Routing

This chapter discusses routing on switches running Cumulus Linux.

Managing Static Routes

You manage static routes using NCLU or the Cumulus Linux ip route command. The routes are added to the FRRouting routing table, and are then updated into the kernel routing table as well.

To add a static route, run:

cumulus@switch:~$ net add routing route 203.0.113.0/24 198.51.100.2
cumulus@switch:~$ net pending
cumulus@switch:~$ net commit

These commands create the following configuration in the /etc/frr/frr.conf file:

!
ip route 203.0.113.0/24 198.51.100.2
!

To delete a static route, run:

cumulus@switch:~$ net del routing route 203.0.113.0/24 198.51.100.2
cumulus@switch:~$ net pending
cumulus@switch:~$ net commit

To view static routes, run:

cumulus@switch:~$ net show route static 
RIB entry for static
====================
Codes: K - kernel route, C - connected, S - static, R - RIP,
       O - OSPF, I - IS-IS, B - BGP, P - PIM, T - Table,
       > - selected route, * - FIB route
S>* 203.0.113.0/24 [1/0] via 198.51.100.2, swp3

Static Multicast Routes

Static mroutes are also managed with NCLU, or with the ip route command. To add an mroute:

cumulus@switch:~$ net add routing mroute 230.0.0.0/24
cumulus@switch:~$ net pending
cumulus@switch:~$ net commit

These commands create the following configuration in the /etc/frr/frr.conf file:

!
ip mroute 230.0.0.0/24
!

To delete an mroute, run:

cumulus@switch:~$ net del routing mroute 230.0.0.0/24
cumulus@switch:~$ net pending
cumulus@switch:~$ net commit

To view mroutes, open the FRRouting CLI, and run the following command:

cumulus@switch:~$ sudo vtysh
switch# show ip rpf 230.0.0.0
Routing entry for 230.0.0.0/24 using Multicast RIB
  Known via "static", distance 1, metric 0, best
  * directly connected, swp31s0

Static Routing via ip route

A static route can also be created by adding post-up ip route addcommand to a switch port configuration. For example:

cumulus@switch:~$ net add interface swp3 ip address 198.51.100.1/24
cumulus@switch:~$ net add interface swp3 post-up routing route add 203.0.113.0/24 via 198.51.100.2
cumulus@switch:~$ net pending
cumulus@switch:~$ net commit

These commands produce the following configuration in the /etc/network/interfaces file:

auto swp3
iface swp3
    address 198.51.100.1/24
    post-up ip route add 203.0.113.0/24 via 198.51.100.2

The ip route command allows manipulating the kernel routing table directly from the Linux shell. See man ip(8) for details. FRRouting monitors the kernel routing table changes and updates its own routing table accordingly.

To display the routing table:

cumulus@switch:~$ ip route show
default via 10.0.1.2 dev eth0
10.0.1.0/24 dev eth0  proto kernel  scope link  src 10.0.1.52
192.0.2.0/24 dev swp1  proto kernel  scope link  src 192.0.2.12
192.0.2.10/24 via 192.0.2.1 dev swp1  proto zebra  metric 20
192.0.2.20/24  proto zebra  metric 20
     nexthop via 192.0.2.1  dev swp1 weight 1
     nexthop via 192.0.2.2  dev swp2 weight 1
192.0.2.30/24 via 192.0.2.1 dev swp1  proto zebra  metric 20
192.0.2.40/24 dev swp2  proto kernel  scope link  src 192.0.2.42
192.0.2.50/24 via 192.0.2.2 dev swp2  proto zebra  metric 20
192.0.2.60/24 via 192.0.2.2 dev swp2  proto zebra  metric 20
192.0.2.70/24  proto zebra  metric 30
     nexthop via 192.0.2.1  dev swp1 weight 1
     nexthop via 192.0.2.2  dev swp2 weight 1
198.51.100.0/24 dev swp3  proto kernel  scope link  src 198.51.100.1
198.51.100.10/24 dev swp4  proto kernel  scope link  src 198.51.100.11
198.51.100.20/24 dev br0  proto kernel  scope link  src 198.51.100.21

Applying a Route Map for Route Updates

To apply a route map to filter route updates from Zebra into the Linux kernel:

cumulus@switch:$ net add ip protocol static route-map <route-map-name>

Configuring a Gateway or Default Route

On each switch, it’s a good idea to create a gateway or default route for traffic destined outside the switch’s subnet, or local network. All such traffic passes through the gateway, which is a host on the same network that routes packets to their destination beyond the local network.

In the following example, you create a default route in the routing table - 0.0.0.0/0 - which indicates any IP address can get sent to the gateway, which is another switch with the IP address 10.1.0.1.

cumulus@switch:~$ net add routing route 0.0.0.0/0 10.1.0.1
cumulus@switch:~$ net pending
cumulus@switch:~$ net commit

Supported Route Table Entries

Cumulus Linux - via switchd - advertises the maximum number of route table entries that are supported on a given switch architecture, including:

• L3 IPv4 LPM (longest prefix match) entries, which have a mask that is less than /32
• L3 IPv6 LPM entries, which have a mask that is /64 or less
• L3 IPv6 LPM entries, which have a mask that is greater than /64
• L3 IPv4 neighbor (or host) entries, which are the next hops seen in ip neighbor
• L3 IPv6 neighbor entries, which are the next hops seen in ip -6 neighbor
• ECMP next hops, which are IP address entries in a router’s routing table that specify the next closest/most optimal router in its routing path
• MAC addresses

In addition, switches on the Tomahawk, Trident II+ and Trident II platforms are configured to manage route table entries using Algorithm Longest Prefix Match (ALPM). In ALPM mode, the hardware can store significantly more route entries.

