Which three BGP attributes are well known and mandatory?

BGP Path Attributes

• Well-Known Mandatory (for example: Origin, AS Path, and Next Hop)
• Well-Known Discretionary (for example: Local Preference)
• Optional Transitive (for example: Community)
• Optional Non-Transitive (for example: Cluster List)

What is the most preferred attribute for BGP?

BGP Best Path Selection Algorithm

• A path with the highest Weight attribute is preferred (other vendors ignore this attribute).
• A path with the highest “local preference” is preferred (usually set to 100).

How many attributes are there in BGP?

Four
BGP Attributes. BGP chooses a route to a network based on the attributes of its path. Four categories of attributes exist as follows: Well-known mandatory: Must be recognized by all BGP routers, present in all BGP updates, and passed on to other BGP routers.

What are the well known communities of the BGP community attribute?

Here are the 4 well known BGP communities:

• Internet: advertise the prefix to all BGP neighbors.
• No-Advertise: don’t advertise the prefix to any BGP neighbors.
• No-Export: don’t advertise the prefix to any eBGP neighbors.
• Local-AS: don’t advertise the prefix outside of the sub-AS (this one is used for BGP confederations).

What is BGP Aigp?

AIGP is a non-transitive attribute that includes the accumulated IGP metric. BGP routers advertise this AIGP metric to neighbors in other ASes. This allows BGP routers to select the best path based on the end-to-end IGP metric. To make this possible, AIGP makes some changes to the BGP best-path algorithm.

What is a BGP attribute and where is it used?

BGP attribute LOCAL_PREF used to determine best exit path for an autonomous system. LOCAL_PREF is best BGP algorithm used to Influence the outbound traffic path towards each destination when there are multiple redundant paths via multiple router in an autonomous system.

How do I set BGP attributes?

BGP Table path selection

1. Prefer the highest local-preference value.
2. Prefer the shortest AS-path length.
3. Prefer the lowest origin value.
4. Prefer the lowest MED value.
5. Prefer routes learned from an EBGP peer over an IBGP peer.
6. Prefer best exit from AS.
7. For EBGP-received routes, prefer the current active route.

Why do we need BGP synchronization?

BGP synchronization is an old rule from the days where we didn’t run IBGP on all routers within a transit AS. The routers within AS2 are configured with OSPF, this is required since R2/R4 have to be able to reach each other to establish the IBGP session.

What is BGP standard community?

A BGP community is an optional, transitive BGP attribute that is recognized and passed to other BGP peers. You might see a BGP community as a tag attached to the BGP routes exchanged between two BGP peers. ‍ To get started, let’s look at what a BGP community set to a route looks like in an Update message.

Does BGP need IGP?

BGP requires TCP transport since it doesn’t have it prepriority mechanisms such as OSPF or EIGRP per say. I always thought that we need IGP as underlay for BGP to work.

Why is IGP used in BGP?

IGP is used to establish and distribute routing information to routers within Autonomous System (AS), the most common routing protocols within this category are RIP (Routing Information Protocol) and OSPF (Open Shortest Path First) [2]. BGP is used to route traffic between ASs within the internet.

What are different BGP message types?

BGP runs by sending five types of messages: Open, Update, Notification, Keepalive, and Route-refresh. These messages use the same header format.