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I have two questions pertaining to BGP. There are as follows;


Q.1 What are the advantages and disadvantages of a BGP free MPLS core?


Q.2. If a BGP neighbor is stuck in the Idle state, what steps would you take to correct to get into the Established state?


Pls, let me know. 

1 Reply 1

Leonid Voronkin
VIP Collaborator VIP Collaborator
VIP Collaborator


advantages of a BGP-Free Core

  • Core devices do not need to be capable of supporting a large number of IPv4/IPv6 routes, allowing you to deploy devices with limited RIB and FIB Capacity
  • As there is no BGP, Core devices will not be impacted by BGP-related issues, such as high CPU utilization during massive BGP re-convergence
  • By not running BGP, you eliminate one of the attack vectors – if a new BGP security vulnerability were to be discovered, Core devices would not be impacted
  • Operators’ mistakes associated with BGP configuration can be eradicated
  • New services such as MPLS VPN, IPv6, EVPN can be introduced without modifying the Core routers
  • If deployed properly, BGP-Free becomes unreachable from the Internet, making DDoS and hacking attacks against ISPs’ Core elements impossible

disadvantages of a BGP-Free Core

  • The edge of your network will be tunneling traffic over BGP-Free Core, meaning that edge devices must support some kind of a tunneling mechanism. Your current edge devices might not be able to do this, or there might be a performance penalty associated with tunneling
  • Increased links utilization is associated with tunnel overhead. Depending on the tunneling mechanism you chose and the average packet size on your network, you will see 1% to 5% link utilization increase associated with tunnels (4-bytes for single-label MPLS, 24-bytes for GRE)
  • It is expected that packets with the size of at least 1,500-bytes can be sent through a Service Provider’s network without fragmentation. You will need to increase interface MTU size on your Core-to-Core and Core-to-Edge links to accommodate tunneling header. Some L2 transport technologies might not allow you to do this
  • Because your core will no longer have BGP, you will not be able to connect customers directly to your core nodes. Although connecting customers to the core is a bad practice, many companies do this to save on cost
  • BGP-Enabled Edge is by far the most common scenario that goes hand-in-hand with BGP-Free Core. This means that your Edge devices will need to support BGP. This might not always be possible or might have a licensing cost associated with BGP features.
  • BGP-Free Core might lead to sub-optimal traffic flows, if not planned properly. We’ll talk about this in the next section




1. ip reachability

2. incorrect AS configuration

3. TCP port 179 allowed across the peers

4. multihop and peer TTL configurations

5. MTU stuff

6. BGP authentication


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