Split-Horizon Feature

---

Let’s have a look into Split-Horizon Feature that prevents routes flooding over same segment If we don’t have this feature enabled so EIGRP routers will keep sending the updates to each other on the same segment, let’s check how.

So here Whenever R7 will send update to f0/0 segment then Both router will get the update and again when R9 will get the update it will share again on the same segment to other neighbor same will happen for R8 and like this prefixes will be flooding to neighbors on the same segment
But EIGRP Split Horizon feature prevent sending the update on same interface on which packet was received
So here whenever R7 will send update on Segment F0/0 then R9 and R8 will get the packet but will not send that update on same interface again.
If we need to disable this feature we can run some commands

Commands to disable this feature:
        *R8(config)#interface fastEthernet 0/0
        *R8(config-if)#no ip split-horizon eigrp 10
        *R8(config-if)#exit

So now Question here is in what case we disable this feature?
Whenever we use EIGRP over DMVPN then we need to disable this feature on HUB Device.

This use-case explained in DMVPN Workbook

Passive-Interface

---

Whenever we run network command in EIGRP, that router start injecting all the active interfaces belong to same subnet in EIGRP and router form the EIGRP neighborship over all the EIGRP enabled interfaces if find any EIGRP neighbor, and send hello in every 5 sec over all the interfaces On some interfaces router will have EIGRP neighbor on some interface EIGRP will be having only LAN connected (Where LAN users will be Connected), and router send EIGRP hello on these LAN interfaces also, that is actually useless

In this case R8 will send EIGRP hello on this interface after every 5 sec and that is really not required on this LAN Segment.

Here we have one loop fall also, here we have security issues, on this segment if any anonymous user connect a device and can send EIGRP packets so that in this case that anonymous router will be having full connectivity to this EIGRP domain and can cause some issues.

So in this case we enable EIGRP Passive interface feature,
When we enable this feature it performs some task:
        1. Disable sending EIGRP hello packets on that segment
        2. Still advertise subnet running on the link to other EIGRP neighbors

So there is no harm to enable this feature on LAN segment it still advertise the information to EIGRP domain, but while enabling this feature we have to be careful, if we enable this feature on a segment where we have EIGRP neighbor connected it will break the neighborship with neighbors present on that segment.

Commands to enable this feature:
        *R8(config)#router eigrp 10
        *R8(config-router)#passive-interface fastEthernet 0/0
        *R8(config-router)#exit

Commands to enable this feature for all interfaces belongs to EIGRP Process using a single Command
        *R8(config)#router eigrp 10
        *R8(config-router)#passive-interface default
        *R8(config-router)#exit
When we enable Passive-Interface Default feature all the interfaces will be enabled with this feature and will break the neighborship so to have a neighborship over any interface we run other commands/delete passive interface feature from a particular interface.
        *R8(config)#router eigrp 10
        *R8(config-router)#passive-interface default
        *R8(config-router)#no passive-interface fastEthernet 1/0
        *R8(config-router)#no passive-interface fastEthernet 2/0
        *R8(config-router)#exit

And after these commands again Router R8 will start sending hello and form neighborship on these 2 interfaces(Fast-Ethernet 1/0 & Fast-Ethernet 2/0)

               Check out our Complete EIGRP Video on Youtube