a dynamic routing protocol in Cisco IOS XR software. For more information, see the Enabling BFD on
a Static Route.
•
A router running BFD in Cisco IOS software can designate a router running BFD in Cisco IOS XR
software as its peer using the bfd neighbor command; the Cisco IOS XR router must use dynamic
routing or a static route back to the Cisco IOS router to establish the peer relationship. See the BFD
Peers on Routers Running Cisco IOS and Cisco IOS XR Software: Example.
BFD Multipath Sessions Support on nV Edge System
The following BFD Multipath Sessions are supported on nV Edge System:
•
BFD over GRE
•
BFD over Logical Bundle
•
BFD over IRB
•
BFD Multihop (only supported from 5.2.2 onwards)
•
BFD over MPLS TE
•
BFD over Satellite
BFD Modes of Operation
Cisco IOS XR software supports the asynchronous mode of operation only, with or without using echo packets.
Asynchronous mode without echo will engage various pieces of packet switching paths on local and remote
systems. However, asynchronous mode with echo is usually known to provide slightly wider test coverage
as echo packets are self-destined packets which traverse same packet switching paths as normal traffic on the
remote system.
BFD echo mode is enabled by default for the following interfaces:
•
For IPv4 on member links of BFD bundle interfaces.
•
For IPv4 on other physical interfaces whose minimum interval is less than two seconds.
When BFD is running asynchronously without echo packets (Figure 35), the following occurs:
• Each system periodically sends BFD control packets to one another. Packets sent by BFD router “Peer
A” to BFD router “Peer B” have a source address from Peer A and a destination address for Peer B.
•
Control packet streams are independent of each other and do not work in a request/response model.
•
If a number of packets in a row are not received by the other system, the session is declared down.
Figure 10: BFD Asynchronous Mode Without Echo Packets
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.1.x
178 OL-30423-03
Implementing BFD
BFD Multipath Sessions Support on nV Edge System
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