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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.
This document includes the following sections:
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.
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.
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.
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.
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.
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.
Both BGP peers must support the route refresh capability. If one side 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.
No new or modified MIBs are supported by this feature.
No new or modified RFCs are supported by this feature.
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.
See the following "Configuring BGP Soft Reset" section for configuration tasks for the BGP Soft Reset Enhancement feature. This task is required.
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:
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 command.
| Command | Purpose |
|---|---|
Router# show ip bgp [network] [network-mask] [longer-prefixes] | Shows whether a neighbor supports the route refresh capability. If the specified router supports the route refresh capability, the following message is displayed: Received route refresh capability from peer. |
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 |
|---|---|
Router# clear ip bgp {* | address | peer-group-name} soft in | Performs a dynamic soft reset on the connection specified in the command. |
Outbound soft resets do not require any preconfiguration. Using the keyword soft specifies that a soft reset be performed.
| Command | Purpose |
|---|---|
Performs a soft reset on the connection specified in the command. |
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 |
|---|---|
Router config# 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.
| Command | Purpose |
|---|---|
Router config# clear ip bgp {* | address | peer-group-name} soft in | Performs a soft reset on the connection specified in the command. |
Verify whether a soft reset is successful by checking information about the routing table and about BGP neighbors.
Step 1 Enter the show ip bgp command to display entries in the BGP routing table. The following output shows that the peer supports the route refresh capability.
Router# show ip bgp
BGP table version is 716977, local router ID is 193.0.32.1
Status codes: s suppressed, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Received route refresh capability from peer.
Network Next Hop Metric LocPrf Weight Path
* i3.0.0.0 193.0.22.1 0 100 0 1800 1239 ?
*>i 193.0.16.1 0 100 0 1800 1239 ?
* i6.0.0.0 193.0.22.1 0 100 0 1800 690 568 ?
*>i 193.0.16.1 0 100 0 1800 690 568 ?
* i7.0.0.0 193.0.22.1 0 100 0 1800 701 35 ?
*>i 193.0.16.1 0 100 0 1800 701 35 ?
* 198.92.72.24 0 1878 704 701 35 ?
* i8.0.0.0 193.0.22.1 0 100 0 1800 690 560 ?
*>i 193.0.16.1 0 100 0 1800 690 560 ?
* 198.92.72.24 0 1878 704 701 560 ?
* i13.0.0.0 193.0.22.1 0 100 0 1800 690 200 ?
*>i 193.0.16.1 0 100 0 1800 690 200 ?
* 198.92.72.24 0 1878 704 701 200 ?
* i15.0.0.0 193.0.22.1 0 100 0 1800 174 ?
*>i 193.0.16.1 0 100 0 1800 174 ?
* i16.0.0.0 193.0.22.1 0 100 0 1800 701 i
*>i 193.0.16.1 0 100 0 1800 701 i
* 198.92.72.24 0 1878 704 701 i
Step 2 Enter the show ip bgp neighbors command to display information about the BGP and TCP connections to neighbors.
Router# show ip bgp neighbors 171.69.232.178 BGP neighbor is 171.69.232.178, remote AS 10, external link Index 1, Offset 0, Mask 0x2 Inbound soft reconfiguration allowed BGP version 4, remote router ID 171.69.232.178 BGP state = Established, table version = 27, up for 00:06:12 Last read 00:00:12, hold time is 180, keepalive interval is 60 seconds Minimum time between advertisement runs is 30 seconds Received 19 messages, 0 notifications, 0 in queue Sent 17 messages, 0 notifications, 0 in queue Inbound path policy configured Route map for incoming advertisements is testing Connections established 2; dropped 1 Connection state is ESTAB, I/O status: 1, unread input bytes: 0 Local host: 171.69.232.181, Local port: 11002 Foreign host: 171.69.232.178, Foreign port: 179 Enqueued packets for retransmit: 0, input: 0, saved: 0 Event Timers (current time is 0x530C294): Timer Starts Wakeups Next Retrans 12 0 0x0 TimeWait 0 0 0x0 AckHold 12 10 0x0 SendWnd 0 0 0x0 KeepAlive 0 0 0x0 GiveUp 0 0 0x0 PmtuAger 0 0 0x0 iss: 133981889 snduna: 133982166 sndnxt: 133982166 sndwnd: 16108 irs: 3317025518 rcvnxt: 3317025810 rcvwnd: 16093 delrcvwnd: 291 SRTT: 441 ms, RTTO: 2784 ms, RTV: 951 ms, KRTT: 0 ms minRTT: 0 ms, maxRTT: 300 ms, ACK hold: 300 ms Flags: higher precedence, nagle Datagrams (max data segment is 1460 bytes): Rcvd: 15 (out of order: 0), with data: 12, total data bytes: 291 Sent: 23 (retransmit: 0), with data: 11, total data bytes: 276
This section provides the following configuration examples:
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.
