Hi les and other authors One conflict case which has not been discussed fully is prefix-sid conflict in different IGP protocols, such as ISIS and OSPF. Let's focus on the default TOPOLOGY based on SPF, both specified ISIS and OSPF instance deployed, both enabled SR. The RIB entrys of the default TOPOLOGY are selected between ISIS and OSPF by preference. For a specified SID, we all aggree that it can only be assigned to a single prefix, in all TOPOLOGYs, including the above ISIS and OSPF instance's prefix database, because an ILM entry in data plane can not represent two different FECs(suppose the label context is platform). Otherwise "SID Conflict" is applied to determine which prefix can possess the SID.
But for one prefix, can it be assigned different SID respectively in the above ISIS and OSPF instance(of the default TOPOLOGY)? Someone would say that SR information is independent of IGP/BGP protocols, the later just distribute the SR information to neighbors. So, in our default TOPOLOGY example, the same prefix in ISIS and OSPF istance are the same SID (also same SRGB). But others would say that SR can be deployed differently in different IGP/BGP protocols, they can be different SIDs (also different SRGBs). I think there must be one is better or reasonable. As SR architecture said, prefix segment forward packet according to the shortest path. It is clearly in SR-IPv6 to see what happend, but it is complex in SR-MPLS because of index SID. Let's look at SR-IPv6, suppose the SR-TE path is calculated by the specified TE database which is produced by ISIS instance and we get an IPv6 address segment list, we can see the forwarding behavior of the SR-TE path is not certainly relevant with ISIS, because the shortest path to an IPv6 prefix segment in data plane maybe a preferred OSPF route. A simple IPv6 address has not restrict which IGP/BGP instance's route can direct forwarding. In SR-IPv6, we reach the simple purpsose, forwarding packet according to the shortest path, and we don't care the protocol type of the preferred route. We can get a conclusion, for the same prefix, the SID in ISIS and OSPF instance are same, which is an IPv6 address. So, in SR-MPLS it is also better for us to assign prefix SID which is independent of route protocol, in other words, both ISIS and OSPF instance(of the default TOPOLOGY) assign same SID for the same prefix, the prefix SID has no protocol implication. Let's look at SR-MPLS more closely, the SR-TE path which is calculated by ISIS-TE database will be translated to the corresponding label-stack, if the translation is done totally based on the ISIS-TE database, we can see: 1) The label-stack will forward the packet according to the expected shortest path, segment by segment, but it is just the ISIS's shortest path, NOT the default TOPOLOGY's shortest path. 2) The label is ISIS instance specified, if OSPF instance don't know it, packet arriving on the node which the corresponding prefix segment FEC is preferred OSPF route will be dropped. In brief, it seems that SR deployed differently in different IGP/BGP protocols brings more complexity. This complexity is no valuable to our simple purpose. If some implementation is like this, do you think it can be applied to "Prefix Conflict"? what's the conflict result? Thanks Deccan -------------------------------------------------------- ZTE Information Security Notice: The information contained in this mail (and any attachment transmitted herewith) is privileged and confidential and is intended for the exclusive use of the addressee(s). If you are not an intended recipient, any disclosure, reproduction, distribution or other dissemination or use of the information contained is strictly prohibited. If you have received this mail in error, please delete it and notify us immediately.
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