- Cisco BGP Overview
- BGP 4
- Configuring a Basic BGP Network
- BGP 4 Soft Configuration
- BGP Support for 4-byte ASN
- Connecting to a Service Provider Using External BGP
- BGP Prefix-Based Outbound Route Filtering
- BGP Route-Map Continue
- BGP Route-Map Continue Support for Outbound Policy
- Removing Private AS Numbers from the AS Path in BGP
- Configuring BGP Neighbor Session Options
- BGP Neighbor Policy
- BGP Dynamic Neighbors
- BGP Support for Next-Hop Address Tracking
- BGP Restart Neighbor Session After Max-Prefix Limit Reached
- BGP Support for Dual AS Configuration for Network AS Migrations
- Configuring Internal BGP Features
- BGP VPLS Auto Discovery Support on Route Reflector
- BGP FlowSpec Route-reflector Support
- BGP Support for BFD
- IPv6 Routing: Multiprotocol BGP Extensions for IPv6
- IPv6 Multicast Address Family Support for Multiprotocol BGP
- IPv6 Routing: Multiprotocol BGP Link-Local Address Peering
- IPv6 NSF and Graceful Restart for MP-BGP IPv6 Address Family
- BGP NSF Awareness
- BGP Graceful Restart per Neighbor
- Configuring Multiprotocol BGP (MP-BGP) Support for CLNS
- BGP Link Bandwidth
- iBGP Multipath Load Sharing
- BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN
- Loadsharing IP Packets Over More Than Six Parallel Paths
- BGP Policy Accounting
- BGP Policy Accounting Output Interface Accounting
- BGP Cost Community
- Regex Engine Performance Enhancement
- BGP Support for IP Prefix Import from Global Table into a VRF Table
- BGP Support for IP Prefix Export from a VRF Table into the Global Table
- BGP per Neighbor SoO Configuration
- BGP Next Hop Unchanged
- Per-VRF Assignment of BGP Router ID
- BGP Event-Based VPN Import
- BGP Support for the L2VPN Address Family
- Detecting and Mitigating a BGP Slow Peer
- Configuring BGP: RT Constrained Route Distribution
- Configuring BGP Consistency Checker
- BGP—Origin AS Validation
- BGP Support for NSR with SSO
- BGP NSR Auto Sense
- BGP NSR Support for iBGP Peers
- BGP Graceful Shutdown
- BGP — mVPN BGP sAFI 129 - IPv4
- BGP-MVPN SAFI 129 IPv6
- BGP Attribute Filter and Enhanced Attribute Error Handling
- BGP Additional Paths
- BGP-RT and VPN Distinguisher Attribute Rewrite Wildcard
- BGP—Selective Route Download
- BFD—BGP Multihop Client Support, cBit (IPv4 and IPv6), and Strict Mode
- BGP MIB Support
- BGP 4 MIB Support for per-Peer Received Routes
- BGP PIC Edge for IP and MPLS-VPN
- BGP IPv6 PIC Edge and Core for IP/MPLS
- BGP Unified MPLS iBGP Client
- Cisco-BGP-MIBv2
- BGP Diverse Path Using a Diverse-Path Route Reflector
- BGP-VRF-Aware Conditional Advertisement
- BGP—Support for iBGP Local-AS
- IOS-XE IBGP local-as dual-as
- VPLS BGP Signaling
- BGP NSR Support for MPLS VPNv4 and VPNv6 Inter-AS Option B
- L3VPN iBGP PE-CE
- eiBGP Multipath for Non-VRF Interfaces (IPv4/IPv6)
- BGP-RTC for Legacy PE
- BGP PBB EVPN Route Reflector Support
- BGP Monitoring Protocol
- VRF Aware BGP Translate-Update
- BGP Support for MTR
- BGP Accumulated IGP
BGP 4 Soft Configuration
BGP4 soft configuration allows BGP4 policies to be configured and activated without clearing the BGP session, hence without invalidating the forwarding cache.
- Finding Feature Information
- Information About BGP 4 Soft Configuration
- How to Configure BGP 4 Soft Configuration
- Configuration Examples for BGP 4 Soft Configuration
- Additional References
- Feature Information for BGP 4 Soft Configuration
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Information About BGP 4 Soft Configuration
BGP Session Reset
Whenever the routing policy changes due to a configuration change, BGP peering sessions must be reset by using the clear ip bgp command. Cisco software supports the following three mechanisms to reset BGP peering sessions:
Hard reset—A hard reset tears down the specified peering sessions including the TCP connection and deletes routes coming from the specified peer.
Soft reset—A soft reset uses stored prefix information to reconfigure and activate BGP routing tables without tearing down existing peering sessions. Soft reconfiguration uses stored update information, at the cost of additional memory for storing the updates, to allow you to apply new BGP policy without disrupting the network. Soft reconfiguration can be configured for inbound or outbound sessions.
