VCS Expressway Dual NIC question

[rfrome]

Team,

Can someone clarify an issue for me.

I have a VCSe, with the Dual NIC option.

The External interface is defined as LAN 2

LAN 1 is a 172.x.x.x network and LAN 2 is a 192.x.x.x

The VCS lets you specify an IPv4 Gateway but it is for the LAN 1 network. How does the VCS know what is the default gateway for the LAN2 network?

rf

[awinter2]

When you configure the default gateway on a dual NIC VCS-E, the default gateway is not necessarily associated with LAN1. The default gateway IP address should reside within the same subnet as either LAN1 or LAN2, and the VCS will understand which interface to use to reach the default gateway based on this.

For instance, if LAN1 is configured to 10.0.10.2/24, LAN2 is configured to 10.0.20.2/24, and you configure the default gateway to 10.0.20.1/24, the VCS will know to use LAN2 to reach the default gateway since LAN2 resides in the same subnet as the default gateway.

This also means that you should never configure LAN1 and LAN2 to reside within the same subnet.

Hope this helps,

Andreas

[rfrome]

Andreas,

Thanks for the info, but how how does the VCS make the correct decision for internal vs external (internet) if there is not a unique default gateway for each network? So, for example, if I have traffic bound for an internet destination, LAN2, how does sending the traffic to the default gateway associated with LAN 1 network get back to the correct network?

rf

[awinter2]

Exceptions to the default gateway/route have to be added by means of static routes, and this principle applies for any network device having more than one network interface, not just the VCS.

For instance, if LAN2 is the externally-facing interface (Facing for instance the Internet), and LAN1 is facing your internal network, you would configure the default gateway to be the router/firewall on the LAN2 subnet, while adding static routes for LAN1 for the hosts/subnets which you would be communicating with on the internal network (Assuming no NAT between these internal hosts/subnet and LAN1).

This is explained in more detail in Appendix 4 of

http://www.cisco.com/en/US/docs/telepresence/infrastructure/vcs/config_guide/Cisco_VCS_Basic_Configuration_Control_with_Expressway_Deployment_Guide_X7-2.pdf.