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OSPF and BGP Routing Example

Within each AS, OSPF is the protocol used to forward anycast advertisements. Between ASs, BGP is the protocol selected to advertise anycast addresses. Using this technique, DNS servers in diverse locations can operate together to ensure continuous service.

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NIOS appliances can use the OSPF routing protocol to advertise routes for DNS anycast addresses to an upstream router within the autonomous system. The upstream router uses the OSPF advertisement to determine the nearest DNS server from a group of servers within the internetwork. In practice, the NIOS appliance relies upon OSPF to determine the best route for DNS queries to take to the nearest DNS server. The upstream router then forwards the query to the chosen DNS server.
As illustrated in the figure Anycast Addressing for DNS Using OSPF below, to enable anycast for DNS queries, you configure two or more DNS servers within the AS routing domain with the same anycast address on their loopback interfaces. When you select OSPF as the routing protocol, the upstream router determines the nearest server within the group of servers configured with that anycast address. (The "nearest" DNS server may not necessarily be the geographically closest DNS server; it is the DNS server with the lowest cost associated with its reachability from the current node. This is calculated through the OSPF routing algorithm, a discussion of which is far beyond the scope of this manual.) The nearest DNS server configured with the correct anycast address then responds to the DNS query. In the case where the nearest server becomes unavailable, the next nearest server responds to the query. OSPF anycast provides a dynamically routed failover to ensure that DNS can always resolve client requests within the AS. From the client perspective, anycasting is transparent and the group of DNS servers with the anycast address appears to be a single DNS server.
 
Anycast Addressing for DNS Using OSPF

After you configure or change DNS anycast settings, you must restart the DNS services for the settings to take effect. When you enter any OSPF command and wait for the interface to return more information, the appliance disconnects your CLI session after you restart services or make other OSPF configuration changes through Grid Manager. Re-enter your credentials to log back in to the CLI. (For information, refer to the Infoblox CLI Guide.)
To enable the appliance to support OSPF and advertising anycast addresses on OSPF from the loopback, you must first configure the LAN1 or LAN1 (VLAN) interface as an OSPF advertising interface. For information about VLAN, seeAbout Virtual LANs.
You can also configure authentication for OSPF advertisements to ensure that the routing information received from a neighbor is authentic and the reachability information is accurate. This process can be implemented for OSPF over IPv4 networks but is not supported for IPv6/OSPFv3.

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Anycast Addressing for DNS using BGP

To enable DNS anycast addressing across different ASs, you configure BGP as the routing protocol on the NIOS appliance. (As illustrated in the figure Anycast and BGP Configuration on Infoblox Appliances below, the AS 65497 network contains the Infoblox DNS anycast servers, and the AS 65499 network contains Router 1 and 2. The routers use BGP and are peered with the DNS servers. You can configure anycast addressing on the loopback interface of the DNS servers and select BGP as the protocol to advertise the anycast addresses to Router 1 and 2 in AS 65499. For information, see Configuring Anycast Addresses. Once you have configured the DNS servers, the appliances automatically add filters on the advertising interfaces to limit the advertisements to the configured anycast IP addresses. Similarly, BGP filters are applied to ensure that the DNS servers only receive default route advertisements from the neighboring routers.

Anycast and BGP Configuration on Infoblox Appliances

BGP uses timers to determine how often the appliance sends keepalive and update messages, and when to declare a neighboring router out of service. You can configure the time intervals for these timers. For information, see Configuring BGP in the NIOS Appliance below.
The BGP protocol service is automatically configured to send SNMP queries about BGP runtime data. The appliance sends SNMP traps to its neighboring routers when it encounters issues with the protocol. BGP is configured to send SNMP traps as defined in RFC4273 Definitions of Managed Objects for BGP-4. You must enable and configure the SNMP trap receiver on the Grid member for the member to send SNMP traps. For information, see SNMP MIB Hierarchy.
You can use the set bgp command to set the verbosity levels of the BGP routing service. The appliance writes BGP statistical information to the syslog. After you configure the settings, you must restart the DNS services for the settings to take effect. For information, refer to the Infoblox CLI Guide. Note that when you enter any BGP command and wait for the interface to return more information, the appliance disconnects your CLI session if you restart services or make other BGP configuration changes through Grid Manager. You must re-enter your credentials to log back in to the CLI.
You can configure BGP on any interface to advertise anycast addresses across multiple ASs.

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