From: Danshtr (danshtr@gmail.com)
Date: Wed May 04 2005 - 10:33:53 GMT-3
Maybe I am missing something, all the answers are about who send
packets into the share media LAN.
But what about packets comming _from_ the LAN?
If there are two routers on a shared media LAN, running PIM-SM, which
one will forward the muticast traffic _from_ the shared media LAN?
On 5/4/05, ccie2be <ccie2be@nyc.rr.com> wrote:
> Hi Jim,
>
> If there are 2 pim SM routers on a Lan segment either of which could
> potentially sends joins up the shared tree to the RP, however, only 1 of
> those routers has a path to the RP, make sure the router with a path to the
> RP is the DR. Recall that the pim router with the highest ip address
> becomes the DR and that only the DR sends joins up the tree to the RP. If
> the DR doesn't have a path to the RP, the joins won't ever get to the RP and
> mcast traffic won't ever flow down the tree. To see which of the 2 routers
> on the segment is the DR, do a show ip pim nei. If the output shows "(DR)"
> on the right side of neighbor's entry, then that nei is the DR. One way to
> change which router becomes the DR is to change the ip addresses of the
> interfaces on the lan segment such that the preferred DR has the highest IP
> address. A better way is to use the interface command, ip pim dr-priority #.
>
> In a DM network where 2 or more pim routers on LAN could potentially send
> mcast pkts onto the lan segment, DM pim prevents this by electing a
> forwarder - a rtr which will send the mcast traffic onto the lan. 1st, the
> AD of the route to the source is compared and the route with the lowest AD
> wins. If the AD's are equal, then the metric of the route is compared and
> the lowest metric wins. If there's still a tie, the ip address is the
> tiebreaker.
>
> HTH, Tim
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Jim
> Sent: Wednesday, May 04, 2005 7:20 AM
> To: ccie2be; 'Danshtr'; 'Cisco certification'
> Subject: Re: Multicast DR...
>
> Tim,
>
> Thanks for getting back to me,
>
> so which one will sends joins up the tree if 2 routers are on the
> shared-media with client?
>
> R1 R2
>
> ----|-------|-------
>
> |
>
> client
>
> the proccess of PIM forwarder election works with both pim dense & spare
> mode and it happens whenever one of the router receive multicast packets on
> its outgoing interface for that packet's group.
>
> When the client sends join message to R2, R2 joins shared tree and the
> traffic will flow from source to client this way. But when R2 forwards
>
> traffic with destination address as multicast packets to clients, switch
> will treats these packets as broadcast and forward to all other ports. As
> the result, R1 receives packets on its outgoing interface for that packet's
> group and it immediately starts the proccess of PIM forwarder election by
> sending assert message. Finally, the winner will join the shared tree and
> take the role of the forwarder for all clients on the shared media.
>
> On TCP/IP vol2 489, we have "the election of designated router on
> multiaccess networks are common to PIM-SM and PIM-DM"
>
> Jim.
>
> ----- Original Message -----
> From: "ccie2be" <ccie2be@nyc.rr.com>
> To: "'Jim'" <quangnn@hptvietnam.com.vn>; "'Danshtr'" <danshtr@gmail.com>;
> "'Cisco certification'" <ccielab@groupstudy.com>
> Sent: Wednesday, May 04, 2005 4:53 PM
> Subject: RE: Multicast DR...
>
> > Jim,
> >
> > I think your remarks are correct only if PIM Dense Mode is being used.
> >
> > If PIM Sparse Mode is used, then the rtr which sends joins up the tree
> > will
> > also forward mcast traffic to hosts.
> >
> > HTH, Tim
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> > Jim
> > Sent: Wednesday, May 04, 2005 5:27 AM
> > To: Danshtr; Cisco certification
> > Subject: Re: Multicast DR...
> >
> > On a shared media, the router selected to forward traffic to client is the
> > one
> >
> > i) who advertises lowest metric preference ( in other words, lowest AD)
> > ii) who advertises lowest metric if the metric preference is equal
> > iii) who has the highest IP address on the network if all other metric are
> > the same.
> >
> > PIM bases on other protocols for its routing so you can verify DR
> > selection
> > by checking the route to Multicast Source in routing and mroute table.
> >
> > HTH, Jim
> >
> > ----- Original Message -----
> > From: "Danshtr" <danshtr@gmail.com>
> > To: "Cisco certification" <ccielab@groupstudy.com>
> > Sent: Wednesday, May 04, 2005 1:47 PM
> > Subject: Multicast DR...
> >
> >
> >> Hello
> >>
> >> Reading through multicast documentation, they are mentioning DR and
> >> queriers which both are intended for deciding which router will
> >> forward multicast packets to the recievers.
> >>
> >> But i couldn't find how the routers, on a shared media, decide which
> >> one will forward the packets from the source.
> >>
> >> Does anyone here knows the answer? I am sure there is... because it
> >> works!
> >>
> >> --
> >> Best regards,
> >> Dan
> >>
> >> _______________________________________________________________________
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> >
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>
-- Best regards, Dan
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