NHT feature for BGP

关于BGP Feature:NHT(Next-Hop Tracking)。之前没接触过这个Feature,正好可以测试下。这个feature主要是当用户通过多个neighbor学来同样的前缀时,优选的下一跳地址在RIB里找不到了,那么他会自动切换到另一个下一跳,不用等待bgp neighbor 超时,这样可以加快收敛,这个Feature主要与IGP联动。另外为了防止默认路由使NHT失效,需要用route-map过滤非明晰路由。

测试Topology:
ASR1k——————CRS
测试信息:

ASR1002-1#sh run | b r b
router bgp 4837
 bgp log-neighbor-changes
 neighbor 1.1.1.1 remote-as 65152
 neighbor 1.1.1.1 ebgp-multihop 3
 neighbor 1.1.1.1 update-source Loopback0
 neighbor 11.11.11.11 remote-as 65152
 neighbor 11.11.11.11 ebgp-multihop 3
 neighbor 11.11.11.11 update-source Loopback1
 !
 address-family ipv4
  bgp nexthop route-map rp_NHT
!--- empty!
  bgp nexthop trigger delay 2
  network 11.11.11.11 mask 255.255.255.255
  network 12.12.12.12 mask 255.255.255.255
  neighbor 1.1.1.1 activate
  neighbor 11.11.11.11 activate
 exit-address-family

ASR1002-1#sh bgp
BGP table version is 44, local router ID is 12.12.12.12
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
              r RIB-failure, S Stale, m multipath, b backup-path, x best-external, f RT-Filter, a additional-path
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path
*> 10.68.0.0/16 ----1.1.1.1                                0 65152 i
*                   11.11.11.11                            0 65152 i

ASR1002-1#
ASR1002-1#
ASR1002-1#sh ip route ospf
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       + - replicated route, % - next hop override

Gateway of last resort is 12.1.1.1 to network 0.0.0.0

      1.0.0.0/32 is subnetted, 1 subnets
O        1.1.1.1 [110/2] via 219.158.2.154, 00:08:20, GigabitEthernet0/0/2
      11.0.0.0/32 is subnetted, 1 subnets
O        11.11.11.11 [110/2] via 219.158.2.154, 00:00:36, GigabitEthernet0/0/2

>>> Shutdown lo1:1.1.1.1 at CRS, check whether NHB feature work and have alarm?

ASR1002-1#sh ip route ospf
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       + - replicated route, % - next hop override

Gateway of last resort is 12.1.1.1 to network 0.0.0.0

      11.0.0.0/32 is subnetted, 1 subnets
O        11.11.11.11 [110/2] via 219.158.2.154, 00:07:27, GigabitEthernet0/0/2

>>>IGP had already remove 1.1.1.1, but base on follow information, bgp not change until hold time expire

ASR1002-1#sh bgp
BGP table version is 44, local router ID is 12.12.12.12
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
              r RIB-failure, S Stale, m multipath, b backup-path, x best-external, f RT-Filter, a additional-path
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path
*> 10.68.0.0/16 ----1.1.1.1                                0 65152 i
*                   11.11.11.11                            0 65152 i
>>> found have default route, lead feature not work:
ASR1002-1#sh route-map rp_NHT
route-map rp_NHT, permit, sequence 20
  Match clauses:
  Set clauses:
  Policy routing matches: 0 packets, 0 bytes
ASR1002-1#
ASR1002-1#
ASR1002-1#sh ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       + - replicated route, % - next hop override

Gateway of last resort is 12.1.1.1 to network 0.0.0.0

S*    0.0.0.0/0 [1/0] via 12.1.1.1
      1.0.0.0/32 is subnetted, 1 subnets

>>> deny default route and non-exact route

ASR1002-1#config ter
Enter configuration commands, one per line.  End with CNTL/Z.
ASR1002-1(config)#no route-map rp_NHT permit 20
ASR1002-1(config)#ip prefix-list pl_NHT seq 10 permit 0.0.0.0/0 le 23
!--- match before 23 prefix.
ASR1002-1(config)#route-map rp_NHT deny 10
ASR1002-1(config-route-map)# match ip address prefix-list pl_NHT
ASR1002-1(config-route-map)#!
ASR1002-1(config-route-map)#route-map rp_NHT permit 20
ASR1002-1(config-route-map)#end

>>> check again, found work and no any alarm appear.

ASR1002-1#sh bgp
BGP table version is 8, local router ID is 21.21.21.21
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
              r RIB-failure, S Stale, m multipath, b backup-path, x best-external, f RT-Filter, a additional-path
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path
*  10.68.0.0/16     11.11.11.11                            0 65152 i
*> -----------------1.1.1.1                                0 65152 i

ASR1002-1#sh ip route ospf
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       + - replicated route, % - next hop override

Gateway of last resort is 12.1.1.1 to network 0.0.0.0

      11.0.0.0/32 is subnetted, 1 subnets
O        11.11.11.11 [110/2] via 219.158.2.154, 00:01:15, GigabitEthernet0/0/2

ASR1002-1#sh ip bgp
BGP table version is 14, local router ID is 21.21.21.21
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
              r RIB-failure, S Stale, m multipath, b backup-path, x best-external, f RT-Filter, a additional-path
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path
*> 10.68.0.0/16 ----11.11.11.11                            0 65152 i
*                   1.1.1.1                                0 65152 I
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