我想配置一个多宿主 BGP 路由器，并优先选择一家 ISP。我的实际设置将仅接收默认路由，而不是来自上游 ISP 的完整 BGP 反馈。但在此测试设置中，我的网络设置如下，我的目标是优先选择 R4 而不是 R2 来处理来自 R1 的流量。
这 4 个路由器是来自GNS3 市场。它们的配置相同。所有路由器的配置都相同，只有 IP 地址根据图所示有所变化。
R1# show running-config
Building configuration...
Current configuration:
!
frr version 7.3.1
frr defaults traditional
hostname R1
service integrated-vtysh-config
!
router bgp 1
neighbor 192.168.1.2 remote-as 2
neighbor 192.168.4.1 remote-as 4
!
address-family ipv4 unicast
network 10.1.0.0/16
exit-address-family
!
line vty
!
end
第一个问题是我没有看到所有路由器上的所有路径。两个路由器各有 7 条路径，而另外两个各有 5 条路径。如果这有任何意义的话，那两个有 7 条路径的路由器是第一个和最后一个配置的。
R1：
R1# show ip bgp
BGP table version is 5, local router ID is 192.168.4.2, vrf id 0
Default local pref 100, local AS 1
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
Network Next Hop Metric LocPrf Weight Path
*> 10.1.0.0/16 0.0.0.0 0 32768 i
* 10.2.0.0/16 192.168.4.1 0 4 3 2 i
*> 192.168.1.2 0 0 2 i
* 10.3.0.0/16 192.168.4.1 0 4 3 i
*> 192.168.1.2 0 2 3 i
*> 10.4.0.0/16 192.168.4.1 0 0 4 i
* 192.168.1.2 0 2 3 4 i
Displayed 4 routes and 7 total paths
R2：
R2# show ip bgp
BGP table version is 4, local router ID is 192.168.2.1, vrf id 0
Default local pref 100, local AS 2
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
Network Next Hop Metric LocPrf Weight Path
*> 10.1.0.0/16 192.168.1.1 0 0 1 i
*> 10.2.0.0/16 0.0.0.0 0 32768 i
*> 10.3.0.0/16 192.168.2.2 0 0 3 i
* 10.4.0.0/16 192.168.1.1 0 1 4 i
*> 192.168.2.2 0 3 4 i
Displayed 4 routes and 5 total paths
R3：
R3# show ip bgp
BGP table version is 4, local router ID is 192.168.3.1, vrf id 0
Default local pref 100, local AS 3
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
Network Next Hop Metric LocPrf Weight Path
* 10.1.0.0/16 192.168.3.2 0 4 1 i
*> 192.168.2.1 0 2 1 i
*> 10.2.0.0/16 192.168.2.1 0 0 2 i
*> 10.3.0.0/16 0.0.0.0 0 32768 i
*> 10.4.0.0/16 192.168.3.2 0 0 4 i
Displayed 4 routes and 5 total paths
R4：
R4# show ip bgp
BGP table version is 5, local router ID is 192.168.4.1, vrf id 0
Default local pref 100, local AS 4
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
Network Next Hop Metric LocPrf Weight Path
*> 10.1.0.0/16 192.168.4.2 0 0 1 i
* 192.168.3.1 0 3 2 1 i
* 10.2.0.0/16 192.168.4.2 0 1 2 i
*> 192.168.3.1 0 3 2 i
* 10.3.0.0/16 192.168.4.2 0 1 2 3 i
*> 192.168.3.1 0 0 3 i
*> 10.4.0.0/16 0.0.0.0 0 32768 i
Displayed 4 routes and 7 total paths
除了 BGP 路径列表不同之外，一切看起来都很好。我可以 ping 各个路由器，并且 traceroute 符合预期。
R1:~# traceroute -s 10.1.0.1 10.2.0.1
traceroute to 10.2.0.1 (10.2.0.1) from 10.1.0.1, 30 hops max, 46 byte packets
1 10.2.0.1 (10.2.0.1) 1.473 ms 1.430 ms 1.328 ms
R1:~# traceroute -s 10.1.0.1 10.3.0.1
traceroute to 10.3.0.1 (10.3.0.1) from 10.1.0.1, 30 hops max, 46 byte packets
1 192.168.1.2 (192.168.1.2) 1.377 ms 1.466 ms 1.356 ms
2 10.3.0.1 (10.3.0.1) 3.149 ms 1.462 ms 1.033 ms
R1:~# traceroute -s 10.1.0.1 10.4.0.1
traceroute to 10.4.0.1 (10.4.0.1) from 10.1.0.1, 30 hops max, 46 byte packets
