Implementing BGP on Cisco IOS XR Software

Information About Implementing BGP on Cisco IOS XR Software

512K (524,288) prefixes for IPv4 unicast.

128K (131,072) prefixes for IPv4 multicast.

128K (131,072) prefixes for IPv6 unicast.

A cease notification message is sent to the neighbor and the peering with the neighbor is terminated when the number of prefixes received from the peer for a given address family exceeds the maximum limit (either set by default or configured by the user) for that address family.

It is possible that the maximum number of prefixes for a neighbor for a given address family has been configured after the peering with the neighbor has been established and a certain number of prefixes have already been received from the neighbor for that address family. A cease notification message is sent to the neighbor and peering with the neighbor is terminated immediately after the configuration if the configured maximum number of prefixes is fewer than the number of prefixes that have already been received from the neighbor for the address family.

BGP Validation of Local Next-Hop Addresses

When Cisco IOS XR BGP receives a route advertisement from a neighbor, it validates the next-hop address contained in the route by verifying that the next-hop address is not the same as an IP address assigned to an interface on this router (for example, a local address). If the received next-hop address is a local address, the update is dropped. However, if the next-hop address is set to a local address by the configured inbound policy, the update is not dropped, is treated as a valid next-hop address, and is processed normally in Cisco IOS XR BGP. This verification means that the router advertises to its neighbors that it has a route to the prefix, but any traffic received for that prefix is dropped.

This “blackholing” effect is often used to automatically protect against Denial of Service (DOS) attacks on user hosts. An inbound policy is configured that sets the next hop to a local address (for example, the address of a loopback interface) when a route with a particular community is received. When a user finds that a host is under a DOS attack, a BGP advertisement is sent to the address of the attacked host with the special community attached. The advertisement causes the Internet service provider (ISP) router to install a route with a local next hop for that address that drops all traffic destined for it.

BGP Configuration

Cisco IOS XR BGP follows a neighbor-based configuration model that requires that all configurations for a particular neighbor be grouped in one place under the neighbor configuration. Peer groups are not supported for either sharing configuration between neighbors or for sharing update messages. The concept of peer group has been replaced by a set of configuration groups to be used as templates in BGP configuration and automatically generated update groups to share update messages between neighbors. BGP configurations are grouped into four major categories:

Router Configuration Mode

Global Address Family Configuration Mode

Neighbor Configuration Mode

Neighbor Address Family Configuration Mode

Configuration Modes

The following sections show how to enter each of the configuration modes. From a mode, you can enter the ? command to display the commands available in that mode.

Cisco IOS XR Routing Configuration Guide

RC-4

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Cisco Systems IOS XR manual BGP Validation of Local Next-Hop Addresses, BGP Configuration, Configuration Modes, RC-4

IOS XR specifications

Cisco Systems IOS XR is an advanced operating system designed specifically for high-performance routers and service provider networks. It serves as the backbone for many of Cisco's high-end routing platforms, enabling service providers to manage their networks with increased efficiency, flexibility, and scalability.

One of the main features of IOS XR is its modular architecture. This allows for the independent operation of various components within the OS, facilitating the deployment of new features and updates without affecting the overall stability of the system. This modularity ensures that service providers can implement rapid changes and enhancements while maintaining service continuity.

Another characteristic of IOS XR is its support for 64-bit architecture, which provides enhanced performance and the ability to manage larger amounts of data. This is particularly beneficial for service providers that deal with high traffic volumes and require robust data processing capabilities. The utilization of 64-bit technology also enables the operating system to utilize memory more efficiently, allowing for greater scalability.

IOS XR incorporates advanced technologies such as Distributed System Architecture (DSA) and Multiple Routing Instances (Merging Routes). DSA allows for the distribution of routing processes across multiple hardware resources, maximizing performance and redundancy. Multiple Routing Instances enable operators to create separate logical routing tables for different services, improving isolation and efficiency in managing network traffic.

The operating system also focuses heavily on security, featuring extensive encryption methods and access controls to safeguard network resources. IOS XR supports various authentication protocols, ensuring secure access to routers and switches. In addition, the OS includes comprehensive logging and monitoring capabilities, allowing network administrators to track activities and respond quickly to potential threats.

Another critical aspect of IOS XR is its adherence to the principles of service-oriented architecture (SOA). This approach permits the development of applications and services that can operate independently, fostering innovation and enabling service providers to tailor their offerings based on customer demands.

Ultimately, Cisco IOS XR is a powerful, reliable operating system that meets the complex needs of modern telecommunications networks. With its focus on modularity, performance, security, and scalability, it enables service providers to deliver high-quality, resilient services to their customers while efficiently managing network resources. As the industry continues to evolve, IOS XR remains a vital tool for those aiming to stay competitive in the ever-changing landscape of networking.