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Friday, August 24, 2012

bgp by doyle...

chap 4, routing tcpip by doyle vol 2...

r1#sh run | begin router
router bgp 100
 bgp log-neighbor-changes
 neighbor remote-as 200

r2#sh run | beg router
router bgp 200
 bgp log-neighbor-changes
 neighbor remote-as 100

*Aug 24 18:05:23: %BGP-5-ADJCHANGE: neighbor Up

r2#sh ip bgp neigh
BGP neighbor is,  remote AS 100, external link
  BGP version 4, remote router ID
  BGP state = Established, up for 00:03:32
  Last read 00:00:48, last write 00:00:52, hold time is 180, keepalive interval is 60 seconds
  Neighbor sessions:
    1 active, is not multisession capable (disabled)
  Neighbor capabilities:
    Route refresh: advertised and received(new)
    Four-octets ASN Capability: advertised and received
    Address family IPv4 Unicast: advertised and received
    Enhanced Refresh Capability: advertised and received
    Multisession Capability:
    Stateful switchover support enabled: NO for session 1
  Message statistics:
    InQ depth is 0
    OutQ depth is 0
                         Sent       Rcvd
    Opens:                  1          1
    Notifications:          0          0
    Updates:                1          1
    Keepalives:             5          5
    Route Refresh:          0          0
    Total:                  7          7
  Default minimum time between advertisement runs is 30 seconds

 For address family: IPv4 Unicast
  BGP table version 1, neighbor version 1/0
  Output queue size : 0
  Index 2, Advertise bit 0
  2 update-group member
  Slow-peer detection is disabled
  Slow-peer split-update-group dynamic is disabled
                                 Sent       Rcvd
  Prefix activity:               ----       ----
    Prefixes Current:               0          0
    Prefixes Total:                 0          0
    Implicit Withdraw:              0          0
    Explicit Withdraw:              0          0
    Used as bestpath:             n/a          0
    Used as multipath:            n/a          0

                                   Outbound    Inbound
  Local Policy Denied Prefixes:    --------    -------
    Total:                                0          0
  Number of NLRIs in the update sent: max 0, min 0
  Last detected as dynamic slow peer: never
  Dynamic slow peer recovered: never
  Refresh Epoch: 1
  Last Sent Refresh Start-of-rib: never
  Last Sent Refresh End-of-rib: never
  Last Received Refresh Start-of-rib: never
  Last Received Refresh End-of-rib: never
                       Sent      Rcvd
    Refresh activity:           ----      ----
      Refresh Start-of-RIB          0          0
      Refresh End-of-RIB            0          0

  Address tracking is enabled, the RIB does have a route to
  Connections established 2; dropped 1
  Last reset 00:04:04, due to BGP Notification received, CEASE: unknown subcode
  Transport(tcp) path-mtu-discovery is enabled
  Graceful-Restart is disabled
Connection state is ESTAB, I/O status: 1, unread input bytes: 0       
Connection is ECN Disabled
Mininum incoming TTL 0, Outgoing TTL 1
Local host:, Local port: 60301
Foreign host:, Foreign port: 179
Connection tableid (VRF): 0

Enqueued packets for retransmit: 0, input: 0  mis-ordered: 0 (0 bytes)

Event Timers (current time is 0xE434C):
Timer          Starts    Wakeups            Next
Retrans             7          0             0x0
TimeWait            0          0             0x0
AckHold             6          4             0x0
SendWnd             0          0             0x0
KeepAlive           0          0             0x0
GiveUp              0          0             0x0
PmtuAger            1          0        0x142B74
DeadWait            0          0             0x0
Linger              0          0             0x0

iss: 4197193326  snduna: 4197193502  sndnxt: 4197193502     sndwnd:  16209
irs: 1924916453  rcvnxt: 1924916629  rcvwnd:      16209  delrcvwnd:    175

SRTT: 182 ms, RTTO: 1073 ms, RTV: 891 ms, KRTT: 0 ms
minRTT: 4 ms, maxRTT: 300 ms, ACK hold: 200 ms
Status Flags: none
Option Flags: higher precendence, nagle, path mtu capable

Datagrams (max data segment is 1460 bytes):
Rcvd: 12 (out of order: 0), with data: 7, total data bytes: 175
Sent: 13 (retransmit: 0 fastretransmit: 0),with data: 7, total data bytes: 175

the state, is it's finite state machine...
add another router with copper...

note in the below diagram the networks are and 1.224/30.  the interface addresses are correct... i'm not fixing the diagram for that flaw... so there...

router bgp 100
neighbor remote-as 100
neighbor remote-as 200

notice the rid for r1...

r3#sh ip bgp neigh
BGP neighbor is,  remote AS 100, internal link
  BGP version 4, remote router ID
  BGP state = Established, up for 00:03:09

the neighbor is .221 but the rid is it's highest interface which happens to be connected to as200...

the rules for rid's are just like ospf... it'll choose the highest loopback, and without a loopback, it chooses the highest physical interface... using a loopback is preferred... for a discussion of this, go here:

also, according to doyle...

Cisco’s BGP continues to use a router ID learned from a physical interface, even if the interface subsequently fails or is deleted. Therefore, the stability of a loopback interface is only a minor advantage. The primary benefit is the capability to control the router ID, making it easily distinguishable from other IP addresses.

add a loopback on r1...

r1(config)#interface loopback 0
r1(config-if)#ip address
*Aug 24 19:10:30: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback0, changed state to up
*Aug 24 19:10:31: %SYS-5-CONFIG_I: Configured from console by console
r1#clear ip bgp *
*Aug 24 19:10:48: %BGP-5-ADJCHANGE: neighbor Down User reset
*Aug 24 19:10:48: %BGP_SESSION-5-ADJCHANGE: neighbor IPv4 Unicast topology base removed from session  User reset
*Aug 24 19:10:48: %BGP-5-ADJCHANGE: neighbor Down User reset
*Aug 24 19:10:48: %BGP_SESSION-5-ADJCHANGE: neighbor IPv4 Unicast topology base removed from session  User reset
*Aug 24 19:10:48: %BGP-5-ADJCHANGE: neighbor Up
*Aug 24 19:10:48: %BGP-5-ADJCHANGE: neighbor Up

you have to clear bgp  for it to show up...

r3# sh ip bgp neigh
BGP neighbor is,  remote AS 100, internal link
  BGP version 4, remote router ID
  BGP state = Established, up for 00:01:21

but you knew that...

you can also set it manually using bgp router-id x.x.x.x

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