BGP soft Inbound

Unanswered Question
Jan 7th, 2010

Hi, I have two routers having BGP peer with each other. Both are working fine.

I want to configure Soft-Inbound in BGP configuration on both end. I want to double confirm, if I will activate neibhor x.x.x.x soft-inbound command under BGP, then my BGP will reset or it will accept the command without breaking BGP neighbor.

Please help.

I have this problem too.
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Reza Sharifi Thu, 01/07/2010 - 05:57

Hello Rupesh.

From the command reference guide:

neighbor soft-reconfiguration

To configure the Cisco IOS software to start storing updates, use the neighbor soft-reconfiguration command in router configuration mode. 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

ip-address

IP address of the BGP-speaking neighbor.

peer-group-name

Name of a BGP peer group.

inbound

(Optional) Indicates that the update to be stored is an incoming update.

Defaults

Soft reconfiguration is not enabled.

Command Modes

Router configuration

Command History

Release
Modification

11.2

This command was introduced.

12.2(33)SRA

This command was integrated into Cisco IOS Release 12.2(33)SRA.

12.2SX

This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.

Usage Guidelines

Entering this command starts the storage of updates, which is required to do inbound soft reconfiguration. Outbound BGP soft reconfiguration does not require inbound soft reconfiguration to be enabled.

To use soft reconfiguration, or soft reset, without preconfiguration, both BGP peers must support the soft route refresh capability, which is advertised in the open message sent when the peers establish a TCP session. Routers running Cisco IOS software releases prior to Release 12.1 do not support the route refresh capability and must clear the BGP session using the neighbor soft-reconfiguration command. Clearing the BGP session using the neighbor soft-reconfiguration command has a negative effect on network operations and should only be used as a last resort. Routers running Cisco IOS software Release 12.1 or later releases support the route refresh capability and dynamic soft resets, and can use the clear ip bgp {* | address | peer-group name} in command to clear the BGP session.

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 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 10.108.1.1. 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 100

 neighbor 10.108.1.1 remote-as 200

 neighbor 10.108.1.1 soft-reconfiguration inbound

HTH
Reza
Peter Paluch Thu, 01/07/2010 - 15:09

Hello Rupesh,

In addition to Reza's answer, I would like to add that activating or deactivating the Soft Reconfiguration for a peer does not reset the peering automatically, however, resetting it manually may be actually necessary, as the Soft Reconfiguration feature requires that an unfiltered, unchanged database of all information sent by that peer is maintained by your router, and this unfiltered information may not be available if the Soft Reconfiguration is activated after the peering has been established.

But I want to ask you - why do you want to activate the Soft Reconfiguration on your routers? Are you perhaps confusing the Soft Reconfiguration with the Route Refresh capability? The Soft Reconfiguration is an obsolete workaround around an old BGP deficiency, however, for several years, this deficiency has been corrected in the BGP protocol and you do not need it anymore. The Route Refresh capability that provides a similar functionality is activated automatically as soon as the routers mutually agree that they support it during the BGP peering establishement phase. This topic has been discussed on NetPro, for example, here:

https://supportforums.cisco.com/message/829228#829228

Please visit that thread for further information about the Soft Reconfig and the Route Refresh. And of course please come back with any questions you might have.


Best regards,

Peter

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