Re: [nvo3] One question about draft draft-tissa-nvo3-oam-fm-00

"Tissa Senevirathne (tsenevir)" <tsenevir@cisco.com> Fri, 13 June 2014 14:12 UTC

From: "Tissa Senevirathne (tsenevir)" <tsenevir@cisco.com>
To: Haoweiguo <haoweiguo@huawei.com>
Thread-Topic: One question about draft draft-tissa-nvo3-oam-fm-00
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Date: Fri, 13 Jun 2014 14:12:34 +0000
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Subject: Re: [nvo3] One question about draft draft-tissa-nvo3-oam-fm-00
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Hi Weiguo

This is a good question.

If the intermediate device is not aware of the nvo3 OAM few thing will happen


1.      When TTL expiry happens the device is supposed to generate ICMP message TTL expiery, the originator can interpret

2.      Assume #1 did not happen

a.      In that case originator device , upon retransmission expiry would increment the TTL and re-transmit.

b.      In the display you would see a * - indicating device timedout or unknown

c.      Output will look like something below

                                                    i.     [ip address of TTL=1]

                                                   ii.     *  [non compatible device]

                                                  iii.     [ip address of TTL=2]

                                                  iv.     And so on.

3.      It is possible the path is broken at (ii). So the drawback is originator has to try max-TTL to figure out path is indeed broken at (ii). Which is a slightly a longer time and a price to pay for mixed network. BTW: this is the exact same result today with IP traceroute and one of the devices disable ICMP response due to security or other reasons.

I will update the draft with backwards compatibility section to include this and other caveats in a mixed mode networks.

From: nvo3 [mailto:nvo3-bounces@ietf.org] On Behalf Of Haoweiguo
Sent: Friday, June 13, 2014 2:07 AM
To: Tissa Senevirathne (tsenevir)
Cc: nvo3@ietf.org
Subject: [nvo3] One question about draft draft-tissa-nvo3-oam-fm-00


Hi Tissa,

In section 10.1 in your draft of draft-tissa-nvo3-oam-fm-00, theory of operation is discribed, you say that originator device should specify the TTL of the transport header as 1 for the first request. Because transit devices in underlying network normally don't support the OAM function, if you specify TTL as 1, the first transit device will drop it, remote MEP or MIP won't receive the message if two or more hops exists between ingress and egress MEPs, so the response timer will expire on originator device.
How can you ensure the OAM state machine on originator runs correctly in this scenario?

Thanks

weiguo

[nvo3] One question about draft draft-tissa-nvo3-… Haoweiguo
Re: [nvo3] One question about draft draft-tissa-n… Tissa Senevirathne (tsenevir)
[nvo3] 答复: One question about draft draft-tissa-n… Haoweiguo