09-07-2007 08:11 PM - edited 03-03-2019 06:39 PM
We've experienced "output drops" on GRE tunnel interfaces with no IPSec. At first we suspected that it's caused by the outbound QoS policy but then we couldn't find any drops when we did a "show policy-map interface tunnel xxx". We've removed the service-policy command but still there're output drops. The WAN link for carrying GRE traffic is not even congested and the CPU utilization of the router is under 10%. The router model is a Cisco 7206VXR. The physical WAN interface is on the GE port on NPE-G1.
interface Tunnel1
bandwidth 20000
ip address 20.x.x.2 255.255.255.252
ip mtu 1440
ip multicast boundary MCAST-ACL
ip route-cache flow
ip tcp adjust-mss 1360
ip ospf network point-to-point
ip ospf cost 1000
qos pre-classify
keepalive 10 3
no clns route-cache
tunnel source GigabitEthernet0/3
tunnel destination 10.1.2.1
!
interface GigabitEthernet0/3
bandwidth 20000
ip address 100.1.2.2 255.255.255.252
ip accounting precedence input
ip accounting precedence output
ip route-cache flow
duplex full
speed 100
media-type rj45
no negotiation auto
no clns route-cache
max-reserved-bandwidth 100
!
R2#sh int t1
Tunnel251 is up, line protocol is up
Hardware is Tunnel
Internet address is 20.1.2.2/30
MTU 1514 bytes, BW 20000 Kbit, DLY 500000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation TUNNEL, loopback not set
Keepalive set (10 sec), retries 3
Tunnel source 100.1.2.2 (GigabitEthernet0/3), destination 10.1.2.1
Tunnel protocol/transport GRE/IP
Key disabled, sequencing disabled
Checksumming of packets disabled
Tunnel TTL 255
Fast tunneling enabled
Tunnel transmit bandwidth 8000 (kbps)
Tunnel receive bandwidth 8000 (kbps)
Last input 00:00:02, output 00:00:01, output hang never
Last clearing of "show interface" counters 6d22h
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 1703
Queueing strategy: fifo (QOS pre-classification)
Output queue: 0/0 (size/max)
5 minute input rate 1000 bits/sec, 1 packets/sec
5 minute output rate 1000 bits/sec, 1 packets/sec
10734208 packets input, 6541019418 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
10374287 packets output, 3059318677 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 output buffer failures, 0 output buffers swapped out
R2#
So what are the factors that can contrubute to the output drops of a GRE tunnel interface without any QOS strategies implemented on the tunnel interface?
09-07-2007 11:46 PM
Looking at the ratio of transmitted vs dropped packets it appears to be a pretty rare issue.
What I can think of are packets that are too large to be encapsulated in GRE but have DF set. You have lagerely ruled this out by setting tcp-mss but this parameter only applies to tcp-traffic.
Regards,
Leo
10-07-2007 11:20 PM
Hi. Did you finally solve the issue cause i 'm now meeting same problem on a new mpls circuit.
Regards
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