Question on EIGRP Debug

[grapevine]

Topology: Two routers connected to each via Gigabit Interfaces 10.1.1.0/30. I have created a loopback interface on R1 172.16.0.0/24.

When I shut the loopback interface, I get the below debug information from the neighbor 10.1.1.2

My question is when I shut the loopback interface, why is the router (that has the loopback interface) sending a query to its neighbor in the first place?

What is this metric 4294967295/4294967295

EIGRP: Sending HELLO on GigabitEthernet0/0

AS 1, Flags 0x0, Seq 5/0 idbQ 0/0 iidbQ un/rely 0/0

EIGRP: Received QUERY on GigabitEthernet0/0 nbr 10.1.1.1

AS 1, Flags 0x0, Seq 5/0 idbQ 0/0

iidbQ un/rely 0/0 peerQ un/rely 0/0

EIGRP: Sending ACK on GigabitEthernet0/0 nbr 10.1.1.1

AS 1, Flags 0x0, Seq 0/5 idbQ 0/0 iidbQ un/rely 0/0

DUAL: rcvupdate: 172.16.0.0/24 via 10.1.1.1 metric 4294967295/4294967295

DUAL: Find FS for dest: 172.16.0.0/24. FD is 130816, RD is 128256

DUAL: 0.0.0.0 metric 4294967295/4294967295 not found Dmin is 4294967295

DUAL: Dest 172.16.0.0/24 (No peers) not entering active state.

DUAL: Removing dest 172.16.0.0/24, nexthop 0.0.0.0

DUAL: No routes. Flushing dest 172.16.0.0/24

EIGRP: Enqueueing REPLY on GigabitEthernet0/0 nbr 10.1.1.1 iidbQ un/rely 0/0 peerQ un/rely 0/0 serno 2-2

EIGRP: Requeued unicast on GigabitEthernet0/0

EIGRP: Sending REPLY on GigabitEthernet0/0 nbr 10.1.1.1

AS 1, Flags 0x0, Seq 5/5 idbQ 0/0 iidbQ un/rely 0/0

EIGRP: Received ACK on GigabitEthernet0/0 nbr 10.1.1.1

AS 1, Flags 0x0, Seq 0/5 idbQ 0/0

iidbQ un/rely 0/0 peerQ un/rely 0/0

EIGRP: Sending HELLO on GigabitEthernet0/0

AS 1, Flags 0x0, Seq 6/0 idbQ 0/0 iidbQ un/rely 0/0

[Mark Malone · Accepted solution]

Hey I would say its because its a hybrid distance vector protocol they don't share full tables but whenever there is a change between neighbours they will notify each other through dual that a change has occurred  , routing by rumour rather than link state where everyone has exact same table like ospf lsdb , the whole table is not passed between router ,queries can be used to ask neighbors whether they have a path to a route which was recently lost too as well as just updating each other that something has dropped off the network

That metric is an infinite metric which can be set because the route is no longer valid and not to be advertised , you can also see that type of metric when a route gets poisoned