ERSPAN without Cat65K Sup3B

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Oct 28th, 2008
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I would like to SPAN some VoIP calls from a distant site to a centralised voice recording facility. However, the only supported solution I can see is to buy a Cat65K with Sup3B, or an ASR1000, both of which are too expensive. Has anyone managed to get RSPAN working across a WAN using Layer 2 GRE tunnelling on routers? Are there any third party products which could do this?

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aghaznavi Mon, 11/03/2008 - 17:52
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As the SPAN / RSPAN is a LAN feature, there are many limitation when attempted on WAN link. First is the fact that WAN link typically resides on routers. In order to use the RSPAN feature, you will need to first have a trunk link to the out bound router. to carry over the RSPAN traffic. As RSPAN creates a separate RSPAN vlan to carry over the traffic, this is necessary. From there, the router will then need to bridge the traffic as the SPAN traffic will require tags to be carried over when it gets to the destination switch. So in order to do that you will need to bridge the link between the routers that are connected to

your WAN link. Only after that, then you will need to create another trunk link to the switch in new location and then traffic will be directed to the destination you desire. As you can see, this method has several potential problems. Since the WAN link will now need to be bridged, it can only pass traffic from one VLAN, specifically the RSPAN VLAN. So only thing that you will see at the other end is SPAN traffic and nothing else, so the existing VLANs will not be able to get out.

PETER NEGUS Wed, 11/05/2008 - 02:28
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One solution that we are considering for this problem is the ME 6524 ME-C6524GT-8S switch. This is still a relatively expensive solution, but less costly than a 6503 or upgrading existing Cat65ks with sup2s. Just sticking a span port into a GRE router with bridging will not work, as the bridge mac-address learning mechanism cannot be switched off in a router.

Amit Singh Wed, 11/05/2008 - 03:23
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I think Cat4500 with Sup6-E does support it. Other fixed config switches are not HW capable for this as of now.


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