RE: [rtgwg] draft-ietf-rtgwg-mrt-frr-algorithm-03

[Chris Bowers <[e-mail]>]

Anil,

Thanks for the suggestion to clarify the use of root to mean gadag_root or spf_root in the pseudo-code, as well as the typo.  I made the changes on github.  The diff can be found at:
https://github.com/cbowers/draft-ietf-rtgwg-mrt-frr-algorithm/commit/ada619050ec9d773b7919a1c622f068d5a5a5e88
Tell me if you agree with these changes.

With respect to comment#3, if ((D is F) or (D.order_proxy is F)), then there are several cases to consider:

1) If the link from S to F is a cut-link,
                a) if this is a single cut-link between S and F, then there is no alternate
                b) if there are parallel cut-links between S and F, then one can, for example, ECMP across the remaining links, noting that there is no link protection.

2) if the link from S to F is not a cut-link, then at least one of the MRT next-hops for D (red or blue) will not be the same as the primary next-hop for D.  In which case, one should use the color that is not the primary next-hop as the alternate, noting that the alternate does not provide node protection.

I agree that the existing pseudo-code is not very clear here.  I am planning to update this part of the pseudo-code in the near future to make it clearer, but hopefully the explanation above suffices for the moment.

Chris


From: rtgwg [mailto:[e-mail]] On Behalf Of Anil Kumar S N (VRP Network BL)
Sent: Tuesday, June 09, 2015 1:27 AM
To: Gábor Sándor Enyedi; [e-mail]; Alia Atlas; Chris Bowers; [e-mail]
Cc: [e-mail]; [e-mail]
Subject: [rtgwg] draft-ietf-rtgwg-mrt-frr-algorithm-03

Hi Authors,

As discussed before, Please find my review comments :

Comment 1: Can we rename parameter which is passed to these functions as real SPF root or GADAG root ?

   Run_DFS(node root)
   Run_Lowpoint(node root)
   Compute_Localroot(root, root)
   Construct_GADAG_via_Lowpoint(topology, root)
   Add_Undirected_Links(topo, root)
   Assign_Block_ID(root, max_block_id)
   Compute_MRT_NextHops(x, root)

Comment 2:  Here parenthesis are not matching, four '(' and five ')'.
           This must be typo mistake.


In_Common_Block(x, y)
  if ( (x.block_id is y.block_id))
       or (x is y.localroot) or (y is x.localroot) )
     return true
  return false


Comment 3:   Is it possible to rephrase "if an MRT doesn't use primary_intf"
What does the sentence "MRT doesn't use primary_intf" mean ? Dose it mean neither Red interface nor Blue interface is same as primary interface ?
What does the sentence "return that MRT color" means ?

Select_Alternates_Internal(S, D, F, primary_intf,
                           D_lower, D_higher, D_topo_order)

    //When D==F, we can do only link protection
    if ((D is F) or (D.order_proxy is F))
        if an MRT doesn't use primary_intf
            indicate alternate is not node-protecting
            return that MRT color


Thanks & Regards
Anil S N

"Be liberal in what you accept, and conservative in what you send" - Jon Postel