[Teas] Re: Comments abount rfc2205 Resource ReSerVation Protocol (RSVP)

[Adrian Farrel <[e-mail]>]

Hi Anh,

 

[Redirecting from MPLS to TEAS as suggested by Tony Li]

 

I think that (given you mention LSPs) you re talking about RSVP-TE (RFC 3209) not plain old RFC 2205 RSVP.

 

In your example, the link R2-R3 has failed in a way that R3 is aware of the failure, but R2 is not aware.

 

There are two questions that arise…

1.	Why isn’t R2 able to notice? Presumably the link failure detection is relying on a lower layer (L2 or L1) failure indication, and that is not happening. The answer to this is to run some other link failure detection mechanism such as BFD.

Such a mechanism would allow R2 to declare the link down and possibly re-route/repair the LSP via R5, or notify the head end (R1) to let it re-route.

2.	How could R3 let R2 know that the LSP has been torn down? The answer is “by sending a PathErr or ResvTear or Notification”. In general, those messages are sent hop by hop, and so they would fail to be routed on the failed link R3-R2, however, it is possible to IP-tunnel to direct-address RSVP packets so that they would be IP-routed to R2 (or direct to R1) via R5.

 

Cheers,

Adrian

 

From: Tuấn Anh Vũ <[e-mail]> 
Sent: 22 October 2024 04:45
To: [e-mail]
Subject: [mpls] Comments abount rfc2205 Resource ReSerVation Protocol (RSVP)

 

Hi IETF team,

I'm AnhVT from the SVTech company in VietNam, I have experienced some RSVP issues in the IPv4 MPLS network.

I suspect that RSVP has a point that needs to be enhanced. I describe this point below:

 

I./ Topology:

    ---------LSP-------->

    R1----R2----R3-----R4

          |    /

          |  /

           R5

II./ Issue

1./ Because of some bugs (exp: R3 experiences a flap link between R3-R2, but R2 does not recognize the interface flap), R3 indicates that LSP is down, then it deletes the LSP state and sends the PathTear downstream to R4.

2./Because R2 does not recognize the interface flap, R2 still keeps it available. It does not know that the LSP should be deleted.

3./ Due to 1./ and 2./ R1 does not know that the LSP is stuck because R3 and R4 deleted the LSP state, and R1 continues forwarding traffic to the LSP, This makes the service down.

 

III./ My comment

I think that RSVP needs a mechanic so that R3 signals to R2 to ensure that R2 knows that R3 deleted the LSP. Based on that signal, R2 will bring down the LSP and continue to send Reserve Tear to R1.

 

I hope that you take a look at my comment.

 

Regards,

AnhVT