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Virtual Router Redundancy - VRR

Virtual Router Redundancy (VRR) enables hosts to communicate with any redundant router without reconfiguration, running dynamic router protocols, or running router redundancy protocols. This means that redundant routers will respond to Address Resolution Protocol (ARP) requests from hosts. Routers are configured to respond in an identical manner, but if one fails, the other redundant routers will continue to respond, leaving the hosts with the impression that nothing has changed.

The diagram below illustrates a basic VRR-enabled network configuration. The network includes several hosts, and two routers running Cumulus Linux configured with Multi-chassis Link Aggregation (MLAG):

/images/download/attachments/5869004/vrr_active-active.png

A production implementation will have many more server hosts and network connections than are shown here. However, this basic configuration provides a complete description of the important aspects of the VRR setup.

As the bridges in each of the redundant routers are connected, they will each receive and reply to ARP requests for the virtual router IP address.

Multiple ARP Replies

Each ARP request made by a host will receive replies from each router; these replies will be identical, and so the host receiving the replies will either ignore replies after the first, or accept them and overwrite the previous identical reply, rather than being confused over which response is correct.

Reserved MAC Address Range

A range of MAC addresses is reserved for use with VRR, in order to prevent MAC address conflicts with other interfaces in the same bridged network. The reserved range is 00:00:5E:00:01:00 to 00:00:5E:00:01:ff.

Cumulus Networks recommends using MAC addresses from the reserved range when configuring VRR.

The reserved MAC address range for VRR is the same as for the Virtual Router Redundancy Protocol (VRRP), as they serve similar purposes.

Configuring a VRR-enabled Network

Configuring the Routers

The routers implement the layer 2 network interconnecting the hosts and the redundant routers. To configure the routers, add a bridge with the following interfaces to each router:

  • One bond interface or switch port interface to each host.

    For networks using MLAG, use bond interfaces. Otherwise, use switch port interfaces.

  • One or more interfaces to each peer router.

    Multiple inter-peer links are typically bonded interfaces, in order to accomodate higher bandwidth between the routers, and to offer link redundancy.

Example VRR Configuration

The example NCLU commands below create a VLAN-aware bridge interface for a VRR-enabled network:

cumulus@switch:~$ net add bridge
cumulus@switch:~$ net add vlan 500 ip address 192.168.0.252/24
cumulus@switch:~$ net add vlan 500 ip address-virtual 00:00:5e:00:01:01 192.168.0.254/24
cumulus@switch:~$ net add vlan 500 ipv6 address 2001:aa::1/48
cumulus@switch:~$ net add vlan 500 ipv6 address-virtual 00:00:5e:00:01:01 2001:aa::1/48
cumulus@switch:~$ net pending
cumulus@switch:~$ net commit

The NCLU commands above produce the following /etc/network/interfaces snippet:

auto bridge
iface bridge
    bridge-vids 500
    bridge-vlan-aware yes
 
auto vlan500
iface vlan500
    address 192.168.0.252/24
    address 2001:aa::1/48
    address-virtual 00:00:5e:00:01:01 2001:aa::1/48 192.168.0.254/24
    vlan-id 500
    vlan-raw-device bridge

Configuring the Hosts

Each host should have two network interfaces. The routers configure the interfaces as bonds running LACP; the hosts should also configure its two interfaces using teaming, port aggregation, port group, or EtherChannel running LACP. Configure the hosts, either statically or via DHCP, with a gateway address that is the IP address of the virtual router; this default gateway address never changes.

Configure the links between the hosts and the routers in active-active mode for First Hop Redundancy Protocol.

