There are a number of deployment options for Expressway depending on your customers environment, which could lead you to having to come up with creative solutions. This is called engineering.

We know external services need to be discovered using “outside” dns, however what happens when a customer uses a single dns server for outside and inside networks? Well, The traversal zone will need to be a FQDN for TLS validation, so it needs to use dns to resolve the inside addresses, but clients on the public internet need to use dns to resolve the outside address of the Expressway E.


Tandberg VCS aka Cisco Expressway runs on linux and uses a lightweight network services package called dnsmasq

Being a linux guy, the first thing I tried was editing the /etc/hosts file, but to prevent hacking, everything is on a read-only filesystem except for the /tandberg mount, which also had an etc but changes were not persistent. After poking around I found the dnsmasq.conf man pages here and an option to specify a “conf-dir” to include configuration files that are loaded on start.

For static A records, create a file called hosts.conf



For static SRV records, create a file called srv.conf


After adding the file, you’ll need to restart dnsmasq:

/etc/init.d/dnsmasq restart


2 Thoughts on “Spoof DNS on Expressway

  1. That’s absolutely amazing !! I have bookmarked this page since years and I always use it.
    Thank you.

    I want just to add here that, since Expressway 8.8 and onwards requires Expressway-C do reverse DNS lookups to Expressway-E :
    This can be done similarly by create a file ptr.conf and put into it the line :,

  2. Tommy Schlotterer on March 22, 2020 at 8:41 pm said:

    Just a note, These files are deleted upon Expressway upgrade, you will have to re-add them after the upgrade.

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