Firewall Traversal on Cisco Expressway Packet Flow

Firewall Traversal With Cisco Expressway Packet Flow. Firewall ASA-C, add an entry from Inside to DMZ , the source IP is (Cisco Expressway-C) and the source port is 25006. The destination IP is (Cisco Expressway-E) and the destination port is 7001, this means that if an inbound connection with source IP : port= : 7001 and destination : port = : 25006 is received from DMZ to Inside (from lower security level to higher security level), the firewall, this connection is allowed.

The Cisco Expressway-E receives the SIP invite and generate a new SIP invite with the source IP : port= : 7001 and destination : port = : 25006, it sends the SIP invite to ASA-C, the ASA-C checks its connection table if there is an entry that matches this connection, and of course the magic happens, this connection is already there, for the ASA-C’s perspective, this is a legitimate return traffic for a pseudo connection initiated from inside, even if the SIP invite is initiated from the Cisco Jabber, in other words from the outside, the Cisco Expressway-E modifies the L3/L4 headers to match the firewall traversal connection, in other words the entry of the connection table of the ASA.

This is the idea behind the firewall traversal concept.

Published by:

Redouane MEDDANE

Redouane MEDDANE is Cisco Instructor CCSI #35458, 3xCCNP Collaboration, Security and Enterprise and he a published author of some of the most important OSPF Protocol, Security and Collaboration books in the world titled OSPF Demystified With RFC, Network Security All-in-one, and Dial Plan and Call Routing Demystified on CUCM. He is also a blogger at and writes articles about collaboration and security to demystify the most complex topics. His books are known for their technical depth and accuracy especially the OSPF Demystified With RFC book, which is considered as the best OSPF book in the world and named "One of the best OSPF ebooks of all time" by BookAuthority It gives you a hint at the ability to explain complex topics with remarkable ease. He worked as a Cisco Instructor and consultant indifferent Cisco Learning Partner and awarded twice as Cisco Distinguished Instructor Award and Cisco Security Instructor Excellence Award on 2018 and 2019, and Cisco Collaboration Instructor Excellence Award on 2020. The Distinguished Instructor Award recognizes the top 5% of Cisco's most influential CCSI's who provide the highest quality training experience and demonstrate the best overall instructor performance across multiple Cisco technologie and Instructor Excellence Award recognizes the top 25% of elite CCSIs being recognized for delivering top quality training and maintaining high customer satisfaction in their field of expertise.

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