# What's the meaning of "dst cache overflow"

## Lore

Hi,

my gateway is running a 2.6.2 vanilla kernel. Since some time it is putting the message "dst cache overflow" in /var/log/messages. What's the meaning of that? Google has'nt given me an answer yet.

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## David_Escott

Where is this error coming from? What program? A message in /var/log/messages will look like:

progname[pid] date and time message

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## Lore

```

Dec 18 02:32:33 t08gate kernel: dst cache overflow

Dec 18 02:32:33 t08gate last message repeated 9 times

Dec 18 02:32:33 t08gate kernel: NET: 266 messages suppressed.

Dec 18 02:32:33 t08gate kernel: dst cache overflow

Dec 18 02:32:33 t08gate last message repeated 3 times

```

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## David_Escott

Its in linux/net/ipv4/route.c. The dst is the protocol independent destination cache (routing cache). A garbage collection routine is run to clear out old old destination entries if the cache is getting too big, and this warning is thrown if that garbage collection is unsuccessful (either interrupted or jiffies) and net_ratelimit() is true, although I can't find where that function is defined.

If you want to fiddle with things you might look at the kernel's routing cache but I suspect this warning arises when there are sudden spikes in traffic volume to different destinations.

PS route.c has lots of interesting comments about martians in it rather funny.

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## Lore

net_ratelimit() is defined in include/linux/net.h and implemented in /net/core/utils.c:

/* 

 42  * This enforces a rate limit: not more than one kernel message

 43  * every 5secs to make a denial-of-service attack impossible.

 44  *

 45  * All warning printk()s should be guarded by this function. 

 46  */ 

http://t08server/extern/statistik/mrtg/ping/172.20.254.254.icmp.html

Here you can see what happend, suddenly packet loss gets to 100%, the gateway doesn't answer any more and the error messages occurs.

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## Instinct82

any ideas howto prevent this error?

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## j-m

 *Lore wrote:*   

> Hi,
> 
> my gateway is running a 2.6.2 vanilla kernel. Since some time it is putting the message "dst cache overflow" in /var/log/messages. What's the meaning of that? Google has'nt given me an answer yet.

 

I don´t know but I know for sure that you should upgrade your kernel ASAP and come back if the problem persists.  :Shocked: 

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