Equal Cost Multipath Load Sharing

Cumulus Linux enables ECMP by default. Load sharing occurs automatically for IPv4 and IPv6 routes with multiple installed next hops. The hardware or the routing protocol configuration determines the maximum number of routes for which load sharing occurs.

How Does ECMP Work?

ECMP operates only on equal cost routes in the RIB. In the following example, the 10.10.10.3/32 route has four possible next hops installed in the RIB:

cumulus@leaf01:mgmt:~$ net show route 10.10.10.3/32
RIB entry for 10.10.10.3/32
===========================
Routing entry for 10.10.10.3/32
  Known via "bgp", distance 20, metric 0, best
  Last update 10:04:41 ago
  * fe80::4ab0:2dff:fe60:910e, via swp54, weight 1
  * fe80::4ab0:2dff:fea7:7852, via swp53, weight 1
  * fe80::4ab0:2dff:fec8:8fb9, via swp52, weight 1
  * fe80::4ab0:2dff:feff:e147, via swp51, weight 1


FIB entry for 10.10.10.3/32
===========================
10.10.10.3 nhid 108 proto bgp metric 20

For Cumulus Linux to consider routes equal, the routes must:

Originate from the same routing protocol. Routes from different sources are not considered equal. For example, a static route and an OSPF route are not considered for ECMP load sharing.
Have equal cost. If two routes from the same protocol are unequal, only the best route installs in the routing table.

When multiple routes are in the routing table, a hash determines through which path a packet follows. To prevent out of order packets, ECMP hashes on a per-flow basis; all packets with the same source and destination IP addresses and the same source and destination ports always hash to the same next hop. ECMP hashing does not keep a record of packets that hash to each next hop and does not guarantee that traffic to each next hop is equal.

Cumulus Linux enables the BGP maximum-paths setting by default and installs multiple routes. Refer to BGP and ECMP.

Next Hop Groups

ECMP routes resolve to next hop groups, which identify one or more next hops. To view next hop information, run the NVUE nv show router nexthop rib or nv show router nexthop rib <id> commands, or the ip nexthop show or ip nexthop show <id> kernel commands.

cumulus@leaf01:mgmt:~$ nv show router nexthop rib
                         
Installed - Install state
                         
ID   Installed  UpTime    Vrf      Valid  Via                        ViaIntf        ViaVrf   Depends
---  ---------  --------  -------  -----  -------------------------  -------------  -------  -------
7    on         00:10:43  default  on     lo                                        default         
8    on         00:13:36  default  on     eth0                                      mgmt            
9    on         00:13:36  default  on     eth0                                      mgmt            
10              00:10:43  default  on                                                               
11   on         00:10:43  default  on     192.168.200.1              eth0           mgmt            
12   on         00:10:43  default  on                                                               
15   on         00:10:43  default  on                                                               
30   on         00:10:43  default  on                                                               
32   on         00:13:33  default  on     swp53                                     default         
34              00:13:33  default  on     swp51                                     default         
36              00:13:33  default  on     swp52                                     default         
38              00:13:33  default  on     swp54                                     default         
68              00:10:50  default  on     peerlink.4094                             default         
76   on         00:10:48  default  on     fe80::4ab0:2dff:fe59:eedc  peerlink.4094  default         
88              00:10:46  default  on     br_default                                default         
89              00:10:46  default  on     vlan10v0                                  RED             
90   on         00:10:46  default  on     vlan10                                    RED             
91              00:10:46  default  on     vlan10v0                                  RED             
92              00:10:46  default  on     vlan4024_l3                               RED             
93              00:10:46  default  on     vlan20                                    RED             
94   on         00:10:46  default  on     vlan10                                    RED             
95   on         00:10:46  default  on     vlan20                                    RED             
96   on         00:10:46  default  on     vlan30                                    BLUE            
97              00:10:46  default  on     vlan4036_l3                               BLUE            
98   on         00:10:46  default  on     vlan30                                    BLUE 
...