Router# clear ip bgp 131.108.1.1 soft in
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 100 neighbor 131.108.1.1 remote-as 200 neighbor 131.108.1.1 soft-reconfiguration inbound
The following example clears the session with the neighbor 131.108.1.1.
clear ip bgp 131.108.1.1 soft in
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:
command | {begin | include | exclude} regular-expression
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:
show atm vc | begin PeakRate
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.
To reset a Border Gateway Protocol (BGP) connection or session, use the clear ip bgp EXEC command.
clear ip bgp {* | address | peer-group-name} [soft [in | out]]
* | Resets all current BGP sessions. |
address | Resets only the identified BGP neighbor. |
peer-group-name | Resets the specified BGP peer group. |
soft | (Optional) Soft reset. Does not reset the session. |
in | out | (Optional) Triggers inbound or outbound soft reset. If the in or out option is not specified, both inbound and outbound soft reset are triggered. |
No default behavior or values.
EXEC
| Release | Modification |
|---|---|
10.0 | This command was introduced. |
12.0(6)T | The dynamic inbound soft reset capability was added. |
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 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.
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.
Use this command whenever any of the following changes occur:
The following example clears all entries from the host name-and-address cache (hard reset):
clear host *
The following example clears the inbound session with the neighbor 131.108.1.1 without resetting the session:
clear ip bgp 131.108.1.1 soft in
The following example clears the outbound session with the peer-group corp without resetting the session:
clear ip bgp corp soft out
| Command | Description |
neighbor soft-reconfiguration | Configures the Cisco IOS software to start storing inbound routing table updates. |
show ip bgp | Displays entries in the BGP routing table. |
To display entries in the Border Gateway Protocol (BGP) routing table, use the show ip bgp EXEC command.
show ip bgp [network] [network-mask] [longer-prefixes]
network | (Optional) Network number, entered to display a particular network in the BGP routing table. |
network-mask | (Optional) Displays all BGP routes matching the address/mask pair. |
longer-prefixes | (Optional) Displays route and more specific routes. |
No default behavior or values.
EXEC
| Release | Modification |
|---|---|
10.0 | This command was introduced. |
12.0 | The display of prefix advertisement statistics was added. |
12.0(6)T | The display of a message indicating support for route refresh capability was added. |
The following is sample output from the show ip bgp command:
Router# show ip bgp
BGP table version is 716977, local router ID is 193.0.32.1
Status codes: s suppressed, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Received route refresh capability from peer.
Network Next Hop Metric LocPrf Weight Path
* i3.0.0.0 193.0.22.1 0 100 0 1800 1239 ?
*>i 193.0.16.1 0 100 0 1800 1239 ?
* i6.0.0.0 193.0.22.1 0 100 0 1800 690 568 ?
*>i 193.0.16.1 0 100 0 1800 690 568 ?
* i7.0.0.0 193.0.22.1 0 100 0 1800 701 35 ?
*>i 193.0.16.1 0 100 0 1800 701 35 ?
* 198.92.72.24 0 1878 704 701 35 ?
* i8.0.0.0 193.0.22.1 0 100 0 1800 690 560 ?
