Jeff,
so I was wrong again. ;-) Here is the relevant text again:
description
"The padded PDU size for the encapsulated BFD control packets.
The minimum size is 24 or 26; see Section 6.8.6 of RFC 5880.
The maximum PDU size may be limited by the supported interface
MTU of the system.";
Perhaps you meant the "The size of encapsulated and padded BFD control
packets"? I may have also been mislead by the "minimum size is 24 or
26" since this seems to be the minimum BFD control packet size without
any encapsulation. In the last sentence, did you mean the "maximum
padded PDU size"?
This may also be a failure of my non-native English language
processor. Hence, adding more explanation may help, i.e., that the
implementation will determine the amount of padding from on the size
of the encapsulation and the size of the BFD control packets to
achieve the padded PDU size (or something like that).
/js
On Sun, May 12, 2024 at 06:39:15PM +0000, Jeff Haas wrote:
> Jürgen,
>
>
> Juniper Business Use Only
> On 12.05.24 16:05, Jeff Haas wrote:
> > > bfd.PaddedPduSize:
> > > The BFD transport protocol payload size is increased to this value. The
> > > contents of this additional payload MUST be zero. The minimum size of this
> > > variable MUST NOT be smaller than permitted by the element of BFD procedure; 24
> > > or 26 - see Section 6.8.6 of [RFC5880].
> >
> > OK. So the padding is added outside the BFD packet before any
> > encapsulation.
>
> The padded pdu is the complete encapsulated PDU, including BFD and its transport protocol plus padding.
>
> So, using single-hop IPv4 BFD as an example:
>
> IPv4 header (20 bytes, e.g.)
> UDP header 8 bytes
> UDP payload length (padded to 9000 bytes)
> BFD (24 bytes)
>
> Thus, if you want to test 9000 byte MTU, your udp padding for this encapsulation is:
> 9000 - 20 - 8 = 8972.
>
> What you configured is 9000 since it's the total size of the padded packet.
>
> We are not asking the users to figure out 8972. That's derived from:
> - The BFD encaupsulation (UDP in this case)
> - The BFD session is to an ipv4 adderss and will encapsulate in a standard IP packet.
>
> Similarly, consider if there's extra tunneling or ip options involved. That
> will further pad the packet and thus the padding is subtracted in the UDP
> layer.
>
> > I am looking for clarity so that I know what the padding means I am
> > configuring without having to dig out the specification.
>
> Understood. "Padded packet" is intended to cover "PDUs as encapsulated to the
> BFD endpoint are this size at the outer layer."
>
> -- Jeff
>
--
Jürgen Schönwälder Constructor University Bremen gGmbH
Phone: +49 421 200 3587 Campus Ring 1 | 28759 Bremen | Germany
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