IP ToS/DSCP
Patrik Lahti
plahti at qnx.com
Tue Jul 6 19:41:15 UTC 2010
On 10-07-06 01:16 PM, sthaug at nethelp.no wrote:
>> dhcp-4.1.1 packet.c:143 ip.ip_tos = IPTOS_LOWDELAY;
>>
>> Just wondering if this should/will change? (would be easy to provide a
>> command line option I guess).
>
> Is it likely to matter at all? I don't consider DHCP a time critical
> service. As long as the server replies within a few seconds, the
> client should be happy.
>
I guess I should have made more of a point so you don't think I'm insane :-)
The first reason for changing is that IPTOS_LOWDELAY is deprecated, and
DSCPs should really be used. Using a command line option lets the user
decide.
I'm coming at this from a different angle - reliability, not low delay.
DHCP can be considered to be network control type traffic. I.e. without
it functioning, there will be no IP connectivity. Consider a situation
where DHCP is renewing and due to excess packet loss (maybe because of a
lot of other traffic is saturating the link at higher priority, above
Best Effort) the renew messages are lost. Therefore DHCP enters
discovery again and the IP address is removed from the interface...
PS. Same thing should really be done for IPv6 using IPV6_TCLASS socket
option.
Cheers!
/P
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