Re: [OSPF] OSPFv2 SR draft

Chris Bowers <> Tue, 16 August 2016 14:03 UTC

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From: Chris Bowers <>
To: Peter Psenak <>, OSPF List <>
Thread-Topic: [OSPF] OSPFv2 SR draft
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Date: Tue, 16 Aug 2016 14:02:57 +0000
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Subject: Re: [OSPF] OSPFv2 SR draft
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I suggest changing the paragraph to read as below to make this clearer.   

   The SR-Algorithm Sub-TLV is optional.  It MAY only be advertised once
   in the Router Information Opaque LSA.  If the SID/Label Range TLV, as
   defined in Section 3.2, is advertised, then the SR-Algorithm TLV MUST
   also be advertised.  If a router C advertises a Prefix-SID sub-TLV for algorithm X 
   but does not advertise the SR-Algorithm Sub-TLV with algorithm X, then 
   a router receiving that advertisement MUST ignore the Prefix-SID 
   advertisement from router C.  If router B does not advertise the 
   SR-Algorithm TLV for algorithm X, then other routers should not 
   forward traffic destined for a prefix-SID for algorithm X advertised by
   some router D using a path that would require router B to forward traffic using
   algorithm X.   


-----Original Message-----
From: Peter Psenak [] 
Sent: Monday, August 15, 2016 6:40 AM
To: Chris Bowers <>; OSPF List <>
Subject: Re: [OSPF] OSPFv2 SR draft

Hi Chris,

sorry for the delay, I was on PTO during last two weeks.
Please see inline:

On 03/08/16 16:45 , Chris Bowers wrote:
> Peter,
> Taking a looking at the whole paragraph into this sentence was added,
> I am not sure how to interpret it.
>     The SR-Algorithm Sub-TLV is optional.  It MAY only be advertised once
>     in the Router Information Opaque LSA.  If the SID/Label Range TLV, as
>     defined in Section 3.2, is advertised, then the SR-Algorithm TLV MUST
>     also be advertised.  If the SR-Algorithm TLV is not advertised by the
>     node, such node is considered as not being segment routing capable.
> Is this sentence intended to imply that if a router does not advertise
> the SR-Algorithm TLV including algorithm X, then any prefix-SIDs for
> algorithm X advertised by that router will be ignored by other routers?

in OSPF we do not have the SR capability TLV. We use SR-Algorithm TLV 
for that purpose. So if a router does not advertise the SR-Algorithm TLV 
for algorithm X, other routers should not send any SR traffic using SIDs 
that were advertised for algorithm X.

If the router does not advertise any SR Algorithm TLV, then the node is 
not SR capable and no SR traffic should be forwarded to such a node.


> If this is the intention, then it would be better to state is more explicitly.
> If not, then the intended meaning should be clarified.
> Thanks,
> Chris
> -----Original Message-----
> From: OSPF [] On Behalf Of Peter Psenak
> Sent: Friday, July 22, 2016 3:30 AM
> To: OSPF List <>
> Subject: [OSPF] OSPFv2 SR draft
> Hi All,
> following text has been added in the latest revision of the OSPFv2 SR
> draft, section 3.1.
> "If the SR-Algorithm TLV is not advertised by node, such node is
> considered as not being segment routing capable."
> Please let us know if there are any concerns regarding this addition.
> thanks,
> Peter
> _______________________________________________
> OSPF mailing list
> .