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Table Of Contents
Managing Routing Policy Changes
Related Features and Technologies
Supported Standards, MIBs, and RFCs
Configuring BGP Dynamic Inbound Soft Reset
Configuring BGP Outbound Soft Reset
Configuring BGP Outbound Soft Reset Under an Address Family
Configuring BGP Soft Reset Using Stored Routing Policy Information
Inbound Soft Reset Using Stored Information
BGP Soft Reset Enhancement
Feature History
12.0(7)T
This feature was introduced.
12.0(2)S
This feature was integrated into Cisco IOS Release 12.0(2)S.
12.0(22)S
Support for IPv6 and VPNv4 address family support was added.
This document describes the BGP Soft Reset Enhancement feature in Cisco IOS Release 12.0(22)S and includes the following sections:
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Related Features and Technologies
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Feature Overview
The BGP Soft Reset Enhancement feature provides automatic support for dynamic soft reset of inbound BGP routing table updates that are not dependent upon stored routing table update information. This method requires no preconfiguration (as with the neighbor soft-reconfiguration command) and requires much less memory than the previous soft reset method for inbound routing table updates.
Configurable routing policies for a peer, including route-maps, distribute-lists, prefix-lists, and filter-lists, may impact inbound or outbound routing table updates. Whenever there is a change in the routing policy, the BGP session must be cleared or reset for the new policy to take effect. The two methods for resetting a BGP session are hard reset and soft reset.
Clearing a BGP session using a hard reset invalidates the cache and results in a negative impact on the network performance when the information in the cache becomes unavailable. A hard reset is also disruptive because active BGP sessions are torn down.
A soft reset, which is performed on a per-neighbor basis, does not clear the BGP session and facilitates the application of new policies. There are two methods of performing a soft reset:
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Before the BGP Soft Reset Enhancement feature, a soft reset for inbound routing table updates was performed by entering the neighbor soft-reconfiguration router configuration command. This command was used to configure the local BGP router to store all received (inbound) routing policy updates. However, this method uses too much memory because inbound updates are not modified and is not recommended.
Note
Managing Routing Policy Changes
When the routing policy of a BGP neighbor changes, the session must be reset (cleared) for the changes to take effect. Because resetting a BGP session can be disruptive to networks, a soft reset method is recommended for reconfiguring the routing table.
In order to reconfigure the inbound routing table before the introduction of this feature, both the local BGP router and the BGP peer first needed to be configured to store incoming routing policy updates using the neighbor soft-reconfiguration command. Additional resources, particularly memory, were required to store the inbound routing table updates. The clear ip bgp command could then initiate the soft reset, which generated a new set of inbound routing table updates using the stored information.
This feature provides an additional method for soft reset that allows the dynamic exchange of route refresh requests and routing information between BGP routers and the subsequent re-advertisement of the respective outbound routing table. Soft reset using the route refresh capability does not require preconfiguration and consumes no additional memory resources.
To use this new method, both BGP peers must support the soft route refresh capability, which is advertised in the OPEN message. Any router that is running BGP with this software release automatically supports the route refresh capability. Routers that are running previous Cisco IOS software releases do not support the route refresh capability and must use the older soft reset method.
If the soft reset fails, you can still clear the BGP session, but it will have a negative impact upon network operations and should only be used as a last resort.
Benefits
Allows Dynamic Route Refresh Requests
This feature provides a way to initiate nondisruptive routing policy changes by allowing the dynamic exchange of route refresh requests between BGP routers and the subsequent re-advertisement of the respective outbound routing tables.
Requires No Preconfiguration
Because support for the soft reset using the route refresh capability is included in this release of the Cisco IOS software, no further router configuration is required. You can initiate a soft inbound reset using only the clear ip bgp in command.
Requires No Additional Memory Resources
Unlike a soft reset using the stored inbound routing table updates provided by the neighbor soft-reconfiguration command, when both BGP peers support the route refresh capability inbound routing table updates are not stored in the local BGP router. The soft reset requests are exchanged dynamically, and no additional memory is required.
Flexibility
There are now two available methods for inbound soft reset; the older method using stored inbound routing table updates, and the method provided by this feature using dynamic exchange of update information.
