From: ccie2be (ccie2be@nyc.rr.com)
Date: Sat Jun 11 2005 - 12:48:08 GMT-3
Hey Lee,
See comments in-line.
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Lee
Carter
Sent: Saturday, June 11, 2005 11:07 AM
To: CCIE LAB
Subject: Stub Multicast Routing
All,
In looking at univercd documentation to configure stub
multicast routing use:
router a... Stub Host or end node
routera(config)# ip multicast-routing
routera(config)# interface ethernet0
routera(config)# description Connection to hosts
routera(config-if)# ip address 10.0.1.1 255.255.255.0
routera(config-if)# ip pim dense-mode
routera(conifg-if)# ip igmp helper-address 10.0.0.2
routera(config)# interface ethernet1
routera(config)# ip addres 10.0.1.1 255.255.255.0
routera(config)# ip pim dense-mode
routera(config)# description to Multicast Rotuer
router b... Real Multicast router
routerb(config)# ip multicast-routing
routerb(config)# access-list 1 deny 10.0.0.1
routerb(config)# interface ethernet 1
routerb(config-if)# ip address 10.0.0.2 255.255.255.0
routerb(config-if)# ip pim dense-mode
routerb(config-if)# ip pim neighbor-filter 1
routerb(config-if)# description To Stub router
My question is on Routerb's configuration...
If I use ACL 1 which is deny host 10.0.0.1 but don't
permit anyting else (per the documentation on
univercd) what will be allowed throubh the neighbor
filter? If nothing.. they why not make the ACL deny
any?
***********************************
Lee, I believe you're not fully understanding the functionality of the ip
pim-filter command. My take on what the Doc-CD says about this command is
that by using this command, you filter only pim traffic from the address
specified in the acl - not any other traffic. IOW, igmp traffic goes through
just fine.
From Doc-CD, "To prevent a router from participating in Protocol Independent
Multicast (PIM) (for example, to configure stub multicast routing), use the
ip pim neighbor-filter command in interface configuration mode."
******************************
Also,
Does igmp helper-addresses work similar to ip helper
addresses in that the interface that is configured
with the helper command will appear as the source when
fowarding the broadcast (multicast in this example)?
If so, then it appears that the point is to say stub
multicast routing is really not making a peer with
your directly connected router and insted to some
router(s) on links not directly attached which I would
then think the neighbor-filter would need a permit any
after the deny host 10.0.0.1...
Thoughts?
***********************
Lee, from the Doc-cd, " To cause the system to forward all Internet Group
Management Protocol (IGMP) host reports and leave messages received on the
interface to the specified IP address, use the ip igmp helper-address
command in interface configuration mode."
It also says, "This command and the ip pim neighbor-filter command together
enable stub multicast routing. The IGMP host reports and leave messages are
forwarded to the IP address specified. The reports are re-sent out the next
hop interface toward the IP address, with the source address of that
interface. This command enables a type of "dense-mode" join, allowing stub
sites not participating in Protocol Independent Multicast (PIM) to indicate
membership in IP multicast groups."
The way I understand this Stub Mcast feature is like this. Usually, igmp
traffic only travels from hosts to the pim router on the same segment. IOW,
igmp traffic doesn't leave the local segment. And, usually, from the
last-hop-router to the next hop router towards the source, pim traffic is
what goes back and forth. But, by configuring stub mcast, you're manually
causing igmp traffic to travel one more hop and causing pim traffic to
travel one less hop.
Now, I suspect there's some brilliant reason to do this besides providing
ccie candidates with something else to think about on the lab, but I'm not
able to intuitively figure that out.
HTH, Tim
*****************************
Link for their configuration (near bottom).
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fipr
_c/ipcpt3/1cfmulti.htm#wp1003543
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