Re: BFD echo mode

[David Ward <[e-mail]>]

The specification and implementation of adaptive timers was expected  
to be the congestion control mechanism.

-DWard

On Nov 30, 2008, at 2:11 PM, Vishwas Manral wrote:

> Dave,
>
> Sounds good. So what you are saying is that adaptive timer support
> needs to be there? Is the understanding correct.
>
> -Vishwas
>
> On Sun, Nov 30, 2008 at 11:50 AM, David Ward <[e-mail]> wrote:
>> Additional congestion control isn't necessary if an implementation  
>> takes
>> into consideration the adaptive timer support. This is if an  
>> implementer
>> believes that BFD configuration would be set by an operator such  
>> that the
>> already inconsequential amount of data being sent actually causes
>> congestion. BFD should not be run over TCP due to overhead or UDP- 
>> lite due
>> to lack of widespread deployment.
>>
>> -DWard
>>
>> On Nov 30, 2008, at 1:14 PM, Vishwas Manral wrote:
>>
>>> Hi Dave,
>>>
>>> Agree to what you say.
>>>
>>> I was also thinking of congestion control considerations to be put
>>> into BFD for the Multi-hop case. The draft does not talk about it  
>>> and
>>> because BFD works on very short duration Hello's it may need to  
>>> be TCP
>>> friendly in some cases.
>>>
>>> Do let me know what you think?
>>>
>>> Thanks,
>>> Vishwas
>>>
>>> On Thu, Nov 27, 2008 at 7:45 AM, David Ward <[e-mail]> wrote:
>>>>
>>>> Nobo -
>>>>
>>>> On Nov 27, 2008, at 3:41 AM, Nobo Akiya (nobo) wrote:
>>>>
>>>>>
>>>>> Hello Vishwas.
>>>>>
>>>>> Couple of add-on comments, for single-hop.
>>>>>
>>>>>> Seeing some vendor documentation it seems they use a seperate
>>>>>> port for the echo mode - as the source and the destination
>>>>>> address.
>>>>>
>>>>> I hope vendors aren't using different udp dest port for echo  
>>>>> packets.
>>>>>
>>>>> http://tools.ietf.org/html/draft-ietf-bfd-v4v6-1hop-08 Sec4.1.
>>>>>
>>>>> BFD Echo packets MUST be transmitted in UDP packets with  
>>>>> destination
>>>>> UDP port 3785 in an IPv4 packet.
>>>>>
>>>>>> Can the asusmption that the echo mode packet is a BFD packet
>>>>>> be made (so the BFD source / dest packet identifiers can be
>>>>>> used)? The base BFD spec seems to state the content of the
>>>>>> packet need not be specified as the packet is just looped back.
>>>>>
>>>>> BFD echo packets can be identified by UDP dest port 3785.
>>>>> Data beyond UDP header is not specified, and that's left up to  
>>>>> vendors.
>>>>>
>>>>>> So I can see how we could look an IP packet in the case of
>>>>>> Single Hop (by having the MAC Destination Address of the
>>>>>> peer) but having IP address and destination the same (as of
>>>>>> the source).
>>>>>
>>>>> I don't think there's anything that specifies that dest & src  
>>>>> addresses
>>>>> must be the same. For dest addresses tho, it maybe easier to
>>>>> demultiplex if dest address is the outgoing interface.
>>>>
>>>>
>>>> DW: there is nothing in the spec that says the addrs have to be  
>>>> the same.
>>>>
>>>>
>>>> -DWard
>>>>
>>>>>
>>>>> Thanx,
>>>>> Nobo
>>>>>
>>>>
>>>>
>>
>>