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RE: [Syslog-sec] I-D ACTION:draft-ietf-syslog-transport-udp-02.txt
Hi,
I recommend that we set three pairs of recommendations, based on the
use cases:
Use Case #1 - Troubleshooting:
A small UDP-based message is important for device and network
**troubleshooting** in a reliability-challenged network, such as one
under DDOS or physical combat situations, where a fragmented message
may have greater difficulty getting delivered, and TCP has difficulty
establishing sessions.
1a) receiver - Recommend the 480 size as the minimum recommended size
for carrying rather small messages for this use case.
1b) sender - We should specify what the resulting payload size is
after subtracting the syslog overhead, and recommend that message
generators not exceed that length for messages reporting device
failures or other conditions expected in a reliability-challenged
network.
Use Case #2 - Device/network status reporting:
Status reporting in a normally-operating network will typically
benefit from larger message sizes. I think it reasonable to think that
a 1k message is large enough to contain "hints" about the nature of a
problem to help an operator understand what steps are needed to
resolve the problem.
2a) reciever - RECOMMEND 1k be supported as a minimum message size to
make it possible to send more information in messages, to provide more
useful information to the reciever.
2b) sender - RECOMMEND messages not exceed 1k for most situations.
Message generators should be encouraged to avoid bloat in their
messages.
Use case #3 - application usage
[soap]
I have difficulty understanding why messages or 32k and 64k are really
necessary - it strikes me that a short message or an SNMP trap could
contain a URL to a web page or a file that contains information of
that size to be communicated. Just because syslog CAN be used to
transmit large messages doesn't mean it SHOULD be used for messages of
that size. Expecting all vendors to implement syslog buffers of that
size, when other means are available for huge messages, seems like a
bad use of the syslog protocol.
[end soap]
I expect the number of use cases that demand this size log message
will be limited, but there are obviously people who do want messages
this size, so we should address the recommendations:
3a) reciever - I suggest we recommend 16k as the recommended minimum
size and 64k as the recommended minimum-maximum size, i.e recommend at
least 64k buffers. 16k is large enough to hold a fair amount of info,
and 64k might be a limit run into in a compiler or malloc()
implementation. Being able to support messages of at least 64k would
be a good thing, for those implementations that want to support such
use cases.
3b) sender - many implementations will not be able to receive greater
than 64k messages, so senders should not send more than 64k.
I recommend that either the message contain a max-message size
indicator in the message (e.g. see SNMNPv3), or that the syslog MIB
contain an object that specifies the maxiumum size supported by a
receiver, so a sender can know not to send larger messages.
David Harrington
dbharrington@comcast.net
-----Original Message-----
From: Moehrke, John (GE Healthcare) [mailto:John.Moehrke@med.ge.com]
Sent: Friday, September 10, 2004 9:57 AM
To: Rainer Gerhards; ietfdbh@comcast.net; Anton Okmianski;
syslog-sec@employees.org
Subject: RE: [Syslog-sec] I-D
ACTION:draft-ietf-syslog-transport-udp-02.txt
I truly don't understand why syslog cares about max-size as defined in
IP. It can say: "Due to a protocol binding to udp, big messages may
get fragmented. This fragmentation increases the risk of the message
not getting delivered." The only reason for syslog to use any
SHOULD/MUST language on this subject is to assure a syslog user that a
'syslog'
implementation will be able to create messages with a payload of n
size, and that if this message gets through the gauntlet that is
udp/ip, it will be consumed without buffer size rejects. Going over
UDP, you can't give any form of assurance that it will be delivered.
This lack of assurance is simply made worse if the udp packet is big.
On the max-size issue... What IHE is concerned with is profiling a
use-case that is forbidden by standards or not implementable given
current systems. Thus we are more interested in the syslog-max-size,
than the assurance issue. If we truly can't expect a syslog
implementation (client and server) to handle a message bigger than 480
octets; then we must abandon the use of udp-syslog. We have no choice
but to go with Reliable syslog. We will have to go to Reliable-syslog,
not for the reliability aspect, but because we know our payload won't
be rejected simply because it is big. In our design of the schema we
understood that a message might not get there if we are bound to
udp-syslog. We understood that the larger the message the bigger this
un-reliability is.
