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I have a network with 2 VLANs running on a Cisco SGE2010 with the switch acting as the gateway for each vlan:

192.168.10.0/24 VLAN 10
192.168.20.0/24 VLAN 20

Servers live on VLAN 10 and Desktops on 20. We have DHCP relay passing requests from VLAN 20 to the DHCP server on 10 but there are some broadcast based services running on our Windows 2008 servers that we would like to broadcast to both subnets.

I originally thought that perhaps multicast would be what I wanted but sysadmin1138 makes me think I have it wrong. My next best guess is a Proxy Arp but it doesn't seem quite right.

So I know I could wire the servers into VLAN20 via trunking or a second NIC but is there a way to have broadcast traffic from a specific port be mirrored into a second VLAN?

EDIT: Thanks for the answers and comments but we've deemed the VLANs overkill and are going to simplify back down.

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Off topic, but if you were using a Linux gateway instead of the cisco device, you could use the BROUTE netfilter table (with ebtables) to pick some traffic to bridge between two interfaces (the rest being routed as usual) –  b0fh Aug 10 '12 at 23:56
    
@b0fh I'm at a different job now but that may have acually been an option. –  Tawm Oct 23 '12 at 18:43
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1 Answer

I believe you need an ip helper-address entry in the remote (to the server) VLAN that points to the Windows server IP(s).

In VLAN 20, something like:

ip helper-address server.ip.address

The following ports/services are forwarded by default with that statement.

   Time Service             Port 37
   TACACS                   Port 49
   Domain Name Services     Port 53
   Trivial File Transfer    Port 69
   DHCP (BootP)             Port 67 and Port 68
   NetBIOS Name Server      Port 137
   NetBIOS Datagram Server  Port 138
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The SGE2010 is really a Linksys switch that does not run IOS, so ip helper-address is not an option. I didn't see anything in the manual that looked like a comparable feature, but I just briefly skimmed through it. –  James Sneeringer Aug 10 '12 at 22:05
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@JamesSneeringer there's a weird way to get into a command line mode where you have a decent subset of the ios commands. The DHCP relay feature from the web interface is really just an ip helper line. –  Tawm Aug 13 '12 at 3:37
    
@Tawm I stand corrected. :) –  James Sneeringer Aug 17 '12 at 13:22
    
@JamesSneeringer when connected via telnet press ctrl-z and run lcli from there you have what feels more like IOS –  Tawm Aug 22 '12 at 17:00
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