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Community Member

Strange results when pinging from a c3750 switch to an attached host. Every 6th packet dropped.

I have a c3750G L3 switch running c3750-ipservicesk9-mz.122-53.SE2.bin image.

Attached to this switch is a server with ip 10.2.158.53 (on vlan 158)

The same switch has the VLAN interface for VLAN158

I am extremely confident that the NIC for the server is OK

 

The symptoms I am seeing is that when I ping the server from the switch (using all possible source addresses) I see this..

 

ping 10.2.158.53 re 100 so vlan 158

Type escape sequence to abort.
Sending 100, 100-byte ICMP Echos to 10.2.158.53, timeout is 2 seconds:
Packet sent with a source address of 10.2.158.126
!!!!!.!!!!!.!!!!!.!!!!!.!!!!!.!!!!!.!!!!!.!!!!!.!!!!!.!!!!!.!!!!!.!!!!
!.!!!!!.!!!!!.!!!!!.!!!!!.!!!!
Success rate is 84 percent (84/100), round-trip min/avg/max = 1/2/9 ms

 

As you can see every sixth packet is dropped but, if I ping the same host at the same time from anywhere else in our global network and with the same ping timeout value (2s) I see no packet loss at all.

 

Im stumped.  Anybody out there have any ideas as to what might be going on here?

 

Cheers in advance

 

Paul

 

 

Everyone's tags (3)
9 REPLIES
Silver

Do you have icmp redirects

Do you have icmp redirects enabled on that VLAN?

Is it possible to run wireshark on the server and capture the packets to see what is actually happening on the wire?

Community Member

No ICMP redirects on that

No ICMP redirects on that VLAN and also I'm unable to do the wireshark thing either as it is a remote site unfortunately.

Hall of Fame Super Blue

A best guess is that it is to

A best guess is that it is to do with control plane policing on the switch.

ICMP to and from an IP on the actual switch itself is handled in software by the control plane and so the 3750 may well be limiting the amount of ICMP packets being processed.

ICMP through the switch ie. from one end device to another is hardware switched and that is why you see normal response times for those pings.

If it is the above then it's not really a problem because generally traffic to and from the server will be from other devices and not the switch itself.

Jon

Community Member

Hi Jon thanks for the

Hi Jon

 

thanks for the informative response.  Do you have any ideas as to how I can check / verify whether your suggested reason is the actual cause?

Hall of Fame Super Blue

Unfortunately no as i don't

Unfortunately no as i don't have access to either of the switch types at the moment hence the reason it is just a best guess really.

Note also i said it could be control plane policing which i'm not sure the 3750 actually supports but the general principle still applies ie. ICMP to the switch itself is handled differently than ICMP through the switch so i still suspect it is linked to this.

Sorry i can't be more help.

Jon

Community Member

Found this post that explains

Found this post that explains this phenomonon which I thought I'd share..  Thanks to those that responded

http://realworldnetworking.blogspot.co.uk/2012/07/6th-ping-dropped-by-cisco-call-manager.html

 

Community Member

Jon your response prompted me

Jon

 

your response prompted me to try some more ping tests which have produced some additional detail that may help.

If I ping the same host from other directly attached network devices (another identical c3750, a stack of c3750s and an ASA that connect directly to the original c3750) I get the same ping response - 5 pings reply then one times out (the ASA gives !!!!!?!!!!!? etc).

Does this add anything to the mix?  Im  still completely stumped..

 

Cheers

Hall of Fame Super Blue

Your tests would suggest it

Your tests would suggest it is not to do with the handling of ICMP on the 3750 itself then because if you ping from the ASA, for example, the packets are actually going through the switch.

And this only happens within the site ie. if you ping from a remote site it all works fine ?

Jon

Community Member

That is correct Jon yes. 

That is correct Jon yes.  Pinging from Cisco devices on site yield the same ping response behaviour; ping from offsite Cisco devices is good.

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