Re: [Lsvr] Need clarification on IGP-Metric TLV for LS Link Attributes in BGP-SPF deployments
Pushpasis Sarkar <pushpasis.ietf@gmail.com> Sun, 22 March 2020 15:43 UTC
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From: Pushpasis Sarkar <pushpasis.ietf@gmail.com>
Date: Sun, 22 Mar 2020 21:13:15 +0530
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To: "Acee Lindem (acee)" <acee@cisco.com>
Cc: "draft-ietf-lsvr-bgp-spf@ietf.org" <draft-ietf-lsvr-bgp-spf@ietf.org>, "lsvr@ietf.org" <lsvr@ietf.org>
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Subject: Re: [Lsvr] Need clarification on IGP-Metric TLV for LS Link Attributes in BGP-SPF deployments
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Hi Acee, Sure. If anyone doesn't prefer any other way we can proceed with this. Thanks -Pushpasis On Sat, Mar 21, 2020 at 7:49 PM Acee Lindem (acee) <acee@cisco.com> wrote: > Hi Pushpais, > > I think we can get away with this w/o modifying RFC 7752 since, as you > noted, it just says it is variable. > > Thanks, > > Acee > > > > *From: *Pushpasis Sarkar <pushpasis.ietf@gmail.com> > *Date: *Saturday, March 21, 2020 at 10:15 AM > *To: *Acee Lindem <acee@cisco.com> > *Cc: *"draft-ietf-lsvr-bgp-spf@ietf.org" <draft-ietf-lsvr-bgp-spf@ietf.org>, > "lsvr@ietf.org" <lsvr@ietf.org> > *Subject: *Re: Need clarification on IGP-Metric TLV for LS Link > Attributes in BGP-SPF deployments > > > > Hi Acee, > > > > I thought RFC7752 says it is a variable length TLV. 1-byte, 2-byte, and > 3-byte metrics are possible lengths. Can't we add a 4th possible length via > this draft? If not then a new TLV may be a better option. > > > > However if I remember correctly, there is a RFC7752 bis being worked upon. > Is there an option we can add it in that document? Not sure if it will be a > proper way or not. Just thinking out loud :) > > > > Thanks > > -Pushpasis > > > > > > On Sat, Mar 21, 2020 at 7:17 PM Acee Lindem (acee) <acee@cisco.com> wrote: > > Hi Pushpasis, > > If we use a length of 4, we’d need a new TLV (or modify RFC 7752). I think > the former would be a better option. > > Thanks, > > Acee > > > > *From: *Pushpasis Sarkar <pushpasis.ietf@gmail.com> > *Date: *Saturday, March 21, 2020 at 9:00 AM > *To: *Acee Lindem <acee@cisco.com> > *Cc: *"draft-ietf-lsvr-bgp-spf@ietf.org" <draft-ietf-lsvr-bgp-spf@ietf.org>, > "lsvr@ietf.org" <lsvr@ietf.org> > *Subject: *Re: Need clarification on IGP-Metric TLV for LS Link > Attributes in BGP-SPF deployments > *Resent-From: *<alias-bounces@ietf.org> > *Resent-To: *Keyur Patel <keyur@arrcus.com>, Acee Lindem <acee@cisco.com>, > Shawn Zandi <szandi@linkedin.com>, Wim Henderickx < > wim.henderickx@nokia.com> > *Resent-Date: *Saturday, March 21, 2020 at 9:00 AM > > > > Hi Acee, > > > > My personal preference will be having it as a 4-byte metric due to ease of > implementation as well as encoding/decoding efficiency due word-size > alignment. It may not be a big thing but encoding/decoding a 3-byte value > to/from byte stream is few more CPU instructions than just a 4-byte read > from a memory address. > > > > Thanks > > -Pushpasis > > > > On Sat, Mar 21, 2020 at 12:10 AM Acee Lindem (acee) <acee@cisco.com> > wrote: > > Hi Pushpasis, > > I think for BGP-LS SPF we should always use 3 octet metrics. This will > offer the most flexibility w/o redefining the TLV. If you agree, I will > update the SPF draft to state this. > > Thanks, > > Acee > > > > *From: *Pushpasis Sarkar <pushpasis.ietf@gmail.com> > *Date: *Monday, March 9, 2020 at 11:31 AM > *To: *"draft-ietf-lsvr-bgp-spf@ietf.org" <draft-ietf-lsvr-bgp-spf@ietf.org > > > *Cc: *"lsvr@ietf.org" <lsvr@ietf.org> > *Subject: *Need clarification on IGP-Metric TLV for LS Link Attributes in > BGP-SPF deployments > *Resent-From: *<alias-bounces@ietf.org> > *Resent-To: *Keyur Patel <keyur@arrcus.com>, Acee Lindem <acee@cisco.com>, > Shawn Zandi <szandi@linkedin.com>, Wim Henderickx < > wim.henderickx@nokia.com> > *Resent-Date: *Monday, March 9, 2020 at 11:31 AM > > > > Hi Authors, > > > > I need a small clarification on how the Link IGP-Metric TLV (type 1095) > for the links originated by an BGP-SPF speaker look like. My doubt is > specifically on what would be the length of the metric value. For example, > following is the excerpt from RFC7752 section 3.3.2.4 which specifies the > length to be 1, 2 or 3 bytes for ISIS narrow-metrics, OSPF and ISIS > wide-metrics. > > > > 3.3.2.4. IGP Metric TLV > > > > The IGP Metric TLV carries the metric for this link. The length of > > this TLV is variable, depending on the metric width of the underlying > > protocol. IS-IS small metrics have a length of 1 octet (the two most > > significant bits are ignored). OSPF link metrics have a length of 2 > > octets. IS-IS wide metrics have a length of 3 octets. > > > > 0 1 2 3 > > 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 > > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > > | Type | Length | > > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > > // IGP Link Metric (variable length) // > > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > > > > Figure 21: IGP Metric TLV Format > > > > What should be the length of the metric field when the origin is a BGP-SPF > speaker? > > > > Looking forward to your clarification on this. Also it will be appreciated > a lot if a sentence or two can be added to the draft clarifying the above > in the next version. > > > > Thanks and regards, > > -Pushpasis > > > >
- [Lsvr] Need clarification on IGP-Metric TLV for L… Pushpasis Sarkar
- Re: [Lsvr] Need clarification on IGP-Metric TLV f… Acee Lindem (acee)
- Re: [Lsvr] Need clarification on IGP-Metric TLV f… Pushpasis Sarkar
- Re: [Lsvr] Need clarification on IGP-Metric TLV f… Acee Lindem (acee)
- Re: [Lsvr] Need clarification on IGP-Metric TLV f… Pushpasis Sarkar
- Re: [Lsvr] Need clarification on IGP-Metric TLV f… Acee Lindem (acee)
- Re: [Lsvr] Need clarification on IGP-Metric TLV f… Pushpasis Sarkar
- Re: [Lsvr] Need clarification on IGP-Metric TLV f… Acee Lindem (acee)
- Re: [Lsvr] Need clarification on IGP-Metric TLV f… Pushpasis Sarkar