Restrictions
Route Refresh Support for BGP Peers
BGP peers must support the route refresh capability to use dynamic inbound soft reset capability. If a peer does not support the route refresh capability, then the only soft reconfiguration option is to use the neighbor soft-reconfiguration command, which initiates the storage of inbound routing table updates and requires additional memory.
Dynamic and Stored Inbound Soft Reset Functions are Mutually Exclusive
The dynamic inbound soft reset and inbound soft reset using stored information functions are mutually exclusive and cannot be configured together. If the inbound soft reset using stored routing table updates is configured for a neighbor, the dynamic inbound soft update method cannot be used.
Related Features and Technologies
The BGP Soft Reset feature is an extension of the BGP routing protocol. For more information about configuring BGP, refer to the "BGP chapter" of the Cisco IOS Release 12.0 Network Protocols Configuration Guide, Part 1 and Cisco IOS Release 12.0 Network Protocols Command Reference, Part 1.
Related Documents
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Supported Platforms
The BGP Soft Reset feature is supported by the following platforms in Cisco IOS Release 12.0(22)S:
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Determining Platform Support Through Cisco Feature Navigator
Cisco IOS software is packaged in feature sets that are supported by specific platforms. To get updated information regarding platform support for this feature, access Cisco Feature Navigator. Cisco Feature Navigator dynamically updates the list of supported platforms as new platform support is added for the feature.
Cisco Feature Navigator is a web-based tool that enables you to determine which Cisco IOS software images support a specific set of features and which features are supported in a specific Cisco IOS image. You can search by feature or release. Under the release section, you can compare releases side by side to display both the features unique to each software release and the features in common.
To access Cisco Feature Navigator, you must have an account on Cisco.com. If you have forgotten or lost your account information, send a blank e-mail to cco-locksmith@cisco.com. An automatic check will verify that your e-mail address is registered with Cisco.com. If the check is successful, account details with a new random password will be e-mailed to you. Qualified users can establish an account on Cisco.com by following the directions at http://www.cisco.com/register.
Cisco Feature Navigator is updated regularly when major Cisco IOS software releases and technology releases occur. For the most current information, go to the Cisco Feature Navigator home page at the following URL:
Availability of Cisco IOS Software Images
Platform support for particular Cisco IOS software releases is dependent on the availability of the software images for those platforms. Software images for some platforms may be deferred, delayed, or changed without prior notice. For updated information about platform support and availability of software images for each Cisco IOS software release, refer to the online release notes or, if supported, Cisco Feature Navigator.
Supported Standards, MIBs, and RFCs
Standards
No new or modified standards are supported by this feature.
MIBs
No new or modified MIBs are supported by this feature.
To obtain lists of supported MIBs by platform and Cisco IOS release, and to download MIB modules, go to the Cisco MIB website on Cisco.com at the following URL:
http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml
RFCs
RFC 2918, Route Refresh Capability for BGP-4
Prerequisites
Peers that exchange reachability information must support the soft reset route refresh capability in order to use the enhancements described in this document. If a peer does not, then the only available soft reconfiguration option is to use the neighbor soft-reconfiguration command, which initiates the storage of inbound routing table updates and requires additional memory, followed by the clear ip bgp in command.
Configuration Tasks
See the following "Configuring BGP Soft Reset" section for configuration tasks for the BGP Soft Reset Enhancement feature. This task is required.
Configuring BGP Soft Reset
Whenever there is a change in the routing policy, the BGP session must be reset (cleared) for the new policy to take effect and the routing table to be reconfigured. Using a hard reset to clear a BGP session causes cache invalidation and results in a negative impact on network operation.
Soft reset is recommended because it allows routing table policies to be reconfigured and activated without clearing the BGP session. Soft reset is done on a per-neighbor basis. Soft resets can be inbound or outbound:
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There is only one way to perform an outbound soft reset.
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Configuring BGP Dynamic Inbound Soft Reset
If both the local BGP router and the neighbor router support the route refresh capability, you can perform a dynamic soft inbound reset. This type of reset has the following advantages over a soft inbound reset using stored routing update information:
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To determine whether a router supports the route refresh capability, use the show ip bgp neighbors command.
If all the BGP routers support the route refresh capability, you can use the dynamic soft reset method for resetting the inbound routing table.
