AT&T MPLS VPN Routing Features Available

1. AT&T MPLS VPN Routing Features Available Restrictive RoutingEnabling this feature instructs the AT&T PE to only advertise a default route over the ePVC. Customer network must still originate the default route at one (or more) sites. AS OverrideEnabling this feature instructs the AT&T PE to overwrite the customer’s AS number in the AS path with the AT&T AS of 13979. This feature is used when customers use the same AS number at multiple sites and want these sites to learn routes from other sites using the same AS number. If using default routes or other routing policies (e.g., “pseudo” hub & spoke) AS Override is not needed. Outbound Route Filtering (ORF)CE routers can indicate to the AT&T PE via a prefix list to only send specific routes over the BGP connection.

2. AT&T MPLS VPN Routing Features Available Well-known Community ValuesCE routers can send well-known community values in their route advertisements to the AT&T PER to indicate that they want the AT&T network to use different Local Pref settings (e.g., 13979:80, 13979:90, 13979:100, 13979:120 13979:120). In addition community values such as no-export and no-advertise can also be sent. When a PER receives a community value from the customer in an eBGP update message, it sets the corresponding local preference value on the route only in the regional AVPN autonomous system the route was received in – e.g., U.S. - The LP setting will not be used globally as the route passes from AT&T MPLS autonomous system to another. Note: AT&T will pass all BGP CVs received from a CER transparently end-to-end. This allows customers to add BGP CVs that they can use to enforce different policies across their network. Since AT&T uses many BGP CVs beginning with 13979:xxxx to implement specific features, care must be used when customers use values in this format.

3. AT&T MPLS VPN Routing Features Available AS Path Prepending A CER can use AS Path prepending in BGP route advertisements to influence primary, secondary, tertiary, etc., routing behavior. AS Path prepending is recommended in these scenarios since it is an attribute that customer routers will see based on the current active route in use in the VPN. MEDS AVPN PERs accept and uses the multi-exit discriminator on routes received from the customer's CER in its BGP path selection process. PERs sets all MEDs to “0” or blank before sending routes to eBGP neighbors such as customer's CERs and other regions (e.g. Canada, Latin America, EMEA, Asia Pac). The BGP path selection process prefers the lowest MED. MED is only compared if the routes come directly from the same AS. (AVPN does not use “always-compare med.”) So, the AT&T MPLS network will not compare MEDs between routes from different regions.

4. Most Common Routing Features Used By Customers Today to Influence Default Routing Decisions • Local-Preference based on BGP community value sent from CER to PER (e.g., 13979:120) • Same LP will be used on all PERs in a single AT&T region (AS) only • AS Path Prepending • Same route priority will be used on all PERs within the same VPN. Behavior may be somewhat different for a global network due to the addition of the AT&T regional ASN before it propagates to another region. • Closest Exit • Routes advertised with equal BGP metrics from multiple locations (except for originating customer AS) will be load split based on the internal AT&T network cost (OSPF metric) to reach one of the potential egress PERs from the ingress PERs perspective. • ei-BGP multipath load balancing • Routes advertised with equal BGP metrics from multiple locations (and using the same originating customer AS) will be load balanced based on a CEF decision made at the ingress PER. Load-balancing is flow based (i.e., by source and destination ip address) and can be split across a maximum of six paths.

5. Load Balancing Multiple Access Links Load Balance for Equal Routes 10.50.1.1 10.1.1.1 10.50.1.2 10.1.1.2 PER CER#1 MPLS PER Remote CER 10.1.1.0/24 AS 64512 10.50.1.0/24 CER#2 PER PER—Provider Edge Router CER—Customer Edge Router Load Balancing based on ei-BGP multipath feature. Uses CEF-based load-balancing across up to 6 paths. Networks must be advertised identically to the MPLS Network.