BGP Local Preference (Well-known discretionary) について記載します。
BGP Local Preferenceの目的
BGP Local Preferenceは宛先NW向けの通信に対して、自ASから他ASに対してどのルータから出ていくか
調整する値になります。
属性優先度
優先順位 属性（attribute）
1: Highetst Weight
2: Highest LOCAL_PREF ←ココ
3: Prefer locally originated
4: Shortest AS_PATH
5: Lowest Origin Type
6: Lowest MED
7: Prefer eBGP over iBGP
8: Lowest IGP metric to the BGP NEXT_HOP
9: Oldest Path
10: Lowest Router ID
11: Minimum Cluster list Length
12: Lowest Neighbor Address
・Cisco IOSのフォルト値は[100]
・値が大きい方が優先されます。
NW構成 ※BGP Local Preferenceは以下LPと記します。
- 通信要件は以下の2種類の通信に関して検証をします。
① R1(Lo 1.1.1.1/32) ⇒ R4 (Lo 5.5.5.5/32)向け通信
② R1(Lo 1.1.1.1/32) ⇒ R4 (Lo 6.6.6.6/32)向け通信 - 通信経路は以下になるようLPを調整します。
① R1(Lo 1.1.1.1/32) ⇒ R4 (Lo 5.5.5.5/32)向け通信
R1 ⇒ R2 ⇒ R4 ⇒ 5.5.5.5
② R1(Lo 1.1.1.1/32) ⇒ R4 (Lo 6.6.6.6/32)向け通信
R1 ⇒ R3 ⇒ R4 ⇒ 6.6.6.6 - LP値の設定
①R2に以下の設定をします。
5.5.5.5向け通信に対して、LP値 [700]を設定②R3に以下の設定をします。
6.6.6.6向け通信に対して、LP値 [150]を設定
- 結果について
通信経路は項番２の通りの経路となります。
Config
R1-config
hostname R1
!
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface GigabitEthernet0/0
ip address 10.12.1.1 255.255.255.0
!
interface GigabitEthernet0/1
ip address 10.13.1.1 255.255.255.0
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 0
network 10.12.1.0 0.0.0.255 area 0
network 10.13.1.0 0.0.0.255 area 0
!
router bgp 100
bgp log-neighbor-changes
network 1.1.1.1 mask 255.255.255.255
neighbor 2.2.2.2 remote-as 100
neighbor 2.2.2.2 update-source Loopback0
neighbor 3.3.3.3 remote-as 100
neighbor 3.3.3.3 update-source Loopback0
!
control-plane
!
end
R2-config
hostname R2
!
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface GigabitEthernet0/0
ip address 10.24.1.2 255.255.255.0
!
interface GigabitEthernet0/1
ip address 10.12.1.2 255.255.255.0
!
interface GigabitEthernet0/2
ip address 10.23.1.2 255.255.255.0
!
router ospf 1
network 2.2.2.2 0.0.0.0 area 0
network 10.12.1.0 0.0.0.255 area 0
network 10.23.1.0 0.0.0.255 area 0
!
router bgp 100
bgp log-neighbor-changes
neighbor 1.1.1.1 remote-as 100
neighbor 1.1.1.1 update-source Loopback0
neighbor 1.1.1.1 next-hop-self
neighbor 3.3.3.3 remote-as 100
neighbor 3.3.3.3 update-source Loopback0
neighbor 3.3.3.3 next-hop-self
neighbor 10.24.1.4 remote-as 200
neighbor 10.24.1.4 route-map LOCAL_PREF in
!
route-map LOCAL_PREF permit 10
match ip address 5
set local-preference 700
!
route-map LOCAL_PREF permit 20
!
access-list 5 permit 5.5.5.5
access-list 6 permit 6.6.6.6
!
control-plane
!
end
R3-config
hostname R3
!
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface GigabitEthernet0/0
ip address 10.34.1.3 255.255.255.0
!
interface GigabitEthernet0/1
ip address 10.13.1.3 255.255.255.0
!
interface GigabitEthernet0/2
ip address 10.23.1.3 255.255.255.0
!
router ospf 1
network 3.3.3.3 0.0.0.0 area 0
network 10.13.1.0 0.0.0.255 area 0
network 10.23.1.0 0.0.0.255 area 0
!
router bgp 100
bgp log-neighbor-changes
neighbor 1.1.1.1 remote-as 100
neighbor 1.1.1.1 update-source Loopback0
neighbor 1.1.1.1 next-hop-self
neighbor 2.2.2.2 remote-as 100
neighbor 2.2.2.2 update-source Loopback0
neighbor 2.2.2.2 next-hop-self
neighbor 10.34.1.4 remote-as 200
neighbor 10.34.1.4 route-map LOCAL_PREF in
!
route-map LOCAL_PREF permit 10
match ip address 6
set local-preference 150
!
route-map LOCAL_PREF permit 20
!