The following example shows information for next hop group 108:

cumulus@leaf01:mgmt:~$ nv show router nexthop rib 93
                 operational
---------------  -----------
type             zebra      
ref-count        2          
vrf              default    
valid            on         
interface-index  67         
uptime           00:12:58   

Via
======
    Nexthop  type       vrf  weight  Summary
    -------  ---------  ---  ------  -------
    vlan20   interface  RED                 

Via BackupNexthops
=====================
No Data

Depends
==========
No Data

ECMP Hashing

You can configure custom hashing to specify what to include in the hash calculation during load balancing between:

Multiple next hops of a layer 3 route (ECMP hashing).
Multiple interfaces that are members of the same bond (bond or LAG hashing). For bond hashing, see Bonding - Link Aggregation.

For ECMP load balancing between multiple next hops of a layer 3 route, you can hash on these fields:

Field	Default Setting	NVUE Command	`traffic.conf`
IP protocol	on	`nv set system forwarding ecmp-hash ip-protocol on` `nv set system forwarding ecmp-hash ip-protocol off`	`hash_config.ip_prot`
Source IP address	on	`nv set system forwarding ecmp-hash source-ip on` `nv set system forwarding ecmp-hash source-ip off`	`hash_config.sip`
Destination IP address	on	`nv set system forwarding ecmp-hash destination-ip on` `nv set system forwarding ecmp-hash destination-ip off`	`hash_config.dip`
Source port	on	`nv set system forwarding ecmp-hash source-port on` `nv set system forwarding ecmp-hash source-port off`	`hash_config.sport`
Destination port	on	`nv set system forwarding ecmp-hash destination-port on` `nv set system forwarding ecmp-hash destination-port off`	`hash_config.dport`
IPv6 flow label	on	`nv set system forwarding ecmp-hash ipv6-label on` `nv set system forwarding ecmp-hash ipv6-label off`	`hash_config.ip6_label`
Ingress interface	off	`nv set system forwarding ecmp-hash ingress-interface on` `nv set system forwarding ecmp-hash ingress-interface off`	`hash_config.ing_intf`
TEID (see GTP Hashing)	off	`nv set system forwarding ecmp-hash gtp-teid on` `nv set system forwarding ecmp-hash gtp-teid off`	`hash_config.gtp_teid`
Inner IP protocol	off	`nv set system forwarding ecmp-hash inner-ip-protocol on` `nv set system forwarding ecmp-hash inner-ip-protocol off`	`hash_config.inner_ip_prot`
Inner source IP address	off	`nv set system forwarding ecmp-hash inner-source-ip on` `nv set system forwarding ecmp-hash inner-source-ip off`	`hash_config.inner_sip`
Inner destination IP address	off	`nv set system forwarding ecmp-hash inner-destination-ip on` `nv set system forwarding ecmp-hash inner-destination-ip off`	`hash_config.inner_dip`
Inner source port	off	`nv set system forwarding ecmp-hash inner-source-port on` `nv set system forwarding ecmp-hash inner-source-port off`	`hash_config.inner-sport`
Inner destination port	off	`nv set system forwarding ecmp-hash inner-destination-port on` `nv set system forwarding ecmp-hash inner-destination-port off`	`hash_config.inner_dport`
Inner IPv6 flow label	off	`nv set system forwarding ecmp-hash inner-ipv6-label on` `nv set system forwarding ecmp-hash inner-ipv6-label off`	`hash_config.inner_ip6_label`

The following example commands omit the source port and destination port from the hash calculation:

NVUE Commands

cumulus@switch:~$ nv set system forwarding ecmp-hash source-port off
cumulus@switch:~$ nv set system forwarding ecmp-hash destination-port off
cumulus@switch:~$ nv config apply

Linux Commands

Use the instructions below when NVUE is not enabled. If you are using NVUE to configure your switch, the NVUE commands change the settings in /etc/cumulus/datapath/nvue_traffic.conf which takes precedence over the settings in /etc/cumulus/datapath/traffic.conf.

