Static NAT functionality in Expressway-E, how this works?

david.alfaro · ‎05-01-2018

Hi Guys,

Is there someone who can explain in detail how the Expressway-E static NAT functionality works?, I have read the documentation (deployment and administration guides) but its is yet unclear for me; I do not understand, how this works, if this is configured with or without additional configuration in the ASA firewall and stuff like that.

Thanks in advance,

best regards,

Marcelo Morais · ‎05-04-2018

Hi @david.alfaro,

first of all, the best document for this is: VCS Basic Configuration (check the Background Information item).

The Static NAT is important to make EXP-E to change the IP Addr inside the SIP Payload ... ASA changes the IP Addr of the SIP Header.

Packet header:
Source IP: 10.0.10.2
Destination IP: 64.100.0.20
SIP payload:
INVITE sip: 64.100.0.20 SIP/2.0
Via: SIP/2.0/TLS 10.0.10.2:5061
Via: SIP/2.0/TLS 10.0.20.3:55938
Call-ID: 20ec9fd084eb3dd2@127.0.0.1
CSeq: 100 INVITE
Contact: <sip:EndpointA@10.0.20.3:55938;transport=tls>
From: "Endpoint A" <sip:EndpointA@cisco.com>;tag=9a42af
To: <sip: 64.100.0.20>
Max-Forwards: 70
Content-Type: application/sdp
Content-Length: 2825
v=0
o=tandberg 1 2 IN IP4 10.0.10.2
s=-
c=IN IP4 10.0.10.2
b=AS:2048


Packet header changed by the Firewall:
Source IP: 64.100.0.10
Destination IP: 64.100.0.20
SIP payload no changed by EXP-E (EXP-E with NO Static NAT):
INVITE sip:64.100.0.20 SIP/2.0
Via: SIP/2.0/TLS 10.0.10.2:5061
Via: SIP/2.0/TLS 10.0.20.3:55938
Call-ID: 20ec9fd084eb3dd2@127.0.0.1
CSeq: 100 INVITE
Contact: <sip:EndpointA@10.0.20.3:55938;transport=tls>
From: "Endpoint A" <sip:EndpointA@cisco.com>;tag=9a42af
To: <sip:64.100.0.20>
Max-Forwards: 70
Content-Type: application/sdp
Content-Length: 2825
v=0
s=-
c=IN IP4 10.0.10.2
b=AS:2048


Packet header changed by the Firewall:
Source IP: 64.100.0.10
Destination IP: 64.100.0.20
SIP payload changed by EXP-E with Static NAT:
INVITE sip: 64.100.0.20 SIP/2.0
Via: SIP/2.0/TLS 10.0.10.2:5061
Via: SIP/2.0/TLS 10.0.20.3:55938
Call-ID: 20ec9fd084eb3dd2@127.0.0.1
CSeq: 100 INVITE
Contact: <sip:EndpointA@10.0.20.3:55938;transport=tls>
From: "Endpoint A" <sip:EndpointA@cisco.com>;tag=9a42af
To: <sip: 64.100.0.20>
Max-Forwards: 70
Content-Type: application/sdp
Content-Length: 2825
v=0
s=-
c=IN IP4 64.100.0.10
b=AS:2048

Hope this helps,

Marcelo Morais