!
access-list 5 permit 5.5.5.5
access-list 6 permit 6.6.6.6
!
control-plane
!
end
R4-config
hostname R4
!
interface Loopback0
ip address 4.4.4.4 255.255.255.255
!
interface Loopback5
ip address 5.5.5.5 255.255.255.255
!
interface Loopback6
ip address 6.6.6.6 255.255.255.255
!
interface GigabitEthernet0/0
ip address 10.24.1.4 255.255.255.0
!
interface GigabitEthernet0/1
ip address 10.34.1.4 255.255.255.0
!
router bgp 200
bgp log-neighbor-changes
network 4.4.4.4 mask 255.255.255.255
network 5.5.5.5 mask 255.255.255.255
network 6.6.6.6 mask 255.255.255.255
neighbor 10.24.1.2 remote-as 100
neighbor 10.34.1.3 remote-as 100
!
control-plane
!
end
Local-Preference設定 ※以下LP
R2
- access-list 5 permit 5.5.5.5
⇒LP値を設定したい経路をACLで定義 - route-map LOCAL_PREF permit 10
match ip address 5
set local-preference 700
⇒route-mapでLP値 “700”を定義 - route-map LOCAL_PREF permit 20
⇒その他経路はLP値定義から除外 - router bgp 100
neighbor 10.24.1.4 route-map LOCAL_PREF in
⇒neighbor 10.24.1.4から入ってくる[5.5.5.5]経路について適用
R3
- access-list 6 permit 6.6.6.6
⇒LP値を設定したい経路をACLで定義 - route-map LOCAL_PREF permit 10
match ip address 6
set local-preference 150
⇒route-mapでLP値 “150”を定義 - route-map LOCAL_PREF permit 20
⇒その他経路はLP値定義から除外 - router bgp 100
neighbor 10.34.1.4 route-map LOCAL_PREF in
⇒neighbor 10.34.1.4から入ってくる[6.6.6.6]経路について適用
R1でどのようにLP値が見えるのか？
R1#show ip bgp
Network Next Hop Metric LocPrf Weight Path
*>i 5.5.5.5/32 2.2.2.2 0 700 0 200 i
*>i 6.6.6.6/32 3.3.3.3 0 150 0 200 i
各機器の経路情報
show ip bgp
R1-show ip bgp
R1#show ip bgp
Network Next Hop Metric LocPrf Weight Path
*>i 5.5.5.5/32 2.2.2.2 0 700 0 200 i
*>i 6.6.6.6/32 3.3.3.3 0 150 0 200 i
R2-show ip bgp
R2#show ip bgp
Network Next Hop Metric LocPrf Weight Path
*> 5.5.5.5/32 10.24.1.4 0 700 0 200 i
*>i 6.6.6.6/32 3.3.3.3 0 150 0 200 i
* 10.24.1.4 0 0 200 i
R3-show ip bgp
R3#show ip bgp
Network Next Hop Metric LocPrf Weight Path
*>i 5.5.5.5/32 2.2.2.2 0 700 0 200 i
* 10.34.1.4 0 0 200 i
*> 6.6.6.6/32 10.34.1.4 0 150 0 200 i
R4-show ip bgp
R4#show ip bgp
Network Next Hop Metric LocPrf Weight Path
*> 5.5.5.5/32 0.0.0.0 0 32768 i
*> 6.6.6.6/32 0.0.0.0 0 32768 i
show ip route bgp
R1-show ip bgp
R1#show ip route bgp Gateway of last resort is not set B 4.4.4.4 [200/0] via 2.2.2.2, 00:18:23 B 5.5.5.5 [200/0] via 2.2.2.2, 00:18:23 B 6.6.6.6 [200/0] via 3.3.3.3, 00:18:22
R2-show ip bgp
R2#show ip route bgp Gateway of last resort is not set B 4.4.4.4 [20/0] via 10.24.1.4, 00:18:38 B 5.5.5.5 [20/0] via 10.24.1.4, 00:18:38 B 6.6.6.6 [200/0] via 3.3.3.3, 00:18:37
R3-show ip bgp
R3#show ip route bgp Gateway of last resort is not set B 4.4.4.4 [20/0] via 10.34.1.4, 00:19:03 B 5.5.5.5 [200/0] via 2.2.2.2, 00:19:03 B 6.6.6.6 [20/0] via 10.34.1.4, 00:19:03
R4-show ip bgp
R4#show ip route bgp Gateway of last resort is not set B 1.1.1.1 [20/0] via 10.24.1.2, 00:19:48