Edit the /etc/cumulus/datapath/traffic.conf file:
- Uncomment the hash_config.enable = true option.
- Set the hash_config.sport and hash_config.dport options to false.

cumulus@switch:~$ sudo nano /etc/cumulus/datapath/traffic.conf
...
# HASH config for  ECMP to enable custom fields
# Fields will be applicable for ECMP hash
# calculation
#Note : Currently supported only for MLX platform
# Uncomment to enable custom fields configured below
hash_config.enable = true

#hash Fields available ( assign true to enable)
#ip protocol
hash_config.ip_prot = true
#source ip
hash_config.sip = true
#destination ip
hash_config.dip = true
#source port
hash_config.sport = false
#destination port
hash_config.dport = false
...

Run the echo 1 > /cumulus/switchd/ctrl/hash_config_reload command. This command does not cause any traffic interruptions.
```
cumulus@switch:~$ echo 1 > /cumulus/switchd/ctrl/hash_config_reload
```

Cumulus Linux enables symmetric hashing by default. Make sure that the settings for the source IP and destination IP fields match, and that the settings for the source port and destination port fields match; otherwise Cumulus Linux disables symmetric hashing automatically. If necessary, you can disable symmetric hashing manually in the /etc/cumulus/datapath/traffic.conf file by setting symmetric_hash_enable = FALSE.

GTP Hashing

GTP carries mobile data within the core of the mobile operator’s network. Traffic in the 5G Mobility core cluster, from cell sites to compute nodes, have the same source and destination IP address. The only way to identify individual flows is with the GTP TEID. Enabling GTP hashing adds the TEID as a hash parameter and helps the Cumulus Linux switches in the network to distribute mobile data traffic evenly across ECMP routes.

Cumulus Linux supports TEID-based ECMP hashing for:

GTP-U packets ingressing physical ports.
VXLAN encapsulated GTP-U packets terminating on egress VTEPs.

For TEID-based load balancing for traffic on a bond, see Bonding - Link Aggregation.

GTP TEID-based ECMP hashing is only applicable if the outer header egressing the port is GTP encapsulated and if the ingress packet is either a GTP-U packet or a VXLAN encapsulated GTP-U packet.

Cumulus Linux supports GTP Hashing on NVIDIA Spectrum-2 and later.
GTP-C packets are not part of GTP hashing.

To enable TEID-based ECMP hashing:

NVUE Commands

cumulus@switch:~$ nv set system forwarding ecmp-hash gtp-teid on
cumulus@switch:~$ nv config apply

To disable TEID-based ECMP hashing, run the nv set system forwarding ecmp-hash gtp-teid off command.

Linux Commands

Edit the /etc/cumulus/datapath/traffic.conf file and change the lag_hash_config.gtp_teid parameter to true:

cumulus@switch:~$ sudo nano /etc/cumulus/datapath/traffic.conf
...
#GTP-U teid
hash_config.gtp_teid = true

Run the echo 1 > /cumulus/switchd/ctrl/hash_config_reload command. This command does not cause any traffic interruptions.
```
cumulus@switch:~$ echo 1 > /cumulus/switchd/ctrl/hash_config_reload
```

To disable TEID-based ECMP hashing, set the hash_config.gtp_teid parameter to false, then reload the configuration.

To show that TEID-based ECMP hashing is on, run the command:

cumulus@switch:~$ nv show system forwarding ecmp-hash
                   applied  description
-----------------  -------  -----------------------------------
destination-ip     on       Destination IPv4/IPv6 Address
destination-port   on       TCP/UDP destination port
gtp-teid           on       GTP-U TEID
...

ECMP Hash Buckets

When there are multiple routes in the routing table, Cumulus Linux assigns each route to an ECMP bucket. When the ECMP hash executes, the result of the hash determines which bucket to use.

