Hi Tony,
Thank you for your explanations.
After moving one byte for the priority from Area Leader Sub-TLV to Dynamic
Flooding Sub-TLV, only one Area Leader Sub-TLV is advertised. For an area with
N nodes supporting both centralized and distributed mode, my understanding is
below.
Before moving, each of N nodes may advertise an Area Leader Sub-TLV and a
Dynamic Flooding Sub-TLV. After moving, only the leader node advertises a
(Updated) Area Leader Sub-TLV. Thus (N - 1) Area Leader Sub-TLVs are saved,
which use space of (N-1)*S1 bytes, where S1 is the size of Area Leader Sub-TLV.
Each of N nodes may advertise a (Updated) Dynamic Flooding Sub-TLV, which has
one extra byte for the priority. Thus N bytes are used.
The saving on space after moving should be (N-1)*S1 - N. S1 is 4 in IS-IS;
S1 is 8 in OSPF.
For N = 1000 and IS-IS, the saving is (1000-1)*4 - 1000 = 2996 (bytes)
For N = 1000 and OSPF, the saving is (1000-1)*8 - 1000 = 6992 (bytes)
Best Regards,
Huaimo
________________________________
From: Tony Li <[email protected]> on behalf of [email protected]
<[email protected]>
Sent: Friday, May 24, 2019 4:56 PM
To: Huaimo Chen
Cc: [email protected]
Subject: Re: Enhancement related to Area Leader Sub-TLV
Hi Huaimo,
Thank you for your proposal.
The area leader sub-tlv is only advertised by systems that are willing to be
area leader. Presumably, that’s not necessarily all of the ones who support
dynamic flooding. Thus, what you’re proposing moves one byte from one TLV into
another TLV that will be more commonly used. So your proposal actually consumes
more LSP space.
The intention here is that the candidates for area leader advertise the Area
Leader Sub-TLV. All nodes that support dynamic flooding would advertise the
Dynamic Flooding Sub-TLV.
Since the priority is part of the Area Leader election, it makes sense for it
to be part of the Area Leader Sub-TLV.
Regards,
Tony
p.s. IS-IS does not depend on word-alignment, so we typically do not leave
reserved bytes in our TLV formats. OSPF is a different kettle of fish… :-)
On May 24, 2019, at 1:44 PM, Huaimo Chen
<[email protected]<mailto:[email protected]>> wrote:
Hi Tony,
An enhancement related to Area Leader Sub-TLV is briefed below for
discussions. A .pdf file is attached in the case that the formats below are
messed up.
The leader of an area advertises an Area Leader Sub-TLV to indicate/instruct
whether centralized or distributed mode is to be used by all the nodes in the
area (Algorithm = 0: centralized mode; Algorithm = N (N>0): distributed mode
and N is the algorithm to be used by every node to compute flooding topology).
Currently for IS-IS, IS-IS Area Leader Sub-TLV below is used by each of the
nodes to advertise its priority for becoming the leader
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 | Priority | Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(Current) IS-IS Area Leader Sub-TLV
It seems hard to understand that every node uses an Area Leader Sub-TLV to
advertise its priority for becoming the leader, and at the same time to
indicate/instruct whether centralized or distributed mode is to be used by all
the nodes in the area.
When every node advertises an Area Leader Sub-TLV, only one for
indication/instruction for flooding reduction mode is used, and all the others
are not used, which consume space and processing time.
An enhancement is to let every node advertise its priority for becoming the
leader and the algorithms that it supports though using a Dynamic Flooding
Sub-TLV, and only the leader advertise the indication for the flooding
reduction mode. To achieve this, some changes to the two Sub-TLVs and the texts
related to the Sub-TLVs should be made.
For IS-IS, IS-IS Area Leader Sub-TLV is updated as follows (Priority is removed)
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 | Reserved | Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(Updated) IS-IS Area Leader
Sub-TLV
The Priority is added into IS-IS Dynamic Flooding Sub-TLV. The current IS-IS
Dynamic Flooding Sub-TLV
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 | Algorithm... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(Current) IS-IS Dynamic Flooding Sub-TLV
is changed to:
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 | Priority |Algorithm... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(Updated) IS-IS Dynamic Flooding Sub-TLV
Similarly for OSPF, the current OSPF Area Leader Sub-TLV below
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Priority | Algorithm | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(Current) OSPF Area Leader
Sub-TLV
is changed to
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Algorithm | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(Updated) OSPF Area Leader
Sub-TLV
The current OSPF Dynamic Flooding Sub-TLV below
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Algorithm ... | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(Current) OSPF Dynamic Flooding Sub-TLV
is changed to
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Priority | Algorithm ... | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(Updated) OSPF Dynamic Flooding Sub-TLV
Best Regards,
Huaimo
<EnhanceOnAdvertisePriority4Leader.pdf>
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