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Cisco Bug: CSCul72712 - CEF load balance issue with multiple levels of loadsharing

Last Modified

Oct 31, 2019

Products (8)

  • Cisco IOS
  • Cisco ME 3600X-24TS-M Switch
  • Cisco 7600 Series Route Switch Processor 720 with 10 Gigabit Ethernet Uplinks
  • Cisco ME 3600X-24FS-M Switch
  • Cisco 7600 Series Route Switch Processor 720 with Multilayer Switch Feature Card
  • Cisco 7600 Series Supervisor Engine 32 with Multilayer Switch Feature Card
  • Cisco ME 3800X-24FS-M Switch Router
  • Cisco 7600 Series Supervisor Engine 720 with Multilayer Switch Feature Card

Known Affected Releases

15.2(2)S

Description (partial)

Symptom:
problem with CEF loadsharing when we  have multiple levels of loadsharing:

When running the following command CEF indicates that there are 2 paths to the Destination IP 10.220.4.1.
It shows 2 options, one of which has 2 sub-options.the problem is, it will never choose one of the two sub options.

HOMEBDCRTRW0002#show ip cef vrf CORP 10.220.4.1 det 10.220.4.0/24, epoch 1, flags rib defined all labels, per-destination sharing
  recursive via 172.22.0.32 label 27
    nexthop 172.23.192.10 GigabitEthernet0/0/2
  recursive via 172.22.0.40 label 63
    nexthop 172.23.192.1 GigabitEthernet0/0/1 label 50
    nexthop 172.23.192.10 GigabitEthernet0/0/2 label 36



e.g.......

show ip cef vrf CORP exa
show ip cef vrf CORP exact-route 10.220.0.1 10.220.4.1
10.220.0.1 -> 10.220.4.1 => label 27 label implicit-null TAG adj out of GigabitEthernet0/0/2, addr 172.23.192.10 HOMEBDCRTRW0002#show ip cef vrf CORP exact-route 10.220.0.1 10.220.4.2
10.220.0.1 -> 10.220.4.2 => label 63 label 36 TAG adj out of GigabitEthernet0/0/2, addr 172.23.192.10 HOMEBDCRTRW0002#show ip cef vrf CORP exact-route 10.220.0.1 10.220.4.3
10.220.0.1 -> 10.220.4.3 => label 27 label implicit-null TAG adj out of GigabitEthernet0/0/2, addr 172.23.192.10 HOMEBDCRTRW0002#show ip cef vrf CORP exact-route 10.220.0.1 10.220.4.4
10.220.0.1 -> 10.220.4.4 => label 63 label 36 TAG adj out of GigabitEthernet0/0/2, addr 172.23.192.10 HOMEBDCRTRW0002#


it will never use the path out via G0/0/1. instead always using the 2 paths available via G0/0/2.

Conditions:
ASR 1k
CEF has multiple sub-options as Next-hop while doing recursive routing.
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