Tuesday, February 21, 2006

 

BGP router boot order. (Question #20)

Note that this really just a question for fun and does not involve any troubleshooting per se.

Assume that a pair of routers that are configured and working correctly with BGP is rebooted in some sequence which is not disclosed to you. After the routers come back up, can you tell by looking only at the output from the "show ip bgp neighbor " command what the sequence in which the routers were rebooted was?

For your reference, here is the output from the show command in question from a running router. Remember that this is the only output made available to you to determine the boot order.


R1#show ip bgp neighbor 10.1.1.1
BGP neighbor is 10.1.1.1, remote AS 100, external link
BGP version 4, remote router ID 10.1.1.1
BGP state = Established, up for 00:01:30
Last read 00:00:31, last write 00:00:30, hold time is 180, keepalive interval is 60 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: 1 1
Notifications: 0 0
Updates: 1 0
Keepalives: 2 2
Route Refresh: 0 0
Total: 4 3
Default minimum time between advertisement runs is 30 seconds

For address family: IPv4 Unicast
BGP table version 2, neighbor version 2/0
Output queue size : 0
Index 1, Offset 0, Mask 0x2
1 update-group member
Sent Rcvd
Prefix activity: ---- ----
Prefixes Current: 1 0
Prefixes Total: 1 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 1, min 1

Connections established 1; dropped 0
Last reset never
Connection state is ESTAB, I/O status: 1, unread input bytes: 0
Local host: 10.1.1.2, Local port: 179
Foreign host: 10.1.1.1, Foreign port: 11000

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

Event Timers (current time is 0x27300):
Timer Starts Wakeups Next
Retrans 4 0 0x0
TimeWait 0 0 0x0
AckHold 3 1 0x0
SendWnd 0 0 0x0
KeepAlive 0 0 0x0
GiveUp 0 0 0x0
PmtuAger 0 0 0x0
DeadWait 0 0 0x0

iss: 488026557 snduna: 488026693 sndnxt: 488026693 sndwnd: 16249
irs: 2648882780 rcvnxt: 2648882864 rcvwnd: 16301 delrcvwnd: 83

SRTT: 124 ms, RTTO: 1405 ms, RTV: 1281 ms, KRTT: 0 ms
minRTT: 8 ms, maxRTT: 300 ms, ACK hold: 200 ms
Flags: passive open, retransmission timeout, nagle, gen tcbs

Datagrams (max data segment is 1460 bytes):
Rcvd: 7 (out of order: 0), with data: 3, total data bytes: 83
Sent: 5 (retransmit: 0), with data: 3, total data bytes: 135
R1#


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