Example VRR Configuration with MLAG

To create an MLAG configuration that incorporates VRR, use a configuration like the following:

leaf01 Configuration

cumulus@leaf01:~$ net add interface eth0 ip address 192.168.0.21
cumulus@switch:~$ net add bond server01 bond slaves swp1-2
cumulus@switch:~$ net add bond server01 clag id 1
cumulus@switch:~$ net add bond server01 mtu 9216
cumulus@switch:~$ net add bond server01 alias LACP etherchannel to uplink on server01
cumulus@switch:~$ net add bond peerlink bond slaves swp49-50
cumulus@leaf01:~$ net add interface peerlink.4094 peerlink.4094
cumulus@leaf01:~$ net add interface peerlink.4094 ip address 169.254.255.1/30
cumulus@leaf01:~$ net add interface peerlink.4094 clag peer-ip 169.254.255.2
cumulus@leaf01:~$ net add interface peerlink.4094 clag backup-ip 192.168.0.22
cumulus@leaf01:~$ net add interface peerlink.4094 clag sys-mac 44:38:39:FF:40:90
cumulus@switch:~$ net add bridge bridge ports server01,peerlink
cumulus@switch:~$ net add bridge stp treeprio 4096
cumulus@switch:~$ net add vlan 100 ip address 10.0.1.2/24
cumulus@switch:~$ net add vlan 100 ip address-virtual 44:38:39:FF:00:01 10.0.1.1/24
cumulus@switch:~$ net add vlan 200 ip address 10.0.2.2/24
cumulus@switch:~$ net add vlan 200 ip address-virtual 44:38:39:FF:00:02 10.0.2.1/24
cumulus@switch:~$ net add vlan 300 ip address 10.0.3.2/24
cumulus@switch:~$ net add vlan 300 ip address-virtual 44:38:39:FF:00:03 10.0.3.1/24
cumulus@switch:~$ net add vlan 400 ip address 10.0.4.2/24
cumulus@switch:~$ net add vlan 400 ip address-virtual 44:38:39:FF:00:04 10.0.4.1/24
cumulus@switch:~$ net pending
cumulus@switch:~$ net commit

These commands create the following configuration in /etc/network/interfaces:

auto eth0
iface eth0
    address 192.168.0.21

auto bridge iface bridge bridge-ports server01 peerlink bridge-vids 100 200 300 400 bridge-vlan-aware yes mstpctl-treeprio 4096

auto server01 iface server01 alias LACP etherchannel to uplink on server01 bond-slaves swp1 swp2 clag-id 1 mtu 9216

auto peerlink iface peerlink bond-slaves swp49 swp50

auto peerlink.4094 iface peerlink.4094 address 169.254.255.1/30 clagd-backup-ip 192.168.0.22 clagd-peer-ip 169.254.255.2 clagd-sys-mac 44:38:39:FF:40:90

auto vlan100 iface vlan100 address 10.0.1.2/24 address-virtual 44:38:39:FF:00:01 10.0.1.1/24 vlan-id 100 vlan-raw-device bridge

auto vlan200 iface vlan200 address 10.0.2.2/24 address-virtual 44:38:39:FF:00:02 10.0.2.1/24 vlan-id 200 vlan-raw-device bridge

auto vlan300 iface vlan300 address 10.0.3.2/24 address-virtual 44:38:39:FF:00:03 10.0.3.1/24 vlan-id 300 vlan-raw-device bridge

auto vlan400 iface vlan400 address 10.0.4.2/24 address-virtual 44:38:39:FF:00:04 10.0.4.1/24 vlan-id 400 vlan-raw-device bridge

leaf02 Configuration

cumulus@leaf01:~$ net add interface eth0 ip address 192.168.0.22
cumulus@switch:~$ net add bond server01 bond slaves swp1-2
cumulus@switch:~$ net add bond server01 clag id 1
cumulus@switch:~$ net add bond server01 mtu 9216
cumulus@switch:~$ net add bond server01 alias LACP etherchannel to uplink on server01
cumulus@switch:~$ net add bond peerlink bond slaves swp49-50
cumulus@leaf01:~$ net add interface peerlink.4094 peerlink.4094
cumulus@leaf01:~$ net add interface peerlink.4094 ip address 169.254.255.2/30
cumulus@leaf01:~$ net add interface peerlink.4094 clag peer-ip 169.254.255.1
cumulus@leaf01:~$ net add interface peerlink.4094 clag backup-ip 192.168.0.21
cumulus@leaf01:~$ net add interface peerlink.4094 clag sys-mac 44:38:39:FF:40:90
cumulus@switch:~$ net add bridge bridge ports server01,peerlink
cumulus@switch:~$ net add bridge stp treeprio 4096
cumulus@switch:~$ net add vlan 100 ip address 10.0.1.3/24
cumulus@switch:~$ net add vlan 100 ip address-virtual 44:38:39:FF:00:01 10.0.1.1/24
cumulus@switch:~$ net add vlan 200 ip address 10.0.2.3/24
cumulus@switch:~$ net add vlan 200 ip address-virtual 44:38:39:FF:00:02 10.0.2.1/24
cumulus@switch:~$ net add vlan 300 ip address 10.0.3.3/24
cumulus@switch:~$ net add vlan 300 ip address-virtual 44:38:39:FF:00:03 10.0.3.1/24
cumulus@switch:~$ net add vlan 400 ip address 10.0.4.3/24
cumulus@switch:~$ net add vlan 400 ip address-virtual 44:38:39:FF:00:04 10.0.4.1/24
cumulus@switch:~$ net pending
cumulus@switch:~$ net commit

