Normen, > I just want to make sure that I'm not misunderstanding this: > > RFC 7597, section 6 describes the last 16 Bits of the construction of the > Ipv6 interface identifier as follows: > > The PSID field is left-padded with zeros to create a 16-bit field. > > RFC7598 Section 5.1. describes the format for provision the PSID to clients > with the following text: > > o PSID: 16 bits long. The PSID value algorithmically identifies a set of > ports assigned to a CE. The first k bits on the left of this field contain > the PSID binary value. The remaining (16 - k) bits on the right are padding > zeros. > > To me this seems that the two RFCs use two different formats to express the > same information in a field with the same name. > > Lets assume an example where the port split ratio is 6 (=k), slicing the IPv4 > address up into up 2**6 = 64 slices, each segment having 1024 ports. > > In RFC 7597, to select the third port-range, the parameters become OFFSET 0, > PSID-LEN 6, PSID 0x2 (left padded with zeros to 16 bits) > In RFC 7598, to select the third port-range, the parameters become OFFSET 0, > PSID-LEN 6, PSID 0x800 (leftmost k-bits on this field contain the PSID binary > value, which is right padded with zeros to fit 16 bits) > > So, > 1, Is my understanding of the two RFC's PSID formats correct?
I believe so. > 2, What's the reason for the difference in the formats? Good question. The 7597 PSID in the IID is mainly there for pretty printing / troubleshooting, and it makes sense to left pad it. I can only guess about the 7598 format, possibly to keep the PSID field consistent with the other fields (prefix) which are all right padded. Best regards, Ole
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