Communication issues on TCP 25 from branch office (IPSEC Tunnel)
We previousely have a working IPSEC tunnel using a Cyberoam Firewall at our main office and a SNAPGEAR firewall at our remote office.
Now that we have replaced it with a Cisco 1921 router at our main office and a Cisco 887VA router on our remote office, our clients on the remote office can no longer connect to our mailserver via the site to site vpn tunnel (IPSEC). The weird thing is that from any remote office machine, we can actually RDP to our server and even telnet to port 389 and a few other open ports on our server but to TCP port 25 and TCP port 143 we cannot.
We hope somebody could enlighten us if there is something missing or wrong on this configuration of ours.
We are not sure if it has to do with some MTU settings why we cannot telnet to the mailserver port 25 from our remote branch. Nothing has changed on our mailserver configurations as far the IPs that are allowed to connect to it.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...