In the following example, four next hops exist. Three different flows hash to different hash buckets. Each next hop goes to a unique hash bucket.

The addition of a next hop creates a new hash bucket. The assignment of next hops to hash buckets, as well as the hash result, sometimes changes with the addition of next hops.

With the addition of a new next hop, there is a new hash bucket. As a result, the hash and hash bucket assignment changes, so the existing flows go to different next hops.

When you remove a next hop, the remaining hash bucket assignments can change, which can also change the next hop selected for an existing flow.

A next hop fails, which removes the next hop and hash bucket. It is possible that Cumulus Linux reassigns the remaining next hops.

In most cases, modifying hash buckets has no impact on traffic flows as the switch forwards traffic to a single end host. In deployments where multiple end hosts use the same IP address (anycast), you must use resilient hashing.

Unique Hash Seed

You can configure a unique hash seed for each switch to prevent hash polarization, a type of network congestion that occurs when multiple data flows try to reach a switch using the same switch ports.

You can set a hash seed value between 0 and 4294967295. If you do not specify a value, switchd creates a randomly generated seed.

To configure the hash seed:

NVUE Commands

cumulus@switch:~$ nv set system forwarding hash-seed 50
cumulus@switch:~$ nv config apply

Linux Commands

If you do not enable NVUE, use the instructions below. If you are using NVUE to configure your switch, the NVUE commands change the settings in /etc/cumulus/datapath/nvue_traffic.conf which takes precedence over the settings in /etc/cumulus/datapath/traffic.conf.

Edit /etc/cumulus/datapath/traffic.conf file to change the ecmp_hash_seed parameter, then restart switchd.

cumulus@switch:~$ sudo nano /etc/cumulus/datapath/traffic.conf
...
#Specify the hash seed for Equal cost multipath entries
# and for custom ecmp and lag hash
# Default value: random
# Value Range: {0..4294967295}
ecmp_hash_seed = 50
...

cumulus@switch:~$ sudo systemctl restart switchd.service

Restarting the switchd service causes all network ports to reset, interrupting network services, in addition to resetting the switch hardware configuration.

cl-ecmpcalc

Run the cl-ecmpcalc command to determine a hardware hash result. For example, you can see which path a flow takes through a network. You must provide all fields in the hash, including the ingress interface, layer 3 source IP, layer 3 destination IP, layer 4 source port, and layer 4 destination port.

cl-ecmpcalc only supports input interfaces that convert to a single physical port in the port tab file, such as the physical switch ports (swp). You can not specify virtual interfaces like bridges, bonds, or subinterfaces.

cumulus@switch:~$ sudo cl-ecmpcalc -i swp1 -s 10.0.0.1 -d 10.0.0.1 -p tcp --sport 20000 --dport 80
ecmpcalc: will query hardware
swp3

If you omit a field, cl-ecmpcalc fails.

cumulus@switch:~$ sudo cl-ecmpcalc -i swp1 -s 10.0.0.1 -d 10.0.0.1 -p tcp
ecmpcalc: will query hardware
usage: cl-ecmpcalc [-h] [-v] [-p PROTOCOL] [-s SRC] [--sport SPORT] [-d DST]
                   [--dport DPORT] [--vid VID] [-i IN_INTERFACE]
                   [--sportid SPORTID] [--smodid SMODID] [-o OUT_INTERFACE]
                   [--dportid DPORTID] [--dmodid DMODID] [--hardware]
                   [--nohardware] [-hs HASHSEED]
                   [-hf HASHFIELDS [HASHFIELDS ...]]
                   [--hashfunction {crc16-ccitt,crc16-bisync}] [-e EGRESS]
                   [-c MCOUNT]
cl-ecmpcalc: error: --sport and --dport required for TCP and UDP frames

Resilient Hashing

In Cumulus Linux, when a next hop fails or you remove the next hop from an ECMP pool, the hashing or hash bucket assignment can change. Resilient hashing is an alternate way to manage ECMP groups. Cumulus Linux assigns next hops to buckets using their hashing header fields and uses the resulting hash to index into the table of 2^n hash buckets. Because all packets in a given flow have the same header hash value, they all use the same flow bucket.

