BGP routing load balancing fault case

BGP routing load balancing fault case
Network Architecture 1. Topology: the actual network structure is simplified considering the privacy of the company's network and a clearer description of fault phenomena. 2. network planning and data Configuration Overview: ◆ ASR9K establishes IBGP neighbor relationships with two n7ks Based on the interconnected addresses respectively; ◆ ASR9K is connected to the Cisco 752 architecture and 752 is used as the CDN server; ◆ the server gateways are both in the N7K type, and the two 7 k servers start with HSRP V2 with the same priority. ◆ plan the CDN server Traffic Load balancer (BOND0) to 752, the N7K then distributes traffic evenly to the ASR9K through BGP, and the final traffic goes out of the public network from ASR9. Data Configuration:

ASR9K：router bgp 65555 nsr bgp router-id 1.1.1.1 bgp graceful-restart bgp log neighbor changes detail address-family ipv4 unicast  redistribute connected route-policy AAAAA  redistribute static route-policy BBBBB  redistribute ospf CCCCC !  neighbor 30.207.7.42   remote-as 65555   update-source TenGigE0/1/0/7.3   address-family ipv4 unicast    route-policy Defaultroutes out    soft-reconfiguration inbound always   !  !  neighbor 30.207.7.46   remote-as 65555   update-source TenGigE0/2/0/7.3   address-family ipv4 unicast    route-policy Defaultroutes out    soft-reconfiguration inbound always   !    N7K-1:  router bgp 65555  router-id 2.2.2.2  address-family ipv4 unicast    redistribute direct route-map AA    redistribute static route-map BB  neighbor 30.207.7.41 remote-as 65555    update-source Ethernet1/28.3    address-family ipv4 unicast      route-map ServersIP out      next-hop-self      soft-reconfiguration inbound       N7K-2:   router bgp 65555  router-id 3.3.3.3  address-family ipv4 unicast    redistribute direct route-map yewudirect    redistribute static route-map yewustatic    maximum-paths ibgp 10  neighbor 30.207.7.45 remote-as 65555    update-source Ethernet1/28.3    address-family ipv4 unicast      next-hop-self      soft-reconfiguration inbound

 

Fault description: The two n7ks distribute traffic evenly to the ASR9K, but the traffic from the ASR9K to the two N7K is not balanced. All the traffic that comes back is in line 1 shown in the figure, as a result, line 1 traffic load reaches 90%. On the cacti monitoring traffic diagram: the incoming traffic of the 10 thousand MB link of the line is more than 9 GB, triggering the traffic threshold to generate an alarm. Line 2 has no inbound traffic. Troubleshooting: 1. The N7K outbound traffic balance is normal but the inbound traffic only runs one side, indicating that ASR9K only receives the return route from the N7K-1, or the N7K-1 receives a higher return route than from the N7K-2. The show server route on ASR9K really only has the next hop of A N7K-1. It is inconsistent with the expected load balancing for the next-hop mode. 2. view the BGP neighbor status of the N7K-2 and ASR9K is normal, you can also receive the server address segment route from the N7K-2, and the number of routes is the same as the N7K-1. 3. Search for information and find out the BGP routing principle. The ninth line shows the balance traffic. If maximum-path is not configured, BGP selects only one optimal route, the final ASR9K selection of N7K-1 flow is based on the routing principle of the last "select a smaller neighbor address routing", N7K-1 neighbor address is 30.207.7.41, N7K-2 is 30.207.7.45, so select the N7K-1. 4. Add a maximum-path ibgp 5 in the BGP configuration. A maximum of five equivalent routing loads are allowed for troubleshooting. N7K-1 dropped traffic and N7K-2 rising traffic size does not match because of other adjustments. Knowledge Summary: by default, BGP only selects one optimal route entry into the route table. You can use the maximum-path ibgp/ebgp [2-32] command to implement BGP Route load balancing.