I'm building on notes I scribbled down during IETF week, so some of
these are debatable and maybe more due to lobby induced fever than
right thinking. Still, I provide them for discussion points (and the
few that are typographical).
1. Introduction;
o I think the text 'as they deem appropriate' is unneeded.
o There are three places that the Relay Agent Information option is
referred to, just for consistency I think it should always be
preceeded by a the;
they deem appropriate and also add 'Relay Agent Information' option
to the DHCP messages. DHCP servers use this option for IP address
to add Relay Agent Information option as they are closer to the end
Layer 2 devices append the Relay Agent Information option and
I think the last one reads better, and the first two would read
better as 'the Relay Agent Information Option'.
o Specifically clarify;
hosts. These Layer 2 devices can not relay the message to the DHCP
servers as they are typically configured in bridging mode. These
My complaint is that 'bridging mode' does not presume a lack of
addressing.
Suggest:
for context the preceeding text, unchanged:
In some network configurations, there is a need for Layer 2 devices
to add Relay Agent Information option as they are closer to the end
hosts.
My suggested edit (keeping the same paragraph):
These Layer 2 devices are typically operating only as media bridges
for the network, and may have no IPv4 addresses on the network in
question. Lacking a valid IPv4 source address, they cannot relay
packets directly to a DHCP server located on another network.
for context the remaining text, unchanged:
A Layer 3 Relay Agent relays it to the DHCP server.
3. Need of Layer 2 Relay Agent
o s/upto/up to/, missing space.
have to intercept unicast DHCP messages as well to keep this
information upto date.
o Suggested reason 3:
3. For the L2 Relay agent to make use of "cookies" it places in
the Relay Agent Information Option's contents, such as using
the Circuit-ID to locate which port to direct the Server's
replies.
4.1.1. Client-server interaction
o Note in step 3 that the server's reply may be either broadcast or
unicast to [End Host #1]'s mac address. In either case, it is
presumed the packet will transit [Layer 2 Device #1].
4.2.2. Issues due to introduction of Layer 2 Relay Agent
o Suggest adding (in addition to similar 4.1.2 issues):
Layer 2 relay agents which maintain persistent state, such as
updating filters or client registration, must be prepared to handle
potentially conflicting responses from different DHCP Servers.
Some Layer 2 relay agents instead use "the most recent DHCP
packet", and this is not necessarily a reflection of which state a
client has actually adopted. Even where a client requests a single
address, and two servers ack the single address, they MAY differ
for example in lease times. If the relay agent selects the server
reply which has a shorter lease time, it would expire its state
possibly before the client even has a chance to renew it.
Therefore, Layer 2 relay agents SHOULD select the longest lease
time of two conflicting but similar replies, by discarding replies
that shorten the lease time.
Or possibly this should be an expanded discussion of 4.2.1's point?
One of the things I've gotten email about in the past from a l2ra
implementor is this subject, and I'm trying to see if we can give
guidance that helps folks avoid falling into the same trap.
--
Ash bugud-gul durbatuluk agh burzum-ishi krimpatul.
Why settle for the lesser evil? https://secure.isc.org/store/t-shirt/
--
David W. Hankins "If you don't do it right the first time,
Software Engineer you'll just have to do it again."
Internet Systems Consortium, Inc. -- Jack T. Hankins
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