RE: [dhcwg] Lease Query to multiple servers

Dan,

I agree that it makes sense to specify what happens when the relay
agent/access concentrator receives multiple responses to the Lease Query
message, and the responses don't agree. In fact, I think that section 6.7 of
the draft attempts to address this problem:

   When using the DHCPLEASEQUERY message in an environment where multi-
   ple DHCP server may contain authoritative information about the same
   IP address (such as when failover [FAILOVER] is operating), there
   could be some difficulty in deciding which results are the most use-
   ful if two servers respond with DHCPLEASEKNOWN messages to the same
   query.

   In this case, the client-last-transaction-time can be used to decide
   which server has more recent information concerning the IP address
   returned in the "ciaddr" field.

However, I don't agree with the statement below that "If more then one DHCP
server claims it has an active lease it should be logged as an error
condition, none of the replies should be used..."

I believe this action is less-than-ideal when the DHCP server is queried in
the middle of a DHCP Failover update. The primary DHCP server presumably has
up-to-date lease information, and the secondary DHCP server might have stale
information before receiving the BNDUPD message for the lease. This
particular situation may persist for some time in Failover's
COMMUNICATIONS-INTERRUPTED or PARTNER-DOWN states. In fact, if the primary
DHCP server is down, the secondary DHCP server may have the up-to-date lease
information.

If the relay agent chooses to use none of the Lease Query replies, then
temporary Failover-related glitches cause one of two undesirable outcomes:
1. The access concentrators drops traffic with legitimate source IP
addresses.
2. The access concentrators can no longer detect and drop traffic with
illegitimate source IP addresses.

-- Rich

-----Original Message-----
From: Hazon, Dan [mailto:dan.hazon@terayon.com]
Sent: Tuesday, March 04, 2003 10:39 PM
To: 'dhcwg@ietf.org'
Subject: [dhcwg] Lease Query to multiple servers

This comment is regarding the document <draft-ietf-dhc-leasequery-04.txt>

There at the end of section 6.2 it says:
"The DHCPLEASEQUERY message MAY be sent to more than one DHCP server, and in
the absence of information concerning which DHCP server might possess
authoritative information concerning the IP address, it SHOULD be sent to
all DHCP servers configured for the associated relay agent (if any are
known)."

Yet the document does not suggest what should a BOOTP Relay Agent do with
multiple answers, (possibly contradicting) from different servers.
My view is the following:
Active lease should be considered first if there is no active lease then a
reservation may be used. 
If more then one DHCP server claims it has an active lease it should be
logged as an error condition, none of the replies should be used, and the
information should be logged to avoid frequent query of the same.

I think a short paragraph clearing this scenario is required the same way
the scenario of no response is discussed in section 6.6

Does it make sense?

Dan
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