Skip navigation
Login   |   Register
Cisco Learning Home > Learning Center > Discussions

_Communities

This Question is Answered
1668 Views 8 Replies Latest reply: Nov 28, 2011 8:54 PM by Nancy RSS

Currently Being Moderated

Cisco 2611XM Nat Statistics

Nov 27, 2011 5:08 AM

Nancy 57 posts since
Nov 9, 2011

Greetings!

 

I am attempting to narrow down a performance issue on my router.  Do the staticis below look normal?

 

Thank you in advance for your great answers.  TheGeekGirl

 

Gateway#show ip nat stat

Total active translations: 286 (0 static, 286 dynamic; 285 extended)

Outside interfaces:

  FastEthernet0/0

Inside interfaces:

  FastEthernet0/1

Hits: 2631382344  Misses: 56338058

Expired translations: 58886021

Dynamic mappings:

-- Inside Source

[Id: 1] access-list 1 pool Client_Pool refcount 286

pool Client_Pool: netmask 255.255.255.248

        start (wan) end (wan)

        type generic, total addresses 3, allocated 2 (66%), misses 400476

Gateway#

  • Brian 2,971 posts since
    Aug 17, 2009
    Currently Being Moderated
    1. Nov 27, 2011 6:02 AM (in response to Nancy)
    Re: Cisco 2611XM Nat Statistics

    It looks like you are getting all the misses because you only allocated a /29 (6 usable) IP address to your NAT pool.

     

    Can you provide the router configuration.

     

    Thanks.

     

    Brian

    Join this discussion now: Login / Register
  • Brian 2,971 posts since
    Aug 17, 2009
    Currently Being Moderated
    3. Nov 28, 2011 12:37 AM (in response to Nancy)
    Re: Cisco 2611XM Nat Statistics

    Hi Nancy,

     

    Thanks for the configuration.  So quick question, the IP address configured on the F0/0 (outside interface), is this the same subnet being used for the NAT pool?  And the default GW?

     

    It looks like you are assigning the 10.5.1.0/24 via DHCP to users on F0/1 (inside interface) and are NATting these to three addresses x.x.x.226, x.x.x.227 and x.x.x.228 with overload.  Thus you are using NAT with PAT.  This would explain the output you have in your previous post.

     

    For example, the first three users would be assigned the IP addresses in order

     

    user 1 = x.x.x.226

    user 2 = x.x.x.227

    user 3 = x.x.x.228

     

    Now what about the 4th user?  or the 40th user? or even the 100th user.  As new users are getting NATted, it is the port number that will set them apart with the same IP address.  You can see as the number of users increases, so will the number of misses as two or more users are trying to use the same port.

     

    Hope this helps.

     

    Brian

    Join this discussion now: Login / Register
  • Brian 2,971 posts since
    Aug 17, 2009
    Currently Being Moderated
    6. Nov 28, 2011 7:22 AM (in response to Nancy)
    Re: Cisco 2611XM Nat Statistics

    You mention in your configuration the following:

     

    interface FastEthernet0/0

    description $FW_OUTSIDE$

    ip address xxxxxxxxxxx 255.255.255.248

     

    ip nat pool Client_Pool xxxxx.226 xxxx.228 netmask 255.255.255.248

    ip nat inside source list 1 pool Client_Pool overload

     

    ip route 0.0.0.0 0.0.0.0 xxxxx.225

     

     

    In the configuration you are "blocking" out the public IP address which is ok.  I understand.  All I want to know is, where the "xxxx" are, is this the same IP address.  For example,

     

    Lets just say the public IP address space is 200.200.200.224/29.  This would give you the following 6 usable IP addresses

     

    200.200.200.224 = network ID

    200.200.200.225 = default GW (from the static route)

    200.200.200.226 = part of NAT pool "Client_Pool"

    200.200.200.227 = part of NAT pool "Client_Pool"

    200.200.200.228 = part of NAT pool "Client_Pool"

    200.200.200.229 = where is this assigned???    --> if unassigned, I would add this to the NAT pool

    200.200.200.230 = Is this the IP address on F0/0?

    200.200.200.231 = broadcast address for the subnet

     

    Depending on the type of traffic and the source ports being used by the private hosts on the 10.5.1.0/24 network, you will most likely always see some misses because your NAT pool is not large enough.  Misses are attempts to create a mapping.  You have 254 private address being NATted to only 3 public addresses with overload.  That means there are over 60 private hosts for each of the public addresses, so you are bound to see misses as some ports are already in use by other hosts.  NAT will always try and use the same source port and if it is already in use must select a new one.

     

    try clearing the NAT translation statistics with the following command, "clear ip nat statistics".

     

    then display the current statistics usinf the command "sh ip nat stat".

     

    Some of what you are seeing is historical data.

     

    Hope this helps.

     

    Brian

    Join this discussion now: Login / Register

Actions

More Like This

  • Retrieving data ...

Bookmarked By (0)