Re: [spring] One question on E-flag of ABR/ASBR in OSPF SR extension
Peter Psenak <ppsenak@cisco.com> Thu, 18 May 2017 09:52 UTC
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Date: Thu, 18 May 2017 11:47:22 +0200
From: Peter Psenak <ppsenak@cisco.com>
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To: Chao Fu <chao.fu@ericsson.com>, "spring@ietf.org" <spring@ietf.org>
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Subject: Re: [spring] One question on E-flag of ABR/ASBR in OSPF SR extension
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Hi Chao, On 18/05/17 11:15 , Chao Fu wrote: > Hi Peter, > > It's right if the NP-flag is not set then the received E-flag is ignored. But, if the NP-flag is SET because the prefix is not directly attached to the ABR, E-flag will not be ignored why would an E-bit be set in such case? It's up to the originator of the SID to decide when to set the E-bit. If the ABR does not set the E-bit no PHP would be done and advertised SID will be preserved. Are you trying to add the text that would say that ABR MUST NOT set the E-bit either? I don't think it's necessary. thanks, Peter > and the upstream neighbor will replace the Prefix-SID with the Explicit-NULL label 0. I guess actually the packet should be forwarded with the original prefix-SID, and no need to pop the 0 label and look up path again. > > Regards, > Chao Fu > > > -----Original Message----- > From: Peter Psenak [mailto:ppsenak@cisco.com] > Sent: Thursday, May 18, 2017 16:54 > To: Chao Fu <chao.fu@ericsson.com>; spring@ietf.org > Subject: Re: [spring] One question on E-flag of ABR/ASBR in OSPF SR extension > > Hi Chao, > > On 18/05/17 09:44 , Chao Fu wrote: >> Hi, >> >> Should we clarify how to set E-flag for ABR/ASBR in OSPF SR extension? >> >> In >> https://www.ietf.org/id/draft-ietf-ospf-segment-routing-extensions-14. >> txt, the draft describes how to set NP-flag on ABR and ASBR (Section 5 >> [Page >> 14]): >> >> The NP-Flag (No-PHP) MUST be set for Prefix-SIDs allocated to >> inter- >> >> area prefixes that are originated by the ABR based on intra-area >> or >> >> inter-area reachability between areas. When the inter-area prefix >> is >> >> generated based on a prefix which is directly attached to the ABR, >> >> the NP-Flag SHOULD NOT be set. >> >> The NP-Flag (No-PHP) MUST be be set for Prefix-SIDs allocated to >> >> redistributed prefixes, unless the redistributed prefix is >> directly >> >> attached to the ASBR, in which case the NP-flag SHOULD NOT be set. >> >> However, the E-flag (Explicit-Null Flag) is not described. Should we >> clarify it also? I think E-flag SHOULD NOT be set if the prefix is not >> directly attached to the ABR or ASBR, and if necessary, it SHOULD be >> set if the prefix is directly attached to the ABR or ASBR. > > The existing draft says: > > "If the NP-flag is not set then the received E-flag is ignored." > > Given that the draft clearly states when the NP-flag is set on ABR/ASBR above statement should be sufficient. > > thanks, > Peter > > >> >> Regards, >> >> Chao Fu >> >> >> >> _______________________________________________ >> spring mailing list >> spring@ietf.org >> https://www.ietf.org/mailman/listinfo/spring >> > > . >