clear ip bgp *soft command

[sarahr202]

Hi everybody.

The command

clear ip bgp *soft command

performs soft reset of bgp neighbors relationship in both direction i.e in and out.

Since this command also performs Soft reset  for " in" direction so  does it not require command

 neighbor soft-reconfiguration inbound

as well ?

thanks and havea great weekend

[Reza Sharifi · Accepted solution]

Hi Sarah,

Only when you are clearing inbound you need to configure the BGP neighbor with soft configuration.

If you are clearing outbound, no need to configure the BGP neighbor with soft configuration.

have a look at the command reference guide for more info:

http://www.cisco.com/en/US/docs/ios/iproute_bgp/command/reference/irg_bgp2.html#wp1107408

HTH

[Peter Paluch]

Hi Reza,

Only when you are clearing inbound you need to configure the BGP neighbor with soft configuration

I respectfully disagree. If both routers support Route Refresh as per RFC 2918, there is no configuration necessary whatsoever. Please read my answer below.

Best regards,

Peter

[Reza Sharifi]

Hi Peter,

The reason I mentioned it is because it is noted in the command reference guide.

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.

Now. as you noted, if both routers support it, then no need to preconfigure it.

Thanks,

Reza

[Peter Paluch · Accepted solution]

Hi Reza,

Aaah, yes, I see. Well, this is a classic play with words:

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

Note that this statement discusses only the stored update information rather than dynamic inbound update - which is exactly the reference to the Soft Reconfiguration as opposed to the Dynamic Inbound Soft Reset. This statement does not directly say what you are supposed to do if you want to use the Route Refresh feature.

In a way, this is one part of the documentation that actually misleads people to believe that the

neighbor soft-reconfiguration inbound

is a necessary command - while it is not. While this documentation snippet does speak about stored updates and tries to put it in contrast with dynamic updates via Route Refresh, the terminology is so convoluted that the difference is not really clear.

Best regards,

Peter

[Peter Paluch · Accepted solution]

Hi Sarah,

You have to distinguish between the Soft Reconfiguration and the Dynamic Inbound Soft Reset.

The Soft Reconfiguration is the older method that had to be configured manually on a per-neighbor basis using the

soft-reconfiguration inbound

whose point was to store a separate unfiltered database of all advertisements sent by the particular neighbor. Using the

clear ip bgp * soft [ in ] 

command simply caused this unfiltered database to be re-filtered anew depending on the actual inbound routing policies. This approach, obviously, was very memory-intensive.

The Dynamic Inbound Soft Reset is the Cisco name for the Route Refresh capability defined by the RFC 2918. This capability is negotiated dynamically with the neighbor and there are no configuration commands related to it. This capability will be negotiated automatically on a per-neighbor basis during the BGP neighborship establishement. After using the

clear ip bgp * soft [ in ]

, the router will automatically send the ROUTE-REFRESH message to all neighbors supporting this feature, requesting them to resend their routing advertisements for the particular address family.

In other words, the

clear ip bgp * soft 

command has the same effect, whether the Soft Reconfiguration or the Route Refresh is used. Obviously, the means to achieve the same effect are very different.

I would like to stress that to this day, I am seeing a lot of BGP configurations even here on CSC to have the

neighbor soft-reconfiguration inbound

command configured for various neighbors. I would like to highlight the fact that this is absolutely useless, ineffective and missing the point. It seems that people are confusing the Soft Reconfig with the Route Refresh capability. Every solid BGP implementation nowadays supports the Route Refresh without needing to configure anything and without consuming those inordinate amounts of RAM. The RFC 2918 was published in September 2000, so it's nearly 12 years old and its support is nearly ubiquitous. I cannot stress this enough - configuring the

neighbor soft-reconfiguration inbound

is neither necessary nor called for.

You may be interested in reading the following article:

http://www.cisco.com/en/US/products/ps6599/products_data_sheet09186a0080087b3a.html

Best regards,

Peter

[sarahr202]

Thanks Peter and I wish you and all members at cisco support comunity a happy new year.

clear ip bgp * soft 

neighbor soft-reconfiguration inbound

Let say we have a router that support refresh capability and so does its neighbor R2. Also assume"

neighbor soft-reconfiguration inbound

  is configured.  Now router has two options to achieve the same goal.  The question is which method router will prefer, will it send refresh message?  will it just use the database of unfilitered packets?

I totally understand in modern routers if we issue

 clear ip bgp * soft" it does not require " neighbor soft-reconfiguration inbound"

Rather router just use refresh capability and sends a refresh request to its neighbor.

Thanks .

[Peter Paluch · Accepted solution]

Hi Sarah,

If both neighbors support the Route Refresh and at the same time, they are configured with

neighbor soft-reconfiguration inbound

then the Soft Reconfiguration is used instead of the Route Refresh. In other words, the Route Refresh capability dynamically negotiated during the peering establishement will be ignored, the ROUTE-REFRESH messaging will not be used, and instead, both routers will store both the unfiltered and the filtered databases.

This is also stressed in the document I've linked in my previous response:

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.

Best regards,

Peter