Dynamic inbound soft reset—The route refresh capability, as defined in RFC 2918, allows the local device to reset inbound routing tables dynamically by exchanging route refresh requests to supporting peers. The route refresh capability does not store update information locally for nondisruptive policy changes. It instead relies on dynamic exchange with supporting peers. Route refresh must first be advertised through BGP capability negotiation between peers. All BGP devices must support the route refresh capability. To determine if a BGP device supports this capability, use the show ip bgp neighbors command. The following message is displayed in the output when the device supports the route refresh capability:
Received route refresh capability from peer.
The bgp soft-reconfig-backup command was introduced to configure BGP to perform inbound soft reconfiguration for peers that do not support the route refresh capability. The configuration of this command allows you to configure BGP to store updates (soft reconfiguration) only as necessary. Peers that support the route refresh capability are unaffected by the configuration of this command.
How to Configure BGP 4 Soft Configuration
Configuring Inbound Soft Reconfiguration When Route Refresh Capability Is Missing
Perform this task to configure inbound soft reconfiguration using the bgp soft-reconfig-backup command for BGP peers that do not support the route refresh capability. BGP peers that support the route refresh capability are unaffected by the configuration of this command. Note that the memory requirements for storing the inbound update information can become quite large.
1.
enable
2.
configure
terminal
3.
router
bgp
autonomous-system-number
4.
bgp
log-neighbor-changes
5.
bgp
soft-reconfig-backup
6.
neighbor
{ip-address |
peer-group-name}
remote-as
autonomous-system-number
7.
neighbor
{ip-address |
peer-group-name}
soft-reconfiguration [inbound]
8.
neighbor
{ip-address |
peer-group-name}
route-map
map-name
{in |
out}
9. Repeat Steps 6 through 8 for every peer that is to be configured with inbound soft reconfiguration.
10.
exit
11.
route-map
map-name
[permit
|
deny] [sequence-number]
12.
set
ip
next-hop
ip-address
13.
end
14.
show
ip
bgp
neighbors
[neighbor-address]
15.
show
ip
bgp
[network]
[network-mask]
DETAILED STEPS
Examples
The following partial output from the show ip bgp neighbors command shows information about the TCP and BGP connections to the BGP neighbor 192.168.2.1. This peer supports route refresh.
BGP neighbor is 192.168.1.2, remote AS 40000, external link Neighbor capabilities: Route refresh: advertised and received(new)
The following partial output from the show ip bgp neighbors command shows information about the TCP and BGP connections to the BGP neighbor 192.168.3.2. This peer does not support route refresh so the soft-reconfig inbound paths for BGP peer 192.168.3.2 will be stored because there is no other way to update any inbound policy updates.
BGP neighbor is 192.168.3.2, remote AS 50000, external link Neighbor capabilities: Route refresh: advertised
The following sample output from the show ip bgp command shows the entry for the network 172.17.1.0. Both BGP peers are advertising 172.17.1.0/24, but only the received-only path is stored for 192.168.3.2.
BGP routing table entry for 172.17.1.0/24, version 11 Paths: (3 available, best #3, table Default-IP-Routing-Table, RIB-failure(4)) Flag: 0x820 Advertised to update-groups: 1 50000 192.168.3.2 from 192.168.3.2 (172.17.1.0) Origin incomplete, metric 0, localpref 200, valid, external 50000, (received-only) 192.168.3.2 from 192.168.3.2 (172.17.1.0) Origin incomplete, metric 0, localpref 100, valid, external 40000 192.168.1.2 from 192.168.1.2 (172.16.1.0) Origin incomplete, metric 0, localpref 200, valid, external, best
Configuration Examples for BGP 4 Soft Configuration
Examples: BGP Soft Reset
The following examples show two ways to reset the connection for BGP peer 192.168.1.1.
Example: Dynamic Inbound Soft Reset
The following example shows the command used to initiate a dynamic soft reconfiguration in the BGP peer 192.168.1.1. This command requires that the peer support the route refresh capability.
clear ip bgp 192.168.1.1 soft in
Example: Inbound Soft Reset Using Stored Information
The following example shows how to enable inbound soft reconfiguration for the neighbor 192.168.1.1. All the updates received from this neighbor will be stored unmodified, regardless of the inbound policy. When inbound soft reconfiguration is performed later, the stored information will be used to generate a new set of inbound updates.
router bgp 100 neighbor 192.168.1.1 remote-as 200 neighbor 192.168.1.1 soft-reconfiguration inbound
The following example clears the session with the neighbor 192.168.1.1:
clear ip bgp 192.168.1.1 soft in
Additional References
Related Documents
Related Topic |
Document Title |
---|---|
Cisco IOS commands |
|
BGP commands |
Standards and RFCs
Standard/RFC |
Title |
---|---|
RFC 2918 |
Route Refresh Capability for BGP-4 |
Technical Assistance
Description |
Link |
---|---|
The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password. |
Feature Information for BGP 4 Soft Configuration
The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Feature Name |
Releases |
Feature Information |
---|---|---|
BGP 4 Soft Configuration |
BGP 4 Soft Configuration allows BGP4 policies to be configured and activated without clearing the BGP session, hence without invalidating the forwarding cache. |