Discuss - Congestion Control
Magnus: But what I think is needed here is some clear and normative
requirement on how to avoid and limit congestion. First of all I would
like to see a restriction on the applicability of this transport to within
a controlled environment unless the rate is capped to a level that is TCP
friendly or the full path is provisioned to handle the traffic. There
should also be
a discussion on how one rate limits SYSLOG traffic.
Magnus: If any higher rates of packets are to be sent over best effort
networks then a feedback mechanism is needed. That would probably need to
include forward path UDP packetization layer with sequence number to
enable loss detection. Complemented with feedback traffic to enable rate
control of outgoing traffic. That could also resolve the PMTUD issue.
Lars:
draft-ietf-syslog-protocol-21, Section 8.5., paragraph 2: > It may be
desirable to use a transport with guaranteed delivery to
mitigate congestion.
Reliable delivery and congestion control are orthogonal features. A
reliable transport will not necessarily have congestion control, and
vice versa.
Lars:
draft-ietf-syslog-protocol-21, Section 8.5., paragraph 3:
It may also be desirable to include rate-limiting features in syslog
originators and relays. This can reduce potential congestion
problems when message bursts happen.
This is too weak a statement on congestion control. See DISCUSS above.
Lars:
Given the issues that the UDP transport has with congestion control,
security and fragmentation, I'd like the document to
recommend the TLS-based transport over the UDP-based one for general use,
i.e., when the network is not specifically
provisioned for this type of traffic.
Prposed Resolution:
+ Place text in syslog-protocol, syslog-transport-tls, and
syslog-transport-udp to state that
- udp transport is to be used only where the network is specifically
provisioned for this type of traffic,
- tls is to be used in all cases where congestion issues may be a
concern.
+ Remove the text in syslog-protocol which states that reliable delivery
will mitigate congestion.
Response from Lars:
I'd like to see the actual text changes, but this proposal exactly
captures what I'd like to see happen.
Response from Magnus:
This mostly addresses my concerns. I still think there is one major issue
around this with congestion control. And that is
some description on how to rate-limit your traffic. Either in UDP to some
pre-configured threshold and in the case of TLS
over TCP the rate actually available. There can occur situations where the
amount of generated data will be larger than
what can be transfered. How does one resolve this? I think it probably
needs to be more text in syslog-protocol spec about this. How to use scope
and prio to determine which messages to throw away or queue up (within
limits).
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