Dell PowerSwitch S4128F-ON OS10 Enterprise Edition User Guide Release 10.4.3.0 - Page 431

Routers B, C, D, E, and G are members of the same AS-AS100. These routers are also in the same route reflection cluster, where Router D is the route reflector. Routers E and G are client peers of Router D, and Routers B and C and nonclient peers of Router D. 1 Router B receives an advertisement from Router A through EBGP. Because the route is learned through EBGP, Router B advertises it to all its IBGP peers - Routers C and D. 2 Router C receives the advertisement but does not advertise it to any peer because its only other peer is Router D (an IBGP peer) and Router D has already learned it through IBGP from Router B. 3 Router D does not advertise the route to Router C because Router C is a nonclient peer. The route advertisement came from Router B which is also a nonclient peer. 4 Router D does reflect the advertisement to Routers E and G because they are client peers of Router D. 5 Routers E and G advertise this IBGP learned route to their EBGP peers - Routers F and H. Multiprotocol BGP Multiprotocol BGP (MBGP) is an extension to BGP that supports multiple address families-IPv4 and IPv6. MBGP carries multiple sets of unicast and multicast routes depending on the address family. You can enable the MBGP feature on a per router, per template, and/or a per peer basis. The default is the IPv4 unicast routes. BGP session supports multiple address family interface (AFI) and sub address family interface (SAFI) combinations, BGP uses OPEN message to convey this information to the peers. As a result, the IPv6 routing information is exchanged over the IPv4 peers and vice versa. BGP routers that support IPv6 can set up BGP sessions using IPv6 peers. If the existing BGP-v4 session is capable of exchanging ipv6 prefixes, the same is used to carry ipv4 as well as ipv6 prefixes. If the BGP-v4 neighbor goes down, it also impacts the IPv6 route exchange. If BGP-v6 session exists, it continues to operate independently from BGP-v4. Multiprotocol BGPv6 supports many of the same features and functionality as BGPv4. IPv6 enhancements to MBGP include support for an IPv6 address family and Network Layer Reachability Information (NLRI) and next hop attributes that use the IPv6 addresses. Attributes Routes learned using BGP have associated properties that are used to determine the best route to a destination when multiple paths exist to a particular destination. These properties are called BGP attributes which influence route selection for designing robust networks. There are no hard-coded limits on the number of supported BGP attributes. BGP attributes for route selection: • Weight • Local preference • Multiexit discriminators • Origin • AS path Layer 3 431