On Mon, Jun 04, 2007 at 12:32:49PM +0800, Wei Yongjun wrote:
>
> The latest kernel 2.6.21.3 also doing so. The rule to send ICMP message
> limit this.
> Ref to net/ipv4/icmp.c
> line 433 void icmp_send(struct sk_buff *skb_in, int type, int code,
> __be32 info)
> line 434 {
> ...
> line 572 /* RFC says return as much as we can without exceeding 576
> bytes. */
> line 573
> line 574 room = dst_mtu(&rt->u.dst);
> line 575 if (room > 576)
> line 576 room = 576;
> line 577 room -= sizeof(struct iphdr) + icmp_param.replyopts.optlen;
> line 578 room -= sizeof(struct icmphdr);
> line 579
> line 560 icmp_param.data_len = skb_in->len - icmp_param.offset;
> line 561 if (icmp_param.data_len > room)
> line 562 icmp_param.data_len = room;
> line 563 icmp_param.head_len = sizeof(struct icmphdr);
>
> line 576 do this.
But this is not the old_mtu field that we were talking about. The
old_mtu field comes from iph->tot_len which is the length of field
in the *original* IP header. We're certainly not allowed touch that
field.
Cheers,
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