what is load balance method of ospf multiple equal cost links?

[Herman2022]

Hi , can someone please advise what load balance method (source & destination IP or other methods) for multiple equal cost links of ospf? our both end routers are nexus 7k. Please advise, thanks. 

[MHM Cisco World]

Show ip interface x/x 

Check cef load balance mode use 

MHM

[Herman2022]

Thanks @MHM Cisco World . I didn't find cef in the output. It only shows : load sharing is off. 

below is the output of the command you advised. 

IP Interface Status for VRF "default"(1)
Ethernet1/40, Interface status: protocol-up/link-up/admin-up, iod: 94,
IP address: , IP subnet:  route-preference: 0, tag: 0
IP broadcast address: 255.255.255.255
IP multicast groups locally joined:
224.0.0.5 224.0.0.13 224.0.0.22 224.0.0.1 224.0.0.2
IP MTU: 9216 bytes (using link MTU)
IP primary address route-preference: 0, tag: 0
IP proxy ARP : disabled
IP Local Proxy ARP : disabled
IP multicast routing: enabled
IP icmp redirects: disabled
IP directed-broadcast: disabled
IP Forwarding: disabled
IP icmp unreachables (except port): disabled
IP icmp port-unreachable: enabled
IP unicast reverse path forwarding: none
IP load sharing: none
IP interface statistics last reset: never
IP interface software stats: (sent/received/forwarded/originated/consumed)
Unicast packets : 1795682/1788770/0/1795682/3168779
Unicast bytes : 148190808/134390809/0/180513084/243125314
Multicast packets : 6517057/6343208/0/6517057/12686409
Multicast bytes : 438917592/433628119/0/556224618/433628079
Broadcast packets : 0/0/0/0/0
Broadcast bytes : 0/0/0/0/0
Labeled packets : 0/0/0/0/0
Labeled bytes : 0/0/0/0/0
WCCP Redirect outbound: disabled
WCCP Redirect inbound: disabled
WCCP Redirect exclude: disabled

[MHM Cisco World]

I am in meeting now 
I will answer you later 
thanks for waiting 

MHM

[MHM Cisco World]

ip load-sharing address <<- this command is available in your N7K

MHM

[Jens Albrecht]

Hello @Herman2022,

to display the the current unicast FIB load-sharing algorithm, you can use the following command:

show ip load-sharing

The default can be modified if needed using the global config command 'ip load-sharing address [options]'.

For details regarding the various options please refer to the Configuring Load Sharing in the Unicast FIB section of the Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide.

HTH!

[Herman2022]

Thanks @Jens Albrecht for your advice. the command "show ip load-sharing " is not valid on nexus 7k. Any other command can be used? 

[Jens Albrecht]

What software version and license are you running on your nexus 7k?

The commands are taken directly from Cisco's configuration guides for the nexus 7k switches as you can see from the reference that I linked in my answer.

[M02@rt37]

Hello @Herman2022 

CEF does the switching of the packet based on the routing table which is being populated by the routing protocol such as OSPF, and so on... CEF does the load-balancing once the routing protocol table has been calculated !

Do this under config terminal:

ip load-sharing address ?

[MHM Cisco World]

Friend 

There is no cef in Nexus

MHM

[M02@rt37]

Right!

So, hardware-based forwarding via the ASIC ?

[Herman2022]

Thanks @MHM Cisco World , so what is the default load balancing methods ? 

[M02@rt37 · Accepted solution]

Hello @Herman2022 

Although this is from the Nexus 9000 series, the principles align with NX-OS design on 7K:

ECMP does not guarantee equal load-balancing across all links. It guarantees only that a particular flow will choose one particular next hop at any point in time.

So, this reflect the standard “per-flow hashing” behavior, where each traffic flow sticks to one path to prevent packet reordering.

--

https://www.cisco.com/c/en/us/td/docs/dcn/nx-os/nexus9000/104x/unicast-routing-configuration/cisco-nexus-9000-series-nx-os-unicast-routing-configuration-guide/m-n9k-overview-93x.html

[MHM Cisco World · Accepted solution]

[Herman2022]

thanks @MHM Cisco World M02@rt37 for your advice