[44net] Perl Script for Encap file to Cisco Clarifications needed

Hi there With the help of a Good Friend I have got today the first time the output of a perl script that take Encap file and convert it to tunnel commands here is one part of the tunnel commands

interface tunnel 746844928 description Link to 44.131.243.0 ip unnumbered loopback1 tunnel source xxx.xxx.xxx.xxx tunnel destination 80.68.61.60 ip tcp adjust-mss 1436 ip access-group acl_44 in ! tunnel mode ipip ! ip route 44.131.243.0 255.255.255.0 tunnel746844928

I have some questions 1) why the acl 44 in needed for ? 2) why the tcp MSS set to 1436 ? 3) why interface loopback is used ? I use the interface tunnel and do the 44 net on ethernet interface not using loopback at all

Please advice Thanks Forward Ronen - 4Z4ZQ