In IS-IS networks, the backup designated router (BDR) forms adjacencies to what router or routers?

The correct answer is D. There is no BDR in IS-IS. IS-IS networks do not use the concept of a Backup Designated Router (BDR); instead, they utilize a Designated Intermediate System (DIS) on multi-access segments.

Advanced Addressing and Routing Solutions

Question

Options

AIt forms an adjacency only with the DR
BIt forms adjacencies with all routers
CThe BDR only becomes adjacent when the DR is down
DThere is no BDR in IS-IS

How the community answered

(18 responses)

A
6% (1)
C
6% (1)
D
89% (16)

Why each option

IS-IS networks do not use the concept of a Backup Designated Router (BDR); instead, they utilize a Designated Intermediate System (DIS) on multi-access segments.

AIt forms an adjacency only with the DR

This is incorrect because IS-IS does not have a BDR role.

BIt forms adjacencies with all routers

This is incorrect because IS-IS does not have a BDR role.

CThe BDR only becomes adjacent when the DR is down

This is incorrect because IS-IS does not have a BDR role.

DThere is no BDR in IS-ISCorrect

IS-IS uses a Designated Intermediate System (DIS) on multi-access segments for pseudo-node functionality and route distribution, but it does not have a separate BDR role for redundancy as seen in OSPF. All other routers form adjacencies directly with the DIS.

Concept tested: IS-IS DR/BDR concept

Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_isis/configuration/15-s/irs-15-s-book/irs-config-isis.html

Topics

#IS-IS#Designated IS (DIS)#Adjacencies#Routing Protocol Concepts

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