12-20-2007 09:06 PM - edited 03-03-2019 08:01 PM
We've experiencing bgp dropping that also causes our phones on remote site to drop but it will be up again in sec. Can someone help me what could be causing it.
below is the sho bgp results:
3750Switch#sho ip bgp neighbors x.x.x.x
BGP neighbor is x.x.x.x, remote AS 7474, external link
BGP version 4, remote router ID y.y.y.y
BGP state = Established, up for 21:02:37
Last read 00:00:00, hold time is 10, keepalive interval is 3 seconds
Configured hold time is 10, keepalive interval is 3 seconds
Minimum holdtime from neighbor is 0 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: 4 3
Notifications: 1 2
Updates: 39 33
Keepalives: 2721668 2449710
Route Refresh: 0 0
Total: 2721712 2449748
Default minimum time between advertisement runs is 30 seconds
For address family: IPv4 Unicast
BGP table version 178, neighbor version 178/0
Output queue sizes : 0 self, 0 replicated
Index 1, Offset 0, Mask 0x2
1 update-group member
Sent Rcvd
Prefix activity: ---- ----
Prefixes Current: 27 18 (Consumes 936 bytes)
Prefixes Total: 27 18
Implicit Withdraw: 9 0
Explicit Withdraw: 0 0
Used as bestpath: n/a 18
Used as multipath: n/a 0
Outbound Inbound
Local Policy Denied Prefixes: -------- -------
Total: 0 0
Number of NLRIs in the update sent: max 16, min 0
Connections established 3; dropped 2
Last reset 21:04:21, due to BGP Notification sent, hold time expired
Connection state is ESTAB, I/O status: 1, unread input bytes: 0
Local host: x.x.x.x, Local port: 64932
Foreign host: x.x.x.x, Foreign port: 179
Enqueued packets for retransmit: 1, input: 0 mis-ordered: 0 (0 bytes)
Event Timers (current time is 0x1E6B03675):
Timer Starts Wakeups Next
Retrans 26239 977 0x0
TimeWait 0 0 0x0
AckHold 22737 19460 0x0
SendWnd 0 0 0x0
KeepAlive 0 0 0x0
GiveUp 0 0 0x0
PmtuAger 0 0 0x0
DeadWait 0 0 0x0
iss: 32448291 snduna: 32928771 sndnxt: 32928771 sndwnd: 15776
irs: 514194396 rcvnxt: 514626744 rcvwnd: 15624 delrcvwnd: 760
SRTT: 300 ms, RTTO: 303 ms, RTV: 3 ms, KRTT: 0 ms
minRTT: 0 ms, maxRTT: 604 ms, ACK hold: 200 ms
Flags: higher precedence, retransmission timeout, nagle
Datagrams (max data segment is 1460 bytes):
Rcvd: 46518 (out of order: 0), with data: 22737, total data bytes: 432347
Sent: 45056 (retransmit: 977), with data: 25263, total data bytes: 480479
3750Switch#
12-21-2007 12:00 AM
You have very aggressive timers set on your BGP session. this could be a problem if the latency between the endpoints is higher
Narayan
12-21-2007 07:46 AM
I agree with you that the timers are aggressive.
However, the latency between the 2 endpoints of an external BGP session is normally counted in milliseconds.
From Athens/Greece to New York you can certainly find links with RTT just 136 msec. Half a second round-trip delay is noticable and unacceptable for an end-user, so no question about a session via a single direct link (or even a multi-hop session a few hops away).
The problem with aggressive timers demonstrates itself when another more fundamental one appears, namely a constant flap of the physical layer.
A malfunctioning physical layer that goes up and down, will cause your BGP to also flap, and the BGP flaps will be often if your timers are aggressive. BGP flaps can potentially affect other parts of your network and cause general instability.
In summary, timers need to be fixed to protect rest of you network and your router's CPU, rather than the session itself.
Also check your physical layer (cabling, contact your circuit provider), since this is the usual suspect for constant BGP flaps.
Do not forget to also check that the BGP peer router is ok.
Kind Regards,
M.
01-03-2008 06:52 PM
Thanks marikakis
Could you tell what could be the timer we could set? The link is just w/in the country.
thnx again
01-03-2008 06:58 PM
I work for an ISP and we use 15 second keep alive and 45 second hold time and it seems to work fine.
router bgp 65000
timers 15 45
Just thought I'd give you some other real world config, I am sure others have different values.
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