*>i 193.0.16.1 0 100 0 1800 690 560 ?
* 198.92.72.24 0 1878 704 701 560 ?
* i13.0.0.0 193.0.22.1 0 100 0 1800 690 200 ?
*>i 193.0.16.1 0 100 0 1800 690 200 ?
* 198.92.72.24 0 1878 704 701 200 ?
* i15.0.0.0 193.0.22.1 0 100 0 1800 174 ?
*>i 193.0.16.1 0 100 0 1800 174 ?
* i16.0.0.0 193.0.22.1 0 100 0 1800 701 i
*>i 193.0.16.1 0 100 0 1800 701 i
* 198.92.72.24 0 1878 704 701 i
Table 1 describes significant fields shown in the display.
| Field | Description |
|---|---|
BGP table version | Internal version number of the table. This number is incremented whenever the table changes. |
local router ID | IP address of the router. |
Status codes | Status of the table entry. The status is displayed at the beginning of each line in the table. It can be one of the following values: s---The table entry is suppressed. *---The table entry is valid. >---The table entry is the best entry to use for that network. i---The table entry was learned via an internal BGP session. |
Origin codes | Indicates the 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: i---Entry originated from IGP and was advertised with a network router configuration command. e---Entry originated from EGP. ?---Origin of the path is not clear. Usually this is a router that is redistributed into BGP from an IGP. |
route refresh capability | Indicates that the peer supports dynamic soft reconfiguration using the route refresh capability. |
Network | IP address of a network entity. |
Next Hop | IP address of the next system that is used when forwarding a packet to the destination network. An entry of 0.0.0.0 indicates that the router has some non-BGP routes to this network. |
Metric | If shown, this is the value of the interautonomous system metric. This field frequently is not used. |
LocPrf | Local preference value as set with the set local-preference route-map configuration command. The default value is 100. |
Weight | Weight of the route as set via autonomous system filters. |
Path | Autonomous system paths to the destination network. There can be one entry in this field for each autonomous system in the path. |
The following is sample output from the show ip bgp command when you specify longer-prefixes:
Router# show ip bgp 198.92.0.0 255.255.0.0 longer-prefixes BGP table version is 1738, local router ID is 198.92.72.24 Status codes: s suppressed, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path *> 198.92.0.0 198.92.72.30 8896 32768 ? * 198.92.72.30 0 109 108 ? *> 198.92.1.0 198.92.72.30 8796 32768 ? * 198.92.72.30 0 109 108 ? *> 198.92.11.0 198.92.72.30 42482 32768 ? * 198.92.72.30 0 109 108 ? *> 198.92.14.0 198.92.72.30 8796 32768 ? * 198.92.72.30 0 109 108 ? *> 198.92.15.0 198.92.72.30 8696 32768 ? * 198.92.72.30 0 109 108 ? *> 198.92.16.0 198.92.72.30 1400 32768 ? * 198.92.72.30 0 109 108 ? *> 198.92.17.0 198.92.72.30 1400 32768 ? * 198.92.72.30 0 109 108 ? *> 198.92.18.0 198.92.72.30 8876 32768 ? * 198.92.72.30 0 109 108 ? *> 198.92.19.0 198.92.72.30 8876 32768 ? * 198.92.72.30 0 109 108 ?
The following is sample output from the show ip bgp command, showing information for prefix 3.0.0.0:
show ip bgp 3.0.0.0 BGP routing table entry for 3.0.0.0/8, version 628 Paths: (1 available, best #1) Advertised to peer-groups: ebgp Advertised to non peer-group peers: 171.69.232.162 109 65000 297 701 80 171.69.233.56 from 171.69.233.56 (172.19.185.32) Origin incomplete, localpref 100, valid, external, best, ref 2
| Command | Description |
clear ip bgp | Resets a BGP connection or session. |
neighbor soft-reconfiguration | Configure the Cisco IOS software to start storing inbound routing table updates. |
Posted: Wed Jul 26 19:11:04 PDT 2000
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