Contents
- 1 Which class of BGP path attributes is supported by all BGP implementations and is not advertised between autonomous systems?
- 2 How does it use the AS path attribute?
- 3 What is next hop self BGP?
- 4 Why use BGP next hop self?
- 5 When to use weight attribute in router routing?
- 6 When to use as-path manipulation as path prepend?
Which class of BGP path attributes is supported by all BGP implementations and is not advertised between autonomous systems?
Several communities are defined as well known, or global, communities, which should be recognized by all BGP implementations: The NO_EXPORT community, which states that the group of routes marked with this community should not be advertised outside of the local autonomous system.
How does it use the AS path attribute?
The BGP AS path is a well-known mandatory attribute, which means that it’s present for all prefixes exchanged between BGP neighbors. So the AS path lists all the ASes that need to be traversed to reach the location where the prefix that the path is attached to is advertised from.
How many path attributes are there in BGP?
This BGP router has 5 paths for network 1.0….Attributes.
| Priority | Attribute |
|---|---|
| 7 | eBGP path over iBGP path |
| 8 | Shortest IGP path to BGP next hop |
| 9 | Oldest path |
| 10 | Router ID |
What are the mandatory well-known BGP attributes?
There are four categories of BGP attributes:
- Well-known mandatory: Recognized by all BGP peers, passed to all peers, and present in all Update messages.
- Well-known discretionary: Recognized by all routers, passed to all peers, and optionally included in the Update message.
- Optional transitive:
- Optional non-transitive:
What is next hop self BGP?
When a BGP router reports itself as the next hop, whether because of an explicit neighbor next-hop-self configuration or implicitly as a result of participating in an EBGP session, BGP allocates a new in label and adds an entry to the MPLS forwarding table, creating a label-to-next-hop mapping.
Why use BGP next hop self?
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. In the above example, RTC will advertise 170.10.
How does the as _ PATH attribute work in BGP?
AS_PATH attribute is like a path-vector routing protocol like RIP protocol which calculate HOP (Here BGP consider one Autonomous System as Hop) to determine the best path to a destination. BGP router adds it’s own AS number to the AS_PATH sequence when it advertise the update to a neighbor in another AS.
Which is the best attribute for path selection?
Weight attribute is designated for a best path selection process where highest weight is preferred. The Weight attribute is also used to manipulate traffic going out of your Autonomous System but this attribute is local to the router on which it is configured and is not exchanged with any IBGP or EBGP peers.
When to use weight attribute in router routing?
Weight attribute is a Cisco proprietary and can be used where only have cisco router in you networking domain. Weight attribute is designated for a best path selection process where highest weight is preferred.
When to use as-path manipulation as path prepend?
This can come as a workaround if a specific path is required to be followed, and other means like Multi-Exit Discriminator (MED) is not supported. By the help of AS-Path Prepend you are going to add the virtual AS’s between your path so that BGP will again look for the best path and re-route the traffic from the other reachability path.