400-007 · Question #79
An enterprise network has two core routers that connect to 200 distribution routers and uses full- mesh IBGP peering between these routers as its routing method. The distribution routers are…
The correct answer is A. Implement route reflectors on the two core routers. Full-mesh IBGP between 202 routers creates an unsustainable number of peering sessions and BGP update processing load, and route reflectors resolve this by centralizing update distribution with only configuration changes.
Question
An enterprise network has two core routers that connect to 200 distribution routers and uses full- mesh IBGP peering between these routers as its routing method. The distribution routers are experiencing high CPU utilization due to the BGP process. Which design solution is the most cost effective?
Options
- AImplement route reflectors on the two core routers
- BIncrease the memory on the core routers
- CImplement e BGP between the core and distribution routers
- DIncrease the memory on the distribution routers
- EIncrease bandwidth between the core routers
How the community answered
(64 responses)- A75% (48)
- B13% (8)
- C8% (5)
- D2% (1)
- E3% (2)
Why each option
Full-mesh IBGP between 202 routers creates an unsustainable number of peering sessions and BGP update processing load, and route reflectors resolve this by centralizing update distribution with only configuration changes.
Configuring the two core routers as route reflectors eliminates the full-mesh IBGP requirement, reducing each distribution router's IBGP peer count from 201 down to 2 sessions. This directly eliminates the BGP process CPU overhead caused by maintaining hundreds of sessions and processing redundant updates on every distribution router. It is the most cost-effective fix because it requires only configuration changes - no hardware purchases.
Increasing memory on the core routers does not address CPU utilization on the distribution routers, which are the devices experiencing the high BGP process load.
Implementing eBGP between core and distribution routers requires assigning separate AS numbers to network segments and fundamentally restructures the routing design, adding complexity without efficiently resolving the CPU issue.
Increasing memory on distribution routers addresses RAM capacity constraints, not CPU cycles consumed by maintaining a large number of IBGP sessions and processing BGP updates.
Increasing bandwidth between the two core routers does not reduce the number of IBGP sessions or the BGP update processing burden on the distribution routers.
Concept tested: BGP route reflectors eliminating full-mesh IBGP overhead
Source: https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/26634-bgp-toc.html
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