Question

Refer to the PE1 router routing table output exhibit.
RP/0/RSP0/CPU0:PE1#show route ipv4 isis i su 10.1.10.0/24 [115/30] via 0.0.0.0. 00:41:14 Null0 i L1 10.1.10.1/32 [115/30] via 192.168.101.11 00:43:19 GigabitEthernet0/0/0/0 i L1 10.1.10.2/32 [115/24] via 192.168.112.21 00:45:20 GigabitEthernet0/0/0/1 i L1 10.1.10.3/32 [115/32] via 192.168.113.22 00:39:03 GigabitEthernet0/0/0/2 i L1 10.1.10.4/32 [115/22] via 192.168.114.23 00:15:01 GigabitEthernet0/0/0/3 <output omitted>
What is causing the i su 10.1.10.0/24 [115/30] via 0.0.0.0, 00:40:34, Null0 entry on the PE1 router routing table?

A.	The PE1 router is receiving the 10.1.10.0/24 summary route from the upstream L1/L2 IS-IS router.
B.	The PE1 router has been configured to summarize the 10.1.10.x/32 IS-IS routes to 10.1.10.0/24.
C.	The 10.1.10.0/24 has been suppressed because IS-IS auto-summary has been disabled on the PE1 router.
D.	The 10.1.10.0/24 has been suppressed because of a route policy configuration on the PE1 router.
E.	The 10.1.10.0/24 has been suppressed because the more specific 10.1.10.x/32 IS-IS routes have been configured to leak into the IS-IS non-backbone area.

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Accepted Answer

The PE1 router has been configured to summarize the 10.1.10.x/32 IS-IS routes to 10.1.10.0/24.

Accepted Answer


Cedes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
       0 - OSPF, IA - OSFF inter area, N1 - OSPF NSSA external type 1
       N2 - OSFF NSSA external type 2, E1 - OSFF external type 1
       E2 - OSFF external type 2, E - EGP, i - ISIS, LI - IS-IS level-1
       L2 - IS-IS level-2, ia - IS-IS inter area
       su - IS-IS summary null, * - candidate default
       U - per-user static route, o - ODR, L - local