In the following
example, the EIGRP network contains RouterA, RouterB, and RouterC. The Gigabit
Ethernet interface 0/0/1 on RouterA is connected to the same network as Gigabit
Ethernet interface 0/0/1 on Router B. The Gigabit Ethernet interface 0/0/1 on
RouterB is connected to the same network as Gigabit Ethernet interface 0/0/1 on
RouterC.
RouterA and RouterB
are running BFD Version 1, which supports echo mode, and RouterC is running BFD
Version 0, which does not support echo mode. The BFD sessions between RouterC
and its BFD neighbors are said to be running echo mode with asymmetry because
echo mode will run on the forwarding path for RouteA and RouterB, and their
echo packets will return along the same path for BFD sessions and failure
detections, while their BFD neighbor RouterC runs BFD Version 0 and uses BFD
controls packets for BFD sessions and failure detections.
The example,
starting in global configuration mode, shows the configuration of BFD.
Configuration for
RouterC
!
!
interface Gigabtethernet0/0/0
no shutdown
ip address 10.4.9.34 255.255.255.0
duplex auto
speed auto
!
interface Gigabtethernet0/0/1
ip address 172.16.1.2 255.255.255.0
bfd interval 50 min_rx 50 multiplier 3
no shutdown
duplex auto
speed auto
!
router eigrp 11
network 172.16.0.0
bfd all-interfaces
auto-summary
!
ip default-gateway 10.4.9.1
ip default-network 0.0.0.0
ip route 0.0.0.0 0.0.0.0 10.4.9.1
ip route 172.16.1.129 255.255.255.255 10.4.9.1
!
no ip http server
!
logging alarm informational
!
control-plane
!
line con 0
exec-timeout 30 0
stopbits 1
line aux 0
stopbits 1
line vty 0 4
login
!
!
end
The output from the
show
bfd
neighbors
details command from RouterA verifies that BFD
sessions have been created among all three routers and that EIGRP is registered
for BFD support. The first group of output shows that RouterC with the IP
address 172.16.1.3 runs BFD Version 0 and therefore does not use the echo mode.
The second group of output shows that RouterB with the IP address 172.16.1.2
does run BFD Version 1, and the 50 millisecond BFD interval parameter had been
adopted. The relevant command output is shown in bold in the output.
RouterA# show bfd neighbors details
OurAddr
NeighAddr
LD/RD RH/RS Holdown(mult) State Int
172.16.1.1 172.16.1.3
5/3 1(RH) 150 (3 ) Up Gig0/0/1
Session state is UP and not using echo function.
Local Diag: 0, Demand mode: 0, Poll bit: 0
MinTxInt: 50000, MinRxInt: 50000, Multiplier: 3
Received MinRxInt: 50000, Received Multiplier: 3
Holdown (hits): 150(0), Hello (hits): 50(1364284)
Rx Count: 1351813, Rx Interval (ms) min/max/avg: 28/64/49 last: 4 ms ago
Tx Count: 1364289, Tx Interval (ms) min/max/avg: 40/68/49 last: 32 ms ago
Registered protocols: EIGRP
Uptime: 18:42:45
Last packet: Version: 0
- Diagnostic: 0
I Hear You bit: 1 - Demand bit: 0
Poll bit: 0 - Final bit: 0
Multiplier: 3 - Length: 24
My Discr.: 3 - Your Discr.: 5
Min tx interval: 50000 - Min rx interval: 50000
Min Echo interval: 0
OurAddr NeighAddr
LD/RD RH/RS Holdown(mult) State Int
172.16.1.1 172.16.1.2
6/1 Up 0 (3 ) Up Gig0/0/1
Session state is UP and using echo function with 50 ms interval.
