One saucer of fault for whatever CCNA and CCNP candidates is the disagreement between configuring a noise choice line and using the Cisco routing bidding ip default-network.
At prototypal glance, they materialize to do the aforementioned thing. Both configure a instruction to which packets should be routed if there is no more limited line in the routing table.
The field disagreement between these digit options is that configuring a noise choice line exclusive defines a choice line for the router you're configuring it on, patch ip default-network module move the line via its routing protocol.
Let's investigate the routing tables of a hub-and-spoke meshwork using the ip default-network command. R1 is the hub and R2 and R3 are the spokes. They are direct adjoining via the meshwork 172.12.123.0 /24, and apiece has a loopback with a 32-bit cover that are numbered according to the router sort (1.1.1.1, etc.) RIP is streaming on every threesome routers and the loopbacks are advertised.
R1 has added program programme with the IP come 10.1.1.1 /24, and this meshwork has been flagged as a choice meshwork with the bidding ip default-network 10.0.0.0 . It is not existence advertised by RIP.
The routing prescript module then promote this route. With RIP, the choice meshwork is advertised as 0.0.0.0 . (With IGRP, it appears as the meshwork number, but is scarred as an IGRP External route. ) This line has been designated a politician choice line on R1, as we wager with the grapheme incoming to the 10.0.0.0 /24 meshwork (code plateau distant for brevity):
R1#show ip route
Gateway of terminal ingest is not set
1.0.0.0/32 is subnetted, 1 subnets
C 1.1.1.1 is direct connected, Loopback0
R 2.0.0.0/8 [120/1 via 172.12.123.2, 00:00:11, Serial0
R 3.0.0.0/8 [120/1 via 172.12.123.3, 00:00:11, Serial0
172.12.0.0/16 is variably subnetted, 2 subnets, 2 masks
C 172.12.21.0/30 is direct connected, BRI0
C 172.12.123.0/24 is direct connected, Serial0
* 10.0.0.0/24 is subnetted, 1 subnets
C 10.1.1.0 is direct connected, Serial1
On R2 and R3, a choice RIP line is today seen (code tables again deleted):
R2#show ip line
Gateway of terminal ingest is 172.12.123.1 to meshwork 0.0.0.0
R 1.0.0.0/8 [120/1 via 172.12.123.1, 00:00:00, Serial0.213
2.0.0.0/32 is subnetted, 1 subnets
C 2.2.2.2 is direct connected, Loopback0
R 3.0.0.0/8 [120/2 via 172.12.123.1, 00:00:00, Serial0.213
172.12.0.0/16 is variably subnetted, 2 subnets, 2 masks
C 172.12.21.0/30 is direct connected, BRI0
C 172.12.123.0/24 is direct connected, Serial0.213
R* 0.0.0.0/0 [120/1 via 172.12.123.1, 00:00:00, Serial0.213
R3#show ip line
Gateway of terminal ingest is 172.12.123.1 to meshwork 0.0.0.0
R 1.0.0.0/8 [120/1 via 172.12.123.1, 00:00:27, Serial0.31
R 2.0.0.0/8 [120/2 via 172.12.123.1, 00:00:28, Serial0.31
3.0.0.0/32 is subnetted, 1 subnets
C 3.3.3.3 is direct connected, Loopback0
172.12.0.0/24 is subnetted, 1 subnets
C 172.12.123.0 is direct connected, Serial0.31
R* 0.0.0.0/0 [120/1 via 172.12.123.1, 00:00:28, Serial0.31
And the choice line works, since we crapper sound 10.1.1.1 from both R2 and R3. Since they hit no another correct in their routing tables, they ingest the choice route.
R2#ping 10.1.1.1
Type carelessness ordering to abort.
Sending 5, 100-byte ICMP Echos to 10.1.1.1, timeout is 2 seconds:
!!!!!
Success evaluate is 100 proportionality (5/5), round-trip min/avg/max = 68/68/68 ms
R3#ping 10.1.1.1
Type carelessness ordering to abort.
Sending 5, 100-byte ICMP Echos to 10.1.1.1, timeout is 2 seconds:
!!!!!
Success evaluate is 100 proportionality (5/5), round-trip min/avg/max = 68/68/68 ms
When determining whether to ingest a choice noise line or a choice network, ready in nous that if you poverty the routing prescript to move the choice route, the ip default-network bidding module do that for you. But if you poverty exclusive the topical router to hit the choice route, a noise IP line is the artefact to go.
Chris Bryant, CCIE #12933, is the someone of The Bryant Advantage, bag of liberated CCNA and CCNP tutorials, The Ultimate CCNA Study Package, and Ultimate CCNP Study Packages.
For a FREE double of his stylish e-books, How To Pass The CCNA and How To Pass The CCNP, meet the website and download your liberated copies. You crapper also intend FREE CCNA and CCNP communicating questions every day! Pass the CCNA communicating with The Bryant Advantage!
