Resilient Per-Ce Label Allocation Mode; Bgp Multipath Enhancements; Mvpn With Bgp Safi-2 And Safi-129 - Cisco ASR 9000 Series Routing Configuration Manual

Implementing BGP

Resilient Per-CE Label Allocation Mode

The Resilient Per-CE Label Allocation is an extension of the Per-CE label allocation mode to support Prefix
Independent Convergence (PIC) and load balancing.
At present, the three label allocation modes, Per-Prefix, Per-CE, and Per-VRF have these restrictions:
• No support for ASR 9000 Ethernet Line Card and A9K-SIP-700
• No support for PIC
• No support for load balancing across CEs
• Temporary forwarding loop during local traffic diversion to support PIC
• No support for EIBGP multipath load balancing
• Forwarding performance impact
• Per-prefix label allocation mode causes scale issues on another vendor router in a network
In the Resilient Per-CE label allocation scheme, BGP installs a unique rewrite label in LSD for every unique
set of CE paths or next hops. There may be one or more prefixes in BGP table that points to this label. BGP
also installs the CE paths (primary) and optionally a backup PE path into RIB. FIB learns about the label
rewrite information from LSD and the IP paths from RIB.
In steady state, labeled traffic destined to the resilient per-CE label is load balanced across all the CE next
hops. When all the CE paths fail, any traffic destined to that label will result in an IP lookup and will be
forwarded towards the backup PE path, if available. This action is performed on the label independently of
the number of prefixes that may point to the label, resulting in the PIC behavior during primary paths failure.

BGP Multipath Enhancements

• Overwriting of next-hop calculation for multipath prefixes is not allowed. The next-hop-unchanged
• The ability to ignore as-path onwards while computing multipath is added. The bgp multipath as-path

MVPN with BGP SAFI-2 and SAFI-129

BGP supports Subsequent Address Family Identifier (SAFI)-2 and SAFI-129 for multicast VPNs (MVPNs).
SAFI-129 provides the capability to support multicast routing in the core IPv4 network. SAFI-129 supports
BGP-based MVPNs. The addition of SAFI-129 allows multicast to select an upstream multicast hop that may
be independent of the unicast topology. Multicast routes learned from the customer edge (CE) router or
multicast VPN routes learned from remote provider edge (PE) routers are installed into the multicast Routing
Information Base (MuRIB). This MuRIB will be populated with routes that are specific to multicast, and are
not used by unicast forwarding. The PE-CE BGP prefixes are advertised using SAFI-2, the PE-PE routes are
advertised using SAFI-129.
multipath command disables overwriting of next-hop calculation for multipath prefixes.
ignore onwards command ignores as-path onwards while computing multipath.
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.3.x
Resilient Per-CE Label Allocation Mode
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