You can use cl-resource-query to determine the current table sizes on a given switch.

Forwarding Table Profiles

Mellanox Spectrum and some Broadcom ASICs provide the ability to configure the allocation of forwarding table resources and mechanisms. Cumulus Linux provides a number of generalized profiles for the platforms described below. These profiles work only with layer 2 and layer 3 unicast forwarding.

Cumulus Linux defines these profiles as default, l 2-heavy, v4-lpm-heavy and v6-lpm-heavy. Choose the profile that best suits your network architecture and specify the profile name for the forwarding_table.profile variable in the /etc/cumulus/datapath/traffic.conf file.

cumulus@switch:~$ cat /etc/cumulus/datapath/traffic.conf | grep forwarding_table -B 4
# Manage shared forwarding table allocations
# Valid profiles - 
# default, l2-heavy, v4-lpm-heavy, v6-lpm-heavy
#
forwarding_table.profile = default

After you specify a different profile, restart switchd for the change to take effect. You can see the forwarding table profile when you run cl-resource-query.

TCAM Resource Profiles for Mellanox Switches

The Mellanox Spectrum ASIC provides the ability to configure the TCAM resource allocation, which is shared between IP multicast forwarding entries and ACL tables. Cumulus Linux provides a number of general profiles for this platform: default, ipmc-heavy and acl-heavy. Choose the profile that best suits your network architecture and specify that profile name in the tcam_resource.profile variable in the /usr/lib/python2.7/dist-packages/cumulus/__chip_config/mlx/datapath.conf file.

cumulus@switch:~$ cat /usr/lib/python2.7/dist-packages/cumulus/__chip_config/mlx/datapath.conf | grep -B3 "tcam_resource"
#TCAM resource forwarding profile
 
 
    1. Valid profiles -
    2. default, ipmc-heavy, acl-heavy, ipmc-max
       tcam_resource.profile = default

After you specify a different profile, restart switchd for the change to take effect.

When nonatomic updates are enabled (that is, the acl.non_atomic_update_mode is set to TRUE in /etc/cumulus/switchd.conf file), the maximum number of mroute and ACL entries for each profile are as follows:

When nonatomic updates are disabled (that is, the acl.non_atomic_update_mode is set to FALSE in /etc/cumulus/switchd.conf file), the maximum number of mroute and ACL entries for each profile are as follows:

Number of Supported Route Entries, by Platform

The following tables list the number of MAC addresses, layer 3 neighbors and LPM routes validated for each forwarding table profile for the various supported platforms. If you are not specifying any profiles as described above, the default values are the ones that the switch will use.

Mellanox Spectrum Switches

Broadcom Tomahawk Switches

Broadcom Trident II/Trident II+ Switches

Broadcom Helix4 Switches

Note that Helix4 switches do not have profiles

Caveats and Errata

Unsupported IPv6 Prefixes on Hurricane2 Switches

Switches with the Hurricane2 ASIC do not support IPv6 prefixes between /65 and /127. This is a well known ASIC limitation.

Don’t Delete Routes via Linux Shell

Static routes added via FRRouting can be deleted via Linux shell. This operation, while possible, should be avoided. Routes added by FRRouting should only be deleted by FRRouting, otherwise FRRouting might not be able to clean up all its internal state completely and incorrect routing can occur as a result.

Adding IPv6 Default Route with src Address on eth0 Fails without Adding Delay

Attempting to install an IPv6 default route on eth0 with a source address fails at reboot or when running ifup on eth0.

The first execution of ifup -dv returns this warning and does not install the route:

cumulus@switch:~$ sudo ifup -dv eth0
warning: eth0: post-up cmd '/sbin/ip route add default via 2001:620:5ca1:160::1 /
src 2001:620:5ca1:160::45 dev eth0' failed (RTNETLINK answers: Invalid argument)<<<<<<<<<<

Running ifup a second time on eth0 successfully installs the route.

There are two ways you can work around this issue.

• Add a sleep 2 to the eth0 interface in /etc/network/interfaces:

  cumulus@switch:~$ net add interface eth0 ipv6 address 2001:620:5ca1:160::45/64 post-up /bin/sleep 2s
  cumulus@switch:~$ net add interface eth0 post-up /sbin/ip route add default via 2001:620:5ca1:160::1 src 2001:620:5ca11:160::45 dev eth0
  

• Exclude the src parameter to the ip route add that causes the need for the delay. If the src parameter is removed, the route is added correctly.

  cumulus@switch:~$ net add interface eth0 post-up /sbin/ip route add default via 2001:620:5ca1:160::1 dev eth0
  
  cumulus@switch:~$ ifdown eth0
  Stopping NTP server: ntpd.
  Starting NTP server: ntpd.
  cumulus@switch:~$ ip -6 r s
  cumulus@switch:~$ ifup eth0
  Stopping NTP server: ntpd.
  Starting NTP server: ntpd.
  cumulus@switch:~$ ip -6 r s
  2001:620:5ca1:160::/64 dev eth0  proto kernel  metric 256 
  fe80::/64 dev eth0  proto kernel  metric 256 
  default via 2001:620:5ca1:160::1 dev eth0  metric 1024 
  

Related Information

• Linux IP - ip route command
• FRRouting docs - static route commands