[AusNOG] DHCP going astray on NBN tails

[Karl Auer]

On Fri, 2015-12-04 at 10:33 +0000, Mark ZZZ Smith wrote:
> What is wrong with what Cisco is doing? The DHCP RFC specifies
> destination ports, it doesn't say anything about source ports, so
> source ports could be anything

I'm not sure that's what Matt is saying:

> The DHCP standard RFC 2131 states that “DHCP messages from a client to
> a server are sent to the 'DHCP server' port (67), and DHCP messages
> from a server to a client are sent to the 'DHCP client' port (68)". It
> would appear that in Cisco IOS both the DHCP discovery and offer
> packets having a source and destination port of UDP 67.

The issue as I read the above is that discovery packets AND offer
packets BOTH have destination port 67 - which would certainly be broken,
because offers should be sent to port 68. That both types of packet have
a source port of 67 is not technically broken, but certainly looks a bit
odd.

One wonders if the "minor defect" was actually a workaround, and the
newer models don't have it because someone "corrected" the
workaround :-)

Regards, K.

-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Karl Auer (kauer at biplane.com.au)
http://www.biplane.com.au/kauer
http://twitter.com/kauer389

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