BGP neighbors are not in an established state

[TCC_2]

Core Issue

These issues may prevent the Border Gateway Protocol (BGP) neighbors from being established:

• The neighbor IP address or Autonomous System (AS) number is incorrect.
• In a non-directly connected neighbor, no routes to the neighbor IP address exist, or the default route (0.0.0.0/0) is used to reach the peer.
• The neighbor update-source command is missing under the BGP.
• The typing error results in the wrong IP address or as-number in the neighbor statement. Check your configurations.
• The unicast is broken due to one of these reasons:
  • The wrong Virtual Circuit (VC) maps in an ATM or Frame Relay environment and in a highly redundant network.
  • The Access Control List (ACL) blocks the unicast or Transmission Control Protocol (TCP) packet at port 179.
  • The Network Address Translation (NAT) runs on the router and translates the unicast packet.
  • Layer 2 is down.
  • The lack of the neighbor ebgp-multihop command keeps the peers from coming up.

Resolution

To resolve this issue, refer to Why Do BGP Neighbors Toggle Between Idle, Connect, and Active States?.

show ip bgp neighbors {neighbor  address}

State is active