I have an mGRE tunnel configured between 6504 switches ( running IOS12.2(18)SXF7). The two switchs are at remote sites with an IPSec tunnel connecting the 2 sites.
My issue is that I am seeing Output drops on the Tunnel interface, which is usually associated with failed network connection or data transfers. While the load level on the interface looks to be pretty minimal. This looks to be leading to lost connections during large data transfers and application connections that tend to send large data packets.
I have tried setting the MTU size to 1400 on the Tunnel interface and the next hop equipment just in case it is an issue with GRE tunnel packet fragmentation but it has not seems to make a difference. I have also increased teh Hold-Queue with out any affect.
This only seems to be a problem with connections that are sending large data packets.
The interfaces\ports used for the link between the switch and the IPSec tunnel device are set to be routeed ports (as opposed to switch ports).
The Tunnel interface config is below, this is the hub mGRE interface:
interface Tunnel1
description Test
ip address 172.23.254.1 255.255.255.0
no ip redirects
ip mtu 1400
ip flow ingress
ip nhrp authentication test
ip nhrp map multicast dynamic
ip nhrp network-id 123
ip nhrp holdtime 600
ip route-cache flow
no ip split-horizon eigrp 123
load-interval 30
tunnel source GigabitEthernet5/1
tunnel mode gre multipoint
tunnel key 123
hold-queue 500 out
end
Show Interface for the Tunnel interface:
Tunnel1 is up, line protocol is up
Hardware is Tunnel
Description: Test
Internet address is 172.25.254.1/24
MTU 1514 bytes, BW 9 Kbit, DLY 500000 usec,
reliability 255/255, txload 113/255, rxload 1/255
Encapsulation TUNNEL, loopback not set
Keepalive not set
Tunnel source 172.25.242.5 (GigabitEthernet5/1), fastswitch TTL 255
Tunnel protocol/transport multi-GRE/IP, key 0x313, sequencing disabled
Checksumming of packets disabled, fast tunneling enabled
Last input 00:00:01, output 00:00:00, output hang never
Last clearing of "show interface" counters 00:20:27
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 115
Queueing strategy: fifo
Output queue: 0/500 (size/max)
30 second input rate 0 bits/sec, 0 packets/sec
30 second output rate 4000 bits/sec, 3 packets/sec
L2 Switched: ucast: 0 pkt, 0 bytes - mcast: 0 pkt, 0 bytes
L3 in Switched: ucast: 0 pkt, 0 bytes - mcast: 0 pkt, 0 bytes mcast
L3 out Switched: ucast: 0 pkt, 0 bytes mcast: 0 pkt, 0 bytes
555 packets input, 72176 bytes, 0 no buffer
Received 0 broadcasts (332 IP multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
3481 packets output, 935513 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 output buffer failures, 0 output buffers swapped out
