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20 hours ago •
FRRouting
FRRouting
Not correct reason description in bgp bestpath
example topo:
|---------------------- R3 -------- 192.168.199.0/24
| 192.16.3.0/24 RID 1.1.1.3
| AS 65003
| MED 150
|
|
| 192.16.2.0/24
R1 -------------------- R2 -------- 192.168.199.0/24
AS 65001 RID 1.1.1.2
| AS 65024
| MED 200
|
|
|---------------------- R4 -------- 192.168.199.0/24
192.16.4.0/24 RID 1.1.1.4
AS 65024
MED 100
R1:
debug bgp bestpath 192.168.199.0/24
router bgp 65001
no bgp ebgp-requires-policy
neighbor 192.168.2.2 remote-as 65024
neighbor 192.168.3.3 remote-as 65003
neighbor 192.168.4.4 remote-as 65024
exit
R2:
ip prefix-list ned_pref_out seq 10 permit 192.168.199.0/24
router bgp 65024
bgp router-id 1.1.1.2
no bgp ebgp-requires-policy
neighbor 192.168.2.1 remote-as 65001
!
address-family ipv4 unicast
network 192.168.199.0/24
neighbor 192.168.2.1 route-map med_rp_out out
exit-address-family
exit
!
route-map med_rp_out permit 10
match ip address prefix-list ned_pref_out
set metric 200
exit
R3:
ip prefix-list med_pref_out seq 10 permit 192.168.199.0/24
!
router bgp 65003
bgp router-id 1.1.1.3
no bgp ebgp-requires-policy
neighbor 192.168.3.1 remote-as 65001
!
address-family ipv4 unicast
network 192.168.199.0/24
neighbor 192.168.3.1 route-map med_rp_out out
exit-address-family
exit
!
route-map med_rp_out permit 10
match ip address prefix-list med_pref_out
set metric 150
exit
R4:
ip prefix-list med_pref_out seq 10 permit 192.168.199.0/24
!
router bgp 65024
bgp router-id 1.1.1.4
no bgp ebgp-requires-policy
neighbor 192.168.4.1 remote-as 65001
!
address-family ipv4 unicast
network 192.168.199.0/24
neighbor 192.168.4.1 route-map med_rp_out out
exit-address-family
exit
!
route-map med_rp_out permit 10
match ip address prefix-list med_pref_out
set metric 100
exit
Run R2, then R3, then R4
- Run R2 R1 info:
bgp_process_main_one: p=192.168.199.0/24(VRF default) afi=IPv4, safi=unicast start
192.168.199.0/24(VRF default): After path selection, newbest is path 192.168.2.2 oldbest was NONE
192.168.199.0/24(VRF default): path 192.168.2.2 is the bestpath, add to the multipath list
192.168.199.0/24(VRF default): starting mpath update, newbest 192.168.2.2 num candidates 1 old-mpath-count 0 old-cum-bw 0
192.168.199.0/24(VRF default): comparing candidate 192.168.2.2 with existing mpath NONE
192.168.199.0/24(VRF default): New mpath count (incl newbest) 1 mpath-change NO all_paths_lb 0 cum_bw 0
bgp_process_main_one: p=192.168.199.0/24(VRF default) afi=IPv4, safi=unicast, old_select=0x0, new_select=0x1721190
bgp_process_main_one: 192.168.199.0/24 setting SELECTED flag
# do show bgp ipv4 192.168.199.0/24
BGP routing table entry for 192.168.199.0/24, version 6
Paths: (1 available, best #1, table default)
Advertised to non peer-group peers:
192.168.2.2
65024
192.168.2.2 from 192.168.2.2 (1.1.1.2)
Origin IGP, metric 200, valid, external, best (First path received)
Last update: Wed Sep 25 13:12:45 2024
- Run R3 R1 info:
bgp_process_main_one: p=192.168.199.0/24(VRF default) afi=IPv4, safi=unicast start
192.168.199.0/24(VRF default): Comparing path 192.168.3.3 flags Valid Counted Unsorted with path 192.168.2.2 flags Selected Valid Counted
192.168.199.0/24: path 192.168.3.3 loses to path 192.168.2.2 due to oldest external
192.168.199.0/24(VRF default): After path selection, newbest is path 192.168.2.2 oldbest was 192.168.2.2
192.168.199.0/24(VRF default): path 192.168.2.2 is the bestpath, add to the multipath list
192.168.199.0/24(VRF default): Comparing path 192.168.3.3 flags Valid Counted with path 192.168.2.2 flags Selected Valid Counted
192.168.199.0/24: path 192.168.3.3 loses to path 192.168.2.2 due to oldest external <---------- OK
192.168.199.0/24(VRF default): starting mpath update, newbest 192.168.2.2 num candidates 1 old-mpath-count 0 old-cum-bw 0
