Cisco 3560G 48TS Software Configuration Guide - Page 659

Chapter 30 Configuring IP Unicast Routing Configuring BGP 3. Prefer the route with the highest local preference. Local preference is part of the routing update and exchanged among routers in the same AS. The default value of the local preference attribute is 100. You can set local preference by using the bgp default local-preference router configuration command or by using a route map. 4. Prefer the route that was originated by BGP running on the local router. 5. Prefer the route with the shortest AS path. 6. Prefer the route with the lowest origin type. An interior route or IGP is lower than a route learned by EGP, and an EGP-learned route is lower than one of unknown origin or learned in another way. 7. Prefer the route with the lowest multi -exit discriminator (MED) metric attribute if the neighboring AS is the same for all routes considered. You can configure the MED by using route maps or by using the default-metric router configuration command. When an update is sent to an IBGP peer, the MED is included. 8. Prefer the external (EBGP) path over the internal (IBGP) path. 9. Prefer the route that can be reached through the closest IGP neighbor (the lowest IGP metric). This means that the router will prefer the shortest internal path within the AS to reach the destination (the shortest path to the BGP next-hop). 10. If the following conditions are all true, insert the route for this path into the IP routing table: • Both the best route and this route are external. • Both the best route and this route are from the same neighboring autonomous system. • maximum-paths is enabled. 11. If multipath is not enabled, prefer the route with the lowest IP address value for the BGP router ID. The router ID is usually the highest IP address on the router or the loopback (virtual) address, but might be implementation-specific. Beginning in privileged EXEC mode, follow these steps to configure some decision attributes: Step 1 Step 2 Step 3 Step 4 Step 5 Step 6 Command Purpose configure terminal Enter global configuration mode. router bgp autonomous-system Enable a BGP routing process, assign it an AS number, and enter router configuration mode. bgp best-path as-path ignore (Optional) Configure the router to ignore AS path length in selecting a route. neighbor {ip-address | peer-group-name} next-hop-self (Optional) Disable next-hop processing on BGP updates to a neighbor by entering a specific IP address to be used instead of the next-hop address. neighbor {ip-address | peer-group-name} weight weight (Optional) Assign a weight to a neighbor connection. Acceptable values are from 0 to 65535; the largest weight is the preferred route. Routes learned through another BGP peer have a default weight of 0; routes sourced by the local router have a default weight of 32768. default-metric number (Optional) Set a MED metric to set preferred paths to external neighbors. All routes without a MED will also be set to this value. The range is 1 to 4294967295. The lowest value is the most desirable. 78-16156-01 Catalyst 3560 Switch Software Configuration Guide 30-51