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Cisco Bug: CSCun33591 - Per prefix load-sharing method to per destination load-sharing

Last Modified

May 25, 2020

Products (14)

  • Cisco IOS
  • Cisco 7206 Router
  • Cisco 7301 Router
  • Cisco Service Application Module for IP
  • Cisco 7206VXR Router
  • Cisco 7204 Router
  • Cisco 7202 Router
  • Cisco 7600 Series Route Switch Processor 720 with 10 Gigabit Ethernet Uplinks
  • Cisco 7600 Series Route Switch Processor 720 with Multilayer Switch Feature Card
  • Cisco 7600 Series Supervisor Engine 32 with Multilayer Switch Feature Card
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Known Affected Releases

12.2(33)SB13 12.2(33)SRE5 15.3(2.16)S 15.4(3)S5.1 16.6(1) Everest-16.6.1

Description (partial)

Symptom:
Load sharing mode is changed to per-prefix accidentally and you want to change it back to per-destination. 

Current load-share method on a particular interface can be verified with command "show cef int <int>"

SMRTVLG-R01C-GZ-EG#sh cef int gig0/2.902
GigabitEthernet0/2.902 is up (if_number 209)
  Corresponding hwidb fast_if_number 64
  Corresponding hwidb firstsw->if_number 3
  Internet address is 163.121.207.73/29
  ICMP redirects are always sent
  Per packet load-sharing is disabled
  Per prefix load-sharing is enabled   <<<<<<<<<<<<<<<<<<<<<<<
  IP unicast RPF check is disabled
  Output features: QoS Classification
  IP policy routing is disabled
  BGP based policy accounting on input is disabled
  BGP based policy accounting on output is disabled
  Hardware idb is GigabitEthernet0/2
  Fast switching type 1, interface type 27
  IP CEF switching enabled
  IP CEF switching turbo vector
  IP CEF turbo switching turbo vector
  IP prefix lookup IPv4 mtrie 8-8-8-8 optimized
  Input fast flags 0x60080004, Output fast flags 0x10004008
  ifindex 3(3)
  Slot  Slot unit 2 VC -1
  IP MTU 1500
SMRTVLG-R01C-GZ-EG#

You also see "IPv4 load share mode(10009)" feature called for a particular interface in output of show idb.

SMRTVLG-R01C-GZ-EG#sh idb | i load share mode
S   201   209   U      GigabitEthernet0/2.902 (IPv4 load share mode(10009), DHCPD Sw subblock(47), NetBIOS(6), MFIB_IPv4(33), SW CDP(26), MPLS FEATURE(18), Qos sw subblock(17), Tagswitch(29), MPLSMIB(28), LDP(27), SW OSPF(10), ARP IDB Subblock(8), IEEE 802.1q(19), SWSB IPROUTING(4))
S   275   256   U      GigabitEthernet0/3.903 (IPv4 load share mode(10009), DHCPD Sw subblock(47), NetBIOS(6), MFIB_IPv4(33), SW CDP(26), Tagswitch(29), MPLSMIB(28), LDP(27), SW OSPF(10), ARP IDB Subblock(8), IEEE 802.1q(19), SWSB IPROUTING(4), MPLS FEATURE(18))
S   694   921   U      POS3/0 (Qos sw subblock(17), IPv4 load share mode(10009), MFIB_IPv4(33), Tagswitch(29), MPLSMIB(28), LDP(27), SW OSPF(10), NetBIOS(6), SWSB IPROUTING(4), SW CDP(26), MPLS FEATURE(18), KEEPALIVE(1))
S   695   922   U      POS3/1 (Qos sw subblock(17), IPv4 load share mode(10009), MFIB_IPv4(33), Tagswitch(29), MPLSMIB(28), LDP(27), SW OSPF(10), NetBIOS(6), SWSB IPROUTING(4), SW CDP(26), MPLS FEATURE(18), KEEPALIVE(1))
SMRTVLG-R01C-GZ-EG#

Conditions:
QOS is applied on a dynamic session which is mapped to multiple interfaces then QOS requests to CEF to change load-share method to per-prefix load-sharing.
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