Router# clear ip bgp * | ip-address | peer-group-name soft in
Performs a dynamic soft reset on the connection specified in the command.
Configuring BGP Outbound Soft Reset
Outbound soft resets do not require any preconfiguration. Using the keyword soft specifies that a soft reset be performed.
Router# clear ip bgp * | address | peer-group-name soft out
Performs a soft reset on the connection specified in the command.
Configuring BGP Outbound Soft Reset Under an Address Family
Outbound soft resets do not require any preconfiguration. Using the keyword soft specifies that a soft reset be performed.
Configuring BGP Soft Reset Using Stored Routing Policy Information
If all of the BGP routers in the connection do not support the route refresh capability, use the soft reset method that generates a new set of inbound routing table updates from information previously stored. To initiate storage of inbound routing table updates, you must first preconfigure the router using the neighbor soft-reconfiguration command.
Keep in mind that the memory requirements for storing the inbound update information can become quite large.
Router(config-router)# neighbor ip-address | peer-group-name soft-reconfiguration inbound
Initiates storage of inbound routing table updates from the specified neighbor or peer group.
Once you have initiated storage of inbound routing table updates for a specific neighbor or peer group, you can perform a soft inbound reset for that neighbor or peer group.
Router# clear ip bgp * | ip-address | peer-group-name soft in
Performs a soft reset on the connection specified in the command.
Verifying BGP Soft Reset
Enter the show ip bgp neighbors command to display information about the BGP and TCP connections to neighbors and verify the status and configuration of the BGP soft reset feature. The following sample output shows that a soft reset has been configured for neighbor 10.4.9.8:
Router# show ip bgp neighborsBGP neighbor is 10.4.9.8, remote AS 101, internal linkBGP version 4, remote router ID 10.4.9.8BGP state = Established, up for 00:03:50Last read 00:00:50, hold time is 180, keepalive interval is 60 secondsNeighbor capabilities:Route refresh: advertised and received(new)Address family IPv4 Unicast: advertised and receivedReceived 7 messages, 0 notifications, 0 in queueSent 7 messages, 0 notifications, 0 in queueDefault minimum time between advertisement runs is 5 secondsFor address family: IPv4 UnicastBGP table version 1, neighbor version 1Index 1, Offset 0, Mask 0x2Route refresh request: received 0, sent 00 accepted prefixes consume 0 bytesPrefix advertised 0, suppressed 0, withdrawn 0Number of NLRIs in the update sent: max 0, min 0Connections established 1; dropped 0Last reset neverConnection state is ESTAB, I/O status: 1, unread input bytes: 0Local host: 10.4.9.21, Local port: 179Foreign host: 10.4.9.8, Foreign port: 11004Enqueued packets for retransmit: 0, input: 0 mis-ordered: 0 (0 bytes)Event Timers (current time is 0x134F4D2B4):Timer Starts Wakeups NextRetrans 8 0 0x0TimeWait 0 0 0x0AckHold 7 3 0x0SendWnd 0 0 0x0KeepAlive 0 0 0x0GiveUp 0 0 0x0PmtuAger 0 0 0x0DeadWait 0 0 0x0iss: 4229692689 snduna: 4229692849 sndnxt: 4229692849 sndwnd: 16225irs: 339739239 rcvnxt: 339739399 rcvwnd: 16225 delrcvwnd: 159SRTT: 540 ms, RTTO: 3809 ms, RTV: 1364 ms, KRTT: 0 msminRTT: 0 ms, maxRTT: 300 ms, ACK hold: 200 msFlags: passive open, nagle, gen tcbsDatagrams (max data segment is 1460 bytes):Rcvd: 10 (out of order: 0), with data: 7, total data bytes: 159Sent: 11 (retransmit: 0, fastretransmit: 0), with data: 7, total data bytes: 159
Configuration Examples
This section provides the following configuration examples:
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Dynamic Inbound Soft Reset
The following examples shows the clear ip bgp 131.108.1.1 soft in command used to initiate a dynamic soft reconfiguration in the BGP peer 131.108.1.1. This command requires that the peer supports the route refresh capability.
clear ip bgp 131.108.1.1 soft inInbound Soft Reset Using Stored Information
The following example enables inbound soft reconfiguration for the neighbor 131.108.1.1. 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 100neighbor 131.108.1.1 remote-as 200neighbor 131.108.1.1 soft-reconfiguration inboundThe following example clears the session with the neighbor 131.108.1.1.
clear ip bgp 131.108.1.1 soft inCommand Reference
This section documents new or modified commands. All other commands used with this feature are documented in the Cisco IOS Release 12.0 command reference publications.
