This attribute identifies the autonomous systems through which routing information carried in the Update message has passed. NOTE: The current implementation supports using the neighbor allow-as-loop command to receive routes containing the local AS number. It involves three types of values, as shown in the following figure.
When a BGP router obtains multiple routes to the same destination but with different next hops, it considers the route with the smallest MED value the best route if other conditions are the same.
It indicates the priority of a BGP router. It identifies a collection of destination addresses having identical attributes, without physical boundaries in between, and having nothing to do with the local AS. Well known community attributes involve:. By default, all routes belong to the Internet community. Routes with this attribute can be advertised to all BGP peers.
After being received, routes with this attribute cannot be advertised out the local AS. Which path does the BGP take? Well, it starts with the Weight attribute which is at the very top of the BGP attributes list as shown in Table 2.
If one path has a better weight, the BGP selects that path as the best path. If the weight is equal, it moves down to the next attribute Local Preference. If one path has a better local preference, it selects that path as the best path.
If the local preference is equal, it moves down to the next attribute on the list, until we have a tiebreaker to select the best path. We will go through each attribute in detail. The Weight attribute is applied to inbound routes, where decisions about the best exit outbound path are made. Here are the key points you need to know about Weight:. A route originating on the local router will be assigned a weight of , by default.
All other routes will be assigned a weight of 0, by default. Using the diagram in Figure 1. It is applied to inbound external routes, where decisions about the best exit outbound path for an autonomous system are made. Here are some key points you need to know about Local Preference:.
Users can always make an informed choice as to whether they should proceed with certain services offered by Cisco Press. If you choose to remove yourself from our mailing list s simply visit the following page and uncheck any communication you no longer want to receive: www.
While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest pearson.
California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.
This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site. Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.
We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting.
Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance.
Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions. All rights reserved. Cisco Press. Join Sign In. Date: Mar 24, For example, AS path, origin, and next hop. 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.
If not recognized, it is marked as partial, for example, aggregator, community. Table lists common BGP attributes, their meanings, and their category. Table Origin How BGP learned of this network. Multi-Exit Discriminator MED Suggests to a neighboring autonomous system which of multiple paths to select for traffic bound into your autonomous system.
Weight Cisco proprietary, to tell a router which of multiple local paths to select for traffic leaving the AS. To do so, it examines the path attributes of any loop-free, synchronized if synchronization is enabled routes with a reachable next-hop in the following order: Choose the route with the highest weight. If weight is not set, choose the route with the highest local preference.
Choose routes that this router originated. Choose the path with the shortest Autonomous System path. However it evaluates one of the attributes that was changed due to matching a specific community. Start a Trial Log In. Catchpoint Platform. Monitoring Use Cases. Synthetic Monitoring. Monitor everything from development to production that can affect your end-user experience. Real User Monitoring. Resolve performance issues faster, optimize conversions, and make better business decisions.
Network Insights. Get complete visibility of every network layer to detect and resolve issues quickly. Endpoint Monitoring. Monitor your end-to-end employee experiences starting from their devices. Case Studies. Guide to Synthetic Monitoring. Guide to Network Admin. Want to know how to boost your website performance?
Who We Are. Log In. Log In Log In. Chapter 4. Introduction The Border Gateway Protocol BGP is responsible for finding the best route for data transmission between two endpoints connected across the internet.
0コメント