RE: Size of CR in CRH

[Ron Bonica <[e-mail]>]

Robert,

Consider the following network:


  *   Contains 65,000 routers
  *   Each router has 500 directly connected neighbors or fewer
  *   Uses 16-bit CRH

In this network, each node might have 65,499 CRH-FIB entries:


  *   64,999 CRH-FIB entries cause packets to follow the least-cost path to another node in the domain
  *   500 CRH-FIB entries cause packets to traverse a specific link to a specific neighbor.

As a mnemonic device, an operator might assign identifiers as follows:


  *   0-65,000 identify CRH-FIB entries that cause packets to follow the least-cost path to another node in the domain
  *   65,001 - 65,565 identify CRH-FIB entries that that cause packets to traverse a specific link to a specific neighbor.

Now recall that identifiers have node local significance. So, Node A and Node B might both have a CRH-FIB entry that is identified by the value 65,001. However:


  *   The CRH-FIB entry on Node A causes packets to traverse a particular link towards Node X
  *   The CRH-FIB entry on Node B causes packets to traverse a different link towards Node Y.

I think that this example refutes the premise of your argument, so there is not further need to address the conclusion.

                                                                                         Ron





Juniper Business Use Only
From: Robert Raszuk <[e-mail]>
Sent: Wednesday, May 20, 2020 6:20 PM
To: Ron Bonica <[e-mail]>
Cc: 6man <[e-mail]>
Subject: RE: Size of CR in CRH

[External Email. Be cautious of content]

HI,

So just to make sure I understand this analogy of 16 bit -- 2^16 = 65536 nodes. I think this is only on paper.

Imagine I have 1000 routers so if I divide the 16 bit space by 1000 I get at most 65 local node behaviours if anyone would like to embed such into the SID.

That means that if my router have more then 65 interfaces I am not able to steer packets by src route out of my router ... I must always depend on the lookup of next SID how to forward the packets.

That also means that if I want to apply any form of NP in segment endpoint I am quite limited to the number of local functions I could use.

To conclude - Let me restate to what I and others already said - flat SID space domain wide in mapping plane is a mistake. Yes this is like MPLS, but this does not make it great again due to that legacy.

Many thx,
R.