Frequently Asked Questions on Multi-homing and BGP
Connect uses BGP communities to control routing announcements, i.e. the routes we send to customers as well as the routes we send to our peers and providers.
- These communities are divided into two groups:
- public communities
- these can be set by customers to influence how Connect treats a route, either internally or externally.
- private communities
- are used to classify routes. Customers should not try setting these communities as we will clear all customer set communities if a private community is present in a routing announcement.
These communities allow customers to modify AAPT's routing system behaviour in some way. The current communities are:
- Only announce the route to customers or to "national" rate peers (currently Worldcom/OzEmail).
- Don't announce the route outside of the local POP. This also means that traffic sourced by this route will be dropped if it attempts to leave the local POP. If using this community then you should request a "local scope only" routing table to avoid blackholing traffic.
- Modify the local preference of a route so that it is lower than a route received from a peer but not lower than a provider.
- Modify the local preference of a route so that it is lower than a route received from a normal customer announcement but not lower than one received from a peer. This is normally used to indicate a backup path. Note that traffic filtering may drop traffic sourced through an interface where the route is being announced with a local preference altering community set if there is another announcement of the route without the community set.
- Announce the route to customers and all peers. This means that we will announce it to all customers and to Telstra, Optus, Worldcom, etc, as well as to Telecom NZ and Singapore IX, but not our major upstream transit providers.
- Only announce the route to customers.
- Announce the route to customers and Australian peers only. This is similar to 2764:6, but excludes international peers. This means that we will announce it to all customers and to Australian peers such as Telstra, Optus, Worldcom, etc, but not to Telecom NZ, Singapore IX, or our major upstream transit providers.
- This community is defined by the MBONE community at FIXW-MBONE and while Connect does not currently connect to the MBONE or provide IP multicast service this community is reserved for potential future use.
Private communities are used internally to the AAPT network to control routing announcements. There are two main classes of private community and although customers cannot set these communities their meaning may be useful when using the Connect "Looking Glass" to diagnose problems.
- Class of route
- Communities 2764:65408 to 2764:65412 indicate the "basic" location of the origin of the route and are used to determine which routes are sent to a customer (based on their routing table type request).
2764:65408 Route originated by Connect or a Connect customer 2764:65409 or 2764:65410 Route originated within Australia i.e. Telstra, Optus, Worldcom etc.. 2764:65412 Route reachable via the USA
- These communities are referenced by AAPT's routing policy, accessible via whois at either whois.connect.com.au or at whois.ra.net. The policy is described in the Routing Policy Specification Language (RFC 2622).
- Location of route
- Communities starting at 2764:65280 indicate the origin POP of a Connect originated route. Some routes within AAPT's provider blocks will not be tagged with 2764:65408 but will have a POP community and there are a small number of special case routes that while originated by Connect don't have a POP community.
How do I restrict announcements so they don't go to AAPT's providers?
If you want only some of your networks to be globally routed by Connect you must use communities. Note that some router vendors do not support communities even though they claim to have a conformant BGP implementation.
If there are some networks you don't want us to globally route you must tag them with the community 2764:1 or 2764:7.
On a Cisco router this is best achieved by using a route map on your link to Connect. For example:ip bgp-community new-format ! router bgp ASN neighbor neighbor remote-as remote-AS neighbor neighbor send-community neighbor neighbor route-map AS2764-EXPORT out ! route-map AS2764-EXPORT permit 1 match ip address 100 set community 2764:1 route-map AS2764-EXPORT permit 2