Resilient hashing supports both IPv4 and IPv6 routes.
Resilient hashing prevents disruption when you remove next hops but does not prevent disruption when you add next hops.

The NVIDIA Spectrum ASIC assigns packets to hash buckets and assigns hash buckets to next hops. The ASIC also runs a background thread that monitors buckets and can migrate buckets between next hops to rebalance the load.

When you remove a next hop, Cumulus Linux distributes the assigned buckets to the remaining next hops.
When you add a next hop, Cumulus Linux assigns no buckets to the new next hop until the background thread rebalances the load.
The load rebalances when the active flow timer expires only if there are inactive hash buckets available; the new next hop can remain unpopulated until the period set in active flow timer expires.
When the unbalanced timer expires and the load is not balanced, the thread migrates buckets to different next hops to rebalance the load.

Any flow can migrate to any next hop, depending on flow activity and load balance conditions. Over time, the flow can get pinned, which is the default setting and behavior.

When you enable resilient hashing, Cumulus Linux assigns next hops in round robin fashion to a fixed number of buckets. In this example, there are 12 buckets and four next hops.

Unlike default ECMP hashing, when you need to remove a next hop, the number of hash buckets does not change.

With 12 buckets and four next hops, instead of reducing the number of buckets, which impacts flows to known good hosts, the remaining next hops replace the failed next hop.

After you remove the failed next hop, the remaining next hops replace it. This prevents impact to any flows that hash to working next hops.

Resilient hashing does not prevent possible impact to existing flows when you add new next hops. Because there are a fixed number of buckets, a new next hop requires reassigning next hops to buckets.

As a result, some flows hash to new next hops, which can impact anycast deployments.

Cumulus Linux does not enable resilient hashing by default. When you enable resilient hashing, all ECMP groups share 65,536 buckets. An ECMP group is a list of unique next hops that multiple ECMP routes reference.

An ECMP route counts as a single route with multiple next hops.

All ECMP routes must use the same number of buckets (you cannot configure the number of buckets per ECMP route).

A larger number of ECMP buckets reduces the impact on adding new next hops to an ECMP route. However, the system supports fewer ECMP routes. If you install the maximum number of ECMP routes, new ECMP routes log an error and do not install.

You can configure route and MAC address hardware resources depending on ECMP bucket size changes. See NVIDIA Spectrum routing resources.

To enable resilient hashing:

NVUE Commands

Cumulus Linux does not provide NVUE commands for this setting.

Linux Commands

Edit the /etc/cumulus/datapath/traffic.conf file to uncomment and set the resilient_hash_enable parameter to TRUE.
You can also set the resilient_hash_entries_ecmp parameter to the number of hash buckets to use for all ECMP routes. On Spectrum switches, you can set the number of buckets to 64, 512, 1024, 2048, or 4096. On NVIDIA Spectrum-2 and later, you can set the number of buckets to 64, 128, 256, 512, 1024, 2048, or 4096. The default value is 64.
```
# Enable resilient hashing
resilient_hash_enable = TRUE

# Resilient hashing flowset entries per ECMP group
# 
# Mellanox Spectrum platforms:
# Valid values - 64, 512, 1024, 2048, 4096
#
# Mellanox Spectrum2/3 platforms
# Valid values -  64, 128, 256, 512, 1024, 2048, 4096
#
# resilient_hash_entries_ecmp = 64
```
Restart the switchd service:

cumulus@switch:~$ sudo systemctl restart switchd.service

Restarting the switchd service causes all network ports to reset, interrupting network services, in addition to resetting the switch hardware configuration.

