On Sun, 30 Jan 2005, cranium 2003 wrote:
> 1) How Router knows destinations mtu. In IP forwarding case following
> function is used that checks pmtu value to decide whether outgoing
> packet is required to fragment a packet or not?
There is specific ICMP message for getting the MTU of the path. The PTMU
stands for Path MTU discovery (see RFC 1191).
> 2) Can anybody help me how following function works in calcualting checksum?
> static inline int ip_decrease_ttl(struct iphdr *iph)
> {
> u32 check = iph->check;
> check += __constant_htons(0x0100);
> iph->check = check + (check>=0xFFFF);
> return --iph->ttl;
> }
This function just decreases the TTL of the IP packet and repairs the
checksum to be valid even after subtracting 1 from the TTL field.
--
JiKos.
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