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clear ip bgp
To reset a BGP connection using BGP soft reconfiguration, use the clear ip bgp privileged EXEC command at the system prompt.
clear ip bgp {* | neighbor-address | peer-group-name [soft [in | out]} [ipv4 {multicast | unicast} | vpnv4 {unicast} {soft | in | out}]
Syntax Description
Defaults
A session reset is initiated by default.
Command Modes
Privileged EXEC
Command History
Usage Guidelines
You can reset inbound routing table updates dynamically or by generating new updates using stored update information. Using stored update information required additional memory for storing the updates.
To reset inbound routing table updates dynamically, all BGP routers must support the route refresh capability. To determine whether a BGP router supports this capability, use the show ip bgp neighbors command. If a router supports the route refresh capability, the following message is displayed:
Received route refresh capability from peer.If all BGP routers support the route refresh capability, use the clear ip bgp {* | address | peer-group -name} in command. You need not use the soft keyword, because soft reset is automatically assumed when the route refresh capability is supported.
The route refresh capability can also be initiated specifically for IPv4 and VPNv4 address families. When an soft refresh is initiated, the in or out keyword does not need to be specified because soft keyword specifies both.
To generate new inbound updates from stored update information (rather than dynamically) without resetting the BGP session, you must preconfigure the local BGP router using the neighbor soft-reconfiguration inbound command. This preconfiguration causes the software to store all received updates without modification regardless of whether an update is accepted by the inbound policy. Storing updates is memory intensive and should be avoided if possible.
Outbound BGP soft configuration has no memory overhead and does not require any preconfiguration. You can trigger an outbound reconfiguration on the other side of the BGP session to make the new inbound policy take effect.
Use this command whenever any of the following changes occur:
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Examples
The following example clears the inbound session with the neighbor 131.108.1.1 without resetting the session:
Router# clear ip bgp 131.108.1.1 soft inThe following example clears the outbound session with the peer group named corp without resetting the session:
Router# clear ip bgp corp soft outThe following example clears both the inbound and outbound VPNv4 session without resetting the session for 10.0.0.1 neighbor:
Router# clear ip bgp vpnv4 unicast 10.0.0.1 softThe following example clears the outbound IPv4 multicast session without resetting the session for 192.168.0.1 neighbor:
Router# clear ip bgp ipv4 multicast 192.168.0.1 outThe following example clears the inbound IPv4 unicast session without resetting the session for 172.16.0.1 neighbor:
Router# clear ip bgp ipv4 multicast 172.16.0.1 inRelated Commands
Configures the Cisco IOS software to start storing updates.
Displays entries in the BGP routing table.
neighbor soft-reconfiguration
To configure the Cisco IOS software to start storing updates, use the neighbor soft-reconfiguration router configuration command. To not store received updates, use the no form of this command.
neighbor {ip-address | peer-group-name} soft-reconfiguration [inbound]
no neighbor {ip-address | peer-group-name} soft-reconfiguration [inbound]
Syntax Description
Defaults
Soft reconfiguration is not enabled
Command Modes
Router configuration
Command History
Usage Guidelines
This command requires at least one keyword. Currently the only keyword available is inbound, so the use of inbound is not optional.
Entering this command starts the storage of updates, required to do inbound soft reconfiguration. Outbound BGP soft reconfiguration does not require inbound soft reconfiguration to be enabled.
If you specify a BGP peer group by using the peer-group-name argument, all the members of the peer group will inherit the characteristic configured with this command.
Examples
The following example enables inbound soft-reconfiguration for the neighbor 131.108.1.1. All the updates received from this neighbor will be stored unmodified, regardless of the inbound policy. When inbound soft reconfiguration is done later, the stored information will be used to generate a new set of inbound updates.
router bgp 100neighbor 131.108.1.1 remote-as 200neighbor 131.108.1.1 soft-reconfiguration inboundRelated Commands
Resets a BGP connection using BGP soft reconfiguration.
