IMHO, there is no need for tie-breakers here (or it really *can't* help much).
This is a non-issue for OSPF. For the other IGP, if this is the perceived problem: (plz confirm) - PQ node may not accept TLDP session from PLR, if PLR chooses an incorrect IP represented by PQ node (IGP/ISIS database). Because, today there is no document mandates an IP address which effectively represents the ISIS node. We can't *fully* rely on TLV 134 because this is not mandated for non TE environments. Instead of inventing a new thing here, the closest and one possible approach is to have a document which mandates a reachable prefix (loopback) in TLV 134, **regardless of TE present/supported or not**. This is the key and it fully solves the issue (it's important to note here - though today it's optional to have TLV 134 per 5305, some vendors including Ericsson do emit this regardless of TE in the local ISIS LSP). Does it make sense? (Les ?) Advantage of this approach is, lot of vendors need not do any thing for this and for the remaining folk who are *not* doing this; should upgrade to have this TLV (probably upgrade may be necessary with any other always "workable" approach too) to represent reachable loopback IP address of the node always. Quick replies in-line [Uma]: -- Uma C. -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Monday, October 28, 2013 6:42 PM To: [email protected]; Hannes Gredler Cc: [email protected]; rogeriomariano; [email protected] Subject: RE: I-D Action: draft-ietf-rtgwg-remote-lfa-02.txt Hi Stewart, It sounds good to me, except for the proposed tie breaker mechanism. As you know, today there is no existing mechanism for LDP to advertise the TLDP listening IP address in the IGP. So in short/mid term rLFA deployment, no IGP solution would be available. [Uma]: True, only if a non-TE ISIS node doesn't advertise TLV 134 today. So the draft must propose a last resort "working" tie breaker. [Uma]: If the above is TRUE, I don't think you can do much by defining a "working" tie breaker here. Also, I don't think there is one possible really in that situation. IMHO, using the lowest numerical value would be a very bad idea ... because this has no sense (just tie break, but without any insurance that the chosen prefix would be good). In order to bring more insurance, at least, I think the the tie breaker must check that the prefix used is an internal one (when possible ...) and is a /32. [Uma]: /32 is fine but you don't know from the TLV if it is a internal prefix or external prefix always (IMO, this could be the blocker for proposing any "working" tie breaker). I don't think we could make something more precise because otherwise we would need to address IGP protocol specifities (TLVs, LSAs ... fields to check...). [Uma]: I don't think there is any issue for OSPF in this regard (LSA.. as you mentioned) For ISIS (TLV as you said), yes at times one may quickly lost in TLV 135s, if one wants to really figure out this /32 (TLV 135) is indeed represents the PQ node. Thoughts ? _______________________________________________ rtgwg mailing list [email protected] https://www.ietf.org/mailman/listinfo/rtgwg