1 10.4.0.1 (10.4.0.1) 0.556 ms 1.243 ms 1.271 ms
R3:~# traceroute -s 10.3.0.1 10.1.0.1
traceroute to 10.1.0.1 (10.1.0.1) from 10.3.0.1, 30 hops max, 46 byte packets
1 192.168.2.1 (192.168.2.1) 0.468 ms 1.461 ms 1.135 ms
2 10.1.0.1 (10.1.0.1) 3.038 ms 3.332 ms 3.734 ms
偏好設定： 我希望从 R1 发出的流量通过 R4 而不是 R2，因此我在 R1 上将从 R4 获知的路径的本地优先级设置为 300。R1：
frr(config)# ip prefix-list allow_all_pref seq 10 permit any
frr(config)# route-map rmap permit 10
frr(config-route-map)# match ip address prefix-list allow_all_pref
frr(config-route-map)# set local-preference 300
frr(config-route-map)# exit
frr(config)# router bgp 1
frr(config-router)# address-family ipv4 unicast
frr(config-router-af)# neighbor 192.168.4.1 route-map rmap in
frr(config-router-af)# do show ip bgp
BGP table version is 8, local router ID is 192.168.4.2, vrf id 0
Default local pref 100, local AS 1
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
Network Next Hop Metric LocPrf Weight Path
*> 10.1.0.0/16 0.0.0.0 0 32768 i
*> 10.2.0.0/16 192.168.4.1 300 0 4 3 2 i
* 192.168.1.2 0 0 2 i
*> 10.3.0.0/16 192.168.4.1 300 0 4 3 i
* 192.168.1.2 0 2 3 i
*> 10.4.0.0/16 192.168.4.1 0 300 0 4 i
* 192.168.1.2 0 2 3 4 i
Displayed 4 routes and 7 total paths
但现在一切都崩溃了。我无法再 ping 通 R2 和 R3。当我从 R1 ping 通 R2 时，我可以通过 wireshark 看到回应请求通过 R4 到达 R3，但 R3 和 R2 之间的流量没有显示。
traceroute to 10.2.0.1 (10.2.0.1) from 10.1.0.1, 30 hops max, 46 byte packets
1 192.168.4.1 (192.168.4.1) 1.480 ms 1.514 ms 1.499 ms
2 * * *
3 * * *
4 * * *
其他路由器的 show ip bgp 输出如下。R2：
R2# show ip bgp
BGP table version is 4, local router ID is 192.168.2.1, vrf id 0
Default local pref 100, local AS 2
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
Network Next Hop Metric LocPrf Weight Path
*> 10.1.0.0/16 192.168.1.1 0 0 1 i
*> 10.2.0.0/16 0.0.0.0 0 32768 i
* 10.3.0.0/16 192.168.1.1 0 1 4 3 i
*> 192.168.2.2 0 0 3 i
* 10.4.0.0/16 192.168.1.1 0 1 4 i
*> 192.168.2.2 0 3 4 i
Displayed 4 routes and 6 total paths
R3：
R3# show ip bgp
BGP table version is 4, local router ID is 192.168.3.1, vrf id 0
Default local pref 100, local AS 3
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
Network Next Hop Metric LocPrf Weight Path
* 10.1.0.0/16 192.168.3.2 0 4 1 i
*> 192.168.2.1 0 2 1 i
*> 10.2.0.0/16 192.168.2.1 0 0 2 i
*> 10.3.0.0/16 0.0.0.0 0 32768 i
*> 10.4.0.0/16 192.168.3.2 0 0 4 i
Displayed 4 routes and 5 total paths
R4：
R4# show ip bgp
BGP table version is 5, local router ID is 192.168.4.1, vrf id 0
Default local pref 100, local AS 4
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
Network Next Hop Metric LocPrf Weight Path
*> 10.1.0.0/16 192.168.4.2 0 0 1 i
* 192.168.3.1 0 3 2 1 i
*> 10.2.0.0/16 192.168.3.1 0 3 2 i
*> 10.3.0.0/16 192.168.3.1 0 0 3 i
*> 10.4.0.0/16 0.0.0.0 0 32768 i
Displayed 4 routes and 5 total paths
当我从 R4 ping R2 时，数据包按预期从 R3 移动到 R2。
任何帮助都将不胜感激。我是网络新手，对 BGP 的理解可能存在缺陷。如果我做错了什么，请指出。
答案1
似乎这个问题是 FRRouting 特有的。使用 IOS 的本地偏好和精确设置可以获得所需的结果。将使用更多版本的 FRRouting 进行测试，看看问题是否仍然存在。