[c-nsp] TCP throttle on directly connected 10G 9000 MTU 8940 MSS

[schilling]

IOS (tm) s72033_rp Software (s72033_rp-ADVENTERPRISEK9_WAN-M), Version
12.2(18)SXF7,
RELEASE SOFTWARE (fc1)
Supervisor Engine 720 (Active)            WS-SUP720-3BXL
CEF720 8 port 10GE with DFC            WS-X6708-10GE


We had a directly connected 10G link with MTU 9000. BGP session had MSS 8940
negotiated. But it is complaining tcp throttle due to closed TCP window.
When we disabled the ip tcp path-mtu-discovery, bgp session is fine and MSS
is only 516 which is not what we want.
debug bgp keepalive showed that one peer is not able to send  KEEPALIVE to
the peer with colsed tcp window.

We are so confused since we have another directly connected 10G link, BGP
with MSS 8940 is fine. we do have big traffic, but it usually around 1G.

we don't have any mls rate-limit other than the default configured.

configuration on switch with closed TCP window.

on vlan level
 mtu 9000
 bandwidth 10000000
  ip mask-reply
 no ip proxy-arp
 ip pim sparse-mode
 no ip mroute-cache
 load-interval 30
 no mop enabled
 hold-queue 4096 in
 hold-queue 4096 out


int te1/1
 mtu 9216
 no ip address
 load-interval 30
 keepalive 1
 udld port
 wrr-queue cos-map 1 1 1
 wrr-queue cos-map 1 2 0 2 3
 wrr-queue cos-map 2 1 4
 wrr-queue cos-map 2 2 6 7
 rcv-queue threshold 1 100 100 100 100
 rcv-queue cos-map 1 1 1
 rcv-queue cos-map 1 2 0 2 3
 rcv-queue cos-map 1 3 4 6 7
 no snmp trap link-status
 mls qos trust dscp
 flowcontrol receive on
 flowcontrol send on
  random-detect
 fair-queue

sh queueing int te1/1
interface TenGigabitEthernet1/1 queueing strategy:  Weighted Round-Robin
  Port QoS is enabled
  Trust state: trust DSCP
  Extend trust state: not trusted [COS = 0]
  Default COS is 0
    Queueing Mode In Tx direction: mode-cos
    Transmit queues [type = 1p7q4t]:
    Queue Id    Scheduling  Num of thresholds
    -----------------------------------------
       01         WRR                 04
       02         WRR                 04
       03         WRR                 04
       04         WRR                 04
       05         WRR                 04
       06         WRR                 04
       07         WRR                 04
       08         Priority               01

show queueing did not show any drop on any queue. on vlan input queue, there
is some drops/flushes, but no any drops.

Any suggestion will be greatly appreciated.

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