Basic knowledge of BGP

1. Characteristics

Use the Tcp179 port to build a neighbor, not to use multicast or broadcast, so you can only set up a neighbor by hand unicast

2. Four kinds of packages

Open package: For building a neighbor relationship, use only when building a neighbor, when the neighbor is established, no longer send

KeepAlive package: Used to keep a neighbor relationship, it plus open is equivalent to the IGP Hello package. Send once every 60 seconds, holdtime 180 seconds

Update package: Contains the update of the route, and the properties of the route

Notification Package: When an error occurs, use the package. The neighbor relationship is typically reset.

3. Neighbor State Machine

Idle: No BGP resources are allocated, incoming BGP connections are not allowed

CONNECT:TCP connection established successfully, waiting to send open package

Open sent: An open package has been sent to each other

Open confirm: Wait for each other's keepalive package, successfully receive, will become establish state

Active: Initializing a TCP connection to establish a BGP neighbor relationship

Establish: Neighbor relations have been established

Four reasons to be active:

A. Neighbors do not have a route to the update source interface of the local router

B. Neighbor's peer address configuration error, not the local Update source interface address

C. Neighbors did not configure the neighbor command

D.as Number Configuration Error

4. Why the routing is not excellent

There are two reasons: first, the IGP and BGP are not synchronized, and the second is not up to the next jump

Suboptimal routing: Not placed in routes, and not passed on to other neighbors

5. How to solve the suboptimal routing

Workaround: First, the IBGP neighbor full mesh, and turn off synchronization, and the second is to ensure that the Local has a route to the next hop attribute of the route

6. When is the route identified as R and when is it identified as s?

Identified as R: a route is learned at the same time through IGP and BGP, and the IGP management distance is smaller than the BGP management distance, and when the BGP table is viewed, such route entries are identified as R

Identified as S: a suppressed route that, when using aggregations, carries the supp map parameter, and the route permit by the Route-map is identified as S, noting that Route-map is used at this time and that no empty statement needs to be written to match other routes.

This article is from the "Divine Strategy" blog, please be sure to keep this source http://liu008qing.blog.51cto.com/151315/463422