Stub Routing

Stub routing is used to reduce the size of the query domain.

Query will be generated when the topology get changes due to any problem if in the topology for any network if it lost the successor and it doesn't have the feasible successor then router will send the query packet to the downstream / upstream router asking the lost network reachability.

So in our topology if loopback 0 on R5 shutdown by mistake then R5 will send the Query to all routers. The query will be reaching till R3, R6, BB1 and BB2. This is unnecessary we can eliminate this query packet by one hop making the end router as stub router.

In this case we goanna do on BB1 

R5(config)#int lo 0

R5(config-if)#sh

BB1#

*Mar  1 00:26:30.791: EIGRP: Received QUERY on Ethernet0/0 nbr 155.1.21.2

*Mar  1 00:26:30.795:   AS 100, Flags 0x0, Seq 23/0 idbQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 0/0

*Mar  1 00:26:30.811: EIGRP: Enqueueing REPLY on Ethernet0/0 nbr 155.1.21.2 iidbQ un/rely 0/1 peerQ un/rely 0/0 serno 43-43

*Mar  1 00:26:30.823: EIGRP: Sending REPLY on Ethernet0/0 nbr 155.1.21.2

*Mar  1 00:26:30.827:   AS 100, Flags 0x0, Seq 12/23 idbQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 0/1 serno 43-43

Now lets make the BB1 as the stub router.

BB1#sh run | sec eigrp

 ip hello-interval eigrp 100 3

 ip hold-time eigrp 100 9

router eigrp 100

 network 0.0.0.0

 no auto-summary

 eigrp stub connected summary

*Mar  1 00:12:42.627: EIGRP: Enqueueing QUERY on Ethernet0/0 iidbQ un/rely 0/1 serno 25-25

*Mar  1 00:12:42.631: EIGRP: Enqueueing QUERY on Ethernet0/0 nbr 155.1.21.2 iidbQ un/rely 0/0 peerQ un/rely 0/0 serno 25-25

*Mar  1 00:12:42.639: EIGRP: Sending QUERY on Ethernet0/0

*Mar  1 00:12:42.639:   AS 100, Flags 0x0, Seq 12/0 idbQ 0/0 iidbQ un/rely 0/0 serno 25-25

*Mar  1 00:12:43.063: EIGRP: Received REPLY on Ethernet0/0 nbr 155.1.21.2

*Mar  1 00:12:43.067:   AS 100, Flags 0x0, Seq 26/12 idbQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 0/0

Note: We are not receiving query from R2.Lets check it on R2

*Mar  1 00:12:33.523: EIGRP: Received QUERY on Serial0/0 nbr 155.1.123.1

*Mar  1 00:12:33.527:   AS 100, Flags 0x0, Seq 41/23 idbQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 0/0

*Mar  1 00:12:33.547: EIGRP: Enqueueing REPLY on Serial0/0 nbr 155.1.123.1 iidbQ un/rely 0/1 peerQ un/rely 0/0 serno 29-29

*Mar  1 00:12:33.563: EIGRP: Sending REPLY on Serial0/0 nbr 155.1.123.1

*Mar  1 00:12:33.567:   AS 100, Flags 0x0, Seq 24/41 idbQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 0/1 serno 29-29

*Mar  1 00:12:33.583: EIGRP: Received QUERY on Ethernet1/0 nbr 155.1.21.1

*Mar  1 00:12:33.587:   AS 100, Flags 0x0, Seq 12/0 idbQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 0/0