Re: [NFS] nfs-over-tcp still needs udp ports? (SLES 11)

[Aaron Wiebe <epiphani@gmail.com>]

On Thu, May 7, 2009 at 1:08 PM, Tom Talpey <tmtalpey@gmail.com> wrote:
> At 12:42 PM 5/7/2009, Chuck Lever wrote:
>>It's not portmap... lockd decides which listeners to start.

Thanks Chuck and Tom - that clarifies it.

Take care,
-Aaron

> Also, there is an important distinction between NLM and NLM *callback=
s*.
> The NLM client follows the NFS protocol selection in many client kern=
els,
> i.e. if you mount with proto=3Dtcp, you get both NFS and NLM over TCP=
=2E
>
> The issue is NLM callbacks, which are used only in specific cases whe=
re
> clients take blocking locks, which actually need to block due to bein=
g already
> held by another client. The server replies over NLM (e.g. TCP) with a=
n indication
> that a callback will arive later. But when the other lock is released=
, the callback
> comes on a second connection, initiated from the server back to the c=
lient and
> not on the original NLM channel. To make matters worse, some servers =
only
> ever perform the callback on UDP in order to simplify and reduce the =
overhead
> required.
>
> If this callback doesn't arrive at the client, or arrives in such a w=
ay that
> it's not recognized (e.g traverses a NAT and therefore changes source=
 IP),
> then the client only wakes up on a timer. The long pauses can be a re=
al
> problem, and one which only arises occasionally - i.e. very hard to t=
race down.
>
> Just something to be aware of... it's a day-one defect in the NLM pro=
tocol,
> actually.
>
> Tom.
>
>>
>>> =A0I know there
>>> are servers out there that will always speak NLM over UDP
>>> (netapp/ontap being the prominent one), and as a result there can b=
e
>>> problems without firewalls. =A0If servers are out there that will s=
peak
>>> NLM over UDP regardless of the mount itself, shouldn't we be bindin=
g
>>> NLM/UDP regardless of the mount transport?
>>>
>>> (Or did I miss this change being reverted a while back?)
>>
>>This change was reverted upstream; see commit 8c3916f4.
>>
>>--
>>Chuck Lever
>>chuck[dot]lever[at]oracle[dot]com
>>
>
>

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