Creates a BGP peer group.
show ip bgp neighbors
To display information about the TCP and BGP connections to neighbors, use the show ip bgp neighbors EXEC command.
show ip bgp neighbors [neighbor-address] [received-routes | routes | advertised-routes | {paths regexp} | dampened-routes]
Syntax Description
Command Modes
EXEC
Command History
Examples
The following is sample output from the show ip bgp neighbors command in privileged EXEC mode:
Router# show ip bgp neighborsBGP neighbor is 10.4.9.8, remote AS 101, internal linkBGP version 4, remote router ID 10.4.9.8BGP state = Established, up for 00:03:50Last read 00:00:50, hold time is 180, keepalive interval is 60 secondsNeighbor capabilities:Route refresh: advertised and received(new)Address family IPv4 Unicast: advertised and receivedReceived 7 messages, 0 notifications, 0 in queueSent 7 messages, 0 notifications, 0 in queueDefault minimum time between advertisement runs is 5 secondsFor address family: IPv4 UnicastBGP table version 1, neighbor version 1Index 1, Offset 0, Mask 0x2Route refresh request: received 0, sent 00 accepted prefixes consume 0 bytesPrefix advertised 0, suppressed 0, withdrawn 0Number of NLRIs in the update sent: max 0, min 0Connections established 1; dropped 0Last reset neverConnection state is ESTAB, I/O status: 1, unread input bytes: 0Local host: 10.4.9.21, Local port: 179Foreign host: 10.4.9.8, Foreign port: 11004Enqueued packets for retransmit: 0, input: 0 mis-ordered: 0 (0 bytes)Event Timers (current time is 0x134F4D2B4):Timer Starts Wakeups NextRetrans 8 0 0x0TimeWait 0 0 0x0AckHold 7 3 0x0SendWnd 0 0 0x0KeepAlive 0 0 0x0GiveUp 0 0 0x0PmtuAger 0 0 0x0DeadWait 0 0 0x0iss: 4229692689 snduna: 4229692849 sndnxt: 4229692849 sndwnd: 16225irs: 339739239 rcvnxt: 339739399 rcvwnd: 16225 delrcvwnd: 159SRTT: 540 ms, RTTO: 3809 ms, RTV: 1364 ms, KRTT: 0 msminRTT: 0 ms, maxRTT: 300 ms, ACK hold: 200 msFlags: passive open, nagle, gen tcbsDatagrams (max data segment is 1460 bytes):Rcvd: 10 (out of order: 0), with data: 7, total data bytes: 159Sent: 11 (retransmit: 0, fastretransmit: 0), with data: 7, total data bytes: 159Table 1 describes the significant fields shown in the display.
The following is sample output from the show ip bgp neighbors command with the advertised-routes keyword in privileged EXEC mode:
Router# show ip bgp neighbors 172.16.232.178 advertised-routesBGP table version is 27, local router ID is 172.16.232.181Status codes: s suppressed, d damped, h history, * valid, > best, i - internalOrigin codes: i - IGP, e - EGP, ? - incompleteNetwork Next Hop Metric LocPrf Weight Path*>i110.0.0.0 172.16.232.179 0 100 0 ?*> 200.2.2.0 0.0.0.0 0 32768 iThe following is sample output from the show ip bgp neighbors command with the routes keyword in privileged EXEC mode:
Router# show ip bgp neighbors 172.16.232.178 routesBGP table version is 27, local router ID is 172.16.232.181Status codes: s suppressed, d damped, h history, * valid, > best, i - internalOrigin codes: i - IGP, e - EGP, ? - incompleteNetwork Next Hop Metric LocPrf Weight Path*> 10.0.0.0 172.16.232.178 40 0 10 ?*> 20.0.0.0 172.16.232.178 40 0 10 ?Table 2 describes the significant fields shown in the displays.
The following is sample output from the show ip bgp neighbors command with the paths keyword in privileged EXEC mode:
Router# show ip bgp neighbors 171.69.232.178 paths ^10Address Refcount Metric Path0x60E577B0 2 40 10 ?Table 3 describes the significant fields shown in the display.