192.168.199.0/24(VRF default): comparing candidate 192.168.2.2 with existing mpath NONE
192.168.199.0/24(VRF default): New mpath count (incl newbest) 1 mpath-change NO all_paths_lb 0 cum_bw 0
bgp_process_main_one: p=192.168.199.0/24(VRF default) afi=IPv4, safi=unicast, old_select=0x1721190, new_select=0x1721190
# do show bgp ipv4 192.168.199.0/24
BGP routing table entry for 192.168.199.0/24, version 6
Paths: (1 available, best #1, table default)
Advertised to non peer-group peers:
192.168.2.2 192.168.3.3
65024
192.168.2.2 from 192.168.2.2 (1.1.1.2)
Origin IGP, metric 200, valid, external, best (Older Path) <---------- OK
Last update: Wed Sep 25 13:12:45 2024
65003
192.168.3.3 from 192.168.3.3 (1.1.1.3)
Origin IGP, metric 150, valid, external
Last update: Wed Sep 25 13:15:32 2024
- Run R4 R1 info:
bgp_process_main_one: p=192.168.199.0/24(VRF default) afi=IPv4, safi=unicast start
192.168.199.0/24(VRF default): Comparing path 192.168.4.4 flags Valid Counted Unsorted with path 192.168.2.2 flags Selected Valid Counted
192.168.199.0/24: path 192.168.4.4 wins over path 192.168.2.2 due to MED 100 < 200
192.168.199.0/24(VRF default): After path selection, newbest is path 192.168.4.4 oldbest was 192.168.2.2
192.168.199.0/24(VRF default): path 192.168.4.4 is the bestpath, add to the multipath list
192.168.199.0/24(VRF default): Comparing path 192.168.2.2 flags Selected Valid Counted with path 192.168.4.4 flags Valid Counted
192.168.199.0/24: path 192.168.2.2 loses to path 192.168.4.4 due to MED 200 > 100 <------- OK: 192.168.4.4 is best
192.168.199.0/24(VRF default): Comparing path 192.168.3.3 flags Valid Counted with path 192.168.4.4 flags Valid Counted
192.168.199.0/24: path 192.168.3.3 wins over path 192.168.4.4 due to Router-ID comparison <-------- rewrite dest->reason
192.168.199.0/24(VRF default): starting mpath update, newbest 192.168.4.4 num candidates 1 old-mpath-count 0 old-cum-bw 0
192.168.199.0/24(VRF default): comparing candidate 192.168.4.4 with existing mpath NONE
192.168.199.0/24(VRF default): New mpath count (incl newbest) 1 mpath-change NO all_paths_lb 0 cum_bw 0
bgp_process_main_one: p=192.168.199.0/24(VRF default) afi=IPv4, safi=unicast, old_select=0x1721190, new_select=0x17360a0
bgp_process_main_one: 192.168.199.0/24 setting SELECTED flag
# do show bgp ipv4 192.168.199.0/24
BGP routing table entry for 192.168.199.0/24, version 7
Paths: (3 available, best #1, table default)
Advertised to non peer-group peers:
192.168.2.2 192.168.3.3 192.168.4.4
65024
192.168.4.4 from 192.168.4.4 (1.1.1.4)
Origin IGP, metric 100, valid, external, best (Router ID) <-- 192.168.4.4 is best via MED, but have dest->reason=router-id
Last update: Wed Sep 25 13:17:51 2024
65024
192.168.2.2 from 192.168.2.2 (1.1.1.2)
Origin IGP, metric 200, valid, external
Last update: Wed Sep 25 13:12:45 2024
65003
192.168.3.3 from 192.168.3.3 (1.1.1.3)
Origin IGP, metric 150, valid, external
Last update: Wed Sep 25 13:15:32 2024
192.168.4.4 is best via MED, but have dest->reason=router-id
here bgp_path_info_cmp use for find paths_eq, but also update reason ? https://github.com/FRRouting/frr/blob/2203dc4777a3b72c0be428de224e398e523809f2/bgpd/bgp_route.c#L3245-L3257
reason is OK. Select route wrong. it seems necessary:
diff --git a/bgpd/bgp_route.c b/bgpd/bgp_route.c
index 666adc4..ac22581 100644
--- a/bgpd/bgp_route.c
+++ b/bgpd/bgp_route.c
@@ -3251,9 +3251,10 @@ void bgp_best_selection(struct bgp *bgp, struct bgp_dest *dest,
continue;
}
- bgp_path_info_cmp(bgp, pi, new_select, &paths_eq,
+ if (bgp_path_info_cmp(bgp, pi, new_select, &paths_eq,
mpath_cfg, debug, pfx_buf, afi, safi,
- &dest->reason);
+ &dest->reason))
+ new_select = pi;
if (paths_eq) {
if (debug)
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