OSI layers are GOOD...
John
-----Original Message-----
From: syslog-sec-bounces@willers.employees.org
[mailto:syslog-sec-bounces@willers.employees.org] On Behalf Of Rainer
Gerhards
Sent: Friday, September 10, 2004 8:19 AM
To: ietfdbh@comcast.net; Anton Okmianski; syslog-sec@employees.org
Subject: RE: [Syslog-sec] I-D
ACTION:draft-ietf-syslog-transport-udp-02.txt
Hi List,
I think there is a lot of wisdom and obviously a lot of experience in
what David says. So even though I have strong concerns that a
guaranteed size of just 480 octets is not wise, I would accept it if
nobody else objects violently.
Rainer
> -----Original Message-----
> From: David B Harrington [mailto:ietfdbh@comcast.net]
> Sent: Friday, September 10, 2004 3:06 PM
> To: Rainer Gerhards; 'Anton Okmianski'; syslog-sec@employees.org
> Subject: RE: [Syslog-sec] I-D
> ACTION:draft-ietf-syslog-transport-udp-02.txt
>
> Hi,
>
> Please keep in mind that MUST is used for an absolute requirement of
> the specification, i.e. the specification won't work if you don't
> support this. MUST should NOT be used to set some arbitrary size
> selected by the authors as looking like a nice round number that
could
> be useful in many circumstances. It sounds like you are trying to
> create a MUST.
>
> I recommend that you set the 480 as a RECOMMENDED minimum size, but
> also RECOMMEND 16k or 64k be supported to make it possible to send
> larger messages. You could also identify some expected use cases,
such
> as the IHE case to demonstrate that potential users might expect
> support for larger sizes.
>
> You express a concern that if 480 is the recommended minimum, then
> implementors will only implement that size, not a more useful size.
> The market can decide whether those implementations that only
support
> 480 will actually be used widely. I suspect only free
> 480-implementations would get much usage, and you get what you pay
> for. Better implementations, both free and commercial, will probably
> be preferred by operators, and therefore vendors. It shouldn't be
the
> author's decision what sizes MUST be supported based on their own
> preferences and their company's use cases.
>
>
> Dbh
>
> -----Original Message-----
> From: syslog-sec-bounces@www.employees.org
> [mailto:syslog-sec-bounces@www.employees.org] On Behalf Of Rainer
> Gerhards
> Sent: Friday, September 10, 2004 4:10 AM
> To: Anton Okmianski; syslog-sec@employees.org
> Subject: RE: [Syslog-sec] I-D
> ACTION:draft-ietf-syslog-transport-udp-02.txt
>
> Anton,
>
> > > - In 3.4, the draft says:
> > >
> > > ######
> > > All implementations MUST support sending and receiving syslog
> > > messages up to and including the size which does not require
> > > fragmentation (507 bytes for IPv4 and 1191 bytes for IPv6).
> This
> > > size excludes the overhead of the syslog transport and UDP/IP
> > > headers. Support for larger messages is encouraged.
> > Implementors
> > > SHOULD clearly state the maximum supported message size in
> > > documentation.
> > > ######
> > >
> > > Actually, all implementations MUST support a message size of
> 65,000
> > > bytes, because this is the required minimum in -protocol 4.1. We
> > > agreed on this minimum after long discussions on the message
size.
>
> > > I'd actually prefer not to re-iterate this. But if we must, let
me
>
> > > say that a guaranteed message size of 507 bytes looks far too
low
> to
> > > me.
> > >
> > > Please note that the -protcol requirement meant that all
> > > implementations MUST support fragmentation.
> > >
> > > Sorry I didn't spot this in the -01 version...
> > >
> > > I've also noticed that in -protocol, I have limited that max
> message
> > > size to 16,000,000 bytes in -protocol. It might make sense to
sync
>
> > > this. I can go up with my number.
