icmp_ratelimit seems to be too low (related to NAT?)

From: Christian Hammers (ch@westend.com)
Date: Mon May 05 2003 - 04:35:23 EST

Hello

icmp_ratelimit has, as of kernel 2.4.20, a default of 100 (which unit
btw?). This seems to be too low as I have packet loss when doing two
"mtr" to the same 4 hops away host simultaneously. As this suggerates
packet loss on the network to the administrator, a too low limit will
certainly annoy network admins as it gives wrong information.

My tests gave the following results:

src. linux --> SNAT'ing linux router --> cisco1 --> cisco2 --> dst. linux

On the src linux host I opened _two_ mtr at the same time and watched
the packet loss at the first host after 30 rounds (seconds).

        icmp_ratelimit | loss at hop1 for both mtr
        0 0
        10 0
        20 0
        40 0
        80 34% and 37%
        100 44% and 57% (default)
        160 64% and 75%
        320 87% and 83%
        999 100% and 100%

For 2*(4*icmp_request + 4*icmp_timeexceeded/reply) = 16 packets per
second the loss seems to be a bit high at the default value of 100.

Is this related to any other setting? Maybe NAT?
My /proc/net/ip_conntrack only has 1200 lines and the max in
/proc/sys/net/ipv4/ip_conntrack_max is 32767.

bye,

-christian- 

-- 
Christian Hammers             WESTEND GmbH  |  Internet-Business-Provider
Technik                       CISCO Systems Partner - Authorized Reseller
                              Lütticher Straße 10      Tel 0241/701333-11
ch@westend.com                D-52064 Aachen              Fax 0241/911879

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