Resilient hashing in hardware does not work with next hop groups; the switch remaps flows to new next hops when the set of nexthops changes. To work around this issue, configure zebra not to install next hop IDs in the kernel with the following vtysh command:

cumulus@switch:~$ sudo vtysh
switch# configure terminal
switch(config)# zebra nexthop proto only
switch(config)# exit
switch# write memory
switch# exit
cumulus@switch:~$

Considerations

When the router adds or removes ECMP paths, or when the next hop IP address, interface, or tunnel changes, the next hop information for an IPv6 prefix can change. FRR deletes the existing route to that prefix from the kernel, then adds a new route with all the relevant new information. In certain situations, Cumulus Linux does not maintain resilient hashing for IPv6 flows.

To work around this issue, you can enable IPv6 route replacement.

For certain configurations, IPv6 route replacement can lead to incorrect forwarding decisions and lost traffic. For example, it is possible for a destination to have next hops with a gateway value with the outbound interface or just the outbound interface itself, without a gateway address. If both types of next hops for the same destination exist, route replacement does not operate correctly; Cumulus Linux adds an additional route entry and next hop but does not delete the previous route entry and next hop.

To enable the IPv6 route replacement option:

In the /etc/frr/daemons file, add the configuration option --v6-rr-semantics to the zebra daemon definition. For example:

cumulus@switch:~$ sudo nano /etc/frr/daemons
...
vtysh_enable=yes
zebra_options=" -M cumulus_mlag -M snmp -A 127.0.0.1 --v6-rr-semantics -s 90000000"
bgpd_options=" -M snmp  -A 127.0.0.1"
ospfd_options=" -M snmp -A 127.0.0.1"
...

Restart FRR with this command:
```
cumulus@switch:~$ sudo systemctl restart frr.service
```
Restarting FRR restarts all the routing protocol daemons that are enabled and running.

To verify that IPv6 route replacement, run the systemctl status frr command:

cumulus@switch:~$ systemctl status frr

    ● frr.service - FRRouting
      Loaded: loaded (/lib/systemd/system/frr.service; enabled; vendor preset: enabled)
      Active: active (running) since Mon 2020-02-03 20:02:33 UTC; 3min 8s ago
        Docs: https://frrouting.readthedocs.io/en/latest/setup.html
      Process: 4675 ExecStart=/usr/lib/frr/frrinit.sh start (code=exited, status=0/SUCCESS)
      Memory: 14.4M
      CGroup: /system.slice/frr.service
            ├─4685 /usr/lib/frr/watchfrr -d zebra bgpd staticd
            ├─4701 /usr/lib/frr/zebra -d -M snmp -A 127.0.0.1 --v6-rr-semantics -s 90000000
            ├─4705 /usr/lib/frr/bgpd -d -M snmp -A 127.0.0.1
            └─4711 /usr/lib/frr/staticd -d -A 127.0.0.1

Adaptive Routing

Adaptive routing is a load balancing feature that improves network utilization for eligible IP packets by selecting forwarding paths dynamically based on the state of the switch, such as queue occupancy and port utilization.

The benefits of using adaptive routing include:

The switch can forward adaptive routing eligible IP packets over all the available ECMP member ports to maximize the total traffic throughput, while removing potential ECMP flow collisions.
The switch distributes incoming traffic equally (or according to their weights) between the available IP next hops, which helps to minimize latency and network congestion.
If the cumulative rate of one or more flows exceeds the link bandwidth of the individual uplink port, adaptive routing can distribute the traffic dynamically between multiple uplink ports; the available bandwidth for these flows is not limited to the link bandwidth of an individual uplink port.

With adaptive routing, the switch forwards packets to the less loaded path on a per packet basis to best utilize the fabric resources and avoid congestion. The change decision for port selection is set to one microsecond; you cannot change it.

Cumulus Linux supports adaptive routing with:

Switches with the Spectrum-4 ASIC at 400G and 200G speeds.
RoCE2 unicast traffic.
VXLAN-encapsulated RoCE traffic.
Layer 3 interfaces.
Next hop router interfaces in the default VRF.

