Table of Contents
BGP Soft Reset EnhancementFeature Overview
Managing Routing Policy Changes
Benefits
Restrictions
Related Documents
Supported Platforms
Supported Standards, MIBs, and RFCs
Prerequisites
Configuration Tasks
Configuring BGP Soft Reset
Configuring BGP Dynamic Inbound Soft Reset
Configuring BGP Outbound Soft Reset
Configuring BGP Soft Reset Using Stored Routing Policy Information
Verifying BGP Soft ResetConfiguring BGP Outbound Soft Reset
Configuring BGP Soft Reset Using Stored Routing Policy Information
Configuration Examples
Dynamic Inbound Soft Reset
Inbound Soft Reset Using Stored Information
Command Reference
clear ip bgp
show ip bgp neighbors
BGP Soft Reset Enhancement
This feature module describes
the Border Gateway Protocol (BGP) Soft Reset Enhancement feature. It
includes information on the benefits of the new feature, supported
platforms, related documents, and so forth.
Feature Overview
Routing policies for a peer
include all the configurations such as route-map, distribute-list,
prefix-list, and filter-list that 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. There are two types of reset, hard reset and soft reset.
Clearing a BGP session using a
hard reset invalidates the cache and results in a negative impact on
the operation of networks as the information in the cache becomes
unavailable.
Soft reset is recommended
because it allows routing tables to be reconfigured and activated
without clearing the BGP session. Soft reset is done on a per-neighbor
basis. There are two types of soft reset:
Previously, in order to perform a soft reset for inbound routing table updates, the neighbor soft-reconfiguration
command directed the Cisco IOS software in the local BGP router to
store all received (inbound) routing policy updates without
modification. This method is memory-intensive and not recommended unless
absolutely necessary. (Outbound updates have never required the extra
memory and are not affected by this feature.)
With this software release,
the BGP Soft Reset Enhancement feature provides automatic support for
dynamic soft reset of inbound BGP routing table updates that is not
dependent upon stored routing table update information. The new 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.
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.
Previously, in order to
reconfigure the inbound routing table, 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 sent when a peer sends its routing table
update. Any router running BGP with this software release automatically
supports the route refresh capability. Routers 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.
Note Outbound resets have never required preconfiguration or storing of routing table updates, and remain unchanged by the BGP Soft Reset Enhancement. The procedure for an outbound reset is described in the section "Reset BGP Connections" in the Cisco IOS Release 12.0 Network Protocols Configuration Guide, Part 1.
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 Documents
Supported Platforms
Supported Standards, MIBs, and RFCs
Standards
MIB
RFCs
Prerequisites
Both BGP peers must support
the soft reset route refresh capability, first included in this software
release. If one router does not, then the only soft reconfiguration
option is to use the neighbor soft-reconfiguration command, which initiates 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:
There are two ways to perform an inbound soft reset: dynamically, and using stored routing update information.
Note 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.
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:
To determine whether a router supports the route refresh capability, use the show ip bgp neighbors command.
Command | Purpose |
---|---|
If all the BGP routers
support the route refresh capability, you can use the dynamic soft reset
method for resetting the inbound routing table.
Command | Purpose |
---|---|
Configuring BGP Outbound Soft Reset
Outbound soft resets do not require any preconfiguration. Using the keyword soft specifies that a soft reset be performed.
Command | Purpose |
---|---|
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.
Command | Purpose |
---|---|
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.
Command | Purpose |
---|---|
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:
Configuration Examples
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.
Inbound 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.
Command 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.
In Cisco IOS Release 12.0(1)T or later, you can search and filter the output for show and more
commands. This functionality is useful when you need to sort through
large amounts of output, or if you want to exclude output that you do
not need to see.
To use this functionality, enter a show or more command followed by the "pipe" character (|), one of the keywords begin, include, or exclude, and an expression that you want to search or filter on:
Following is an example of the show atm vc command in which you want the command output to begin with the first line where the expression "PeakRate" appears:
For more information on the search and filter functionality, refer to the Cisco IOS Release 12.0(1)T feature module titled CLI String Search.
clear ip bgp
- clear ip bgp {* | address | peer-group-name} [soft [in | out]]
Syntax Description
Defaults
Command Modes
Command History
Release | Modification |
---|---|
Usage Guidelines
You can reset inbound routing
table updates dynamically or by generating new updates using stored
update information. Using stored update information requires 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:
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.
To generate new inbound
updates from stored update information (rather than dynamically),
without resetting the BGP session, you must first preconfigure the local
BGP router using the neighbor soft-reconfiguration
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.
Examples
The following example clears the inbound session with the neighbor 131.108.1.1 without resetting the session:
The following example clears the outbound session with the peer-group corp without resetting the session:
Related Commands
Command | Description |
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
Command History
Release | Modification |
---|---|
Examples
Table 1 describes the significant fields shown in the display.
Table 1 show ip bgp neighbors Field Descriptions
The following is sample output from the show ip bgp neighbors command with the advertised-routes keyword in privileged EXEC mode:
The following is sample output from the show ip bgp neighbors command with the routes keyword in privileged EXEC mode:
Table 2 describes the significant fields shown in the displays.
Table 2 show ip bgp neighbors advertised-routes and routes Field Descriptions
Field | Description |
---|---|
Origin of the entry. The origin code is placed at the end of each line in the table. It can be one of the following values:
|
|
The following is sample output from the show ip bgp neighbors command with the paths keyword in privileged EXEC mode:
Table 3 describes the significant fields shown in the display.
Table 3 show ip bgp neighbors paths Field Descriptions
Field | Description |
---|---|