Question: What Are The BGP Attributes?

What is weight in BGP attributes?

The BGP Weight Attribute Weight is a value that is assigned to our prefixes as a locally significant value.

Weight is a simple number in the range of 0 through 65535, and the higher the weight value, the higher the preference for that path.

When the prefix is locally generated, it will get a weight of 32768..

What protocol does BGP use?

TCPAmong routing protocols, BGP is unique in using TCP as its transport protocol. When BGP runs between two peers in the same autonomous system (AS), it is referred to as Internal BGP (i-BGP or Interior Border Gateway Protocol).

What are two BGP Neighborship States?

They are:Idle – BGP resources are initialized by the router. … Connect – BGP waits for the 3WHS to complete. … Active – The ConnectRetry timer is reset, and BGP returns to the Connect state.OpenSent – BGP waits for an OPEN message from its peer. … OpenConfirm – BGP waits for a keepalive message from its peer.More items…•

What are the mandatory well known BGP attributes?

BGP AttributesWell-known mandatory: Must be recognized by all BGP routers, present in all BGP updates, and passed on to other BGP routers. … Well-known discretionary: Must be recognized by all BGP routers and passed on to other BGP routers but need not be present in an update, for example, local preference.More items…•

How do I set BGP attributes?

BGP Table path selectionPrefer the highest local-preference value.Prefer the shortest AS-path length.Prefer the lowest origin value.Prefer the lowest MED value.Prefer routes learned from an EBGP peer over an IBGP peer.Prefer best exit from AS.For EBGP-received routes, prefer the current active route.More items…

How does BGP choose the best path?

If there are no specific settings that can affect the outcome, BGP Best Path Selection Algorithm determines the best route by selecting the shortest path to the destination. An Autonomous System is a single network or a set of networks and routers, which are under the control of one administrative entity.

What are the BGP states?

BGP forms a TCP session with neighbor routers called peers. BGP uses the Finite State Machine (FSM) to maintain a table of all BGP peers and their operational status….The BGP session may report in the following states:Idle.Connect.Active.OpenSent.OpenConfirm.Established.

Which three BGP attributes are well known and mandatory?

BGP Attributes list:Type Code valueAttribute NameAttribute Type1ORIGINWell-known mandatory2AS_PATHWell-known mandatory3NEXT_HOPWell-known mandatory4MULTI_EXIT_DISC (MED)Optional non-transitive13 more rows•May 15, 2012

What are the BGP message types?

BGP makes use of four different message types to perform its function namely: OPEN, UPDATE, KEEPALIVE, and NOTIFICATION. Before we consider these message types, we must look at the BGP message header that is present before all these message types and that indicates the type of message contained in the BGP packet.

How many BGP attributes are there?

fourThere are four basic types of attributes: Well known mandatory attributes; these attributes must be recognized by all BGP speakers, and must be included in all update messages. Almost all of the attributes impacting the path decision process, described in the next section, are well known mandatory attributes.

What metric does BGP use?

Previous versions of BGP (v2 and v3) defined this attribute as the inter-AS metric (INTER_AS_METRIC) but in BGPv4 it is defined as the multi-exit discriminator (MULTI_EXIT_DISC). The MED is an unsigned 32bit integer. The MED value can be any from 0 to 4,294,967,295 (2^32-1) with a lower value being preferred.

Why is BGP used?

Border Gateway Protocol (BGP) is used to Exchange routing information for the internet and is the protocol used between ISP which are different ASes. The protocol can connect together any internetwork of autonomous system using an arbitrary topology.

What port is BGP?

Among routing protocols, BGP is unique in using TCP as its transport protocol. BGP peers are established by manual configuration between routing devices to create a TCP session on port 179. A BGP-enabled device periodically sends keepalive messages to maintain the connection.

What is BGP adjacency?

Just like OSPF or EIGRP, BGP establishes a neighbor adjacency with other BGP routers before they exchange any routing information. It will also start listening for a connection in case the remote BGP neighbor tries to establish a connection. … When successful, BGP moves to the Connect state.

What is BGP origin?

Origin. The origin attribute indicates the origin of a prefix and can take three values: the prefix originates from an interior routing protocol (IGP), it originates from EGP, the predecessor to BGP, or the origin is “incomplete”, if the prefix is learned through “other means”.

What is MED value in BGP?

MED is an optional nontransitive attribute. MED is a hint to external neighbors about the preferred path into an autonomous system (AS) that has multiple entry points. The MED is also known as the external metric of a route. A lower MED value is preferred over a higher value.

What algorithm does BGP use?

Introduction. Border Gateway Protocol (BGP) routers typically receive multiple paths to the same destination. The BGP best path algorithm decides which is the best path to install in the IP routing table and to use for traffic forwarding.

What are BGP Route Reflectors?

Route reflectors (RR) are one method to get rid of the full-mesh of IBGP peers in your network. The other method is BGP confederations. The route reflector allows all IBGP speakers within your autonomous network to learn about the available routes without introducing loops.

What are three valid BGP attributes?

BGP Attributes and Path SelectionWeight.Local Preference.Originate.AS path length.Origin code.MED.eBGP path over iBGP path.Shortest IGP path to BGP next hop.More items…

How does BGP use the next hop attribute?

The BGP nexthop attribute is the next hop IP address that is going to be used to reach a certain destination. For EBGP, the next hop is always the IP address of the neighbor specified in the neighbor command. … For IBGP, the protocol states that the next hop advertised by EBGP should be carried into IBGP.

How does BGP 4 Work?

How does BGP4 work? Unlike the majority of routing protocols, BGP4 is a connection-oriented protocol. When BGP4 is initiated on a router, it establishes a Transmission Control Protocol (TCP) connection with its neighboring router(s). Using this TCP connection, the router exchanges a complete copy of its routing table.