Expressway Clustering Over WAN

[abdul rasheed]

Hello All,

I am planning to deploy the CUCM, IMP, & CUC clustering over wants to provide HA in case of a site failure. In the same setup, we need to have an expressway also clustered over the WAN. 

We are using not using Expressway for the MRA. It is been used to allow remote users to call each other (as the remote access VPN does not support the user to user communication). We will use the VPN to connect to the internal resources including Jabber services. 

Users will have a VPN connection to both the DCs in the Active-Standby model. Users will be able to reach both the DCs no matter they connected to the VPN of the primary DC or secondary DC. 

My plan is as below:

1. Deploy the CUCM publisher in the Primary site and the subscriber in the secondary DC. 

2. Deploy the CUC publisher in the Primary site and the subscriber in the secondary DC.

3. Deploy the IMP publisher in the Primary site and the subscriber in the secondary DC.

4. Deploy the expressway C&E primary node in the primary DC and secondary nodes in the secondary DC.

Below are my concerns:

1. I can priorities the connection to the expressway E modifying the DNS SRV records priority and weight. How can I make sure that the calls from Expressway E in Primary DC don't use the Expressway C in the secondary DC ( I need to make sure the media doesn't cross WAN to reach the expressway C in the secondary site)

2. Is there any alternate solution than implementing Expressway clustering over the WAN. 

[Roger Kallberg]

I’m not sure that Expressway supports cluster over WAN.

[abdul rasheed]

Hello Roger,

As per Cisco TAC, it is supported if the below network requirements are fulfilled. 

■ Each peer has a different LAN configuration (a different IPv4 address and a different IPv6 address, where

enabled).

■ Expressway supports a round trip delay of up to 80ms. This means that each Expressway in the cluster must be

within a 40ms hop of all other peers in the cluster.

■ Each peer in a cluster is directly routable to each and every other Expressway in or to be added to the cluster.

(There must be no NAT between cluster peers – if there is a firewall ensure that the required ports are

opened.)

■ External firewalls are configured to block access to the clustering TLS ports.

■ The network connections between the peers must be reliable during cluster forming or changing procedures.

Clustering procedures are sensitive to sequencing, particularly after the introduction of X8.11. The primary

peer must start first; if other peers start first they can try to assume control of the cluster, resulting in

an inconsistent configuration state that is hard to recover from.