If I run the command iptables -nvL on my VPS server running Ubuntu I get output like (output is much longer - I have only shown the interesting parts)

$ sudo iptables -nvL

Chain INPUT (policy DROP 41439 packets, 2499K bytes)
 pkts bytes target     prot opt in     out     source               destination         
    0     0 DROP       all  --  *      *           
    0     0 DROP       all  --  *      *
    0     0 DROP       all  --  *      *            
 3102  261K ACCEPT     all  --  lo     *             
 174K   54M ACCEPT     all  --  *      *              ctstate RELATED,ESTABLISHED
  495 26116 ACCEPT     tcp  --  *      *              tcp dpt:80
  331 14756 ACCEPT     tcp  --  *      *              tcp dpt:1723
   26  1468 LOG        all  --  *      *              LOG flags 0 level 7 prefix "iptables denied: "

Sometimes when I run this command I get results like

(policy DROP 41439 packets, 2499K bytes)

but then other times - from within the same shell - the data gets reset back to zero and it seems to start counting again. e.g.

(policy DROP 2 packets, 9K bytes)

If I switch to a different shell I will get the same data from the last shell.
My question is

  • Where is iptables is getting this info from?
    • log files?
    • does it start tracking internally from the first invocation of iptables -nvL?
  • How can I ensure the data doesn't reset back to zero?

Iptables keep a count (per chain) of packets processed. This two options could be used to change the count:

-Z, --zero [chain [rulenum]] Zero the packet and byte counters in all chains, or only the given chain, or only the given rule in a chain.

-c, --set-counters packets bytes This enables the administrator to initialize the packet and byte counters of a rule (during INSERT, APPEND, REPLACE operations).

Understand that some other process that calls iptables to execute INSERT, APPEND, or REPLACE operations will also change the count of packets.

  • thanks! this explained why the counter was reseting - it was because I was making changes to the iptables rules – the_velour_fog Feb 1 '16 at 6:57

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