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400-007 · Question #274

Company XYZ is running BGP as their routing protocol. An external design consultant recommends that TCP path MTU discovery be enabled. Which effect will this have on the network?

The correct answer is C. It will improve the convergence time. Enabling TCP path MTU discovery for BGP prevents packet fragmentation on the path, allowing BGP UPDATE messages to be exchanged more efficiently and improving routing convergence time.

Designing Network Infrastructure

Question

Company XYZ is running BGP as their routing protocol. An external design consultant recommends that TCP path MTU discovery be enabled. Which effect will this have on the network?

Options

  • AIt will create a loop free path
  • BIt will enhance the performance of TCP-based applications
  • CIt will improve the convergence time
  • DIt will increase the convergence time

How the community answered

(19 responses)
  • A
    11% (2)
  • B
    5% (1)
  • C
    79% (15)
  • D
    5% (1)

Why each option

Enabling TCP path MTU discovery for BGP prevents packet fragmentation on the path, allowing BGP UPDATE messages to be exchanged more efficiently and improving routing convergence time.

AIt will create a loop free path

Loop-free path calculation is handled by BGP's AS-path attribute and path selection process, not by TCP path MTU discovery, which only affects packet sizing.

BIt will enhance the performance of TCP-based applications

TCP path MTU discovery improves BGP control-plane efficiency, not the performance of data-plane TCP applications traversing the network.

CIt will improve the convergence timeCorrect

BGP runs over TCP, and TCP path MTU discovery allows the session to negotiate the largest packet size that traverses the path without requiring fragmentation. By eliminating fragmentation and reassembly overhead, BGP UPDATE messages are delivered faster and more reliably, reducing the time needed to exchange full routing tables and improving overall BGP convergence time.

DIt will increase the convergence time

Reducing fragmentation lowers BGP update exchange latency, which shortens convergence time rather than increasing it.

Concept tested: BGP TCP path MTU discovery impact on convergence

Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bgp/configuration/xe-16/irg-xe-16-book/bgp-support-for-tcp-path-mtu-discovery.html

Topics

#BGP#TCP path MTU discovery#convergence#routing optimization

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