Adaptive routing does not make use of resilient hashing.
Cumulus Linux does not support adaptive routing on layer 3 subinterfaces, SVIs, bonds or bond members.
The Spectrum-4 switch does not support adaptive routing on 800G links.

Cumulus Linux also supports BGP W-ECMP with adaptive routing; see BGP Weighted Equal Cost Multipath.

Enable Adaptive Routing

To enable adaptive routing:

NVUE Commands

Run the nv set interface <interface> router adaptive-routing enable on command on all the ports that are part of the same ECMP route. NVUE sets adaptive routing on the ports and enables the adaptive routing feature.

cumulus@switch:~$ nv set interface swp51 router adaptive-routing enable on
cumulus@switch:~$ nv set interface swp52 router adaptive-routing enable on
cumulus@switch:~$ nv config apply

To disable adaptive routing, run the nv set router adaptive-routing enable off command. To disable adaptive routing on a specific port, run the nv set interface <interface> router adaptive-routing enable off command.

Enabling or disabling adaptive routing restarts the switchd service, which causes all network ports to reset, interrupts network services, and resets the switch hardware configuration.

Linux Commands

Edit the /etc/cumulus/switchd.d/adaptive_routing.conf file:

Set the adaptive_routing.enable parameter to TRUE to enable the adaptive routing feature.
Set the interface.<port>.adaptive_routing.enable parameter to TRUE in the Per-port configuration section to enable adaptive routing on all the ports that are part of the same ECMP route.

cumulus@switch:~$ sudo nano /etc/cumulus/switchd.d/adaptive_routing.conf
## Global adaptive-routing enable/disable setting
adaptive_routing.enable = TRUE
...
## Per-port configuration
interface.swp51.adaptive_routing.enable = TRUE
interface.swp51.adaptive_routing.link_util_thresh = 70
interface.swp52.adaptive_routing.enable = TRUE
interface.swp52.adaptive_routing.link_util_thresh = 70
...

Restart switchd with the sudo systemctl restart switchd.service command.

To disable adaptive routing, set the adaptive_routing.enable parameter to FALSE in the /etc/cumulus/switchd.d/adaptive_routing.conf file.
To disable adaptive routing on a specific port, set the interface.<port>.adaptive_routing.enable parameter to FALSE in the /etc/cumulus/switchd.d/adaptive_routing.conf file.

When you enable adaptive routing, Cumulus Linux uses the default profile settings for your switch ASIC type. You cannot change the default profile settings. If you need to make adjustments to the settings, contact NVIDIA Customer Support.

Link Utilization

Link utilization, when crossing a threshold, is one of the parameters in the adaptive routing decision. The default link utilization threshold percentage on an interface is 70. You can change the percentage to a value between 1 and 100.

Link utilization is off by default; you must enable the global link utilization setting to use the link utilization thresholds set on adaptive routing interfaces. You cannot enable or disable link utilization per interface.

In Cumulus Linux 5.5 and earlier, link utilization is on by default. If you configured link utilization in a previous release, be sure to enable link utilization after you upgrade.

NVUE Commands

The following example enables link utilization and uses the default link utilization threshold percentage of 70:

cumulus@switch:~$ nv set router adaptive-routing link-utilization-threshold on
cumulus@switch:~$ nv config apply

The following example changes the link utilization threshold percentage to 100 on swp51 and enables link utilization:

cumulus@switch:~$ nv set interface swp51 router adaptive-routing link-utilization-threshold 100
cumulus@switch:~$ nv set router adaptive-routing link-utilization-threshold on
cumulus@switch:~$ nv config apply

Enabling or disabling link utilization restarts the switchd service, which causes all network ports to reset, interrupts network services, and resets the switch hardware configuration.

