Hi Gunter,
On 24/02/2021 07:24, Van De Velde, Gunter (Nokia - BE/Antwerp) wrote:
Hi Peter, All,
I’m am trying to clarify a potential inconsistency between RFC7794 and
draft-ietf-lsr-isis-srv6-extensions.
draft-ietf-lsr-isis-srv6-extensions says that we should advertise
identical prefix-attribute tlv for the ipv6 reachability tlv and for the
locator tlv.
yes, for algo 0 only.
RFC7794 document says that we should not set the X flag in case of ipv6
routes because the ipv6 reachability tlv already has an external indication.
Can you advise.
1. draft-ietf-lsr-isis-srv6-extensions
The Prefix Attribute Flags Sub-TLV can be carried in the SRv6 Locator
TLV as well as the Prefix Reachability TLVs. When a router
originates both the Prefix Reachability TLV and the SRv6 Locator TLV
for a given prefix, and the router is originating the Prefix
Attribute Flags Sub-TLV in one of the TLVs, the router SHOULD
advertise identical versions of the Prefix Attribute Flags Sub-TLV in
For locator TLV, the is X-flag obtained from Prefix Attribute Flags
Sub-TLV, unlike the TLVs 236 and 237. I will add the text to clarify
that difference.
thanks,
Peter
both TLVs.
2. RFC7794
Prefix Attribute Flags
Type: 4
Length: Number of octets of the Value field.
Value:
(Length * 8) bits.
0 1 2 3 4 5 6 7...
+-+-+-+-+-+-+-+-+...
|X|R|N| ...
+-+-+-+-+-+-+-+-+...
Bits are defined/sent starting with Bit 0 defined below. Additional
bit definitions that may be defined in the future SHOULD be assigned
in ascending bit order so as to minimize the number of bits that will
need to be transmitted.
Undefined bits MUST be transmitted as 0 and MUST be ignored on
receipt.
Bits that are NOT transmitted MUST be treated as if they are set to 0
on receipt.
X-Flag: External Prefix Flag (Bit 0)
Set if the prefix has been redistributed from another protocol.
This includes the case where multiple virtual routers are
supported and the source of the redistributed prefix is another
IS-IS instance.
The flag MUST be preserved when leaked between levels.
In TLVs 236 and 237, this flag SHOULD always be sent as 0and MUST
be ignored on receipt. This is because there is an existing X
flag defined in the fixed format of these TLVs as specified in
[RFC5308 <https://tools.ietf.org/html/rfc5308>] and [RFC5120
<https://tools.ietf.org/html/rfc5120>].
G/
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