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Re: Linux IP stack on kernel 2.4.18

To: Rabeeh Khoury <rabeeh@xxxxxxxxxxxxx>
Subject: Re: Linux IP stack on kernel 2.4.18
From: Rabeeh Khoury <rabeeh@xxxxxxxxxxxxx>
Date: Mon, 03 Jun 2002 11:40:11 +0300
Cc: netdev@xxxxxxxxxxx
References: <3CF9DDD0.3080809@xxxxxxxxxxxxx>
Sender: owner-netdev@xxxxxxxxxxx
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.0rc2) Gecko/20020510
I fixed the problems. I'm replying for the record of the mailing list.

Rabeeh Khoury wrote:

Hi All,

I'm using kernel 2.4.18 and developing an ethernet network interface driver.
I have two problems that if you may consult me how to solve them -

1.. How can I adjust the throttling parameter of the IP stack not to drop any packet ? Meantime the IP stack routes 55k packets/sec and all the other it just drops (I can see them by the result of netif_rx).

echo 50000 > /proc/sys/net/core/netdev_max_backlog

This puts the throttling parameter of the IP stack to 50000, instead of 300 which is the defaul in kernel 2.4.18 (the default is set in net/core/dev.c with the variable 'int netdev_max_backlog = 300;')

2.. Routing jumbo packets through IP stack - I send 9K packets in size and IP stack routes the packets but by sending 1K packets in size ! is this possible ? I tripple checked the device driver on receive and transmit and it's ok. Do you know what is the problem ?

The HW I'v used that generates jumbo packets has put a wrong total_length field in the IP header, which made IP stack remove a large chunck of the packet. The relevant code that removes the chunck is in net/ipv4/ip_input.c -

/* Our transport medium may have padded the buffer out. Now we know it
                * is IP we can trim to the true length of the frame.
                * Note this now means skb->len holds ntohs(iph->tot_len).
               if (skb->len > len) {
                     __pskb_trim(skb, len);
                       if (skb->ip_summed == CHECKSUM_HW)
                               skb->ip_summed = CHECKSUM_NONE;

Thank you alot,

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