884
Configuring IP Unicast Routing
Configuring BFD
To create a BFD session, you must configure BFD on both systems (BFD peers). Enabling BFD at the interface and routing
protocol level on BFD peers creates a BFD session. BFD timers are negotiated and the BFD peers send control packets
to each other at the negotiated intervals. If the neighbor is not directly connected, BFD neighbor registration is rejected.
shows a simple network with two routers running OSPF and BFD. When OSPF discovers a
neighbor (1), it sends a request to the BFD process to initiate a BFD neighbor session with the neighbor OSPF router (2),
establishing the BFD neighbor session (3).
Figure 102 Establishing a BFD Session
shows what happens when a failure occurs in the network (1). The BFD neighbor session with
the OSPF neighbor closes (2). BFD notifies the OSPF process that the BFD neighbor is no longer reachable, and the OSPF
process breaks the OSPF neighbor relationship (4). If an alternative path is available, the routers start converging on it.
Figure 103 Breaking an OSPF Neighbor Relationship
BFD clients are routing protocols that register neighbors with BFD. The switch supports IS-IS, OSPF v1 and v2, BGP,
EIGRP, and HSRP clients. You can use one BFD session for multiple client protocols. For example, if a network is running
OSPF and EIGRP across the same link to the same peer, you need to create only one BFD session, and information is
shared with both routing protocols.
The switch supports BFD version 0 and version 1. BFD neighbors automatically negotiate the version and the protocol
always runs at the higher version. The default version is version 1.
By default, BFD neighbors exchange both control packets and echo packets for detecting forwarding failures. The switch
sends echo packets at the configured BFD interval rate (from 50 to 999 ms), and control packets at the BFD slow-timer
rate (from 1000 to 3000 ms).
Failure-rate detection can be faster in BFD echo mode, which is enabled by default when you configure BFD session. In
this mode, the switch sends echo packets from the BFD software layer, and the BFD neighbor responds to the echo
packets through its fast-switching layer. The echo packets do not reach the BFD neighbor software layer, but are
reflected back over the forwarding path for failure detection. You configure the rate at which each BFD interface sends
BFD echo packets by entering the
bfd interval
interface configuration command.
To reduce bandwidth consumption, you can disable the sending of echo packets by entering the
no bfd echo
interface
configuration command. When echo mode is disabled, control packets are used to detect forwarding failures. Control
packets are exchanged at the configured slow-timer rate, which could result in longer failure-detection time. You
configure this rate by entering the
bfd slow-timer
global configuration command. The range is from 1000 to 3000 ms;
the default rate is every 1000 ms.
172.16.10.2
172.16.10.1
172.17.0.1
172.18.0.1
BFD
BFD neighbors
3
OSPF
2
BFD
OSPF
2
127844
OSPF neighbors
1
Router A
Router B
172.16.10.2
172.16.10.1
172.17.0.1
172.18.0.1
BFD
BFD neighbors
2
1
X
X
X
OSPF
3
BFD
Router A
Router B
OSPF
3
127845
OSPF neighbors
4
Содержание IE 4000
Страница 12: ...8 Configuration Overview Default Settings After Initial Switch Configuration ...
Страница 52: ...48 Configuring Interfaces Monitoring and Maintaining the Interfaces ...
Страница 108: ...104 Configuring Switch Clusters Additional References ...
Страница 128: ...124 Performing Switch Administration Additional References ...
Страница 130: ...126 Configuring PTP ...
Страница 140: ...136 Configuring CIP Additional References ...
Страница 146: ...142 Configuring SDM Templates Configuration Examples for Configuring SDM Templates ...
Страница 192: ...188 Configuring Switch Based Authentication Additional References ...
Страница 244: ...240 Configuring IEEE 802 1x Port Based Authentication Additional References ...
Страница 274: ...270 Configuring SGT Exchange Protocol over TCP SXP and Layer 3 Transport Configuring Cisco TrustSec Caching ...
Страница 298: ...294 Configuring VLANs Additional References ...
Страница 336: ...332 Configuring STP Additional References ...
Страница 408: ...404 Configuring DHCP Additional References ...
Страница 450: ...446 Configuring IGMP Snooping and MVR Additional References ...
Страница 490: ...486 Configuring SPAN and RSPAN Additional References ...
Страница 502: ...498 Configuring Layer 2 NAT ...
Страница 559: ...555 Configuring Network Security with ACLs How to Configure Network Security with ACLs Creating a Numbered Extended ACL ...
Страница 770: ...766 Configuring IPv6 MLD Snooping Related Documents ...
Страница 930: ...926 Configuring IP Unicast Routing Related Documents ...
Страница 956: ...952 Configuring IPv6 Unicast Routing Configuring IPv6 network 2010 AB8 2 48 network 2010 AB8 3 48 exit address family ...
Страница 976: ...972 Configuring Cisco IOS IP SLAs Operations Additional References ...
Страница 978: ...974 Dying Gasp ...
Страница 990: ...986 Configuring Enhanced Object Tracking Monitoring Enhanced Object Tracking ...
Страница 994: ...990 Configuring MODBUS TCP Displaying MODBUS TCP Information ...
Страница 996: ...992 Ethernet CFM ...
Страница 1030: ...1026 Working with the Cisco IOS File System Configuration Files and Software Images Working with Software Images ...
Страница 1066: ...1062 Using an SD Card SD Card Alarms ...