1

I've encountered an abnormal behavior of my GRE Tunnel between two routers Cisco. When I ping the remote physical IP of the tunnel, I reach it without any loss. But when I ping the remote Tunnel IP, I have 50% loss. Have anyone already meet this issue and can you help solving it ?

Topology:

R1 Tunnel0 <-> R2 <-> R3 Tunnel1

  • Tunnel0 configuration
interface Tunnel0
 ip address 192.168.1.1 255.255.255.252
 ip mtu 1500
 ip tcp adjust-mss 1400
 qos pre-classify
 tunnel source 192.168.10.2
 tunnel destination 192.168.144.1
  • Tunnel1 configuration
interface Tunnel1
 ip address 192.168.1.2 255.255.255.252
 ip mtu 1500
 ip tcp adjust-mss 1400
 qos pre-classify
 tunnel source 192.168.144.1
 tunnel destination 192.168.10.2
  • Physical remote IP ping : 0% lost OK
R3#ping 192.168.10.2 sou 192.168.144.1 repeat 50

Type escape sequence to abort.
Sending 50, 100-byte ICMP Echos to 192.168.10.2, timeout is 2 seconds:
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Success rate is 100 percent (50/50), round-trip min/avg/max = 76/104/184 ms
  • Tunnel remote IP ping : 50% lost NOK
R3#ping 192.168.1.1 repeat 20   

Type escape sequence to abort.
Sending 20, 100-byte ICMP Echos to 192.168.1.1, timeout is 2 seconds:
.!..!!.!.!..!!.!.!.!
Success rate is 50 percent (10/20), round-trip min/avg/max = 64/87/116 ms
R3#

I have taken a dump and analyzed it with wireshark and the abnormal thing that i see is : Secure Sockets Layer (Ignored Unknown Record).

  • 2
    can you provide any information about the underlaying network? I Wonder why you configure "ip mtu 1500" but are MSS clamping TCP to 1400 Bytes. – Andreas Schaefer Feb 4 at 17:33
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There is not a lot to go on in your output there, but try removing qos pre-classify from the tunnel interface - it may be that you have misconfigured qos settings causing traffic to be dropped.

  • After checking, it's really a misconfiguration of qos settings, thank you – Mamitiana Ra Feb 6 at 14:51

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