RIP & DEFAULT Routes
HELLO ALL,
Again I am just writing this to check my logic and to ensure that I have everything straight in my mind. I have just wrote up a little review on RIP and the default-information Originate command. Please give me feed back so I can fill in any knowldge gaps I might have.
Respectfully,
AntRal
RIP and DEFAULT-INFORMATION Originate
The Basic Issue-
Using the Default-information originate command is a good way to advertise a default route within a network using RIP as the IGP, but there is an issue when you implement it in a network that has any kind of mesh topology. Unchecked the default route will just loop around the network incrementing its hop count until the count of 16 then it will flush the route and start over; a “count to infinity”. To fix this we need to block the default route from coming back into the originating router. This can be accomplished by creating a prefix list on one of the routers going out the interface into the originating router or on the originating router you can create a static route of the 0.0.0.0 directed to null0.
Topology-
Router1—f0/2àRouter2—f0/0 à Router3--f0/1à Router1
Example 1 -
Router1
Router rip
Default-information originate
!
Router3
IP prefix-list DEFAULT-FILTER seq 10 deny 0.0.0.0/0
IP prefix-list DEFAULT-FILTER seq 15 permit 0.0.0.0/0 le 32
!
Router rip
Distribute-list prefix DEFAULT-FILTER out f0/1
!
Example 2 –
Router1
Router rip
Default-information originate
!
IP route 0.0.0.0 0.0.0.0 null
!
Default Route with Route-Map
You can use a route-map with the default-information originate command to generate a default route only if the route-map conditions are satisfied. You can also use it to set the interface you want to advertise the default route. The advantage of making the default route contingent on a route-map is that you can ensure that the route will stop being advertised if the connection that is being tracked by the route-map goes down. Note: You cannot use extended access-lists with the configuration of default-information originate.
Example 1-
Topology-
Router1—f0/2àRouter2—f0/0 à Router3--f0/1à Router1—f0/0à Network_Edge_RT—Loopback0 2.1.1.1/32
Router1
IP prefix-list EDGE_LOOP seq 10 permit 2.1.1.1/32
!
Route-map CHECK_EDGE_LOOP permit 10
Match ip address prefix-list EDGE_LOOP
!
Router rip
Default-information originate route-map CHECK_EDGE_LOOP
!
!
Router3
IP prefix-list DEFAULT-FILTER seq 10 deny 0.0.0.0/0
IP prefix-list DEFAULT-FILTER seq 15 permit 0.0.0.0/0 le 32
!
Router rip
Distribute-list prefix DEFAULT-FILTER out f0/1
!
Example 2-
Topology-
Network to outside 201.1.1.0/24-Router1—f0/2àRouter2—f0/0 à Router3
Router1
Access-list 5 permit 201.1.1.0 0.0.0.255
Route-map SET_DEFAULT_INTER permit 10
Match ip address 5
Set interface f0/2
!
Router rip
Default-information originate route-map SET_DEFAULT_INTER
!
!
Default on passive-interfaces
You can also set your default route to only be generated on passive interfaces. This would be a good implementation for a stub like router.
Topology-
Router1—f0/2àRouter2—f0/0 à Router3--f0/1à Router1—f0/0à Router4
Router1
Router rip
Passive-interface f0/0
Default-information originate on-passive
!
!
Comments
Good Afternoon Sir,
Thank you. The on-passive has been added on the IOS 15.1(2) and later so it is a newer feature, but it does add more simplistic configurations than using route maps.
Respectfully,
AntRal
Ture it is the worst for most designs, but I could still see a few designs that it would work in still. It is no EIGRP or OSPF that is for sure.
All that the blue print says is:
2.4 RIP v2
So minimal at best I would think.
Hi AntRal
On my CSR1000V "on-passive" command dose not work properly.
Example:
interface GigabitEthernet1.101
encapsulation dot1Q 101
ip address 154.1.0.1 255.255.255.0
!
interface GigabitEthernet1.102
encapsulation dot1Q 102
ip address 154.1.1.1 255.255.255.0
!
router rip
version 2
passive-interface GigabitEthernet1.101
network 154.1.0.0
default-information originate on-passive
no auto-summary
R6#debug ip rip
RIP protocol debugging is on
R6#
*Aug 4 21:51:23.153: RIP: sending v2 update to 224.0.0.9 via GigabitEthernet1.101 (154.1.0.1)
*Aug 4 21:51:23.153: RIP: build update entries
*Aug 4 21:51:23.153: 0.0.0.0/0 via 0.0.0.0, metric 1, tag 0
R6#
*Aug 4 21:51:25.523: RIP: sending v2 update to 224.0.0.9 via GigabitEthernet1.102 (154.1.1.1)
*Aug 4 21:51:25.523: RIP: build update entries
*Aug 4 21:51:25.524: 0.0.0.0/0 via 0.0.0.0, metric 1, tag 0
*Aug 4 21:51:25.524: 154.1.0.0/24 via 0.0.0.0, metric 1, tag 0
R6 advertises default route from not only passive interface but also non-passive interface.
Is there any other version of IOS-XE that can advertise default route only from passive interfaces?
Or did I make configurational mistake?
Additional Information:
R6#sh ver
Cisco IOS XE Software, Version 03.13.02.S - Extended Support Release
Cisco IOS Software, CSR1000V Software (X86_64_LINUX_IOSD-UNIVERSALK9-M), Version 15.4(3)S2, RELEASE SOFTWARE (fc3)
(snip)