EIGRP question

[Ruterford]

Hi All,

I have following diagram:

I have two routers(separated geographically in different offices) with EIGRP 100 running internally withing  my internal L2 network and we are planning to have another connection to another company provided by MPLS links, which will be available thru sub interfaces on above mentioned routers.

One link is intended to be primary and the other one - backup (or active/active - does not matter).

The problem is that the other side does not speak EIGRP over this MPLS links.

My question is how to advertise same routes to the remote company from both locations?

I am planning to put static routes on both routers and redistribute static into my internal EIGRP 100 in both locations.

Will above work? As I will have two similar statics redistributed from my two routers in each location...

And what happens if one location has some problems with the link, the static route will still exist and will be redistributed in the EIGRP 100, will EIGRP understand somehow that next-hop from static route does not respond and degrade the route, so all traffic will run over the other router?

Thanks!

[Vaibhava Varma]

HI OlbertGoli

Can you clarify if the new links to the 3rd company will be provisioned over the same Physical Link currently being used for Site 1 and Site 2 interconnectivity. How are the 2 sites currently connected ie via P2P circuit or MPLS L2 VPN. If its MPLS L2 VPN will the same ISP providing connectivity to the 3rd Company also.

If I understand your current and future aimed network setup will be as below

LAN-Site1---EIGRP100------GWRTR-Site1-------------EIGRP100---------------GWRTR-Site2-----------EIGRP100-----LAN-Site2

                                                !                                                                    !

                                       MPLS-VPN/Static                                      MPLS-VPN/Static

                                                !                                                                    !

                                           Primary                                                       Secondary

                                                !                                                                    !

                                                !                                                                    !

                                                           !                                            !

                                                                         3rd Compary

                                                                                 !

                                                                                 !

                                                                              LAN

Now for 3rd company to reach LAN-Site1 and :LAN-Site 2 the required Static Routes with AD manipulation can be created to achieve required redundancy from 3rd Company perspective

Now for each of the Current Site Static routes can be created to point to 3rd party LAN Subnets and also redistributed in EIGRP for routing redundacny. The static route being redistributed will be automatically removed from the routing table of the GWRTRs when their Physical Link connectivity is lost. We can ensure that there is no blackholing of traffic due to the slow detection of physical link failure/non-removal of static route from RT to 3rd company using Static Routes with next-hop as well as outgoing interface in the configuration and by using BFD for static routes.

Hope this helps to answer your question.

Regards

Varma

[Ruterford]

Hi Vaibhava,

Can you please  clarify, when Eigrp decides to degrade the redistributed static route, when physical link is dead or when static route is unable to reach next-hop? Could be a condition when physical link is up, but next hop is dead.

thanks!

[Vaibhava Varma]

HI OlbertGoli

When we create a Static Route with next-hop only , then that next-hop reachability is checked in the routing table which recurses to be a directly connected subnet

Now lets take a case when the connection is as below

R1--SW---R2

R1 has a static route to R2's Loopback with NH as R2's Physical Interface IP. When R1 does a sanity check for the NH reachability of this Static Route it only checks whether the Physical Connection from R1 to SW is up or not and not on the L3 connectivity between R1 and R2. So even if the link betwwen SW and R2 goes off the Static Route is not remove from R1;s RT. Thats why we should use both the outgoing interface and the NH for the static route. If we do not want to use the outgoing interface in the Static Route which can be some typical case of using VLAN SVI for connecting R1 and R2, BFD can help us detect this reachability issue of NH which can not be normally detected.

Regards

Varma