RIP-Frame-relay-Split-Horizon

mguy

Will I have to disable all split horizon rules on all routers in a 3 router point-to-multipoint running over frame-relay?

Or should I just disable the split-horizon on the spoke router (on R1 that connects to both R2 and R3)?

If I enable on all will RIP loop?

NetworkVeteran

http://www.techexams.net/forums/ccna-ccent/79546-rip-trivia-question.html


A careful study of this scenario should answer your questions.

mguy

my guess is to just disable it only in the hub (r1) to prevent the loops... ?

NetworkVeteran

mguy wrote: »

Will I have to disable all split horizon rules on all routers in a 3 router point-to-multipoint running over frame-relay?

Split horizon is disabled by default on interfaces with 'encapsulation frame-relay' configured. Which means it's disabled on the physical interface but enabled on subinterfaces.

Or should I just disable the split-horizon on the spoke router (on R1 that connects to both R2 and R3)?

If R1 connects to R2 and R3, then R1 is actually the HUB and R2 and R3 are the SPOKES.

On the HUB, you want split horizon disabled. Otherwise, the rule "Don't advertise a route out the interface it was learned on" will prohibit R1 from advertising R2's route to R3 and vice-versa.

On the SPOKEs, you want split horizon enabled to reduce the change of routing loops. There's no reason a spoke should need to advertise a HUB's routes back to itself.

If I enable on all will RIP loop?

If split horizon is enabled on all interfaces, you will not have full connectivity. If split horizon is disabled on all interfaces, your topology will be prone to routing loops.

mguy

Thank you very much!!

What command do I issue to see the settings of the split-horizon on the interface?

MrXpert

NetworkVeteran wrote: »

Split horizon is disabled by default on interfaces with 'encapsulation frame-relay' configured. Which means it's disabled on the physical interface but enabled on subinterfaces.

I have heard this before but actual testing seems to proove otherwise.
I have tested this using physical interfaces in hub and spoke topologies and found that routes were not being learnt until i disabled split horizon on the hub. So that does suggest split horizon is enabled on physical interfaces within eigrp.

NetworkVeteran

have heard this before but actual testing seems to proove otherwise.

That's straight from the Cisco 12.4T and 12.2 documentation and I've seen it proven many times via show command output, debugs, and wireshark traces.

The good news--if you're running a legacy version of IOS where you're unsure of the default behavior, it's easy to verify using the "show ip interface" command.

Gehrig#sh ip int s0/1 | inc Split
Split horizon is disabled
Gehrig#sh ip int s0/1.1 | inc Split
Split horizon is enabled
Gehrig#sh ip int s0/1.2 | inc Split
Split horizon is enabled

MrXpert

NetworkVeteran wrote: »

That's straight from the Cisco 12.4T and 12.2 documentation and I've seen it proven many times via show command output, debugs, and wireshark traces.

The good news--if you're running a legacy version of IOS where you're unsure of the default behavior, it's easy to verify using the "show ip interface" command.

Gehrig#sh ip int s0/1 | inc Split
Split horizon is disabled
Gehrig#sh ip int s0/1.1 | inc Split
Split horizon is enabled
Gehrig#sh ip int s0/1.2 | inc Split
Split horizon is enabled

Sorry my mistake, I was thinking of EIGRP over FR.Split horizon is enabled on both physical and multipoint interfaces by default.I'm running 12.4.
I did what you suggested with the show ip int command it states "Split Horizon is enabled". This appears even after disabling split horizon on a multipoint sub interface using no ip split eigrp command.I am working on a lab at the moment with 3 routers using multipoint sub interfaces, running EIGRP connected to the FR switch. I had to disable SPlit on the hub in order to have the spokes learn additional networks. The show ip int command displays SPlit Horizon is enabled when it is enabled or disabled. So the show ip int command only shows split horizon enabled for RIP and not EIGRP? or is there another command to display split horizon status for EIGRP?

Sorry this has gone off topic as it has gone from RIP to EIGRP

mguy

MrXpert wrote: »

Sorry my mistake, I was thinking of EIGRP over FR.Split horizon is enabled on both physical and multipoint interfaces by default.I'm running 12.4.
I did what you suggested with the show ip int command it states "Split Horizon is enabled". This appears even after disabling split horizon on a multipoint sub interface using no ip split eigrp command.I am working on a lab at the moment with 3 routers using multipoint sub interfaces, running EIGRP connected to the FR switch. I had to disable SPlit on the hub in order to have the spokes learn additional networks. The show ip int command displays SPlit Horizon is enabled when it is enabled or disabled. So the show ip int command only shows split horizon enabled for RIP and not EIGRP? or is there another command to display split horizon status for EIGRP?

Sorry this has gone off topic as it has gone from RIP to EIGRP

MrXpert wrote: »

Sorry my mistake, I was thinking of EIGRP over FR.Split horizon is enabled on both physical and multipoint interfaces by default.I'm running 12.4.
I did what you suggested with the show ip int command it states "Split Horizon is enabled". This appears even after disabling split horizon on a multipoint sub interface using no ip split eigrp command.I am working on a lab at the moment with 3 routers using multipoint sub interfaces, running EIGRP connected to the FR switch. I had to disable SPlit on the hub in order to have the spokes learn additional networks. The show ip int command displays SPlit Horizon is enabled when it is enabled or disabled. So the show ip int command only shows split horizon enabled for RIP and not EIGRP? or is there another command to display split horizon status for EIGRP?

Sorry this has gone off topic as it has gone from RIP to EIGRP

I'm experiencing the same. EIGRP over FR where the third router is not receiving updates for some reason.

Disabling FRelay is not reflecting in the "show ip int s0/0/0"

MrXpert

mguy wrote: »

I'm experiencing the same. EIGRP over FR where the third router is not receiving updates for some reason.

Disabling FRelay is not reflecting in the "show ip int s0/0/0"

The command is no ip split eigrp {as#). Or something like that. It is different to the RIP command. I often make the schoolboy error of trying to use the RIP version of the command on the hub. I think it is "no ip split-horizon" whereas EIGRP needs a bit more.