Linux Commands

Edit the /etc/cumulus/switchd.d/adaptive_routing.conf file to set:

interface.<interface>.adaptive_routing.link_util_thresh to a value between 1 and 100.
adaptive_routing.link_util_threshold_disabled to FALSE.

cumulus@switch:~$ sudo nano /etc/cumulus/switchd.d/adaptive_routing.conf
## Global adaptive-routing enable/disable setting
adaptive_routing.enable = TRUE

## Global Link-utilization-threshold on/off
adaptive_routing.link_utilization_threshold_disabled = FALSE

## Per-port configuration
interface.swp51.adaptive_routing.enable = TRUE
interface.swp51.adaptive_routing.link_util_thresh = 100

Restart switchd with the sudo systemctl restart switchd.service command.

Example Configuration

NVUE Commands

The following example enables adaptive routing on swp1 and swp2. Global link utilization is off (the default setting).

cumulus@switch:~$ nv set interface swp51 router adaptive-routing enable on
cumulus@switch:~$ nv set interface swp52 router adaptive-routing enable on
cumulus@switch:~$ nv config apply

The following example enables adaptive routing on swp51 and swp52, sets the link utilization threshold percentage to 100 on both swp51 and swp52, and enables global link utilization:

cumulus@switch:~$ nv set interface swp51 router adaptive-routing enable on
cumulus@switch:~$ nv set interface swp52 router adaptive-routing enable on
cumulus@switch:~$ nv set interface swp51 router adaptive-routing link-utilization-threshold 100
cumulus@switch:~$ nv set interface swp52 router adaptive-routing link-utilization-threshold 100
cumulus@switch:~$ nv set router adaptive-routing link-utilization-threshold on
cumulus@switch:~$ nv config apply

Linux Commands

The following example enables adaptive routing on swp51 and swp52. Global link utilization is off (the default setting).

cumulus@switch:~$ sudo nano /etc/cumulus/switchd.d/ad.aptive_routing.conf
## Global adaptive-routing enable/disable setting
adaptive_routing.enable = TRUE

## Global Link-utilization-threshold on/off
adaptive_routing.link_utilization_threshold_disabled = TRUE

## Per-port configuration
interface.swp51.adaptive_routing.enable = TRUE
interface.swp51.adaptive_routing.link_util_thresh = 0
interface.swp52.adaptive_routing.enable = TRUE
interface.swp52.adaptive_routing.link_util_thresh = 0
...

Reload switchd with the sudo systemctl reload switchd.service command.

The following example enables adaptive routing on swp51 and swp52, sets the link utilization threshold percentage to 100 on both swp51 and swp52, and enables global link utilization.

cumulus@switch:~$ sudo nano /etc/cumulus/switchd.d/adaptive_routing.conf
## Global adaptive-routing enable/disable setting
adaptive_routing.enable = TRUE

## Global Link-utilization-threshold on/off
adaptive_routing.link_utilization_threshold_disabled = FALSE

## Per-port configuration
interface.swp51.adaptive_routing.enable = TRUE
interface.swp51.adaptive_routing.link_util_thresh = 100
interface.swp52.adaptive_routing.enable = TRUE
interface.swp52.adaptive_routing.link_util_thresh = 100

Reload switchd with the sudo systemctl reload switchd.service command.

Show Adaptive Routing Settings

To show adaptive routing settings, run the nv show router adaptive-routing command:

cumulus@leaf01:mgmt:~$ nv show router adaptive-routing
                            operational   applied
--------------------------  ------------  -------
enable                      on            off

To show adaptive routing configuration for an interface, run the nv show interface <interface> router adaptive-routing.

Equal Cost Multipath Load Sharing

How Does ECMP Work?

Next Hop Groups

ECMP Hashing

GTP Hashing

ECMP Hash Buckets

Unique Hash Seed

cl-ecmpcalc

Resilient Hashing

Adaptive Routing

Enable Adaptive Routing

Link Utilization

Example Configuration

Show Adaptive Routing Settings

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