EIGRP Stub Routing

Projects-5 eigrp stub

All of the routers are running “eigrp 100” and advertising all of its local subnets. Please answer below questions for this diagram.

Question 1:- In what way we configure Router R2 for EIGRP so that Router R1 does not receive 100.1.1.1/32 & 40.1.1.0/24 in its routing table?

Ans:-  We need to configure Router R2 as “eigrp stub connected”. By this configuration R2 will only advertise its connected networks i.e. 30.1.1.0/24, 50.1.1.0/24, and 20.1.1.0/24. But not, 100.1.1.1/32 and 40.1.1.0/24 due to stub configuration.  Also note that router configured with eigrp stub will always receive advertisement it learns from its peers. This configuration is applicable for this diagram and subnets only.

Question 2:- What configuration is required at Router R2 for EIGRP so that R1 does not receive any route thru EIGRP?

Ans:- We need to configure Router R2 as “router eigrp receive-only” . It will stop Router R2 for advertising any subnet, not even summary or static route redistribution and Therefore R1 will not get any information from R2. Its negative impact is that R3 and R4 will not be able to reach 20.1.1.0/24 network.

Question 3:- How we can configure EIGRP in Router R2 so that R1 can reach every network except 40.1.1.0/24

Ans:- First, We need to configure a static route at Router R2 i.e. “ip route 100.1.1.1 255.255.255.255 30.1.1.2”. Next hop for this route can be 50.1.1.1 as well. After that, we need to configure Router R2 as “eigrp stub connected static” so that R2 starts advertising route to 100.1.1.1/32 along with connected networks. Don’t forget to redistribute static routes into eigrp 100   with command “redistribute static 1000 100 255 1 1500” under “router eigrp 100”. By this configuration, R1 will be able to reach everywhere except 40.1.1.0/24.

Now, question arises when should eigrp stub be used? Its answer is that it should be used only when router does not have any transit path or in other words, there is no further connectivity. Second reason of eigrp stub usage is when router does not have enough memory or processing resources to cater EIGRP database needs. EIGRP Stub is used when administrator needs more control over advertisement of networks.  It’s also used to remove SIA( Struck in active) state issues in EIGRP as it will restrict further advertisement of Query packets. We can similarly use “eigrp stub connected summary” commands depending upon requirement.

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