BGP Message Type and BGP Configuration

Source: Internet
Author: User

BGP Message Type and BGP * BGP Message Type-Open: used to establish the connection relationship between BGP peers-Keepalive: periodically sends Keepalive messages to BGP peers, used to maintain the connection validity -- Update: carries the route Update (delete, add) Information -- Notification: When BGP detects an error, it sends a Notification message to the peer, then the BGP connection will be immediately closed * BGP status-when a BGP session is established, the relationship between the router and its neighbors goes through the following status: * Idle (Idle): the router views the route table, * Connect: the router discovers the route and completes the three-way handshake of the TCP connection * Open sent (enable and send ): send the connection parameter * Open confirm (Open confirmation) between BGP sessions: the router receives the confirmation of the connection parameter consistency * Established (Established): Build a neighbor relationship Configure the BGP command Router (config) # router bgp autonomous-system -- this command cannot activate BGP -- only one autonomous system can be configured on a vro -- the autonomous system number is used to identify which autonomous system The vrobgp belongs. ID is also used to identify whether the future specified neighbor relationship is an IBGP relationship or an EBGP relationship Router (config-router) # neighbor {ip-address | peer-group-name} remote-as -- specifies the AS number specified after the peer Router -- remote-as that establishes a session with the parent router, it is used to determine whether the specified neighbor is an IBGP neighbor or an EBGP neighbor relationship. The IP address is the destination address of all BGP groups to which the neighbor router belongs. The neighbor relationship must be established, both IBGP and EBGP must ensure that the neighbor is reachable. Both EBGP and IBGP need this command to establish the neighbor * BGP disable the neighbor relationship Router (config-router) # neighbor {ip-address | peer-group-name} shutdown -- disable the neighbor relationship through management (note: the neighbor relationship is not deleted) -- If you want to modify the policy of a neighbor Router, You need to disable the neighbor relationship, and then re-enable the neighbor relationship router (config-Router) # no neighbor {ip-address | peer-group-name} shutdown -- enable neighbor Relationship * BGP configuration Tips When configuring IBGP, generally use the address of the loop back port to specify the neighbor, however, you must specify the source IP address, while EBGP generally uses the address of the physical port of the direct connection to specify the neighbor. * Update source address of BGP neighbor (used in IBGP configuration) Router (config-router) # neighbor {ip-address | peer-group-name} update-source interface-type interface-number -- this command is used to specify the BGP process to use the update address as the update source address for the neighbor -- usually use the loopback address as the update source address, because the loopback address is always available-there must be a route to the update source in the two routers-usually only between the two routers-by default, the EBGP neighbor relationship requires direct connection, the loopback address is not directly connected to each other for EBGP. If EBGP uses loopback to build a neighbor, you must specify multiple hops. * BGP synchronization-synchronization rule: only when the route learned from the IBGP neighbor appears in the local route selection table, the BGP process adds the device to the IP Route Selection table -- ensure the consistency of the AS internal route information -- avoid the black hole problem -- if the full Internet IBGP is running, you can disable the synchronization Router (config-router) # no synchronization -- disable synchronization to reduce the number of routes advertised by IGP and increase the BGP aggregation speed. The default value is disabled (that is, the default value is non-synchronous) Router (config-router) # synchronization * view BGP Router # show ip bgp summary // view BGP summary information * Clearing the BGP Session -- When policies ies such as access lists or attributes are changed, the change takes effect immediately, and the next time that a prefix or path is advertidrf or received, the new policy is used. it can take a long time for the policy to be applied to all networks. -- You must trigger an update to ensure that the policy is immediately applied to all affected prefixes and paths. -- Ways to trigger an update * Hard reset * Soft reset * Route refresh * Hard Reset of BGP Sessions (disconnect all connections) router # clear ip bgp * -- Resets all BGP connections with this router -- Entire BGP forwarding table Is discarded -- BGP session makes the transition from established to Idle; everything must relearned Router # clear ip bgp {neighbor-address} -- Resets only a single neighbor -- BGP session makes the transition from established to Idle; everything from this neighbor must be relearned -- Less severe than clear ip bgp ** Soft Reset Outbound (Force refresh route table) router # clear ip bgp {* | neighbor-address} [soft out] -- Routes learned from this neighbor are not lost -- This router resends all BGP information to the neighbor without resetting the connection -- the connection remains establlshed -- This option is highly recommended when you are changing outbound policy -- The soft out option does not help if you are changing inbound policy

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