Subject: RE: Metric

From: vishwas <[email-masked]>
Date: Tue, 05 Jan 99 11:45:00 PST

In the situation that you described, both RIP and DVMRP will count to 12,
not to infinity.

I'm not sure why you say that DVMRP doesn't use counting to infinity; it
does.

I'm also not sure why it would be important to synchronize DVMRP and RIP.

  Bill
[vishu]  [vishu]  ----------------------
Small correction RIP Infinity metric = 16.
Yes both does use a kind of counting to infinity. But an external entity   
like split-horizon with poison reverse come into picture, which breaks   
this funda in DV protocols.

Assuming Split horizon is disabled (though should not be done) then DVMRP   
will converge faster than PIM-DM using RIP.

Also I see the route expiry timers for RIP and DVMRP differ, so this may   
cause some inconsistancies when running a mixture of PIM-DM and DVMRP   
protocols in an internetwork.

So it may be an issue to to have this discussed here the reasons for   
choosing a metric of 32 for DVMRP. And 16 for RIP (though general   
community of RIP is asking for RIP metric to be increased to higher   
value, it is witheld because of interop problems currently).

I dont know about PIM-DM using OSPF. But any way depending on what PIM-DM   
uses as unicast routing protocol, the internetworking problems will arise   
when it has to co-exist with DVMRP.

Even it is not so clear wether DVMRP is IGP or EGP kind of protocol.

Another issues is synchronization, as it is known due to metric and timer   
differencies in DVMRP and PIM-DM using RIP, co-existancies of both will   
have some impact on route exchange. Thats why synchronization may be of   
importance.

I need more inputs from U, to go indepth in to these issues So do comment   
on this.

 -vishu

---

From: "John M. Zwiebel" <[email-masked]>
Date: Tue, 05 Jan 1999 10:46:53 -0800

Vishu:

PIM depends on the unicast routing protocol to make its forwarding decisions.
If the unicast protocol converges quickly so will PIM.  Several times you
compare DVMRP with PIM-DM/RIP.  IMHO, using RIP is a mistake, but its your
choice.

DVMRP and PIM are both IGPs.  Since MBGP did not exist until recently, there
was no EGP so that was why DVMRP was used to cover the whole world.  Not to
mention that at one time there was no alternative to DVMRP.

I'm curious about what your ultimate goal is in obtaining this information.
If you are trying to determine which multicast routing protocol is "best", I
think you may want to first choose which hardware vendor you want to use based
on other parameters than the multicast routing protocol.  Which multicast
protocol might be used as a "tie-breaker".  But you may also need to consider
whether or not your prospective vendor supports MBGP and/or MSDP.

If you are interested in "checking out" ip multicast to see how it works in
your environment, Bill does an excellent job of providing mrouted on a large
number of unix platforms, so perhaps you should use DVMRP.  There is also
a pimd available, but I am not aware of how widely it is used or how well it
is supported.  The incentive to support pimd as well as Bill supports mrouted
does not exist (in my opinion).

In the "long run" -- meaning over a year from now, probably much longer, it is 
quite possible (maybe probable) that neither DVMRP or PIM will be the 
multicast routing protocol of "choice".  PIM's development was strongly 
influenced by things learned while folks were deploying DVMRP.  If we knew
"then" what we know "now", PIM might look quite different today.  (I know
I'd argue for a lot of changes -- heck I still do.)

So, again, what is it you are trying to determine in your comparisons.

Thanks

z

 ^ 
 ^ In the situation that you described, both RIP and DVMRP will count to 12,
 ^ not to infinity.
 ^ 
 ^ I'm not sure why you say that DVMRP doesn't use counting to infinity; it
 ^ does.
 ^ 
 ^ I'm also not sure why it would be important to synchronize DVMRP and RIP.
 ^ 
 ^   Bill
 ^ [vishu]  [vishu]  ----------------------
 ^ Small correction RIP Infinity metric = 16.
 ^ Yes both does use a kind of counting to infinity. But an external entity   
 ^ like split-horizon with poison reverse come into picture, which breaks   
 ^ this funda in DV protocols.
 ^ 
 ^ Assuming Split horizon is disabled (though should not be done) then DVMRP   
 ^ will converge faster than PIM-DM using RIP.
 ^ 
 ^ Also I see the route expiry timers for RIP and DVMRP differ, so this may   
 ^ cause some inconsistancies when running a mixture of PIM-DM and DVMRP   
 ^ protocols in an internetwork.
 ^ 
 ^ So it may be an issue to to have this discussed here the reasons for   
 ^ choosing a metric of 32 for DVMRP. And 16 for RIP (though general   
 ^ community of RIP is asking for RIP metric to be increased to higher   
 ^ value, it is witheld because of interop problems currently).
 ^ 
 ^ I dont know about PIM-DM using OSPF. But any way depending on what PIM-DM   
 ^ uses as unicast routing protocol, the internetworking problems will arise   
 ^ when it has to co-exist with DVMRP.
 ^ 
 ^ Even it is not so clear wether DVMRP is IGP or EGP kind of protocol.
 ^ 
 ^ Another issues is synchronization, as it is known due to metric and timer   
 ^ differencies in DVMRP and PIM-DM using RIP, co-existancies of both will   
 ^ have some impact on route exchange. Thats why synchronization may be of   
 ^ importance.
 ^ 
 ^ I need more inputs from U, to go indepth in to these issues So do comment   
 ^ on this.
 ^ 
 ^  -vishu  

------------------------------------------------------------------------------
	John Zwiebel                       Phone: 408-526-5303
	Cisco Systems Inc.                 
	Multimedia Group