What is BGP protocol interview questions and answers?
The values of the following characteristics are used to choose BGP paths:
Table of Contents
- Weight.
- Local Preference (highest local value will be preferred, the default value is 100)
- Originate.
- AS path length.
- Origin code.
- Multi-Exit Discriminator (MED)
- eBGP path over iBGP path.
- Shortest IGP path to BGP next-hop.
Which algorithm is used in BGP?
A BGP router forms a neighbor relationship by connecting to its neighbors and exchanging the routes, once the connection is established. BGP Best Path Selection Algorithm is used to choose and install the best routes into the router’s routing table.
How many types of BGP are there?
In a network with route reflectors, there are three types of BGP routers: Route reflectors. Route reflector clients. Non-client peers.
What are the two most important BGP attributes?
BGP Attribute Categories
Well-known mandatory:Recognized by all BGP peers, passed to all peers, and present in all Update messages. Well-known mandatory attributes include:- Next-hop- Origin- AS PATH. Well-known discretionary:Recognized by all routers, passed to all peers, and optionally included in the Update message.
What is BGP port number?
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.
What is split horizon in BGP?
The BGP split-horizon rule states that a BGP router that receives a BGP route via an iBGP peering shall not advertise that route to another router that is an iBGP peer. It is important that you commit this rule to memory. By doing so, you will be able to recognize when this is the reason for missing routes.
What OSI layer is BGP?
BGP in networking is based on TCP/IP. It operates on the OSI Transport Layer (Layer 4) to control the Network Layer (Layer 3).
Why is BGP slow protocol?
Keep in mind, though, BGP is a “slow to converge” protocol. Routing changes on the Internet occur all the time. If BGP had to react to every change, it would flood the Internet with routing updates that could slow traffic all over the globe. So, BGP plays a waiting game to give routes time to settle down.
What is BGP hold time?
The default value for the hold time suggested in the BGP specification (RFC 4271) is 90 seconds, and keepalives should be sent at intervals of one third the hold time (30 seconds). However, Cisco uses defaults of 180 and 60 seconds.
What are the four types of BGP messages?
To do all of this, BGP uses 4 messages:
- Open Message.
- Update Message.
- Keepalive Message.
- Notification Message.
What is the default weight in BGP?
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. Otherwise, the default weight is 0 for a prefix.
Is BGP TCP or UDP?
TCP
BGP uses TCP port 179 to communicate with other routers. TCP allows for handling of fragmentation, sequencing, and reliability (acknowledgement and retransmission) of communication packets.
What is BGP backdoor?
The term “backdoor” is a very controversial term when it comes to privacy and security. However, when it comes to BGP, it is a well-known feature that is used to change the administrative distance of eBGP in order for an interior gateway routing protocol (IGP) to take precedence over an eBGP route.
What is Synchronisation rule in BGP?
The BGP synchronization rule states that if an AS provides transit service to another AS, BGP should not advertise a route until all of the routers within the AS have learned about the route via an IGP.
What is BGP flapping?
BGP Flapping can occur when you have an unstable peer. This occurs when the BGP route disappears and reappears in the routing table. There is a NetScreen configuration setting that addresses this issue. This is a flap-damping setting, which stalls the advertisement of a route.
Why BGP convergence is slow?
Failure detection and propagation by means of BGP mechanics is slow, and depends on the number of affected prefixes. Therefore, the more severe is the damage, the slower it is propagated. Some other, non-BGP mechanism needs to be used to report network failures and trigger BGP re-convergence.
Why BGP is preferred over OSPF?
BGP and OSPF are two of the most common routing protocols. While BGP excels with dynamic routing for large networks, OSPF offers more efficient path choice and convergence speed.
What is BGP incomplete?
Incomplete means that BGP is unsure of exactly how the prefix was injected into the topology. The most common scenario here is that the prefix was redistributed into Border Gateway Protocol from some other protocol, typically an IGP.
What is origin in BGP?
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 port does BGP use?
port 179
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.
What is black hole in BGP?
BGP blackhole filtering is a routing technique used to drop unwanted traffic. Black holes are placed in the parts of a network where unwanted traffic should be dropped.
What is BGP split horizon rule?
Why is BGP stuck in idle state?
In state Idle, the router is currently not trying to set up a BGP session. Reasons for this can be that there is no route towards the neighbor, or the neighbor refused an earlier connection attempt.
Do BGP routes expire?
Like any distance-vector protocol, BGP routing process accepts multiple incoming routing updates, and advertises only the best routes to its peers. BGP does not utilize periodic updates, and thus route invalidation is not based on expiring any sort of soft state information (e.g prefix-related timers like in RIP).
Why BGP is used in MPLS?
BGP carries routing information for the network and MPLS labels, whereas MPLS transports the data traffic. Figure 1 shows a typical scenario. The service provider backbone comprises two types of routers: Provider edge routers (PE routers)