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Cisco 7603/VLAN configuration to pass GHOST multicast


Forgive me for the basic nature of my questions and for the length of this message.

We have a Cisco 7603 router populated by 3 modules;

WS-X6K-S2U-MSFC2 - Supervisor 2

WS-X6348-RJ-45 - 48 port 10/100 RJ45

WS-X6408A-GBIC - 8 Port 1000Mbps GBIC

These are (interface-wise) Gi1/x, Fa2/x and Gi3/x respectively. IOS version is 12.1(11b)E4.

I have created a VLAN (VLAN 190) and assigned the IP to it.

The 7603 is not currently responsible for most of our internal routing, that is taken care of by a Linux box at and aliases on each of our 192.168.x.x private networks. The default gateway for this box is the IP of VLAN 190. The 7603 connects to the outside world via Gi1/1, and that signal path works fine.

Originally the entire interior LAN was attached to port Fa2/1 which had no VLAN, but the IP assigned to that interface alone. The VLAN was created to allow the other unused 7603 module ports to begin to be utilized. I have granted 'switchport access vlan 190' to interfaces Fa2/1, Gi3/1 and Gi3/2, all of which go to different portions of our LAN.

As I said we have an existing layout of many 192.168.x.x networks internally. On any given segment there will be hosts from many of these networks as well as the network.

Here's were my ignorance will show. The 7603 passes IP traffic from 192.168.x.x hosts on on interface, to those on the others (both on the same IP network and to others, via their gateway). I assume this is because the interfaces are functioning as L2 switchports, and they should. However, we have a Symantec Ghost server on Fa2/1 that needs to multicast software images to hosts on Gi3/1. The server is at The hosts reside on one of these '168 nets and can ping each other via the Linux router. When I go to establish a Ghost session, the clients can "see" the server and connect, but never seem to receive multicast traffic - the session never actuallt begins. So my questions are not so much Ghost related as they are multicast/routing related please;

1.Does the 7603 handle multicast traffic different than unicast, in the sense of passing the latter as layer 2 but the former as layer 3 - and hence a routing issue with my setup?

2.If this is the case, and the problem is that the IP network on which the VLAN exists will not allow multicast forwarding to 224.x.x.x for instance, how do I overcome this?

If I can provide more info to anyone who may have ideas, please let me know. Thank you,

Bob Kirk


Re: Cisco 7603/VLAN configuration to pass GHOST multicast

Some statically configured multicast router ports disappear when the timer for the dynamically learned router ports expires (ages out). Ports that are configured as multicast router ports are not supposed to age out but will do so if snooping discovers the port as a multicast router port prior to it being configured by the user. The disappearance of multicast router ports can result in the loss of VLANs from the router port list, even though they are statically configured

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