There are significant differences between an ASA5505 and a C876. The ASA was designed and built as a firewall and VPN concentrator while the C876 was designed and built as a router. There are many things for which the ASA is best (especially in terms of stateful inspection of traffic) and many things for which the C876 is best (especially in terms of routing and switching).
For the purpose of the site to site VPN either the ASA or the C876 should do fine. If your background is in security type things you may prefer to use the ASA while if your background is more in routing and switching then you may perfer to use the C876.
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...
[toc:faq]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 and UDP are I...