IGPのネットワークをBGPテーブルからけすとECMPが発動しない謎

自分の知識不足ですね、はい。

#spine/leaf
ip prefix-list LOOPBACK-ONLY permit 172.16.0.0/24 ge 32
route-map OSPF-TO-BGP permit 10
 match ip address prefix-list LOOPBACK-ONLY
!
router bgp 65000
 address-family ipv4 unicast
 # 再配送時にルートマップを適用
  redistribute ospf route-map OSPF-TO-BGP

特定範囲のループバックアドレスのみをBGPに注入する

ibgp-spine2# show ip bgp
BGP table version is 10, local router ID is 172.16.0.2, vrf id 0
Default local pref 100, local AS 65000
Status codes:  s suppressed, d damped, h history, * valid, > best, = multipath,
               i internal, r RIB-failure, S Stale, R Removed
Nexthop codes: @NNN nexthop's vrf id, < announce-nh-self
Origin codes:  i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

   Network          Next Hop            Metric LocPrf Weight Path
*> 172.16.0.1/32    10.0.0.6                20         32768 ?
* i                 20.0.0.1                10    100      0 ?
* i                 10.0.0.1                10    100      0 ?
*> 172.16.0.3/32    20.0.0.6                10         32768 ?
*> 172.16.0.4/32    10.0.0.6                10         32768 ?
* i                 10.0.0.1                20    100      0 ?

アンダーレイを除外した後の影響
iBGPによるECMPが効かなくなる可能性がある
LocPrf を揃える

全Spineで同じLocal Preferenceを付与して揃える

route-map OSPF-TO-BGP permit 10
 match ip address prefix-list LOOPBACK-ONLY
 !自分自身が再配送するものも他から再配送されたものも、同じ値に揃える
 set local-preference 100
 !redistribute（再配送）した経路にはルーターが32768 を付与するデフォルト仕様があるため
 !ECMPのためにはWeight を揃える必要がある
 set weight 0

なぜECMPにならないのか確認する

ibgp-spine2# show ip bgp 172.16.0.1/32
BGP routing table entry for 172.16.0.1/32, version 17
Paths: (3 available, best #3, table default)
  Advertised to non peer-group peers:
  172.16.0.3 172.16.0.4
  Local, (Received from a RR-client)
    20.0.0.1 (metric 20) from 172.16.0.4 (172.16.0.4)
      Origin incomplete, metric 10, localpref 100, valid, internal
      Last update: Sun Jun 14 01:31:08 2026
  Local, (Received from a RR-client)
    10.0.0.1 (metric 20) from 172.16.0.3 (172.16.0.3)
      Origin incomplete, metric 10, localpref 100, valid, internal
      Last update: Sun Jun 14 01:31:08 2026
  Local
    10.0.0.6 from 0.0.0.0 (172.16.0.2)
      Origin incomplete, metric 20, localpref 100, valid, sourced, best (Local Route)
      Last update: Sun Jun 14 01:30:54 2026

router bgp 65000
 address-family ipv4 unicast
  maximum-paths 4
  bgp bestpath as-path multipath-relax

ibgp-spine2# show ip bgp
BGP table version is 19, local router ID is 172.16.0.2, vrf id 0
Default local pref 100, local AS 65000
Status codes:  s suppressed, d damped, h history, * valid, > best, = multipath,
               i internal, r RIB-failure, S Stale, R Removed
Nexthop codes: @NNN nexthop's vrf id, < announce-nh-self
Origin codes:  i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

   Network          Next Hop            Metric LocPrf Weight Path
* i172.16.0.1/32    20.0.0.1                10    100      0 ?
* i                 10.0.0.1                10    100      0 ?
*>                  10.0.0.6                20    100      0 ?
*> 172.16.0.3/32    20.0.0.6                10    100      0 ?
* i172.16.0.4/32    10.0.0.1                20    100      0 ?
*>                  10.0.0.6                10    100      0 ?

Displayed  3 routes and 6 total paths

しないほうが賢明かなあ。