GRE over MPLS txload 255/255 rxload 255/255

[vishalsinha]

Hi friends,

I have a MPLS cloud between sites and i usually send all my internet traffic to data centre as i have a MIS circuit there. recently we took a MIS circuit in AP region on one of our site. we created GRE tunnels to send the internet traffic of other AP locations to this site and if that circuit goes down then your the Data Centre internet circuit.

The tunnel i have created shows me

Tunnel1 is up, line protocol is up

  Hardware is Tunnel

  Description: << GRE tunnel for Internet traffic >>

  Internet address is 1.1.1.1/30

  MTU 17916 bytes, BW 100 Kbit/sec, DLY 50000 usec,

     reliability 255/255, txload 255/255, rxload 255/255

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 164

  Queueing strategy: fifo

  Output queue: 0/0 (size/max)

  5 minute input rate 937000 bits/sec, 185 packets/sec

  5 minute output rate 124000 bits/sec, 153 packets/sec Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 164
  Queueing strategy: fifo
  Output queue: 0/0 (size/max)
  5 minute input rate 937000 bits/sec, 185 packets/sec
  5 minute output rate 124000 bits/sec, 153 packets/sec

I was getting error IP_VFR-4-FRAG_TABLE_OVERFLOW: Tunnel1: the fragment table has reached its maximum threshold 16 alos. that i corrected by adding "ip virtual-reassembly in max-reassemblies 512" command to tunnel interface.

Need your help.

.

[Joseph W. Doherty]

Disclaimer

The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.

Liability Disclaimer

In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.

Posting

Need your help.

For?

PS:

BTW, if your IOS supports it, are you using the tcp mss-adjust command?

[vishalsinha]

Thanks

why my load is 255/255? though the traffic on the interface is not even 1MB.

what is this command for-  tcp mss-adjust?

[Richard Burts · Accepted solution]

There is a quite simple explanation about 255/255. Look at the actual input and output rates

  5 minute input rate 937000 bits/sec

5 minute output rate 124000 bits/sec

and compare them to the bandwidth assigned for the tunnel interface

BW 100 Kbit/sec

It is pretty obvious that both transmit and especially receive are greater than 100 Kbit/sec.

tcp mss-adjust is one way to address potential issues with fragmentation, which is sometimes an issue when using GRE tunnels. Since GRE is adding additional data in the header the size of the IP packet will be larger than the original packet was. This greater size may cause fragmentation, which increases CPU load and may impact performance.

HTH

Rick

[Joseph W. Doherty]

Disclaimer

The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In   no event shall Author be liable for any damages whatsoever (including,   without limitation, damages for loss of use, data or profit) arising  out  of the use or inability to use the posting's information even if  Author  has been advised of the possibility of such damage.

Posting

why my load is 255/255? though the traffic on the interface is not even 1MB. 
what is this command for-  tcp mss-adjust?

Rick has answered both your question, but just to clarify, if you set the bandwidth (via the bandwidth statement) to match available bandwidth, the loading stats will be correctly computed.  (Tunnels, not being bound to a physical interface, have a "default" bandwidth which seldom matches actual bandwidth.)

For most typical GRE tunnels, you set mss-adjust to MSS (usually 1460) less GRE overhead (24) = 1436.

PS:

You may find this of interest: http://www.cisco.com/en/US/tech/tk827/tk369/technologies_white_paper09186a00800d6979.shtml