unconditional packet marking, see “Configuring Modular QoS Packet Classification” in the Cisco ASR 9000
Series Aggregation Services Router Modular Quality of Service Configuration Guide.
BFD for IPv4
Cisco IOS XR software supports bidirectional forwarding detection (BFD) singlehop and multihop for both
IPv4 and IPv6.
In BFD for IPv4 single-hop connectivity, Cisco IOS XR software supports both asynchronous mode and echo
mode over physical numbered Packet-over-SONET/SDH (POS) and Gigabit Ethernet links, as follows:
•
Echo mode is initiated only after a session is established using BFD control packets. Echo mode is
always enabled for BFD bundle member interfaces. For physical interfaces, the BFD minimum interval
must also be less than two seconds to support echo packets.
•
BFD echo packets are transmitted over UDP/IPv4 using source and destination port 3785. The source
address of the IP packet is the IP address of the output interface (default) or the address specified with
the router-id command if set or the address specified in the echo ipv4 source command, and the
destination address is the local interface address.
•
BFD asynchronous packets are transmitted over UDP and IPv4 using source port 49152 and destination
port 3784. For asynchronous mode, the source address of the IP packet is the local interface address,
and the destination address is the remote interface address.
BFD multihop does not support echo mode.Note
Consider the following guidelines when configuring BFD on Cisco IOS XR software:
•
BFD is a fixed-length hello protocol, in which each end of a connection transmits packets periodically
over a forwarding path. Cisco IOS XR software supports BFD adaptive detection times.
•
BFD can be used with the following applications:
◦
BGP
◦
IS-IS
◦
OSPF
and OSPFv3
◦
MPLS Traffic Engineering (MPLS-TE)
◦
Static routes (IPv4 and IPv6)
◦
Protocol Independent Multicast (PIM)
◦
Hot Standby Router Protocol (HSRP)
◦
Virtual Router Redundancy Protocol (VRRP)
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.1.x
184 OL-30423-03
Implementing BFD
BFD for IPv4
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