EIGRP NULL Route

Sagar Purohit · ‎10-02-2014

Hi Guys,

We can remove null route created by EIGRP when summarized from the routing table by setting the administrative distance to 255 on the router who advertises that summary. To do that it would be enough to do this:

First take off the summary address:
no ip summary-address eigrp 1 10.1.0.0 255.255.0.0

Then create it again with the AD as 255:
ip summary-address eigrp 1 10.1.0.0 255.255.0.0 255

I tried with IOS ver 15.2(4)S2. The output is entirely different it does't support distance at the end of summary address on interface but will create an additional command under router eigrp and the route will be removed from local table but will also not advertise the route to other routers.

R1(config-router)‪#‎int‬ g0/0
R1(config-if)# ip summary-address eigrp 1 10.1.0.0 255.255.0.0 255
%EIGRP: summary accepted, admin distance value ignored, use summary-metric command for distance

On R1
router eigrp 1
summary-metric 10.1.0.0/16 distance 255
network 10.1.0.0 0.0.0.255
network 10.1.1.0 0.0.0.255
network 10.1.2.0 0.0.0.255
network 10.1.3.0 0.0.0.255
network 192.168.1.0

R2#sh ip ro
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
+ - replicated route, % - next hop override
Gateway of last resort is not set
20.0.0.0/8 is variably subnetted, 8 subnets, 2 masks
C 20.2.0.0/24 is directly connected, Loopback0
L 20.2.0.2/32 is directly connected, Loopback0
C 20.2.1.0/24 is directly connected, Loopback1
L 20.2.1.2/32 is directly connected, Loopback1
C 20.2.2.0/24 is directly connected, Loopback2
L 20.2.2.2/32 is directly connected, Loopback2
C 20.2.3.0/24 is directly connected, Loopback3
L 20.2.3.2/32 is directly connected, Loopback3
192.168.1.0/24 is variably subnetted, 2 subnets, 2 masks
C 192.168.1.0/24 is directly connected, GigabitEthernet0/0
L 192.168.1.2/32 is directly connected, GigabitEthernet0/0

Cisco document also states the same. Please check under ip summary address command.

http://www.cisco.com/…/ipr…/command/ire-cr-book/ire-i1.html…

The summary address is not advertised to the peer if the administrative distance is configured as 255.

Can someone provide a solution on how to remove this and still advertise the route.

Thanks,
Sagar

Richard Burts · ‎10-02-2014

Sagar

I am not sure that there is a way to remove that null route and still advertise the summary. Why do you want to remove the null route? Cisco put it there for a reason and it might help us find a suggestion if we understood what you are trying to accomplish.

HTH

Rick

HTH

Rick

Sagar Purohit · ‎10-02-2014

Hi Rick,

It's not for some production. It is just for study purpose. Read on a lot of blogs as well that adding distance 255 would remove null route from local router but would advertise to other router. But now it's not happening hence wanted to know the solution.

Thanks,

Sagar