Subject: [pim] Secondary ip address in transit network

From: "iamredheart22 ." <[email-masked]>
Date: Wed, 18 Feb 2015 17:40:31 +0530

Hello,

        I have some doubt about PIM on secondary ip address in transit
network. Please refer the topology shown below.

Source(10.10.10.1)-----------------sw1---------------------------sw2------------Rcv

         RFC 4601 mentions the following points.

     "*4.3.4 <https://tools.ietf.org/html/rfc4601#section-4.3.4>Maintaining
Secondary Address List*

*
   Communication of a router's interface secondary addresses to its PIM
   neighbors is necessary to provide the neighbors with a mechanism for
   mapping next_hop information obtained through their MRIB to a primary
   address that can be used as a destination for Join/Prune messages."*

*          Then RFC also talks about the macros mentioned below..*

*     neighbor RPF'(*,G) {
         if ( I_Am_Assert_Loser(*, G, RPF_interface(RP(G))) ) {
              return AssertWinner(*, G, RPF_interface(RP(G)) )
         } else {
              return NBR( RPF_interface(RP(G)), MRIB.next_hop( RP(G) ) )
         }
     }   "The function MRIB.next_hop( S ) returns an address of the next-hop
   PIM neighbor toward the host S, as indicated by the current MRIB.  If
   S is directly adjacent, then MRIB.next_hop( S ) returns NULL.  At the
   RP for G, MRIB.next_hop( RP(G)) returns NULL."
   "The function NBR( I, A ) uses information gathered through PIM Hello
   messages to map the IP address A of a directly connected PIM neighbor
   router on interface I to the primary IP address of the same router
   (Section 4.3.4
<https://tools.ietf.org/html/rfc4601#section-4.3.4>).  The primary IP
address of a neighbor is the address
   that it uses as the source of its PIM Hello messages*."

    What I understand from this is that MRIB.next_hop(S) can return a
secondary ip address
    as a nexthop which then will pass through NBR macro which returns
the primary
    address associated with this secondary address. This primary
address is then used
    as the final nexthop neighbor.

    My question is that in a transit network by what configuration I
    can achieve a scenario so that nexhop(10.10.10.1) on sw2 returns a
    nexthop address which is configured as a secondary address on sw1?

    Can someone please help?

Thanks,

Indranil

---

From: "iamredheart22 ." <[email-masked]>
Date: Thu, 19 Feb 2015 02:04:50 +0530

Hi,

   SRC-----------sw1(10.10.10.1)----------------------------------(
5.5.5.1/24)sw2-------------RCV
                            20.20.20.1
20.20.20.2
                                              (20.20.20.0/24)
<<<<<<<<<<Secondary subnet

Lets say, sw1 has primary subnet 10.10.10.1/24 and sw2 has primary subnet
in 5.5.5.1/24. Then I connect them via secondary subnet 20.20.20.0/24. Is
that a valid configuration?
If yes then are the below two assumptions correct?

1. In this case ospf neighborship forms on 20.20.20.0 subnet.
2. RPF(SRC) on sw2 should return 20.20.20.1 and NBR(20.20.20.1) should
return 10.10.10.1.and all joins should be sent to 10.10.10.1.

In this case, who should be the DR on the LAN connecting sw1 and sw2?

Thanks,
Indranil

On Wed, Feb 18, 2015 at 5:40 PM, iamredheart22 . <[email-masked]>
wrote:

>      "*4.3.4
> <https://tools.ietf.org/html/rfc4601#section-4.3.4>Maintaining Secondary
> Address List*
>
> *
>    (Section 4.3.4 <https://tools.ietf.org/html/rfc4601#section-4.3.4>).  The primary IP address of a neighbor is the address
>     What I understand from this is that MRIB.next_hop(S) can return a secondary ip address
>     as a nexthop which then will pass through NBR macro which returns the primary
>     address associated with this secondary address. This primary address is then used

---

From: Stig Venaas <[email-masked]>
Date: Thu, 26 Feb 2015 12:57:44 -0800

Hi

Although the Address List Option isn't specifically restricted to IPv6,
I doubt there are implementations using it for IPv4.

Does anyone know of any implementations? Do you agree it could make
sense for IPv4 when you have multiple addresses on an interface?

Stig