These commands create the following configuration in /etc/network/interfaces:

auto eth0
iface eth0
    address 192.168.0.22

auto bridge iface bridge bridge-ports server01 peerlink bridge-vids 100 200 300 400 bridge-vlan-aware yes mstpctl-treeprio 4096

auto server01 iface server01 alias LACP etherchannel to uplink on server01 bond-slaves swp1 swp2 clag-id 1 mtu 9216

auto peerlink iface peerlink bond-slaves swp49 swp50

auto peerlink.4094 iface peerlink.4094 address 169.254.255.1/30 clagd-backup-ip 192.168.0.22 clagd-peer-ip 169.254.255.2 clagd-sys-mac 44:38:39:FF:40:90

auto vlan100 iface vlan100 address 10.0.1.3/24 address-virtual 44:38:39:FF:00:01 10.0.1.1/24 vlan-id 100 vlan-raw-device bridge

auto vlan200 iface vlan200 address 10.0.2.3/24 address-virtual 44:38:39:FF:00:02 10.0.2.1/24 vlan-id 200 vlan-raw-device bridge

auto vlan300 iface vlan300 address 10.0.3.3/24 address-virtual 44:38:39:FF:00:03 10.0.3.1/24 vlan-id 300 vlan-raw-device bridge

auto vlan400 iface vlan400 address 10.0.4.3/24 address-virtual 44:38:39:FF:00:04 10.0.4.1/24 vlan-id 400 vlan-raw-device bridge

server01 Configuration

Create a configuration like the following on an Ubuntu host:

auto eth0
iface eth0 inet dhcp

auto eth1 iface eth1 inet manual bond-master uplink

auto eth2 iface eth2 inet manual bond-master uplink

auto uplink iface uplink inet static bond-slaves eth1 eth2 bond-mode 802.3ad bond-miimon 100 bond-lacp-rate 1 bond-min-links 1 bond-xmit-hash-policy layer3+4 address 172.16.1.101 netmask 255.255.255.0 post-up ip route add 172.16.0.0/16 via 172.16.1.1 post-up ip route add 10.0.0.0/8 via 172.16.1.1

auto uplink:200 iface uplink:200 inet static address 10.0.2.101

auto uplink:300 iface uplink:300 inet static address 10.0.3.101

auto uplink:400 iface uplink:400 inet static address 10.0.4.101

install ifenslave

modprobe bonding

server02 Configuration

Create a configuration like the following on an Ubuntu host:

auto eth0
iface eth0 inet dhcp

auto eth1 iface eth1 inet manual bond-master uplink

auto eth2 iface eth2 inet manual bond-master uplink

auto uplink iface uplink inet static bond-slaves eth1 eth2 bond-mode 802.3ad bond-miimon 100 bond-lacp-rate 1 bond-min-links 1 bond-xmit-hash-policy layer3+4 address 172.16.1.101 netmask 255.255.255.0 post-up ip route add 172.16.0.0/16 via 172.16.1.1 post-up ip route add 10.0.0.0/8 via 172.16.1.1

auto uplink:200 iface uplink:200 inet static address 10.0.2.101

auto uplink:300 iface uplink:300 inet static address 10.0.3.101

auto uplink:400 iface uplink:400 inet static address 10.0.4.101

install ifenslave

modprobe bonding