Anycast: IP-SLA HOWTO

As promised, here’s the con­densed step-by-step ver­sion of the series on Anycasting, com­plete with a legend:

Configuration to be performed on a server

Configuration to be performed on the router in site A

Configuration to be performed on the router in site B

The first step is to setup the loop­back inter­face on the servers (they should be identical):

[root@server1 ~]# cat <<EOF >/etc/sysconfig/network-scripts/ifcfg-lo:2
DEVICE=lo:2
ONBOOT=yes
IPADDR=10.10.10.10
NETMASK=255.255.255.255
EOF
[root@server1 ~]# ifup lo:2
[root@server1 ~]# ssh -l root server2
[root@server2 ~]# cat <<EOF >/etc/sysconfig/network-scripts/ifcfg-lo:2
DEVICE=lo:2
ONBOOT=yes
IPADDR=10.10.10.10
NETMASK=255.255.255.255
EOF
[root@server2 ~]# ifup lo:2

The next step is to con­fig­ure the routers to route pack­ets des­tined for the any­cast address via the pri­mary net­work inter­face on the servers, run test queries against named on the pri­mary net­work inter­face of that server, and remove the route to the any­cast address if those queries take longer than 2 sec­onds to return:

Router1(config)#ip sla 500
Router1(config-ip-sla)#dns example.org name-server 10.20.20.20
Router1(config-ip-sla-dns)#frequency 9
Router1(config-ip-sla-dns)#timeout 2000
Router1(config-ip-sla-dns)#exit
Router1(config)#ip sla schedule 500 life forever start-time now
Router1(config)#track 500 ip sla 500
Router1(config)#ip route 10.10.10.10 255.255.255.255 10.20.20.20 name dns.example.org track 500
Router1(config)#ip access list standard static-to-ospf-list
Router1(config-ip-access)#permit 10.10.10.10
Router1(config-ip-access)#exit
Router1(config)#route-map static-to-ospf-map 10
Router1(config-route-map)#match ip address static-to-ospf-list
Router1(config-route-map)#exit
Router1(config)#router ospf 1
Router1(config-router)#redistribute static metric-type 1 subnets route-map static-to-ospf-map
Router1(config-router)#exit
Router1(config)#

Router2(config)#ip sla 500
Router2(config-ip-sla)#dns example.org name-server 10.30.30.30
Router2(config-ip-sla-dns)#frequency 9
Router2(config-ip-sla-dns)#timeout 2000
Router2(config-ip-sla-dns)#exit
Router2(config)#ip sla schedule 500 life forever start-time now
Router2(config)#track 500 ip sla 500
Router2(config)#ip route 10.10.10.10 255.255.255.255 10.30.30.30 name dns.example.org track 500
Router2(config)#ip access list standard static-to-ospf-list
Router2(config-ip-access)#permit 10.10.10.10
Router2(config-ip-access)#exit
Router2(config)#route-map static-to-ospf-map 10
Router2(config-route-map)#match ip address static-to-ospf-list
Router2(config-route-map)#exit
Router2(config)#router ospf 1
Router2(config-router)#redistribute static metric-type 1 subnets route-map static-to-ospf-map
Router2(config-router)#exit
Router2(config)#

Confused? Read the other entries in this series:

1. Anycast: Networking Introduction
2. Anycast: The Loophole
3. Anycast: The Interface
4. Anycast: Handling Routes
5. Anycast: DGRAM vs. STREAM
6. Anycast: IP-SLA HOWTO