Dshow memory

7-86 Configuring BGP on Cisco Routers (BGP) v3.2 2005, Cisco Systems, Inc. Q5) The output of a show interfaces fastethernet 0 0 command follows Fast Ethernet0 is up, line protocol is up Hardware is DEC21140, address is 0000.0c0c.1111 (bia 0 0 02.eaa3.5a60) Internet address is 112.64.101.17 2 55.255.255.240 MTU 1460 bytes, BW 100000 Kbit, DLY 100 usec, rely 255 255, load 200 255 Encapsulation ARPA, loopback not set, keepalive not set, hdx, 100BaseTX ARP type ARPA, ARP Timeout 4 00 00 Last input...

Module Self Check

Use the questions here to review what you learned in this module. The correct answers and solutions are found in the Module Self-Check Answer Key. Q1) Which three characteristics are common to typical service provider networks (Choose three.) (Source Scaling IGP and BGP in Service Provider Networks) A) The provider network uses two IGPs, one for customer routes and one for internal provider routes. B) Service providers exchange routes with other providers using BGP. C) Service providers run...

Example Peer Group Requirements Edge Router at a Peering Point

This example illustrates an edge router at a peering point. The edge router that is located in the network where the service provider exchanges routes with other service providers is also a suitable place to use peer groups. From the edge router, the service provider AS can peer with a large number of other service providers. All peering autonomous systems should receive the same set of routes, namely the routes local to the service provider AS and the routes that are received from customer...

Define communities that signal individual goals

- Community 387 17 is used to indicate that the local preference of the route should be lowered to 50. This table lists the goals and the community values. This table lists the goals and the community values. Prepend the AS path once when sending the network to external neighbors. Prepend the AS path twice when sending the network to external neighbors. Prepend the AS path three times when sending the network to eXternal neighbors. All customers of the service provider should know this list so...

Default Return Path

Result The return traffic flows over the path with the shortest AS-path length. Result The return traffic flows over the path with the shortest AS-path length. If no BGP path selection tools are configured on the route to influence the traffic flow, AS 387 will use the shortest AS path. This action will result in unwanted behavior because the return traffic to AS 213 will be sent over the low-speed WAN link. AS 213 announces network 10.0.0.0 8 over EBGP sessions to both AS 462 and AS 387. When...

Proper Return Path Selection

Q How do you select the proper return path from AS 387 A Use local preference in AS 387. Q How do you select the proper return path from AS 387 A Use local preference in AS 387. Q Will the administrator of AS 387 configure it A Unlikely. Remember that the incoming traffic flow (from the perspective of AS 213) will be a result of the route selection for outgoing traffic in AS 387. The traffic that is going out from AS 387 will end up as incoming traffic in AS 213. If AS 387 configures some...

Primary Backup Link Selection

This topic describes how you can implement a typical backup setup between a multihomed customer and multiple service providers in a BGP environment. When using BGP on multiple links between a customer and several service provider networks, the customer is solely responsible for controlling the use of the links between them for outgoing traffic. The customer chooses whether to use these links in a primary backup or a load-sharing configuration. If one link is primary and the other is used for...

Always works

To remove incoming traffic from the backup link, the customer must influence route selection in the backup AS. The backup ISP must be forced to prefer the primary path to reach the customer network, although this choice means selecting a route with a longer AS path. One way to influence route selection is to use local preference in the network of the backup ISP. Using local preference creates an administrative scalability issue if each customer requires its use, because the ISP must maintain...

Static Route Propagation Static Routes on the Provider Edge Router

The show ip route command displays information from the routing table about subnet 11.2.3.0 24. The route is learned by static configuration and is redistributed via BGP. The router, through the use of a statically assigned tag, has assigned a tag value of 1000 to the customer route, and the route must pass through the route-map into BGP before being inserted into the BGP table. The show ip bgp command displays information from the BGP table about subnet 11.2.3.0 24. The route is local within...

IBGP Scalability Issues in a Transit AS

This topic explains the need for BGP route reflectors by describing the scalability issues of BGP transit backbones. Classic Internal Border Gateway Protocol (IBGP) split-horizon rules specify that updates that are received on an External Border Gateway Protocol (EBGP) session should be forwarded on all IBGP and EBGP sessions, but updates that are received on an IBGP session should be forwarded only to all EBGP sessions. This rule requires a BGP boundary router to be able to send routing...

Gold customers Define static route tags

In this scenario, the service provider offers two different service levels to its customers Normal and Gold. Customers are also assigned IP address blocks. Some customers have PA addresses, which the ISP does not announce as explicit routes. The large route summary block announced by the ISP covers these customers. Other customers use provider-independent PI addresses that must be explicitly announced to the Internet by the service provider. Because there are two different quality of service...