it was consistently choosing a 10000+ metric path through
another area, despite having a direct 10-metric path to the origin in
the same backbone area.

It seems that this was because the rule 16.2 metric comparison was
backwards and always chose highest metric.

Note - the patch is probably *not* 100% right; I am not very sure
whether both checks are backwards or only the orta_pref() one. It's
merely my first successful attempt at fixing the issue (which only
affected Bird, not any other OSPFv2 implementation I have here).

Regardless, it did happen to fix the issue I was having, and now
Bird2 chooses the path I expect it to choose:

Before:
Table master4:
172.20.0.0/14        unicast [ospf4 10:09:35.865] * E2 (150/10080/100) [31.220.42.129]
	via 10.147.255.10 on homegw
	Type: OSPF-E2 univ
	OSPF.metric1: 10080
	OSPF.metric2: 100
	OSPF.tag: 0x00000000
	OSPF.router_id: 31.220.42.129

After:
Table master4:
172.20.0.0/14        unicast [ospf4 12:48:02.452] * E2 (150/30/100) [31.220.42.129]
	via 10.147.240.122 on gre-land
	Type: OSPF-E2 univ
	OSPF.metric1: 30
	OSPF.metric2: 100
	OSPF.tag: 0x00000000
	OSPF.router_id: 31.220.42.129
---
 proto/ospf/rt.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/proto/ospf/rt.c b/proto/ospf/rt.c
index d7753ce0a..c6bf5699e 100644
--- a/proto/ospf/rt.c
+++ b/proto/ospf/rt.c
@@ -200,7 +200,7 @@ orta_compare_asbr(const struct ospf_proto *p, const orta *new, const orta *old)
 
   if (!p->rfc1583)
   {
-    r = epath_preferred(new) - epath_preferred(old);
+    r = epath_preferred(old) - epath_preferred(new);
     if (r) return r;
   }
 
@@ -242,7 +242,7 @@ orta_compare_ext(const struct ospf_proto *p, const orta *new, const orta *old)
   /* 16.4 (6c) - if not RFC1583, prefer routes with preferred ASBR/next_hop */
   if (!p->rfc1583)
   {
-    r = orta_pref(new) - orta_pref(old);
+    r = orta_pref(old) - orta_pref(new);
     if (r) return r;
   }
 
-- 
2.48.1