BGP Soft reset

[lmanavalan]

Hi

In my configuration we have BGP peering with ISP and we have configured route-map to mach particular routes to be learnt from ISP on inward direction.

We are planning to update the route-map but for changes to get into effect i need to perform soft reset but i am not sure where dynamic soft reset is capable or not. Below is the "sh ip bgp neighbor" output.

Please note there is not "neighbor soft-reconfiguration inbound" configured on the switch.

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Current Version 12.2(18)SXF13

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Edge_switch_C6509#sh ip bgp neighbors 10.x.x.x
BGP neighbor is 10.x.x.x,  remote AS xxxxx, external link
 Member of peer-group toxxxxx for session parameters
  BGP version 4, remote router ID 10.x.x.x
  BGP state = Established, up for 32w2d
  Last read 00:00:01, last write 00:00:02, hold time is 15, keepalive interval is 5 seconds
  Configured hold time is 15, keepalive interval is 5 seconds
  Neighbor capabilities:
    Route refresh: advertised and received(new)
    Address family IPv4 Unicast: advertised and received
  Message statistics:
    InQ depth is 0
    OutQ depth is 0
                         Sent       Rcvd
    Opens:                  2          2
    Notifications:          0          0
    Updates:             7909       3640
    Keepalives:       9264100    9045990
    Route Refresh:          0          0
    Total:            9272011    9049632
  Default minimum time between advertisement runs is 30 seconds
 
 For address family: IPv4 Unicast
  BGP table version 88049, neighbor version 88049/0
 Output queue size : 0
  Index 4, Offset 0, Mask 0x10
  4 update-group member
  to65000 peer-group member
  Private AS number removed from updates to this neighbor
  Inbound path policy configured
  Route map for incoming advertisements is Route_From_ISP
                                 Sent       Rcvd
  Prefix activity:               ----       ----
    Prefixes Current:             614          3 (Consumes 144 bytes)
    Prefixes Total:              5778        108
    Implicit Withdraw:           3630        105
    Explicit Withdraw:           1739          0
    Used as bestpath:             n/a          0
    Used as multipath:            n/a          3
 
                                   Outbound    Inbound
  Local Policy Denied Prefixes:    --------    -------
    route-map:                            0      33848
    AS_PATH loop:                       n/a       5797
    Bestpath from this peer:             13        n/a
    Suppressed due to dampening:          5        n/a
    Total:                               18      39645
  Number of NLRIs in the update sent: max 285, min 0
 
  Connections established 2; dropped 1
  Last reset 32w2d, due to Peer closed the session
Connection state is ESTAB, I/O status: 1, unread input bytes: 0
Local host: 10.2.249.9, Local port: 179
Foreign host: 10.2.249.10, Foreign port: 28117
 
Enqueued packets for retransmit: 0, input: 0  mis-ordered: 0 (0 bytes)
 
Event Timers (current time is 0xACAA19AB0):
Timer          Starts    Wakeups            Next
Retrans       3917546        185             0x0
TimeWait            0          0             0x0
AckHold       3822213    3482847             0x0
SendWnd             0          0             0x0
KeepAlive           0          0             0x0
GiveUp              0          0             0x0
PmtuAger            0          0             0x0
DeadWait            0          0             0x0
 
iss:  711296179  snduna:  785913933  sndnxt:  785913933     sndwnd:  14959
irs:  160149336  rcvnxt:  233251483  rcvwnd:      14997  delrcvwnd:   1387
 
SRTT: 300 ms, RTTO: 303 ms, RTV: 3 ms, KRTT: 0 ms
minRTT: 0 ms, maxRTT: 348 ms, ACK hold: 200 ms
Flags: passive open, retransmission timeout, nagle, gen tcbs
 
Datagrams (max data segment is 1460 bytes):
Rcvd: 7591197 (out of order: 0), with data: 3822932, total data bytes: 73102146
Sent: 7451321 (retransmit: 185), with data: 3918523, total data bytes: 74617753

Thanks

Logesh

[Bilal Nawaz · Accepted solution]

Hello, I kept this bookmarked and sharing - very good read indeed: https://supportforums.cisco.com/discussion/11379456/clear-ip-bgp-soft-command

[Emmanouil Patiniotakis]

Since show ip bgp nei lists  "Route refresh: advertised and received(new)" then you can do a soft reset without affecting the BGP session. This capability gives the ability to request or/and send new advertisement after applying a route policy without the need to tear down BGP session.

[lmanavalan]

Hi

The pre-requirement for executing the "clear ip bgp neighbor" is to have this configured "neightbor re-configuration inbound". But my switch do not have this configured so i am planning to configure it first to allow me to perform soft reset. I have another concern where my switch currently running on avarage of 80% memeory utilistation. Wondering what will the consiquence of adding more memory consuming configuration.

Thanks

Logesh

[Yandy Ramirez]

soft-reconfiguration inbound and route refresh capabilities are two different things. They are not dependent on each other. soft-reconfiguration inbound is used in cases where route refresh capabilities are not supported "this is rarely the case any more". That command is not necessary in fact, should be avoided if you're having memory starvation or just carry full routes unless you're troubleshooting filters.

With the soft-reconfiguration inbound, your router keeps two copies of the bgp table, one with the filters applied and another with full unedited copy. Your router supports router refresh, no need for soft-reconfiguration command.

[Emmanouil Patiniotakis]

As i told on my answer, soft reconfiguration i snot needed in order to clear bgp session without tearing down since route refresh is enables (and it is from the output you provided). In addition soft reconfiguration besides it is useless, it will rise the memory you use because it keeps two copies of routing table.