BGP soft Inbound

[Rupesh Kashyap]

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.

[Reza Sharifi]

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
 

[wellitonjesus]

Thanks for your reply, I had the same problem in my bgp lab. 

To be more specific, my laboratory contains 3 ASN each with 2 iBGP peers, when I used the command "sh ip bgp nei 10.1.1.2 received-routes" received a message:
"%Inbound soft reconfiguration not enabled on 10.1.1.2"

The solution was to apply the command "neighbor 10.1.1.2 soft-reconfiguration inbound" within the BGP process, which I only discovered with the previous post, for which I thank you.

[MHM Cisco World]

make new post it better

MHM

[Peter Paluch]

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

[blue phoenix]

Hi,

How can I see then the advertised routes of my bgp neighbor if the show ip bgp neighbors [a.b.c.d] received-routes needs the soft reconfiguration inbound config?  Is there an alternate way?

router#show ip bgp neighbors [a.b.c.d] received-routes

% Inbound soft reconfiguration not enabled on [a.b.c.d]

Thanks,

[Alan Ng'ethe]

Here is a clear explanation:

https://community.cisco.com/t5/switching/bgp-neighbor-received-routes/td-p/2287645

[blue phoenix]

This concern of mine goes back to @Peter Paluch's comment regarding BGP soft reconfiguration inbound is obsolete or deprecated.  So I am asking if it's obsolete or deprecated, what is the alternative means to see the advertised route of a bgp neighbor?  Also if again the only way to see a bgp neighbor's advertised routes is to configure:

router bgp xxx

neighbor a.b.c.d remote-as yyy

neighbor a.b.c.d soft-reconfiguration inbound

Once I put that 1 line of command, do I need to clear that neighbor's bgp session by doing

clear ip bgp * soft in

Or can I just leave it at that?

The reason I am asking is that we are running an SaaS and we have more than 50K clients coming from our BGP peer.  Will this create a temp outage?

[xAdventix]

To show the received routes without soft configured is:
show ip bgp neigh x.x.x.x routes
I've always used this and it's never failed me.

Just to addon, it won't show rejected routes however. 

[Peter Paluch]

Hello,

So I am asking if it's obsolete or deprecated, what is the alternative means to see the advertised route of a bgp neighbor?

I believe we need to put Soft Reconfig into a correct perspective.

Soft Reconfig, as a means to re-apply updated inbound routing policies to routes received from a neighbor without tearing down the peering with him, is truly obsolete. The Route Refresh capability has been around for more than 18+ years and solves the fundamental deficiency of BGP for which the Soft Reconfig was merely a proprietary workaround.

If you are using Soft Reconfig as a troubleshooting tool to see if a route was even sent to you from the neighbor, regardless of whether you filter it out or not, this is a different thing - it is a valid use of Soft Reconfig but not the one for which the Soft Reconfig was initially implemented. Of course, as a troubleshooting tool, Soft Reconfig is still very much valid, but that use case was not my focus in my previous posts.

Once I put that 1 line of command, do I need to clear that neighbor's bgp session [ ... cut ... ]

This depends on whether the neighbor already supports Route Refresh (you can always check with show ip bgp neighbor X.X.X.X command - look for "Route refresh: advertised and received" and/or "Enhanced Refresh Capability: advertised and received" lines in the output; the capability must be both advertised and received to be effective). If the Route Refresh is supported, then after enabling Soft Reconfig, your router will send out a Route Refresh message to the neighbor to request all routes of the particular address family again to populate the Soft Reconfig database. In this case, there will be no disruption.

I am honestly not sure what exactly will happen if the neighbor does not support Route Refresh. Obviously, without it, there is no way to populate the Soft Reconfig database with the complete unaltered list of routes from the neighbor, aside from tearing down the peering and letting it come up again. In that case, either the peering will reset automatically, or you will need to clear it using clear ip bgp X.X.X.X command manually. Either way, in this case, the full deployment of the Soft Reconfig will be disruptive.

Please feel welcome to ask further!

Best regards,
Peter

[blue phoenix]

Thank you so much for answering my  concern.  Pardon me if you have answered this already.

After configuring the soft-reconfiguration inbound in the bgp neighbor config.  Will the session restart and all my existing connection would drop?

Do I need:

Clear ip bgp * soft in !!! In order for the new config to kick in? as I understand clearing with soft in will not drop connections?!!!