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

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
[email protected]                D-52064 Aachen              Fax 0241/911879

On Mon, 5 May 2003 11:35:23 +0200 Christian Hammers <[email protected]> wrote:

| 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.

icmp_ratelimit is init to 1 * HZ (where HZ == 100 most likely), so I'll guess that unit is jiffies (100ths of a second).

| 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.

Only other value that I see related to it is icmp_ratemask, which has a default value of 0x1818.

/*
* Configurable global rate limit.
*
* ratelimit defines tokens/packet consumed for dst->rate_token bucket
* ratemask defines which icmp types are ratelimited by setting
* it's bit position.
*
* default: [for ratemask -RDD]
* dest unreachable (3), source quench (4),
* time exceeded (11), parameter problem (12)
*/

--
~Randy