If you use multiprotocol BGP (MP-BGP) in your network to support MPLS VPN, IPv6 or IP Multicast over BGP, it's best if you go all the way and configure an explicit ipv4 address family; the resulting BGP configuration is significantly easier to read and understand as the session-specific parameters are clearly separated from the routing-specific parameters and the IPv4 settings are nicely grouped in an explicit section.
To change the format of the BGP configuration, configure the IPv4 address family with the address-family ipv4 unicast router configuration command (the neighbor statements and other configuration settings pertinent to IPv4 configuration are automatically moved into the new address family) or manually activate a BGP neighbor for IPv4 route exchange with the neighbor activate router configuration command.To illustrate the differences between the traditional BGP configuration and the per-address-family configuration, consider a simple MPLS VPN+Internet setup. First the traditional approach:
router bgp 65000
template peer-policy Internal
send-community both
exit-peer-policy
!
template peer-session
Internal
remote-as 65000
update-source Loopback0
exit-peer-session
!
no synchronization
bgp
log-neighbor-changes
network 10.0.1.1 mask 255.255.255.255
neighbor 10.0.1.5 inherit peer-session Internal
neighbor 10.0.1.5
description PE-C(RR)
neighbor 10.0.1.5 inherit peer-policy
Internal
no auto-summary
!
address-family vpnv4
neighbor
10.0.1.5 activate
neighbor 10.0.1.5 send-community extended
exit-address-family
... and the changed configuration after the address-family ipv4 command has been entered:
router bgp
65000
template peer-policy Internal
send-community both
exit-peer-policy
!
template peer-policy InternalV6
send-label
inherit peer-policy Internal 1
exit-peer-policy
!
template peer-session Internal
remote-as 65000
update-source Loopback0
exit-peer-session
!
bgp
log-neighbor-changes
neighbor 10.0.1.5 inherit peer-session
Internal
neighbor 10.0.1.5 description PE-C(RR)
!
address-family ipv4
no synchronization
network 10.0.1.1 mask
255.255.255.255
neighbor 10.0.1.5 activate
neighbor 10.0.1.5
inherit peer-policy Internal
no auto-summary
exit-address-family
!
address-family vpnv4
neighbor 10.0.1.5
activate
neighbor 10.0.1.5 send-community extended
exit-address-family
