To transfer the Cisco CCNA and CCNP authorisation exams, as substantially as decent a world-class networker, you've got to undergo how and when to ingest floating noise routes. And if you're wondering what makes them float -- feature on!
In this example, R1 and R2 are streaming OSPF over a Frame Relay network, 172.12.123.0 /24. They're also adjoining by a BRI ISDN link, 172.12.12.0 /24. R1 is business a loopback network, 1.1.1.1 /32, via OSPF. We poverty R2 to hit a line to that loopback modify if the inclose goes downbound - and here, we'll ingest a floating noise line to attain that happen.
R2 sees the line to the loopback programme via OSPF, and crapper sound that programme successfully.
R2#show ip line ospf
1.0.0.0/32 is subnetted, 1 subnets
O 1.1.1.1 [110/65 via 172.12.123.1, 00:00:02, Serial0
R2#ping 1.1.1.1
Type carelessness ordering to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
!!!!!
Success evaluate is 100 proportionality (5/5), round-trip min/avg/max = 68/68/68 ms
This is when it's essential to undergo your administrative distances.... or at small undergo where to countenance to wager them! The AD of OSPF is 110, which effectuation we crapper configure a noise line to 1.1.1.1 /32, and as daylong as the AD of the noise line is higher than 110, it won't be utilised unless the OSPF line leaves the routing table. That's ground this category of line is titled a floating noise line - the line floats in the routing plateau and isn't seen unless the direct line leaves the table.
You scholarly how to indite a noise line in your CCNA studies, but you also advert that the choice AD of a noise line is either 1 or 0... and both of those values are inferior than 110! To modify the AD of a noise route, configure the desirable indifference at the modify of the ip line command.
R2(config)#ip line 1.1.1.1 255.255.255.255 bri0 ?
Distance amount for this route
A.B.C.D Forwarding router's address
name Specify study of the incoming hop
permanent imperishable route
tag Set attach for this route
R2(config)#ip line 1.1.1.1 255.255.255.255 bri0 111
The noise line has an AD that's exclusive digit higher than that of the OSPF route, but that's sufficiency to attain the line float and not ease be seen in the routing table.
R2#show ip route
1.0.0.0/32 is subnetted, 1 subnets
O 1.1.1.1 [110/65 via 172.12.123.1, 00:06:44, Serial0
172.12.0.0/24 is subnetted, 2 subnets
C 172.12.12.0 is direct connected, BRI0
C 172.12.123.0 is direct connected, Serial0
Let's wager the gist on the routing plateau when the Serial0 programme is closed.
R2(config)#int s0
R2(config-if)#shutdown
12:04:53: %OSPF-5-ADJCHG: Process 1, Nbr 172.12.123.1 on Serial0 from FULL to DOWN, Neighbor Down: Interface downbound or detached
12:04:55: %SYS-5-CONFIGI: Configured from housing by console
12:04:55: %LINK-5-CHANGED: Interface Serial0, denaturized land to administratively down
12:04:56: %LINEPROTO-5-UPDOWN: Line prescript on Interface Serial0, denaturized land to down
R2#show ip route
1.0.0.0/32 is subnetted, 1 subnets
S 1.1.1.1 is direct connected, BRI0
172.12.0.0/24 is subnetted, 1 subnets
C 172.12.12.0 is direct connected, BRI0
The floating noise line appears in the table, but the ISDN unification module not embellish up until the BRI programme has reciprocation to send. Let's sound 1.1.1.1 and wager what happens. debug dialer was organized on R2 before sending the ping.
R2#ping 1.1.1.1
Type carelessness ordering to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
12:16:01: BR0 DDR: Dialing drive ip (s=172.12.12.2, d=1.1.1.1)
12:16:01: BR0 DDR: Attempting to selector 8358661
12:16:01: %LINK-3-UPDOWN: Interface BRI0:1, denaturized land to up.!!
12:16:01: BR0:1 DDR: dialer prescript up!!
Success evaluate is 80 proportionality (4/5), round-trip min/avg/max = 36/37/40 ms
The unification comes up and reciprocation crapper ease accomplish 1.1.1.1. Once R2 becomes an OSPF edge of R1 again, the OSPF line module again embellish the direct line and the floating noise line leaves the routing table.
R2(config)#int s0
R2(config-if)#no shut
R2#show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
172.12.123.1 1 FULL/DR 00:01:57 172.12.123.1 Serial0
R2#show ip route
1.0.0.0/32 is subnetted, 1 subnets
O 1.1.1.1 [110/65 via 172.12.123.1, 00:00:16, Serial0
172.12.0.0/24 is subnetted, 2 subnets
C 172.12.12.0 is direct connected, BRI0
C 172.12.123.0 is direct connected, Serial0
A floating noise line is an superior ack door that module ready the ISDN unification downbound patch allowing that unification to help as a patronage route. Just attain trusty the ISDN unification comes downbound when you wait it to - ever analyse that with exhibit isdn status!
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