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bgpd: allow bestpath to handle mutliple locally-originated paths
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Current code in bgp bestpath selection would accept the newest
locally originated path as the best path.  Making the selection
non-deterministic.  Modify the code to always come to the
same bestpath conclusion when you have multiple locally originated
paths in bestpath selection.

Before:

eva# conf
eva(config)# router bgp 323
eva(config-router)# address-family ipv4 uni
eva(config-router-af)# redistribute connected
eva(config-router-af)# network 192.168.161.0/24
eva(config-router-af)# do show bgp ipv4 uni 192.168.161.0
BGP routing table entry for 192.168.161.0/24
Paths: (2 available, best #1, table default)
  Not advertised to any peer
  Local
    0.0.0.0(eva) from 0.0.0.0 (192.168.161.245)
      Origin IGP, metric 0, weight 32768, valid, sourced, local, bestpath-from-AS Local, best (Origin)
      Last update: Wed Sep 16 15:03:03 2020
  Local
    0.0.0.0(eva) from 0.0.0.0 (192.168.161.245)
      Origin incomplete, metric 0, weight 32768, valid, sourced
      Last update: Wed Sep 16 15:02:52 2020
eva(config-router-af)# no redistribute connected
eva(config-router-af)# do show bgp ipv4 uni 192.168.161.0
BGP routing table entry for 192.168.161.0/24
Paths: (1 available, best #1, table default)
  Not advertised to any peer
  Local
    0.0.0.0(eva) from 0.0.0.0 (192.168.161.245)
      Origin IGP, metric 0, weight 32768, valid, sourced, local, bestpath-from-AS Local, best (First path received)
      Last update: Wed Sep 16 15:03:03 2020
eva(config-router-af)#  redistribute connected
eva(config-router-af)# do show bgp ipv4 uni 192.168.161.0
BGP routing table entry for 192.168.161.0/24
Paths: (2 available, best #2, table default)
  Not advertised to any peer
  Local
    0.0.0.0(eva) from 0.0.0.0 (192.168.161.245)
      Origin incomplete, metric 0, weight 32768, valid, sourced
      Last update: Wed Sep 16 15:03:32 2020
  Local
    0.0.0.0(eva) from 0.0.0.0 (192.168.161.245)
      Origin IGP, metric 0, weight 32768, valid, sourced, local, bestpath-from-AS Local, best (Origin)
      Last update: Wed Sep 16 15:03:03 2020
eva(config-router-af)#

Notice the route choosen depends on order received

Fixed behavior:

eva# conf
eva(config)# router bgp 323
eva(config-router)# address-family ipv4 uni
eva(config-router-af)# redistribute connected
eva(config-router-af)# network 192.168.161.0/24
eva(config-router-af)# do show bgp ipv4 uni 192.168.161.0
BGP routing table entry for 192.168.161.0/24
Paths: (2 available, best #1, table default)
  Not advertised to any peer
  Local
    0.0.0.0(eva) from 0.0.0.0 (192.168.161.245)
      Origin IGP, metric 0, weight 32768, valid, sourced, local, bestpath-from-AS Local, best (Origin)
      Last update: Wed Sep 16 15:03:03 2020
  Local
    0.0.0.0(eva) from 0.0.0.0 (192.168.161.245)
      Origin incomplete, metric 0, weight 32768, valid, sourced
      Last update: Wed Sep 16 15:02:52 2020
eva(config-router-af)# no redistribute connected
eva(config-router-af)# do show bgp ipv4 uni 192.168.161.0
BGP routing table entry for 192.168.161.0/24
Paths: (1 available, best #1, table default)
  Not advertised to any peer
  Local
    0.0.0.0(eva) from 0.0.0.0 (192.168.161.245)
      Origin IGP, metric 0, weight 32768, valid, sourced, local, bestpath-from-AS Local, best (First path received)
      Last update: Wed Sep 16 15:03:03 2020
eva(config-router-af)#  redistribute connected
eva(config-router-af)# do show bgp ipv4 uni 192.168.161.0
BGP routing table entry for 192.168.161.0/24
Paths: (2 available, best #2, table default)
  Not advertised to any peer
  Local
    0.0.0.0(eva) from 0.0.0.0 (192.168.161.245)
      Origin incomplete, metric 0, weight 32768, valid, sourced
      Last update: Wed Sep 16 15:03:32 2020
  Local
    0.0.0.0(eva) from 0.0.0.0 (192.168.161.245)
      Origin IGP, metric 0, weight 32768, valid, sourced, local, bestpath-from-AS Local, best (Origin)
      Last update: Wed Sep 16 15:03:03 2020
eva(config-router-af)#

Ticket: CM-31490
Found-by: Trey Aspelund <taspelund@nvidia.com>
Signed-off-by: Donald Sharp <sharpd@nvidia.com>
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@donaldsharp
donaldsharp committed Oct 9, 2020
1 parent 9ef306b commit 33c6e93
Showing 1 changed file with 8 additions and 4 deletions.
12 changes: 8 additions & 4 deletions bgpd/bgp_route.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -550,6 +550,7 @@ static int bgp_path_info_cmp(struct bgp *bgp, struct bgp_path_info *new,
bool same_esi;
bool old_proxy;
bool new_proxy;
bool new_origin, exist_origin;

*paths_eq = 0;

Expand Down Expand Up @@ -794,8 +795,12 @@ static int bgp_path_info_cmp(struct bgp *bgp, struct bgp_path_info *new,
* - BGP_ROUTE_AGGREGATE
* - BGP_ROUTE_REDISTRIBUTE
*/
if (!(new->sub_type == BGP_ROUTE_NORMAL ||
new->sub_type == BGP_ROUTE_IMPORTED)) {
new_origin = !(new->sub_type == BGP_ROUTE_NORMAL ||
new->sub_type == BGP_ROUTE_IMPORTED);
exist_origin = !(exist->sub_type == BGP_ROUTE_NORMAL ||
exist->sub_type == BGP_ROUTE_IMPORTED);

if (new_origin && !exist_origin) {
*reason = bgp_path_selection_local_route;
if (debug)
zlog_debug(
Expand All @@ -804,8 +809,7 @@ static int bgp_path_info_cmp(struct bgp *bgp, struct bgp_path_info *new,
return 1;
}

if (!(exist->sub_type == BGP_ROUTE_NORMAL ||
exist->sub_type == BGP_ROUTE_IMPORTED)) {
if (!new_origin && exist_origin) {
*reason = bgp_path_selection_local_route;
if (debug)
zlog_debug(
Expand Down

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