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This chapter discusses routing on switches running Cumulus Linux.

Contents

 This chapter covers ...

Managing Static Routes

You manage static routes using NCLU or the Cumulus Linux ip route command. The routes are added to the Quagga 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/quagga/Quagga.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 Routing via ip route

A static route can also be created by adding post-up ip route add command 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

If an IPv6 address is assigned to a DOWN interface, the associated route is still installed into the routing table. The type of IPv6 address doesn't matter: link local, site local and global all exhibit the same problem. 

If the interface is bounced up and down, then the routes are no longer in the route table.

The ip route command allows manipulating the kernel routing table directly from the Linux shell. See man ip(8) for details. quagga 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>

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 defaultl 2-heavyv4-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.

Broadcom ASICs other than Tomahawk and Trident II/Trident II+ support only the default profile.
For Broadcom ASICs, the maximum number of IP multicast entries is 8k.

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
# Valid profiles -
# default, ipmc-heavy, acl-heavy
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:

ProfileMroute Entries ACL Entries
default4501500 (IPv6) or 3500 (IPv4)
ipmc-heavy6000160 (IPv6) or 400 (IPv4)
acl-heavy4502500 (IPv6) or 6000 (IPv4)

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:

ProfileMroute EntriesACL Entries
default450750 (IPv6) or 1750 (IPv4)
ipmc-heavy

6000

80 (IPv6) or 200 (IPv4)
acl-heavy4502000 (IPv6) or 3000 (IPv4)

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.

The values in the following tables reflect results from our testing on the different platforms we support, and may differ from published manufacturers' specifications provided about these chipsets.

Mellanox Spectrum Switches

ProfileMAC AddressesL3 NeighborsLongest Prefix Match (LPM)
default40k32k (IPv4) and 16k (IPv6)64k (IPv4) or 28k (IPv6-long) 
l2-heavy88k48k (IPv4) and 40k (IPv6)8k (IPv4) and 8k (IPv6-long)
l2-heavy-1180K8k (IPv4) and 8k (IPv6)8k (IPv4) and 8k (IPv6-long)
v4-lpm-heavy8k8k (IPv4) and 16k (IPv6)80k (IPv4) and 16k (IPv6-long)
v4-lpm-heavy-18k8k (IPv4) and 2k (IPv6)176k (IPv4) and 2k (IPv6-long)
v6-lpm-heavy40k8k (IPv4) and 40k (IPv6)8k (IPv4) and 64k (IPv6-long)

Broadcom Tomahawk Switches

ProfileMAC AddressesL3 NeighborsLongest Prefix Match (LPM)
default40k40k64k (IPv4) or 8k (IPv6-long)
l2-heavy72k72k8k (IPv4) or 2k (IPv6-long)
v4-lpm-heavy, v6-lpm-heavy8k8k128k (IPv4) or 20k (IPv6-long)

Broadcom Trident II/Trident II+ Switches

ProfileMAC AddressesL3 NeighborsLongest Prefix Match (LPM)
default32k16k 128k (IPv4) or 20k (IPv6-long)
l2-heavy160k96k 8k (IPv4) or 2k (IPv6-long) 
v4-lpm-heavy, v6-lpm-heavy32k16k 128k (IPv4) or 20k (IPv6-long)  

Caveats and Errata

Don't Delete Routes via Linux Shell

Static routes added via Quagga can be deleted via Linux shell. This operation, while possible, should be avoided. Routes added by Quagga should only be deleted by Quagga, otherwise Quagga 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 

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