352-001 · Question #6
You are deploying OSPF on a point-to-multipoint Frame Relay network. The remote sites do not need to be able to communicate with each other and there are a relatively small number of sites (scaling…
The correct answer is B. Configure the link as OSPF broadcast and configure the hub router to always be the designated router. For a hub-and-spoke Frame Relay topology where spokes do not need direct communication, OSPF broadcast mode with the hub as DR minimizes extra routing overhead and simplifies configuration. Point-to-multipoint injects additional host routes, and NBMA requires manual neighbor…
Question
You are deploying OSPF on a point-to-multipoint Frame Relay network. The remote sites do not need to be able to communicate with each other and there are a relatively small number of sites (scaling is not a concern). How should you configure OSPF for this topology to minimize the additional routing information injected into the network and keep the configuration size and complexity to a minimum?
Options
- AConfigure the link at the hub router as OSPF point-to-multipoint and at the remote routers as OSPF point-to-
- BConfigure the link as OSPF broadcast and configure the hub router to always be the designated router.
- CConfigure the link as OSPF nonbroadcast and manually configure each of the remote sites as a neighbor.
- DConfigure the link as OSPF broadcast and configure a mesh group towards the remote routers.
How the community answered
(42 responses)- A7% (3)
- B74% (31)
- C5% (2)
- D14% (6)
Why each option
For a hub-and-spoke Frame Relay topology where spokes do not need direct communication, OSPF broadcast mode with the hub as DR minimizes extra routing overhead and simplifies configuration. Point-to-multipoint injects additional host routes, and NBMA requires manual neighbor statements.
Mixing OSPF network types (point-to-multipoint at hub and point-to-point at remotes) causes adjacency failures because both sides of a link must use the same OSPF network type to form a neighbor relationship.
Configuring OSPF broadcast mode on the Frame Relay hub and forcing the hub to always be the Designated Router (DR) is ideal for this topology because all spoke-to-spoke traffic flows through the hub anyway. Unlike point-to-multipoint mode, broadcast mode does not inject additional /32 host routes into the OSPF database, minimizing routing information. Unlike NBMA mode, broadcast mode does not require manual neighbor configuration, keeping the configuration small and simple.
OSPF nonbroadcast (NBMA) mode requires manually configuring each remote site as a neighbor with the 'neighbor' command, which increases configuration complexity - the opposite of what is required.
Mesh groups are a concept from IS-IS and certain NBMA configurations, not a standard OSPF broadcast configuration option, making this technically inapplicable.
Concept tested: OSPF network type selection for hub-and-spoke Frame Relay
Source: https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13695-7.html
Topics
Community Discussion
No community discussion yet for this question.