Local Diag: 0, Demand mode: 0, Poll bit: 0
MinTxInt: 1000000, MinRxInt: 1000000, Multiplier: 3
Received MinRxInt: 1000000, Received Multiplier: 3
Holdown (hits): 3000(0), Hello (hits): 1000(317)
Rx Count: 305, Rx Interval (ms) min/max/avg: 1/1016/887 last: 448 ms ago
Tx Count: 319, Tx Interval (ms) min/max/avg: 1/1008/880 last: 532 ms ago
Registered protocols: EIGRP
Uptime: 00:04:30
Last packet: Version: 1
- Diagnostic: 0
State bit: Up - Demand bit: 0
Poll bit: 0 - Final bit: 0
Multiplier: 3 - Length: 24
My Discr.: 1 - Your Discr.: 6
Min tx interval: 1000000 - Min rx interval: 1000000
Min Echo interval: 50000
The output from the
show
bfd
neighbors
details command on Router B verifies that BFD
sessions have been created and that EIGRP is registered for BFD support. As
previously noted, RouterA runs BFD Version 1, therefore echo mode is running,
and RouterC runs BFD Version 0, so echo mode does not run. The relevant command
output is shown in bold in the output.
RouterB# show bfd neighbors details
OurAddr NeighAddr
LD/RD RH/RS Holdown(mult) State Int
172.16.1.2 172.16.1.1
1/6 Up 0 (3 ) Up Gig0/0/1
Session state is UP and using echo function with 50 ms interval.
Local Diag: 0, Demand mode: 0, Poll bit: 0
MinTxInt: 1000000, MinRxInt: 1000000, Multiplier: 3
Received MinRxInt: 1000000, Received Multiplier: 3
Holdown (hits): 3000(0), Hello (hits): 1000(337)
Rx Count: 341, Rx Interval (ms) min/max/avg: 1/1008/882 last: 364 ms ago
Tx Count: 339, Tx Interval (ms) min/max/avg: 1/1016/886 last: 632 ms ago
Registered protocols: EIGRP
Uptime: 00:05:00
Last packet: Version: 1
- Diagnostic: 0
State bit: Up - Demand bit: 0
Poll bit: 0 - Final bit: 0
Multiplier: 3 - Length: 24
My Discr.: 6 - Your Discr.: 1
Min tx interval: 1000000 - Min rx interval: 1000000
Min Echo interval: 50000
OurAddr NeighAddr
LD/RD RH/RS Holdown(mult) State Int
172.16.1.2 172.16.1.3
3/6 1(RH) 118 (3 ) Up Gig0/0/1
Session state is UP and not using echo function.
Local Diag: 0, Demand mode: 0, Poll bit: 0
MinTxInt: 50000, MinRxInt: 50000, Multiplier: 3
Received MinRxInt: 50000, Received Multiplier: 3
Holdown (hits): 150(0), Hello (hits): 50(5735)
Rx Count: 5731, Rx Interval (ms) min/max/avg: 32/72/49 last: 32 ms ago
Tx Count: 5740, Tx Interval (ms) min/max/avg: 40/64/50 last: 44 ms ago
Registered protocols: EIGRP
Uptime: 00:04:45
Last packet: Version: 0
- Diagnostic: 0
I Hear You bit: 1 - Demand bit: 0
Poll bit: 0 - Final bit: 0
Multiplier: 3 - Length: 24
My Discr.: 6 - Your Discr.: 3
Min tx interval: 50000 - Min rx interval: 50000
Min Echo interval: 0
When Gigabit
ethernet interface 0/0/1 on RouterB fails, BFD will no longer detect Router B
as a BFD neighbor for RouterA or for RouterC. In this example, Giagbit Ethernet
interface 0/0/1has been administratively shut down on RouterB.
The following
output from the
show
bfd
neighbors command on RouterA now shows only one
BFD neighbor for RouterA in the EIGRP network. The relevant command output is
shown in bold in the output.
RouterA# show bfd neighbors
OurAddr NeighAddr
LD/RD RH/RS Holdown(mult) State Int
172.16.1.1 172.16.1.3
5/3 1(RH) 134 (3 ) Up Gig0/0/1
The following
output from the
show
bfd
neighbors command on RouterC also now shows only
one BFD neighbor for RouterC in the EIGRP network. The relevant command output
is shown in bold in the output.
RouterC# show bfd neighbors
OurAddr NeighAddr
LD/RD RH Holdown(mult) State Int
172.16.1.3 172.16.1.1
3/5 1 114 (3 ) Up Gig0/0/1