> >
> > Indeed we discussed this at length, but my recollection of
> conclusions
> > was different. :) Let's revisit. We decided (I thought) that we
> > can't force transport implementors into supporting fragmentation
as
> it
> > was too complicated. Plus, we can't them into supporting the
maximum
>
> > message size as the common denominator may be too small.
>
> I've tried to find something definitive in the mailing list archive.
> Actually, I couldn't come up with such a thing... So it looks like
> there were some private conversations or we both had a wrong
> understanding of concensus. Anyhow, let's try to finalize it now.
>
> I thought that the concensus was that we can not force implementors
to
> support very large messages. Thus, the minimum-to-be-supported size
> should be just 64K. Please remember that the IHE healthcare
initiative
> tries to use syslog for auditing and has a size requirement of at
> least 32K. So there is some industry need for larger size messages.
> >
> > Hence, only the size that can be transported without fragmentation
> > must be supported by transport implementors.
>
> This means we are going down with the actual message limit from 1K
> (which already was very small) to just 480 octets. Given the
> additional overhead we have introduced, there is not much left for
the
> acutal message.
>
> Of course, you can argue that it is just the minimum size that MUST
be
> supported. But I think if we face reality, that minimum will soon
> become the maximum supported by most implementations. I am very
> concerend that such a short guaranteed message size really makes
> sense... If we really take that route, we should eventually be bold
> enough to go back to 1K without fragmentation, even though we have
> some reliability concerns. At least that seems to have worked for
> several years now. I don't think we will get much acceptance for a
> standard that leaves around 400 bytes for the actual message (not
> counting meta data in structured ids....).
>
> > However, a full
> > transport implementation will support fragmentation and size of up
> to
> > 16777216 bytes.
> >
> > I think what we need is a statement in -protocol that it supports
a
> > message size up to 16777216, but transports MAY impose a different
> > limit.
>
> That's already there ;)
>
> >
> > It was mentioned that some devices will physically not be able to
> > handle large messages, where "large" can be quite a small number.
> > Restricting all messages to this common denominator is not good,
so
> we
> > have a multi-tier support system. People are not likely to support
> > streaming of message parts in their implementations, so available
> > memory will be an issue.
> >
> > Administrators will choose the appropriate implementations. Should
> we
> > add a statement that transport implementations MUST document
maximum
>
> > supported message size?
> >
> > I know it is less than optimal, but requiring all transports to
> > support some huge size is not a good idea either IMO.
> >
> > You also had an idea for doing fragmentation within the -protocol
by
>
> > upper layer. I originally liked it. But later people commented
that
>
> > this was improper layering and shifted responsibilities of
transport
>
> > layer up the stack. I agree with this. It would have introduced
> > potential fragmentation on several layers and we would have still
> > forced the higher layer to deal with UDP sizing constraints.
> >
> > I agree this issue deserves discussion. Let's have it and put it
bed
>
> > for good.
> >
> > > I do not fully understand what you mean in 4.2 by:
> > >
> > > #####
> > > No concurrent port reuse on the same host is
> > > allowed.
> > > #####
> > >
> > > It's probably just my English, but I do not get it. I'd
appreciate
>
> > > if you could elaborate a little.
> >
> > What this refers to is the use of SO_REUSEPORT socket option which
> > allows multiple sockets to be bound to the same port. I guess it
> > would not be a problem if the two different consumers of the
socket
> > (maybe threads) use different MessageId numbers. And this is
stated
>
> > as requirement elsewhere: all message parts must be send using the
> > same MessageId and source port among other things.
> >
> > Following your suggestion, we already allow multiple different
ports
>
> > to be used concurrent within a single process, so I have no
problem
> > with removing this restriction. It is too implementation-specific
> > anyway. What do you think?
>
> I agree. I simply did not fully understand what you were saying ;)
> Eventually the sentence could be a bit more verbose - but this might
> just have been my personal problem ;)
>
> Rainer
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>
>
>
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