Ping Timeout if at 1500

[cindylee27]

Hi Experts,

I have tried to find the solution but to no avail. Have tried to do a ping from a remote PC to a printer, but seems like pinging with 1500 makes it timed out.

Is there any reasons for this?

Thanks in advanced.

[Richard Burts]

Cindy

I have seen symptoms like this when data was going through a segment with a smaller frame size or when the segment would have extra headers added to the packet (like a GRE tunnel or an IPSec VPN). Would either of these conditions be possible in your environment?

Perhaps you can give us a bit more information about your network topology? Would a traceroute (tracert) from the remote PC to the printer help us to understand the topology of the network?

If a ping fails at 1500, how much smaller does it have to be to get through?

HTH

Rick

[cindylee27]

Well, i am not too sure if GRE Tunnelling is up on the remote side but I can confirm that there is no IPSEC VPN. Well, the connection is actually from diff geographical area where it passed through the ATM 55M connection before printing to the printer.

Well, trace route as below:

Tracing route to 16.21.11.18 over a maximum of 30 hops

1 16 ms 6 ms 7 ms 16.11.4.250

2 <1 ms <1 ms <1 ms 16.11.10.253

3 2 ms 1 ms 1 ms 16.11.254.48

4 3 ms 3 ms 1 ms 16.11.19.1

5 5 ms 4 ms 1 ms 16.21.11.18

Trace complete.

The smallest it can go is 1472.

Thanks Rick..

[sundar.palaniappan]

Cindy,

Anytime you are unable to send 1500 byte datagrams over the network the application mayn't work correctly. In your case the problem could be anywhere in the path as indicated by your traceroute.

If the printing application uses TCP then you may want to try configuring this command 'ip tcp adjust-mss 1450' on the LAN interface facing either the client or printer itself. If this resolves your application problem then you can either leave it this way or pursue troubleshooting further to isolate the part of the network that's preventing 1500 byte packets from getting across.

HTH

Sundar

[cindylee27]

Thanks Sundar for your reply.

First of all, what is the command means? referring to ip tcp adjust-mss 1450 and how it will help? I got to cisco site but still can't figure out what that means..:) Cause need to explain to management if this to be implemented on the router lan end.

For your info, I have done a -l 1500 to all of the hops from the remote PC ,is just that the end-to-end not able to go through..which is the remote PC and the printer..

Thanks.

[sundar.palaniappan · Accepted solution]

This command would cause the MTU negotiated by the TCP client/server to use 1450. The router would transparently lower the MTU to 1450 bytes during the TCP negotiation between the TCP client and server. I have found this command to be effective to address MTU problems.

Here's a couple of documents that can help your understanding.

http://www.cisco.com/en/US/products/sw/iosswrel/ps1839/products_feature_guide09186a00804247fc.html

http://www.cisco.com/en/US/tech/tk827/tk369/technologies_white_paper09186a00800d6979.shtml

HTH

Sundar

[cindylee27]

Hi Sundar,

If I ping from pc using -l 1500 to the printer, will it work in this case?

Thanks.

[Richard Burts · Accepted solution]

Cindy

The command that Sundar is talking about works for TCP traffic but not for ICMP. So it will have no effect on your ping.

HTH

Rick

[cindylee27]

Rick,

Can I say that when i ping, i will still get request timed out with buffer size 1500?

thanks..

[Richard Burts]

Cindy

It depends on whether the ping is sent with the DF bit set in the IP header.

HTH

Rick

[cindylee27]

Rick,

I ping with "Set don;t fragment" and it says that i need to fragment it. Anyway, have put in sniffers to see what are the result is as the customers didn;t complain already. They can print bash job..so,suspecting could be the host too..

Have rated you guys post..

Thanks a lot! will update if have anything.

[Richard Burts]

Cindy

Please do update when you learn anything else. This is an interesting problem.

Thanks for the rating.

HTH

Rick