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:
James Cape 
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