Configure basic Border Gateway Protocol (BGP)

Source: Internet
Author: User

The basic Border Gateway Protocol (BGP) routing selection protocol is divided into two types: l Internal Gateway Protocol (IGP) l external Gateway Protocol (EGP) BGP is an Inter-Domain Routing Protocol, also known as EGP autonomous system, the same internal gateway protocol and unified measurement value are used to forward data packets within the AS, and an external gateway protocol is used to forward data packets to A group of vro autonomous systems in other a s, you can also use multiple metric values. From the perspective of BGP, an important feature of AS is that AS has a unified internal routing plan for another autonomous system and shows a consistent picture for its reachable destination. All parts within a s must be fully interconnected.
The indicator of the autonomous system is a 16-bit number ranging from 1 ~ 65535,64512 ~ The AS number of 65535 is reserved for private use. The main goal of BGP is to provide an Inter-Domain Routing System that can ensure the non-loop routing information exchange between autonomous systems. The BGP router exchanges information about the route path to the destination network. Comparison of scalable routing selection protocols: whether to systematically measure the Protocol's internal or external distance vector type/link state type. The OSPF internal link state is overhead (COST) EGIP internal advanced distance vector type no composite BGP external advanced distance vector type no path vector or attribute
When to use BGP? LAS allows data to pass through it to other Autonomous Systems lAS has multiple connections to other Autonomous Systems l must control the data streams entering and leaving the AS. BGP is designed to allow communications between ISPs and when does BGP be used for Packet Exchange? L only a single connection to the Internet or another AS; l no need to consider routing policies or routing selection; l vro lacks regular bgp update memory or processor l limited understanding of Route filtering and BGP path selection processes l low bandwidth between Autonomous Systems
BGP terms and concepts: BGP uses the transmission control protocol TCP, which is self-bound to its transfer layer protocol. This can provide reliable edge-oriented transmission, and BGP uses TCP port 179. On the reliable listening link, it does not need regular route updates, so the update is triggered. B GP sends the keepalive message, which is similar to the hello message sent by OSPF and OSPF. The BGP router exchanges network accessibility information, which is called a path vector and consists of path attributes, including the full path list that the route should pass to the destination. BGP peers can be set in the AS system or in the AS system's external routing policies or rules. These policies are based on the routing information and the properties configured on the router. BGP requires that the BGP router can only advertise the routes used by the peer in the adjacent autonomous system. The router sends bgp update messages about the destination network. These update messages include information about BGP metric values, which are called Path attributes.
There are four types of path attributes: ---- accepted and compliant; lAS path (AS-path) type encoding 2; l next hop) type encoding 3 l origin type encoding 1 AS path attribute is used by BGP to ensure a non-loop environment; the next hop attribute describes the next hop IP address used to go to the destination. What is the penalty? The origin attribute defines the origin of the path information. It can have one of three values: 1. IGP-the ingress is inside the starting AS and expressed as I in the BGP table; 2. EGP-routes are learned through the external gateway protocol, expressed in E in the BGP table; 3. incomplete-the route origin is unknown or learned through other methods. What should I use in the BGP table? .
---- Accepted and self-determined; l local preference type code 5; it provides a router in AS with an indication of which path is preferentially selected AS the AS exit, it is the property configured on the router and can only be exchanged between routers in AS. The default value is 1 00 l Atomic aggregation (Atomic aggregate) type code 6 ---- optional, deliverable; l aggregator type code 7 l group type code 8 (Cisco defined) it is a method used to filter inbound or outbound routes, any BGP router can update the ingress or outbound route, or re-publish the ingress. Any BGP router can filter routes in inbound or outbound route updates based on group attributes, or select a preferred route.
---- Optional, non-transmitted. L Multi-exit-discriminator (MED) type code 4 MED is used to indicate the priority path to the external neighbors into the. The MED attribute is also called the PATH value. Source ID (Originator-ID) Type Code 9 (Cisco defined) Cluster list (Cluster list) type code 10 (Cisco defined) in addition, Cisco defines a weight attribute (Cisco-specific) for BGP. The weight attribute is a custom attribute defined by CISCO and is used for path selection. It is locally configured on the vro and targeted at different neighbors. It only provides local routing policies and cannot be passed to any B GP neighbor. The weight value ranges from 0 ~ 65535. The default value of the path originating from the local router is 32768. The default weight of other paths is 0, and routes with high weights are preferred. A recognized attribute is a type of attribute that must be recognized by all BGP implementations. Optional attributes are not required to be supported by all BGP implementations. It may be a private attribute. BGP synchronization is enabled by default in the current IOS version
Message Type of BGP: l open (open) -- version -- my Autonomous System -- Retention Time -- BGP identifier (vroid ID) -- optional parameter domain length -- optional parameter lKeepalive l Update (updata) -- undo route -- path attribute -- network-layer accessibility information l notification Keepalive messages are only composed of message headers, the length is 19 bytes. It is sent every 60 seconds by default. Messages of other types are between 19 bytes and 4096 bytes. The default retention time is 1 80 seconds. Configure BGP to activate the BGP protocol: router bgp autonomous-system identifies the peer router neighbor {ip-address | peer-group-name} remote-as autonomous-system that will be established with the local router to change the next hop attribute neighbor {ip-address | peer-group-name} next-hop-self disable BGP synchronization no synchronization create an inductive address aggregate-address ip-address mask [summary-only] In the BGP table [as-set] reset BGP clear ip bgp {* | address} [soft [in | out] show ip bgp display entries in the BGP Route table show ip bgp summary show all BGP connections status sh Ow ip bgp neighbors displays TCP and BGP connection information about neighbors. Dampening BGP attenuation Events BGP event Keepalives BGP keepalive Updates BGP UPDATE

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