Cisco® CCNP Routing Exam Notes : Route Reflector, Bgp Updates, External And Summary Routes, And Bgp Commands.
41. When a route reflector in a BGP AS receives an update, it takes the following actions, depending on the type of peer that sent the update:
- If the update is from a non-client peer : It sends the update to all clients in the cluster.
- If the update is from a client peer: It sends the update to all nonclient peers and to all client peers.
- If the update is from eBGP peer: It sends the update to all nonclient peers and to all client peers.
42. The following are well known communities in BGP:
- Internet: All routers belong to this community by default. Advertises the route to internet community.
- No-export: This indicates not to advertise a route to eBGP
- No-advertise: This indicates not to advertise a router to peers.
The community attribute in BGP can contain a value in the range 0 to 4294967200.
43. The correct syntax to configure a router as a BGP route reflector is:
RouterA(config-router)#neighbor <ip-address> route-reflector-client
Here, it is:
RouterA(config-router)#neighbor route-reflector-client 184.108.40.206
The above command will configure RouterA as a route reflector with the specified neighbor 220.127.116.11 as the route reflector's client.
44. Methods available for filtering BGP updates:
- Distribute lists: To restrict the routing information can be filtered based on routing updates to/from a particular neighbor. An access list that is applied to updates to/from a neighbor serves as a filter.
- AS_Path filtering: Here, you specify an access list on both incoming and outgoing updates based on the value of the AS_path attribute.
- Route Map Filtering: Here, the "neighbor route-map" command is used to apply a route map to incoming and outgoing routes.
- Community Filtering: You can filter by setting the community attribute on router updates.
45. External and summary routes are not injected into a totally stubby area in an OSPF network. The advantages of totally stubby areas are reduced routing tables, faster convergence, and stability.
46. To enable the synchronization between Border Gateway Protocol (BGP) and Interior Gateway Protocol (IGP) system, synchronization command is used. To advertise a network route without waiting for the IGP, use the no synchronization command. By default, synchronization is enabled.
The following router configuration mode is an example that enables a router to advertise a network route without waiting for the IGP:
router bgp 160
47. Show ip bgp neighbors is a command most often used to see neighbor details, which include the following:
- AS number,
- BGP messages received / sent
- Hold time, Keepalive intervals
- Remote router ID etc.
48. BGP AS-PATH length:
You can increase the AS-PATH length by adding dummy AS numbers.
The route map configuration command:
set as-path prepend 100
causes a router to prepend 100 once to the value of the AS_path attribute before it sends updates to the specified neighbor.
If you want to prepend 100 twice, use the command
set as-path prepend 100 100
This will increase the AS-PATH length in the updates being sent to the neighbor and hence the path selection.
49. BGP Distribute lists are created using IP standard access lists and IP extended access lists. The range of numbers for standard access list is 1 to 99 and extended access list is 100 to 199. Therefore, the allowed range of numbers is 1 to 199.
50. EIGRP uses multicasts to send queries to neighbor routers.